Post 492  by Gautam Shah



Thinners are combination of ‘solvents’ whereas a solvent is single liquid material. Thinners and solvents are used for many purposes. These can be categorized in roughly THREE categories: 1 as a solvent for reducing the viscosity, 2 as a diluent an intermediating agent, and 3 as a non active carrier agent.

Stone Conservation cleaning mainly with balanced ph water

As a viscosity reduction agent it is used with resins, coating materials, adhesives, etc. As a diluent it is used as an extender medium in thinners to extend thereby reduce the cost of costly solvents. As non active material it is used with pesticides, chemicals to achieve greater spread. Some solvents of very low boiling point temperature are used as carrier for sprays etc. Thinners or solvents are used for cleaning surfaces such as restoration of artwork, removal of oil-grease deposits, removal of moisture from very thin crevices such as electronic circuits.

Distillation of crude oil at different temperatures

One of the earliest needs for a solvent was to reduce the viscosity of wax without warming it with heat. Wax was one of the best and easily available waterproofing material, but required heat for softening, a highly dangerous fire prone processes. Similar problems were encountered while thinning vegetable oils, tallow and other fats. These issues were solved with some of the earliest solvent materials the turpentine and the spirits (crude ethanol-based products from fermentation-distillation processes). Turpentine has been known as: spirit of turpentine, natural turpentine, genuine turpentine, oil of turpentine, wood turpentine and turps.

Common solvents used as paint thinners – Mineral spirits (US) / White spirit (UK) – Acetone – Turpentine – Naphtha – Toluene – Methyl ethyl ketone (MEK) – Dimethylformamide (DMF) – 2-Butoxyethanol, or other glycol ethers. Other less common solvents used as paint thinner  – Ethylbenzene – Xylene – n-Butyl acetate – Butanol.


Turpentine is a steam distillation product from leaves of pine trees which also yields gum turpentine, turpentine oil and colophony (rosin). All these products have been used by artist for artwork and by crafts persons. The primary use of turpentine has been as a solvent for paints. During last century menthol and camphor were produced for turpentine, of this camphor was used for early Nitro-cellulose lacquer (NC Lacquer). Artists preferred distilled Turpentine as paint medium as it was more viscous than white spirit, and for being slow to evaporate. The later property was useful for ‘touching’ the colours, and keep it alive (green or wet) for longer duration. Residues or trace gum rosin in Turpentine prevents fast drying of film and keeps it tacky for along time.

White_spiritDuring the last century Genuine Turpentine has been replaced by Mineral Turpentine. Mineral Turpentine is petroleum distillate and is also known as white spirit, petroleum spirits, solvent naphtha. It is a very efficient solvent for oil and alkyd-based paints and varnishes. It is as low cost as Kerosene and so used for cleaning oil-grease from engineering products and other dry-cleaning (non-water cleaning of garments, wools) purposes. Turpentine has very little or no odour, so for paint thinner of domestic use, little terpene oil or genuine turpentine is added as a flavouring agent.

ethanol1Alcohol is produced through fermentation-distillation. The resultant product is Ethyl alcohol (Ethanol). The word Ethyl derives from French word ether, meaning a substance that evaporates fast at room temperature. Alcoholic drinks through fermentation of grapes, berries, honey and rice were produced since 7000 BC. Spirit or ethanol was used to dissolve plant gums. Ethanol is miscible with water and its presence reduces the surface tension of water. Pure ethanol is misused for consumption, so many countries have made it compulsory to denature it adding 5% or more methanol. This is also called methylated spirit. Denatured spirits are used for dissolving gums and shellac to formulate ‘French Polish’ and Lac and rosinated Varnishes. It is also used as cleaning agent.

Kerosene is chiefly used as a fuel. There are commercial and superior grades available. It has very strong solvent properties. In far off regions where Mineral turpentine is not available, Kerosene is used as oil paint solvent.

Naphtha sold as Camp-fuel

Naphtha is a flammable liquid mixture consisting of hydrocarbons, and it is very similar to kerosene or gasoline. It is a feed material for fertilizer and chemical plants. It is used for cleaning(flushing out) petroleum product tankers and as a tool machine cleaning solvent.

Gasoline is basically a fuel product, but is used for removing grease, tars and waxes from tools, parts and equipment. It is not used for paints.


Water is universal solvent. Water was used for water-based coatings produced from gums, casein, egg-whites etc. and with cementious compounds like lime, gypsum, etc. Water emulsified, polymer paints are able to meet the ecological concerns for VOC (Volatile organic compounds are organic chemicals that has a high vapour pressure at ordinary room temperature). Water is capable of dissolving a variety of different substances, which is why it is the best and universal solvent. Water can dissolve more substances than any other liquid. Water molecules have a polar arrangement of the oxygen and hydrogen atoms -one side (hydrogen) has a positive electrical charge and the other side (oxygen) had a negative charge. Water is attracted to a different molecule, like salt (NaCl), to disrupt the attractive forces that hold the sodium and chloride in the salt molecule together to dissolve it. Rain is generally mildly acidic, with a pH between 5.2 and 5.8.


Acetone is a simplest ketone and called mother of solvents. It is colourless and flammable liquid utilized as an important constituent of lacquer thinner, nail polish remover and grease-oil cleansing. In restoration and conservation practices acetone is often used to clean dirt, soot and grime and old varnishes from paintings and furniture.

Olivia Boteler Porter before and after restoration – removal of yellowing due to dirt and ageing

Methyl ethyl ketone (MEK) is an industrial solvent which is easily miscible with water. It is used as thinner solvent and as a remover-softener of stubborn paints.

Carbon tetra-chloride fire extinguisher 1930

Carbon tetra-chloride is also known as tetrachloromethane, carbon tet (cleaning industry), Halon-104 (firefighting) and Refrigerant-10 (HVACR). It was very popular cleaning agent for amateur electronics people. It is a colourless liquid with a sweet smell detectable at low levels. It is no longer preferred as a solvent or cleaning fluid.

 Sistine Chapel, the prophet Daniel before and after Restoration

> A decision was made that all of the shadowy layer of animal glue and “lamp black”, all of the wax, and all of the over-painted areas were contamination of one sort or another: smoke deposits, earlier restoration attempts, and painted definition by later restorers in an attempt to enliven the appearance of the work. Based on this decision, according to Arguimbau’s critical reading of the restoration data that have been provided, the chemists of the restoration team decided upon a SOLVENT that would effectively STRIP the ceiling down to its paint-impregnated plaster.

6 Heritage_architectural_features_cleaned_and_restored



Post 485  –by Gautam Shah



During 1930-50s Paint shops used to offer Oil-bound Distempers (OBD) and combination of Zinc pastes and double-boiled Linseed oil, for household painting. These were mixed with pigment pastes for shade creation. Post 1950s ready mixed oil paints or General purpose enamels (GP) became popular. But than paints’ shops had to stock several tins of different measures, for each of the shades and varieties (oil paints, distemper paints, flat and egg-shell plastic paints). And to match a desired shade, it was necessary to buy small bottles or vials of concentrated pigment pastes called tinters and top up an available shade or create one from a white.

Paint Shop of earlier era

There were two whites available, a ‘super-whitewith some form of ‘optical whitener or brightener, an ‘opacifier’ or colourants like blue or violet, and pure stuff called base-white, without any additives. Few lay people were aware of the later variety, or considered it to be some inferior stuff due to its less romantic name (super white versus base-white), and discounted price.

Zinc paste-based paints and General purpose enamels had linseed oil or its alkyd resins as the chief film forming material. The linseed has a tendency to oxidize and turn yellow over the age. This began to change due to strong demand from manufacturers of white-goods (consumer goods painted white such as ovens, fans, washing machines, refrigerators, etc.) for long-term non yellowing finishes. This led to use of non yellowing oils for resins, and new generation formulations of Urethane, Amino resins and epoxies. The same innovations began to percolate to home-paint markets. From 1960s Plastic polymer-based emulsion paints (called Latex paints in USA) began to be available. This offered non-yellowing white paints.

Shade Card

Titanium Dioxide as a whitest pigment had few technical problems of paint formulations, but these were initially solved with use of Zinc and Lithopone as additives. Oil paints in glossy and flat varieties, and Plastic Paint with, sheen, egg-shell-matt and flat varieties now were offered as one or two coat systems. This high hiding-covering was due to excellent pigment grinding-dispersion in machines like attritors that replaced ball and roller mills.

United States Capitol west front


Paint markets are now radically changed. Paints manufacturing companies depend on shops to match the colour shades. The shades are created from basic, and few vials of ground pigments, which inject exact-micro quantity of colours into range of base formulations. The base formulations, include nearly clear to several types of white paints. White bases have natural shades of white pigments, and some have whitening-opacifiers. A white base is used for light tints, but not more than 100 ml paste can be added for darker shades to avoid loss of gloss or the effect on drying time. A neutral, pastel or mid-base contains lesser quantity of white pigment and is used for creating darker colours. And a clear base is used (it may contain white powders of low refractivity or extenders, but is free of high refractivity white pigments), for very deep colours. Some manufacturers use this base to add little sheen to matt paint.

Whites are affected by surroundings and show many variations

Whites are affected by smallest amount of additive colourants. These colourants may come from residues of earlier colour in brushes or rollers, any loose particles on the surface to be painted and thinners (solvents and water). Some additive colourants, if not thoroughly mixed, begin to darken the colour shade over brushing or rolling. Extra ordinary care is required in selecting, buying, mixing and using, white and ‘off-white’ shades. Shops have a file of colour shade cards, which are rarely fresh. The shade card viewing must be done in natural light, as it is affected by the surroundings and type of illumination. Shop computer calibrated and mixed shades, are not necessarily exactly right as per the shade card or as per your need.

A colour shows many variations at different angles of viewing and so colour matching must be done perceiving it from as many positions > Pic by

One of the best ways is to buy a small trial pack, and apply it on two different walls (preferably at right angles), at the site location. Once a right shade is achieved, leave some quantity (see the next paragraph) in the trial pack for master batching and matching.

HOW to mix a white shade with very light tinge of other colours at home? Buy the most appropriate white-base out of several ones available at a paint shop (usually 2-6 varieties). Now separately mix the concentrated tint to small quantity of white-base, with shade as close matching to your desire. Such faint tinges of colours are very difficult to visually perceive. So place a drop of experimental mix over the quantity left in trial pack. Your shade will be either darker or lighter, but easily perceptible.Mixed Whites

Most plastic emulsion paints now have a ‘Thixotropic’ compound, which gives a heavy, butter like false viscosity to the paint, to prevent separation or settlement of heavier phases or solids. Stirring is required to reconvert the stuff to a temporary liquid phase. Plastic paints come with good odours, to suppress the unpleasantness of paints, but one need not judge a paint on that count.

Color Blue Church Terrace Architecture White


COATINGS as thin Surfacing

Post 482 –by Gautam Shah


Coatings are thin surfacing with or without a colourant additive. The colourant if present, may be transparent, translucent or opaque. Coatings consist of many different components, such as a film forming substance, and additives like, colourant, reactive agents, solvents etc. In a very complex coating composition such clear-cut distinctions are not apparent, because film forming substances and additives serve purposes beyond their nominal roles. Historically coatings were created as art medium for illustrative and decorative effects. These then began to be used to alter the appearance, improve the tangibility and to provide a protective cover to objects and human body.


Phenolic Varnish coated Copper coil

Coatings are used for 1 changing the quality of the existing surface, and 2 applied as a permanent cover over an object. In the first case the changes are just few molecules deep, like: removal of few molecules of the object or some products from the surface section, rearrangement of the molecules, varied chemical formulation. In second case a composition is applied as a permanent coating, through bonding processes like adhesion, cohesion, chain linking, and material-phase change, intermolecular interactions including van der Waals forces, hydrogen bonds and strong covalent bonds.

Internal coating

Surface Treatments form a very important section of coating technology. Some surface treatments are temporary and are removed once the required action is accomplished, others remain as full or partial deposition. Many surface treatments serve specific purposes such as cleaning, roughening, smoothening, etching, moisture proofing, rust inhibiting, air barriers, static arresters etc. Some others only facilitate the application, setting or drying of the coating.

Anti Glare / Anti reflection coating on Glass

Traditional Coatings are usually liquids of low solids content. These first ‘dried’ by evaporation of substantial content of organic solvents, and later ‘set or hardened through oxidation and long chain formation. This technology began to fad out with use of Plastic or latex paints. These are applied as aqueous dispersions or water-based emulsion of polymers. Now formulations are also solvent less or powder coatings.

Micro Surfacing Road Paver

At application-stage the film-forming mediums are in various phases such as liquid, solid or vapour, or a combination thereof like, suspensions, solutions, dispersions, emulsions, thermoplastic compounds, thixotropic compounds, etc., but coatings once applied ultimately settle to a heavier phase, usually (but not necessarily) a solid phase.

Roof underside fireproof coating

At an application stage a lower phase helps in many ways. Mainly due to liquid state there is uniform and thin level of application. Liquid state of the material permits better dispersion of costly or rare constituents. During application the integrity (thorough dispersion of constituents) can be maintained. Energy required for application of coating is very small. Liquid coatings can be formulated for varied but controlled deposition and rate of phase conversion, to match the substrate and environmental conditions.

Glazed Bakery products

Coatings form a continuous film and so do not have joints, except at junctions where coating application is delayed (a dried out portion and a fresh coat touch each other or overlap). Coatings are thin surfacing so the coated entity remains malleable, and allow the post-forming operations (e.g. coated metal sheets). A coating film has a thickness ranging from 0.0005 to 0.5 mm (0.00002 to 0.02 inch). Coatings are deposited on the entity by many different techniques such as daubing, brushing, spraying, screen printing, roller coating, and dipping.

Wood Deck staining – Coating



Post 469 by Gautam Shah



Joints are very important section of a surface finish. Joints create pattern, texture, contrast, equalize variegated colours of the surface, endow a discipline and unity, create an orientation, divide a space into proportioned sets, provide flexibility, prevent or direct cracking. A surface finish gains its value as much for the quality of the surface as the careful design consideration for the joints.


Joints in surface systems arise as the components of the surface finish has smaller size than the space, fixing becomes easier, of assurance of adhesion, and to help divide the task in lots. Surface-finishes are applied as coatings with on-site application, also need scheduled joints to manage continuity. Such depositions, though known as seamless or joint-less system, have nearly imperceptible joints. These joints always have some inherent drawbacks of quality or consistency.


Designing a joint in surface system is a followup process once the surface components have been devised or accepted. In a good design Joints are never of secondary importance. In creation of assembled entities joining is an integrated effort. For all systems joining, un-joining and rejoining, are important strategies of design.



Joints occur with or without a material in an assemblage Fused joints (by chemical solution or heat fusion) have a traceable joint. Edge to edge joining is, both created and avoided intentionally. Wooden floorings for decks (exterior) and performance stages (interior) have spaced joints to allow the wood to adjust to the changes in moisture content of air. Similarly metal assemblies have free joints to accommodate the expansion caused by the temperature. Edge joints have an intervening material (such as a ductile or conductive material) or none, to allow or curtail the transmission of energy and vibratory forces (mechanical, sound, electrical, etc.). Structures require separation joints to sustain their integrity, and the same are identically placed in their surface finishes.



Very closely placed joints create a virtually continuous surface finish. Stone masonry and wood often have very thin or knife edge joints. Thin joints are for sensorial reasons like touch, fill, visual, etc., and for structural or functional causes. Thin joints provide some flexibility to the surface component, but there is insufficient space for displacement such as in bricks and cobble stone flooring.


Widely spaced joints occur for many different reasons. The prime reasons are: non matting planes at the joint, geometric deviations of the surface components’ shapes. Deep joints require greater width for filling up. Wide unfilled or shallow filled joints create crevices, enhancing the light-shadow contrast over the surface


Bricks, Stone and Blocks masonry surfaces have etched joints called pointing, these enhance the visual texture of the surface due to shadows of the depth, or deposition to form rendered joints. Such joints are formed of matching or different materials and colour. The deep etched  joints allow space hair cracks.

Brick Pointing

Brick joints



Post 454 -by Gautam Shah


One can rationalize the demands faced by an object or its surface system in many different ways. The processes of rationalizing the demands for surface finish begin with the object-modification, but may eventually include changing the environment. For a good designer, however, it is often more efficient (functionally, technologically and economically) to compose a new entity, than expend too much effort in modifying the entity or change its environment.

5 chamber plastic window profile

There are many fables where the advice is: cover your own feet, rather than cover the streets of the town, or carry an umbrella than cover up the sun. It is better to buy a new razor blade with a sharp edge, than polish the blunt one.

Objects and the surface systems, if of a single material, than operative demands are simpler, but if composed of many, similar or dissimilar materials, these have very complex and often in-specifiable demands.

Metal turning

It is ideal to reform the object entity by integrating the surface system with it. Where such direct integration is not possible, the object and its surface system both are individually refashioned, and then integrated into a single material entity.

Roman bath roof of multiple layers of materials / Hollowed blocks to reduce weight

First step in integrating several surface systems is to place them close together. Next step should be to eliminate any space that remains between them by tight packing or joining them. The joining of the surface system, than must allow the layered system to structurally function as one unit. When the layered systems begin to function as one, it is time to plan ‘a new integrated system’ to replace it. As one can see, the strategy is to invent a new replacement system and NOT to improvise the combined system.

Calendaring -pressing machine

At any cross section of time, we find a large number of surface systems either are overtly attached to the object or are in the process of being integrated to the entity base. It is very necessary that a surface system in such a situation, be singular in constitution or at least be effective in that manner. Finish makers aspire to provide a singular surface system in place of a multi-component system. However, in a finish maker’s world there are very few situations where singular surface system can satisfy all the demands. Multi-component surface systems are reality.

Human skin -an integrated but multi component surface system

A surface system can be facilitated by delaying or curtailing the effects of environment, for the functional period of the entity. Environmental effects are from specific orientation or comprehensive, and so one can design a surface system to be local or total, momentous or everlasting.

Multi layered but integrated surface system -polymer modified cement floor

Ordinarily surface finishes are fashioned, only after the object and its relevant environment have been conceived. But sometimes an object could be so hazardous that until an actual workable surface system is designed, it cannot be allowed to occur (such as atomic materials and isotopes). Similarly an environment could be so harmful that till an appropriate finish system is devised, the object cannot exist, much less function in it.

Air craft wall layers

Liquids and gases have no stable object boundary, so must be contained, and for such material phases the container becomes the apparent surface system.

The environment influences objects in such a complex way, that any search for logic is impossible. This is the reason why many surface makers seem to work with their intuitive faculties. To some people, providing a surface system is an art or craft, rather than a scientific discipline.

Concrete pavement



Post 453 -by Gautam Shah


Stone Old Church Architecture Ancient Wall Gate


Materials respond to

Other Materials,



Old Wood Windows Shutters Architecture Broken



Materials respond to other materials within their realm. The reactions occur both, in the presence or absence, of the environment and the user. A material of a higher phase reacts more readily to a material of the lower phase, e.g. solid to a liquid. Material with an ion charge reacts to a material with opposite ion charge. A material with lower latent energy becomes recipient.

Screenshot 2021-06-12 at 09-50-16 Seaman Audriana Wheeler, from Hell, Mich , scrapes barnacles from the bottom of a rigid-h[...]

Materials respond to not only weather and on quality of the constituents, but their positional exposure. So design can aggravate a response mechanism or restrict it. The positional exposure is acutely governed by the joints and the materials, if any.

Federation Square Melbourne -tessellated grid Wikipedia Image by Cookaa

The response of a material, occurs through the surface, more emphatically, than anywhere else. Materials with their own surface systems (inherent finish) respond in the same manner as their body would. However, applied surface systems of the same or of foreign materials show different behaviour. In such reactions, the important factors are, surface preparation, application method, and bonding techniques.



Materials are affected by many aspects of the environment. The effects are local, if environment effects are directional (through specific orientation), or occur comprehensively. The various constituents of the object also respond differently. Single, or mono material systems are often inadequate for such multilateral environmental demands. Multi-material objects or composites are conceived to serve such demands, separately as well as unitedly.

Farshid Moussavi, Detail, façade of Edificio Bambú =Bamboo Building Madrid Wikipedia Image from Francisco Andeyro (Alejandro García González & Francisco Andeyro)(

An applied surface material system, covering an entity, forms its own environment. Here the situation can also be equated to material to environment response.


Effects of the environment substantially relate to the movement of earth-sun, and so have a time dimension. The time dimension makes such environmental effects to be temporary, permanent, recurrent, or variable. One perhaps cannot terminate the processes of nature, however, the effects of environment can be temporarily delayed or quickened and spatially diffused, or intensified, to programme the functioning of an object.

The effects of environment are structurally causative (capable of causing structural changes in a material), and also sensually attributive (capable of providing the sensorial experiences).

Material Response


A user perceives a material-object in different terms like: Engineering attributes, Dimensional features, Surface properties and for Other considerations. A surface is the most proximate and tangible part of an object. A surface, is often the reason, why an object continues to survive in a particular setting. A user perceives the surface of a material-object through factors such as:

EMP Museum founded by Microsoft co-founder Paul Allen in 2000, located at Seattle, designed by Frank Gehry

  • proximity (closeness, intimacy, distance)
  • duration (of encounter)
  • frequency and extent (area) of contact
  • mode of handling
  • our past experiences
  • our sensory capabilities
  • our physiological state
  • atmospheric conditions (temperature, humidity)
  • light (direction and level of illumination)
  • orientation, or point of observation.

Close up of a peyote cactus growing in the wild as mentioned in The Doors of Perception, by Aldus Huxley

There are more than 20 mathematical parameters applied to surface description, and some of the terms are: roughness, irregular features of wave, height, width, lay, and direction on the surface; camber, deviation from straightness; out of flat, measure of macroscopic deviations from flatness of a surface.



Post 442 -by Gautam Shah


Primer coat is the first surface build up on any substrate. It is designed to receive one or several more coats, immediately or some times later. A primer-coat is a surface preparation layer. It covers the surface irregularities like, chemical reactivity, and physical variations -colour, texture, porosity. A primer coat also offers a next application worthy surface.

Eiffel Tower Painting.jpg

A primer coat serves two distinct purposes: 1 It touches the substrate, often of many different types, and so must adhere to it, well, 2 It receives the next coat so functionally must be compatible with it. A primer coat helps in levelling the surface, and must have ‘body’ to fill up the pores, micro crevices, etc. Primer coat is sand papered for levelling, and to roughen up for application of second coat. Its some superfluous part gets rubbed and removed.

Primer coat is nominally applied on ‘virgin’ or an uncoated surface, and sometimes on very old coated surface. In the later case, the primer coat is slightly coloured white, off-white or some colour closer, but lighter then the final intended colour. When an old coat colour is to be ‘masked’ completely, primer coats or undercoats are coloured by a ‘masking colour’, such as Green by darker Red or Red by Blue. It is desirable to have primer of a slightly different and lighter colour shade than the subsequent coat, to differentiate a freshly coated surface and uncoated surface.

Primer failure

Primer coat is a technical coat, so its colour is not very important. The Primer-colours that we see are mainly due to the filler or body-pigments, called extenders. These are chosen for their protective effects and other technical qualities. Primer coats protect the virgin surface, and so are applied soon after the primary manufacturing is over, such as on pipes, sections, sheets, castings, etc. Good primer must remain adhered to the surface, even after other top coats are removed accidentally, or for renovation.


Clear Sealer Coats: These are priming coats for application of clear coats, mainly wood surfaces. A sealer coat, like a primer prepares the fresh surface (of wood) for subsequent application. Sealer coat must be to be low viscosity, but high solid content material. Nitro cellulose clear has been found to be the most versatile sealer material. Other materials include variety modified pine Rosins. Clear sealer coats are often not categorized as priming coat, where the first application is a coat of ‘extender’ such as china clay, barytes or Calcium carbonate mixed with oxide colour. Such a coat covers, the irregularities of colour and grain patterns, fill up pores and micro crevices on wood surfaces. After sand papering-level rubbing it may be coated with a sealer coat. Sealer coats are preceded by staining compounds or coats, to add a translucent tinge on the surface.

white undercoat

A primer or sealer coat is the first coating applied to the objects’ surface, so it is required to:

● Regulate moisture movement in case of wood or masonry surfaces and provide corrosion resistance on metals

● Regulate the PH value and galvanic activity of the surface.

● Seal the surface so that oils, waxes, gases, vapours, salts and other reactive exudations from the object mass do not leach out in adverse conditions

● Fill up micro pores and crevices to level out the surface

● Provide temporary protection to the substrate from actions like abrasion, oxidation, sparking, ignition, insects attack.


A great variety of primers are available in the market, but of following basic THREE categories:

Wood primers generally function as sealers, so have a high pigment + extender ratio. Wood sealers for clear coats are colourless coatings that help in sealing the grain. Commercial wood primers for pigmented paints are white or pinkish in colour due to the presence of white pigments and extenders, compared to metal primers (red-oxide) which, are dark coloured.

white primer on wooden surface 1566994

primer paint

Metal primers have rust inhibitive pigments or extenders like red lead, zinc oxide, zinc chromate, red oxide, calcium boro-silicate, barium metaborate, zinc molybdate, chromium fluoride, basic lead silico chromate, zinc ferrite, calcium ferrite. Under water (submerged) metal structures are coated with zinc rich primers based on epoxy, polyurethane systems or chlorinated rubber paints are used.


Primer on Metal surface

Masonry primers are applied to alkaline surfaces, so are designed as non acidic mediums. Often such surfaces have high degree of loose particles, so Masonry primers have high proportion of binding materials. Commercially these types of primers are known as cement primers, and are available as water or oil-based formulations. Water-based formulations are mainly used on virgin masonry surfaces.



Post 438 – by Gautam Shah 



Metals are coated for many different purposes, and with metals, alloys, non metal substances (carbon, phosphorus, sulfur, selenium, and iodine) and polymeric materials (plastics, elastomers, etc.). Metal coatings provide specific surface properties, like, rust inhibition, preventing tarnishing by weather, improve surface conductance or resistance, for surface alloying, for surface hardening, for pseudo metalizing (providing appearance or behavioural qualities of another metal), for surface alteration like adding gloss or textures, providing insulation, wear resistance, and for imparting colours. Some of the Coatings are discussed here.

Dyed Anodizing of Aluminium

CONVERSION COATINGS are chemical surface treatments which provide temporary corrosion protection to the surface and create an appropriate substrate for subsequent treatments or coatings. There are two main processes: Phosphating and Chromating.

Parkerizing, bonderizing, phosphating, or phosphatizing

Phosphate coatings are mainly applied to ferrous and zinc, and to some extent for aluminium, tin and cadmium metals. It is mainly used as a pre-treatment for painting work of automobiles and sheet metal components. The applied coating is thin and porous. It offers mechanical keying to the paint film. The electrical insulation or inertness restricts the corrosion breaks. The phosphating treatment consists of immersion, brushing or spraying of hot dilute ortho-phosphoric acid solution. Similarly Zinc phosphate coatings are also used.

Stamping steel with zinc chromate conversion coating

Chromating or chromate coating is depositing a chromium oxide layer over a metal surface to enable the metal to react with the oxide layer. The process is used, mainly to increase the corrosion resistance of metals such as aluminium, magnesium, tin, zinc and cadmium, and also increase the tarnish resistance of copper and silver. Pure Aluminum is very soft, so its alloys (mixtures) with copper and other metals were used to make a lightweight but strong parts for aircraft. Chromium metal coatings were used to reduce the corrosion. It is used for hardware items and tools.


DIFFUSION COATINGS are also known as cementation coatings. A part of the coating interacts with the substrate and forms an alloy with it. Cementation coating process is very similar to carburising of iron to produce a surface-hardened steel (iron is heated with carbon particles for the diffusion to occur). Common diffusion processes are Aluminizing (calorising), Chromising and Sherardising (zinc cementation coating). There are other diffusion coatings such as Siliconising and Borating. Hot dip galvanizing, tinning and terneplating also involve alloying between coating and substrate, but the process differs from that of diffusion coating. Diffusion coatings are created by, the gas-phase at high temperatures by exposing the substrate to a volatile (usually halide) compounds of the coating metal, and through a solid-phase by packing the substrate metal in a container with the powdered coating metal and heating them together.

Aluminized Steel for Car muffler (silencer)

Aluminizing can be performed by both solid state and pack diffusion. Aluminizing may also be performed by heating ferrous metals in an inert, or reducing atmosphere containing dry gaseous aluminium chloride at 700-1100°C. It is also possible to produce aluminium diffusion coatings by coating the ferrous surface with aluminium by hot dipping (or with aluminium powder) and then heat treating to permit diffusion to occur.

Zinc coated steel 1 cent coin

Chromising is application of chromium on Steel, for enhanced oxidation, corrosion and wear resistance. For gas phase chromising the articles are heated in a powdered mixture of chromium, alumina or kaolin and an ammonium halide in a hydrogen atmosphere at 1000-1100°C. It is also possible to chromise steel by heating it in a fused salt bath of chromium chloride, chromium metal, barium chloride and sodium chloride in an argon atmosphere.

Inside Part of Tin plated Can

Sherardising is zinc diffusion coating of steel. Sherardising is applied on nuts, bolts, screws and chains. The articles are packed into a drum containing blue zinc powder (zinc containing 5-8% zinc oxide) and alumina or sand, the drum is heated to 360-430°C and rotated. Sherardised coating is a hard matt grey finish of uniform thickness.

Galvanizing is a molten zinc dipped coatings on steel. Steel can also be coated by zinc through electro plating. Such a coating, if it is cut or scratched, then the zinc flows to decay preferentially to the steel and provide continuous protection.


Corrugated Zinc-Iron sheets

VAPOUR DEPOSITION coatings are formed, by ‘condensation of metal vapour originating from molten metal, high voltage discharges between electrodes (cathode sputtering), or from chemical means such as hydrogen reduction or thermal decomposition (gas plating) of metal halides’ A thin specular coating can be achieved on metals, plastics, paper, glass and fabrics by means of vaporization.

Tin coated punches of steel

Siliconising is carried out by heating steel in contact with silicon carbide powder in an atmosphere of silicon tetra-chloride vapour. It case hardens the steel for high surface hardness and wears resistance. Siliconising is done to refractory materials.

Silver art work

METAL CLADDING and PLATING are used for coating, cladding or plating a metal surface with another metal. Hot-dipped coatings of low-melting metals are used for steel articles. Electro plating is used for plating Zinc, Nickel, Gold, Silver, Chrome, Tin, and Nickel-Cobalt alloy through Barrel plating, Rack plating, Strip plating processes. Electro plating nominally provides a very glossy surface, but by reversing the current in electrodes during the final stage a matt finish can be achieved. Other processes very close to this category include Electroless plating, hot dipping, metal spraying, powder spraying, vacuum metalizing and anodizing.



VITREOUS ENAMEL COATINGS often called ceramic coating are glassy but noncrystalline surfacing. A slip is applied by dipping or flow coating, and fired or sintered to form a vitreous coating. Dry enamelling is used for castings, such as bathtubs. ‘The casting is heated to a high temperature, and then dry enamel powder is sprinkled over the surface, where it fuses.’

Ceramic enamel coated steel cooking pot


POWDER COATINGS use polymeric materials such as acrylic, polyester, and epoxies, which are heated and sprayed or sprayed over a heated object. Powders are also applied to electrically charged materials which are attracted to and adhere to the substrate until it can be transported to an oven.

Powder coating



Post 437 – by Gautam Shah 



Coatings are applied as Single or Multi coat systems. The choice depends on several factors, such as:

  • Economics
  • Opportunity offered by technology
  • Emergency or routine application
  • Site accessibility in terms of location, weather, and tools available
  • First or virgin application or a re-coating job
  • Thickness of film required


One-coat system has inherent efficiency, as it requires lesser amounts of material, solvents, curing energy, and takes less time for application. However, in one-coat systems, the coating is required to provide adhesion with the substrate, necessary film build or thickness, and also fully cover up the surface. Single coat systems have to be fail-proof, as there are no remedial opportunities. Performances of single-coat system, depends very closely on the type of (readily available) substrate. If the substrates are large then one has to select different coating system for different substrates or go for ‘All purpose system’.

Ship re painting involves huge effort of surface cleaning before multi-coat application

Multi-coat systems consist of two, three or more layers of applications, such as, Priming-coat (filler or sealing coats), Undercoat (sub coat or intermediate coats) and Finish-coat (top coat or surface coat) These multiple layers are designed to perform specific functions and also take care of any shortcomings of the preceding coats. In multi-coat systems, different coats can be applied at different times and locations, as required. Primer-coat can be a factory application, Intermediate-coat could be part of the installation procedure, while, the Final coat could be applied with other finish systems, just prior to usage. Multi-coat systems have an advantage over many high-build or one coat systems, in that the final coat can be of the same type for different substrates or undercoats. In multi-coat systems, the sub layers could be of economic materials, as it is the final layer that is exposed to the atmosphere, and provides the tangible surface finish.

Rubbing - Sand Papering the primer



Single coat systems are applied to save time and cost of application. Very large walls, giant structures (Eiffel tower, pylons, or Bridges), Road side barricades, Road marking signs, Ships, Marine structures, are some of the entities that must be re-coated in one effort. These are re-application systems, so the substrates have some form of existing coating. The condition could be, severely weathered surface, fatigued or peeled original coating, presence of salts and other reaction products, deposits of dust, grime, etc. Some of these extraneous or by-product matters cannot be removed easily or completely from where they exist (height, nooks, corners, etc.). Such structures are exposed to vagaries of weather, such as very high or low surface temperature, condensation, rains, humidity, high winds and environmental pollution. Where the technology of stripping of aged coatings is available, it may not work for such an extensive surface, including undersides.


Multi-coat systems are as varied as their modes of applications are. Multi-coat systems have a prime or primer coat, followed by one or more finishing coats. Multi-coat systems need an interim ‘rest’ or through drying period, before next coat can be applied. Finishing coats are often designed as ‘removable or stripping system’ by mechanical grinding or chemical scrubbing, or both. Primer coats are specifically designed for the surface to be applied, such as wood, metal or masonry. Multi-coat systems are applied by exclusively by brushing, roller, spraying, dipping, or in combinations of it. With brush application final coating is by vertical strokes.






Post 371 – by Gautam Shah



Floor paints constitute a distinctive category of Architectural coatings. Floor paints are broadly of three classes: Clear coatings, Pigmented or coloured paints and Technical coats. Technical coats could be under coats, super coats or singular coats. Floor paints or coatings can also be differentiated in terms of their placements: such as for top of the roof, under coating for the roof, exterior and interior surfaces of wood or masonry materials, and technical coats for floors of water storage (tanks, moats) and channels (aqueducts and canals).

5331087042_92dc21010d_zFloor paints are used to improve the appearance, increase abrasion resistance, reduce moisture penetration and impart spillage proof qualities. Floor paints, nominally do not include coatings or applications with substantial mass such as various types of plasters or depositions. Some screed applications have dual classifications of floor plaster as well as a thin coating system. Floor paints are thin surface coatings, applied on variety of substrates and with equally varied methods.

pexels-photo-122480Ancient floor coatings were applications of oil mixed with wax, bitumen and creosote. These were used for treating floor decks and seats of seagoing vessels, sea coast wood structures, wood floor boards around wells, and underside boards of roofs over purlins prior to covering with metal sheets or ceramic tiles, all to prevent the rot. Oil-wax was used, for floorings and stage floor boards, to keep intact the visual appearance of the wood. Bitumen and creosote darkened the surface and often remained tacky (due to addition of tallow or fish-oil), but wax-oil coatings, with higher content of wax were non tacky. Wax was hot-melt in bodied oil (double boiled linseed oil or polymerized oil) or oils modified with Pine-rosin. These formulations were nearly like Varnishes used for coating furniture or covering the paintings. The surface had gloss and smoothness. The Varnish coatings lasted a year or one wet season, and required re-application.

Stornoway_Airport_RunwayAncient Floor coatings were mainly applied on wood surfaces, but occasionally dull floors of stones were given a coat to achieve a shiny surface. Dull stone floors of sandstone or lime stones were coated for festive occasions like coronation, marriage and religious functions. These were temporary applications, and no one was bothered about its durability or issues of re-application.

Vera_Project_12The floor coating system saw renewed interest when large size merchant and cruise ships, railway coaches and passenger bus vehicles arrived on the scene during the Industrial age period. These utilities did not have masonry or wood floors. It was necessary to create decks of colourful ambiance, and of wear resistant, non-skidding, sound dampening and maintainable material. The first options then available were linoleum carpets and alkyd-based enamel paints. Both created floors with fewer joints, but paint was a re-applicable surface.

Akshardham temple-931709-1

1024px-Cameron_Indoor_Stadium_interiorRoad and surface signage and functional graphics became a necessity, with the increase in road and rail traffic. There was no space in many urban areas to place vertical signage. The floor signs painted on roads and pavements were warnings in the movement spaces, passengers’ zebra crossing marks, edges of surface drops, road segmentation, danger zones, curvature limits. These were initially by contrast colour paving. Similarly barefoot walk-passages in temples, mosques needed a lighter colour treatment to keep them cooler. The only option, than available was to use lime whitewash or alkyd based white oil paints.


Resort Santorini Greece Building TerracesIn post world war period plastic (or Latex, as known in USA) paints became available. The ‘latex’ paints were water-based emulsion medium. The field of marine coatings was offering many new technologies for water and UV light resistant, hard wearing systems. Rubber-based systems (chlorinated rubber coatings) became synonymous with road marking paints.


Other fields of Indoor floor paints were emerging. Stage show floors, Dance floors, TV programme production sets, TV News room floors, sports arenas, required colourful joint-less extensive surfaces. Food plants, Pharmaceutical units, Hospitals operation theatres and critical care areas, needed not only a joint-less surface, but one that was dust and scratch proof and bio-friendly material. These were first provided by Polyurethane systems and later by Epoxy systems. Electronic assembly plants, computer rooms, electronic exchanges and data server and router areas, needed static proof floor coatings. Fire-prone industrial areas needed a spark erosion flooring systems.

indexOutdoor Floor paint field also has flourished well. Sports facilities, stadiums, exercise areas, malls, food plazas need many different types of a joint-less floor of non skidding and spillage proof surfaces. The colour and texture requirements of these usages can never be found in any natural or manufactured materials. Thin coating systems of floor paints not only satisfy such unique needs but also offer pattern laying facility.

mark-1105984_640Technological innovations include use of Florescent pigments, night glow compounds, high luminescence whitening agents, texturizing additives, wrinkle finishes, two or multi-tone effects.

640px-GeneDavisStreetThe ability of a floor-painted surface to virtually do everything expected of a floor system, has forced changes on substrate technology. There was a time natural floor materials like stone or ceramic tiles were ground to smooth level and then coated. Any joint gaps or remaining surface level irregularities were filled in. But now cast on site surfaces of many materials are preferred. The material options include Ironite (cement+sand mixed with iron turnings), Magnesium Oxy-chloride Flooring, Cement Concrete floors (Tri-mix suction system), etc.