Vinyl Sealer Tips with Maple

Explanations of why vinyl sealer helps prevent blotching when finishing Maple, and advice on getting the best performance with it. February 8, 2008

AWI lists these steps for finishing maple to eliminate blotching. Are these steps accurate?
1) vinyl washcoat
2) stain
3) vinyl sealer
4) sand 220
5) topcoat
6) topcoat

Forum Responses
(Finishing Forum)
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.

From contributor L:
I am a big believer in shellac instead of the lacquer seal coat. Shellac seems to take color better in my experience. Using alcohol dye for the initial color you get the solvent "bite." This can backfire if you get your mix wrong, and nothing sands like a good thin coat of shellac.

From the original questioner:
I am not a pro finisher at all. So what's the purpose of the sealer after the stain? Should that always be done? I normally do stain, then 3 coats pre-cat. Sanding after first 2 coats. I can usually get a pretty good finish with these steps. But I know maple and birch have a tendency to blotch, so I can't go with my normal steps.

From contributor W:
The sealer in some cases is just a modified topcoat made to sand easier. The vinyl type was made to meet certain specifications for chemical protection. You most certainly do not have to use one if your top coat is made to be self sealing, which it sounds like yours is. So no, you really don't have to add that step.

From contributor P:
The steps you list sound fine. The washcoat limits absorption of the stain (see link below for more info). Vinyl sealer is a good choice for a washcoat because it seals the wood evenly, even when you thin it a lot. Vinyl sealer also has excellent adhesion properties and moisture resistance. In a professional finishing system, it's a drop in replacement for shellac.

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

From contributor W:
Contributor P, according to KCMA, vinyl sealer used under a regular lacquer will yield you a KCMA approved finish. However, using a regular lacquer sealer will not. So using vinyl under a regular lacquer does improve its overall durability.

From contributor P:
Vinyl sealer improves moisture resistance, not other durability factors like chemical resistance, heat resistance, scratch and wear resistance, etc. Improved moisture resistance comes in handy for kitchen and bath cabinets.

What document does the KCMA make that statement in? Are you sure you're not thinking of the AWI specs?

From contributor D:
So, what about a stain base instead of the vinyl washcoat? Someone just told me a stain base on maple or birch is just as good, if not better, than a vinyl washcoat.

From contributor P:
Stain base can work, depending on the solids content and whether or not it is dissolved when you apply the stain with pigment/dye. If the solids content is too low or too high, either the wood won't be sealed enough to prevent blotching or it will be sealed too much and the wood won't get enough color from the stain. Low solids content is the more likely problem.

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.