Long lengths and boards glued with cold-setting resin glues must be cramped and are first planed fractionally hollow. In theory one sash-cramp should suffice, but in practice it is better to use three or more, with one at each end underneath and one in the middle on top to counteract any tendency for the cramps to pull the assembly in warp, checking that the boards seat on the sash-bars, and testing the upper surface with a straight-edge. If resin glues are used, there will be plenty of time to adjust the assembly, tapping down any boards which are inclined to spring. In all gluing operations with resin glues containing acid hardeners, scraps of polythene should be used to isolate glue-covered wood from steel jaws or bars, as otherwise iron staining may result. Surplus glue should be scraped off, for resin glues are hard on cutting edges.
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