Wash Coat Tips

Mix ratios and application methods for wash coats. November 13, 2005

Do you sand a wash coat before you stain it? What is a good ratio of thinner to lacquer to make a wash coat for soft maple? I'm starting with 50/50 but I'd like to hear what you all use.

Forum Responses
(Finishing Forum)
From contributor A:
I do not think a 50/50 cut will do the trick for soft maple or any other species of wood for that matter. You need to make a mix of 2 parts sealer to 10 parts thinner. I would also say a quick scuff with a sponge pad will be fine. If you use a 50/50 mix you will only be wiping your stain clean.

From contributor B:
A 50/50 mix is still too heavy. It will seal your wood. For maple I use 1 part sealer to 4 parts thinner when using lacquer. But I use 1 part sealer to 5 parts thinner when using conversion varnish because of the higher solids content in the varnish. Normally I would give the wash coat a quick scuff with 320, but it's not absolutely necessary.

From Paul Snyder, forum technical advisor:
Yes - sand the washcoat smooth before staining. Don't oversand - just enough to make it smooth. I've found that the thinning ratio varies depending on the wood and the stain/glaze. I usually use Chemcraft's low-solids vinyl sealer for a washcoat and thin it 1 part finish to 1-1/2 parts thinner which gives me a 5% solids washcoat. I'll do a color sample and see if it works okay. If I get blotching, I'll use less thinner. The data sheet for the lacquer you're using should tell you the solids content. Starting with that, you can figure out exactly how much to thin to get a 5% washcoat. There's a description of the process at this link: Making a Washcoat

From the original questioner:
I didn't even use the washcoat. I'm using MLC WoodSong II and I was surprised at how little blotchiness I got straight out of the can. I sanded out the Maple to150 grit before staining. The only problem I had was sanding swirls. It may be called soft Maple but itís not soft. I had to start off with 80 grit - my planer is in dire need of a knife change and I have quite a few knicks so there are a lot of striations to knock down. I was wondering about a card scraper. Would that take down the planer lines?

From contributor C:
I have the same problem with Maple and Hickory. 150 grit always leaves swirl marks that the stain reveals. On softer woods I can get away with ending at 150 grit, but on the hard woods I have to go to a 180 grit. I also use a 5% wash coat and sand lightly with p220 grit and I get great results with that.

From contributor D:
The best way to get a feel for what ratio wash coat you need is to do a step sample. Start with a 4' board and every 5 - 6" make a step. 1st would be a no-washcoat control section and then start with 1:1 and go all the way to 10:1 ratio. Scuff with a scotch brite pad and wipe stain on the entire board. You will then see the variation in the stain penetration by using different ratios of washcoat. Just pick the one that works best for the client you are working with.

From contributor E:
To contributor D: If I use the 1:10 and step the applications from 0 to 10 passes, how closely will that approximate mixing and applying 10 different dilutions?

From contributor D:
I don't know about your shop but my shop likes me to work fast. Unless I am really going to spray 10 coats on the project I like to do my samples exactly like I will do the job. You won't need to do this for every job, but it gives you a good idea of how varying the ratio of thinner will affect your stain penetration. After you do this one time, save the board and you will usually be able to figure out what you need on the first sample.

From contributor E:
To contributor D: It's the concept of working fast that generated the question. I'd like to avoid the hassle of mixing, spraying, and cleaning after each of 10 samples. But I hadn't thought of it as a long term sample rather than order specific, and that makes a lot of sense.