Mastic (filler compound)

Putty is a material with high plasticity, similar in texture to clay or dough, typically used in domestic construction and repair as a sealant or filler. Painter's Putty is typically a linseed oil-based product used for filling holes, minor cracks and defacements in wood only. Putties can also be made intumescent, in which case they are used for firestopping as well as for padding of electrical outlet boxes in fire-resistance rated drywall assemblies. In the latter case, hydrates in the putty produce an endothermic reaction to mitigate heat transfer to the unexposed side.

Putty has been used extensively in glazing for fixing and sealing panes of glass into wooden frames (or sashes), although its use is decreasing with the prevalence of PVC and metal window frames which use synthetic sealants such as silicone. Glazing putty is traditionally made by mixing a base of whiting (finely ground chalk) with linseed oil in various proportions. There are a number of synthetic alternatives such as polybutene based putties, where the polybutene is a low molecular weight oligomer replacing the linseed oil. Butyl rubber is also added to the mixture to provide some strength and flexibility.

In woodworking, water-based putties are more commonly used, as these emit very little odour, are more easily cleaned up and are compatible with water-based and latex sealers.

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