Post 231 –by Gautam Shah
These are heavy consistency compounds used for several purposes: for filling in cracks and gaps, levelling the surface, fixing objects over surfaces and as interlining and pointing material. Due to their heavy consistency these compounds do not run. High viscosity is achieved by heavier phase formation (polymerization), foaming, or by addition of bulky filler materials. Some are designed to dry out completely slowly or quickly, whereas many are designed to remain green (ever wet or soft) so as to be removable, or to absorb the vibrations and movements.
Sealants are very viscous, to very thin or fluid materials. Viscous materials stay put, except they have a capacity to level out, whereas fluid materials run or flow out to penetrate very thin cracks and crevices, often by designed reduced surface tension and by means of capillary action.
One of the most common of such compounds is glass fixing putty or mastic. This is made by mixing china clay, water and alkyd resin or bodied linseed oil. In earlier periods asbestos and mica, were used in place of china clay. Other commercial compounds in this category include butadiene, poly-sulfide and silicone compounds. Some of these are two pack (resin + hardener) high strength and high bonding materials often used as industrial crack filler or sealant. These are also used for temporary bonding so that clamps may not be required for assembly work (e.g. truss erection), and also to eliminate mechanical fastenings like nut-bolts and rivets. Such industrial sealants offer greater assurance of the joint, better distribution of stresses.
Wooden boats were constructed with overlapping wood planks. The joints were sealed by traditional caulking method, where hemp fibres soaked in pine-tar were pushed into V shaped seam joints. Specific head formed caulking mallet and a caulking iron, a chisel-like tool, were used. The caulked joint was then lined with putty.
Epoxy putty compounds such as M-seal etc., are also of this category. Asphalt-based water proofing caulking compounds are widely used in crack filling over roofs or terraces, for sealing pipe and duct joints, and lining the joints in sheet structures. Epoxy based caulking compounds are also used in fixing composite aluminium sheets, frame-less glass facades, fibre glass sheets, PVC door frames, and aluminium sections to masonry faces. Polymer-based water soluble compounds help fix tiles and panels as floors or claddings. Caulking compounds of heavier viscosity give assured fixing, compared to low viscosity contact adhesives. Mastic are sold in cans, tubes, or canisters that fit into hand-operated or air-operated caulking guns.