AWI lists these steps for finishing maple to eliminate blotching. Are these steps accurate?
1) vinyl washcoat
3) vinyl sealer
4) sand 220
From contributor W:
The step that AWI refers to that *helps* eliminate the blotching is the first one. The vinyl washcoat, so yes, in a sense that is correct. Depending on the stain and finishing products you are using, there are more ways to do it. A lot of the time, you can spray a wet coat of the clear base stain you are using. Then spray or wipe a coat of the stain over that while it is still a little damp. There is little difference between that and washcoating with sealer in my book. If you cannot get a clear base of the stain you are using and do not normally buy vinyl sealer, just use your regular lacquer sealer in its place. Cut it down to a >5% solution and apply a wet but not puddling pass. Let dry, then depending on time restraints, lightly scuff or just stain away over the top of that. After all that, just go off the AWI schedule for the rest of the system.
Vinyl sealer is also used over the stain. Its ability to promote good adhesion is superior to going straight to a topcoat. Applying stain over a washcoat is basically the same as using a glaze. Intercoat adhesion problems are avoided by sandwiching the glaze between two coats of vinyl sealer. This practice is standard procedure. But to avoid making the overall film finish weaker than it should be, two coats of vinyl sealer are the most you would normally want to use. It's not as durable as the finish used for the topcoats.
By the way, vinyl sealer is not the same as sanding sealer. Sanding sealer contains "soaps" that make it easy to sand in comparison to the topcoats. Vinyl sealer isn't always that easy to sand, which varies by brand. And it doesn't offer any added protection from chemicals. The topcoats will determine that property.
How and When to Use a Washcoat
What document does the KCMA make that statement in? Are you sure you're not thinking of the AWI specs?
Many fast dry stains use a relatively weak binder. When you apply wet stain over dry stain, it dissolves the dry stain. A benefit of this is that you can make repairs to the stained surface and blend them in almost perfectly. For example, if you find a glue spot in the stained surface, you can sand it out and re-stain the spot without getting the dark halo that you would typically get with consumer grade wood stains. The downside of this is that when you're counting on the clear stain base to seal the wood and prevent blotching, the wet coat of stain dissolves the clear coat of stain base and it no longer seals the wood. This is going to vary by brand.
With vinyl sealer (among others), you can easily adjust the solids content to get the exact amount of control you want. You can lower the solids content to allow the wood to retain more color or you can raise the solids content to reduce the amount of stain the wood holds. It dries fast - you can scuff sand smooth and stain in a short time.