Finishing veneers

Overview

Veneer is a layer of real wood, often only about 1/32 inch thick in modern work; the furniture-restoration article in Popular Woodworking contrasts a chest's old veneer as "double or triple the thickness of modern 1/32 inch veneer". Everything about finishing it follows from that: there is very little wood to sand away, and a mistake cannot be sanded out. The rule of thumb in the sources is to start with a finer grit than you would use on solid wood, sand less, and know how to patch a sand-through. The sources opened for this guide do not cover veneer bubbles, contact-cement lifting or burl veneer, and they are not described here.

When to use

• Veneered plywood or MDF panels, doors and tabletops (Finishing sheet goods (plywood, MDF, MDO) covers the substrate and edges).
• Antique and restored veneered furniture, where patches and old glue are the problem (Repairing defects before finish).
• Not for solid wood, where the full Sanding schedule and Scraping and planing for finish apply.

Materials and tools

A random-orbit sander and sanding block; 120 to 220 grit paper; a pencil; for a patch, a router and straight bit (or a box knife and chisel), matching hardwood or veneer and glue. Stains and conditioners as for any face (Pre-stain conditioner and washcoat, Gel stain, Water-soluble dye stain, Alcohol and oil-soluble dye stain).

Steps

1. Start fine. Flexner says to begin pre-sanded veneered plywood or MDF at #120 or #150, not #80 or #100: starting coarser is a waste of effort and "you would risk sanding through". Finish-sanding both these surfaces with #180 is his example.
2. Mark your work. The Popular Woodworking Tricks of the Trade answer to a sand-through suggests drawing a squiggly pencil line along the veneer joint: it helps you keep track of how much material you are removing.
3. Sand with the grain by hand at the end, where the pattern allows. Flexner notes that this is seldom possible on decorative veneer patterns such as sunbursts and marquetry. Cross-grain scratches show under stain far more than under a clear finish, so on stained patterns practise on scrap to find a grit that hides scratches while still letting the stain darken (Sanding schedule).
4. If you sand through, patch before finishing. The Tricks of the Trade fix for a sand-through at solid-wood edging: remove the damaged veneer with a router and a straight bit, cut a hardwood strip whose colour and grain resemble the veneer, and fit it into the groove. Then sand it flush.
5. Patching old veneer. The restoration article makes straight cuts with the grain at the edge of the damage using a box knife or chisel, fits replacement veneer with straight cuts into the void, clamps it, and trims it level. It used solid wood for patches because the original veneer was thick, and says that matching old pieces made the finishing much easier.
6. Clean off hide glue first. On old hide-glued veneer the same article crystallises the glue with denatured alcohol and washes it off with hot water so there is clean wood before regluing (Glue squeeze-out and common finish failures).
7. Stain and finish as for any face, testing on offcuts first (Wipe-on application, Spraying with HVLP).

Common problems

• Blotching on cherry-type veneer. Flexner says most cherry boards blotch when stained or when simply finished clear, and that the only way to avoid it is to find boards or veneer without the tendency. Veneers are graded for curly and mottled figure, but not for blotching in other species (Finishing resinous and blotchy woods).
• Patch shows as a lighter or darker rectangle. A colour match is made before finishing; see the glue-splotch and defect entries for disguising with pigment (Repairing defects before finish).
• Heat guns and caustic strippers. Flexner warns that these are risky on furniture because of damage to the wood, veneer and glue joints (from his refinishing tips). He describes paint stripper or the finish's own solvent as the two broad ways to remove an old finish.
• Not covered by the sources opened: bubbles, lifted corners, contact cement, veneer thickness for new work, and burl or crotch veneer.

Safety and environment

Wood dust, and in MDF-core panels the resin binder dust: use extraction and a respirator. Routers and box knives are cut hazards. Alcohol used to crystallise hide glue is flammable.

Related

• Finishing sheet goods (plywood, MDF, MDO), Repairing defects before finish, Sanding schedule
• Pre-stain conditioner and washcoat, Finishing resinous and blotchy woods
• Shellac, Wipe-on application