Water-Based Glue, Lamination, and Warping
From contributor R:
Inexpensive backer material is available for this. Have you tried looking into contact cement instead of PVA?
From contributor M:
PVA glue is water-based and expands the surface as it is spread on causing the board to warp. Solvent based contact cement has no water and will not do this. However, if you put no laminate on the bottom surface, that naked surface will eventually soak up or shed humidity and cause the panel to warp anyway.
From contributor C:
When using any water-borne adhesive to laminate only one side of a panel, warping will always occur to some degree due to the fact that the core expands when it absorbs water from the adhesive. This is particularly true of MDF. After the panel is removed from the press the core is still expanded due to the remaining water trapped in the wood fibre. At this point I've seen the panel warp away from the HPL due to expansion of the surface the adhesive was applied to.
If you're lucky, when the water eventually dries out, the core will shrink back to its original dimensions and the panel will be flat again. If the panel actually over-dries or if the backside picks up moisture later on (manufactured under low humidity but installed into humid conditions) then the panel may warp forward or towards the HPL surface. Using a very high solids PVA (65%+) may help somewhat. However the preferred solution is to use an inexpensive HPL "backer" sheet and laminate both sides of the panel to balance the forces which would otherwise cause the panel to warp. This is the method specified by the Architectural Woodworking Institute for it members when doing laminated panel construction for architectural millwork.
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