Prepping plywood for paint

[Alex Borshov]

I'm getting ready to build some cabinets and book cases from birch plywood. I'll be painting them white. One suggestion I heard from a coworker is to brush a thin layer of urethane on the bare plywood and then sand it before priming and painting. This is supposed to keep those little wood fibers from sticking up through the paint. Has anyone done this before? Sound like a decent idea? I was sort of afraid of the paint not adhering but I guess if it's a thin coat it'll soak in pretty well and then get sanded.

[Prashun Patel]

You're better off (IMHO) using dewaxed shellac or a shellac based primer (e.g., Zinsser Sealcoat or Zinsser BIN). Lightly sanding after the primer will remove any raised fibers. Because of shellac's price, speed-to-dry, ability to seal in stains, and adhesive properties, it's a very good primer. It'll also (like any primer) reduce the # of topcoats you'd otherwise need.

[Lee Schierer]

I concur with not using polyurethane. Paints don't like to stick to it very well. You can also use http://lh5.googleusercontent.com/public/amd1X0FRWjaQTgi5rZolfunhdumta0dDDSbOG7Yq2R3fDeMh0C lgHMmIMuPr4Z-pAMv-qqOpdv9L10jZlYHYocBaZOe-bkj30H9lP27jqWbVdT_Tn2VuKzn6f0Y2fwzHIHgi6wGHPhpxDQ BM-gt5C52Y1vkqScJ7dbfqD3EV5bWRZlRNM7le9NKKmWjjnmLlD9S xJ3qvJxUwITjkdC2afDdbL8IoRg5PGRyuacC_MoyFXxZXwlbaE hdEPwk-te-Lx5uXjaF30Dxr-6xm9l7NOLIIPeqtLQKrWY8H=s90which will do the same thing.

[Howard Acheson]

>>>> supposed to keep those little wood fibers from sticking up through the paint

The first coat of ANY finish will seal the surface and cause the wood fibers to swell and raise from the surface. So just apply the first coat, let if dry and then scuff sand with 320 paper on a flat sanding block. No need for any special primer, just thin the first coat of your top coat about 10%.

The above is the normal process for any clear or paint finish.

Here is a reference to a more detailed discussion of "Raising the Grain".

www.hardwoodlumberandmore.com/Articles/ArticleViewPage/tabid/75/ArticleId/28/Pre-Raising-The-Grain.aspx

[Jonathan Link]

+1 for dewaxed shellac. We did a puppet stage for my daughter and we wanted a very smooth texture. I did two light coats of shellac, sanding with 220 between coats. My next paint grade I'll try a finer grit, but I'm generally happy with the texture.

[lowell holmes]

I use Sherwin Williams lacquer based enamel undercoater. It is sprayed on (using a Harbor Freight HVLP spray gun). You can recoat or sand in 20 minutes. You can apply any enamel over it.

It fills voids, sand smooth and will give a glassed out enamel finish.

I know some of you will have a problem with this, but if you haven't tried it, don't bark too loud. :)


I recently repaired a daughters cabinet after a new refrigerator went in. I used the under coater, and S/W high gloss enamel (to match old cabinets). It looks really good.

I used this product the first time 25 years ago.

[Ken Garlock]

Hello Alex, ;and welcome to the creek.

I would jump on my horse and trot over the Sherwin Williams. I have used their Pro Block primer followed by their top of the line white. Both are water based... The people at S-W are helpful, so tell them what you are doing and they will have a good recommendation. (I try to get one of the older clerks.)

[Alex Borshov]

I use Sherwin Williams lacquer based enamel undercoater. It is sprayed on (using a Harbor Freight HVLP spray gun). You can recoat or sand in 20 minutes. You can apply any enamel over it.

Which Harbor Freight gun do you use? This one? http://www.harborfreight.com/professional-automotive-hvlp-spray-gun-kit-94572.html

[David Cefai]

Why not use undercoat? It will bring up the fibres, then when you sand them off you will also be smoothing the surface. Most of your smoothing should come from two coats of undercoat. After all it is designed for this purpose, as well as to obliterate anything underneath. Then apply 2 coats of finish.

For interior applications I have never regretted not using a primer.

[Jim Heffner]

The other posters have made some good suggestions here and I'll second the vote for shellac. I use the Zinsser bullseye spray shellac, in a can on a lot of my projects, makes
paint flow like it it is warm butter!

[Peter Quinn]

I'm getting ready to build some cabinets and book cases from birch plywood. I'll be painting them white. One suggestion I heard from a coworker is to brush a thin layer of urethane on the bare plywood and then sand it before priming and painting. This is supposed to keep those little wood fibers from sticking up through the paint. Has anyone done this before? Sound like a decent idea? I was sort of afraid of the paint not adhering but I guess if it's a thin coat it'll soak in pretty well and then get sanded.

You could use thinned urathane as a sanding sealer for "paint" but it wouldn't be my first choice for a variety of reasons, the top two being adhesion of the top coat and cost. Those little fibers are a result of " raising the grain" which is caused by exposing raw wood to water. Can I assume your paint is latex or water borne? In any event, there are a number of better options as a first coat under paint than urathane. You could simply moisten the wood with a spray bottle or damp rag, let it dry, then sand with 220 lightly to cut the raised grain. Grain will only raise once unless you sand through to fresh wood. This won't seal the wood however. Sanding sealer or a good primer will both raise the grain and reduce the woods porosity, which will avoid leaving dry spots in future top coats where too much finish has been absorbed by more porous areas of the wood. Shellac, water based primer, and oil based primer sealer like zinnser are all good choices under paint. Be prepared to sand the primer back with a fine sponge before the top coat is applied. A good sealer or primer is easy to sand. The problem with urathane is it is not generally easy to sand, and not everything likes to stick to it.

[lowell holmes]

http://www.harborfreight.com/hvlp-turbine-spray-system-66297.html

The one I have is a plastic version of this one. Mine is a single stage. It's the same gun Woodcraft and Rockler are selling for more money. The two you linked to have been getting good write ups.

[Alex Borshov]

Thanks all for the great advice. There's a HF store not too far so I think I'll pick up this HVLP gun with a 2.0mm tip: http://www.harborfreight.com/household-low-volume-low-pressure-spray-gun-92841.html and then use a shellac undercoat and enamel paint.

[art san jr]

Alex, you may also wish to pick up an 'inline filter' while at HF, $6.00 or so. Prevents/reduces contamination of the paint by any gunk in your tank.
It filters the air between the compressor and the airline and the gun.

Just a suggestion.

Art.

AND OH, Seasons Greetings to you and all here at the Creek.

HAVE A GOOD ONE EVERYBODY !!!!

[Bob Wingard]

Glidden makes and excellent primer/sealer for painted projects whic does exactly what you're asking for. It strengthens the fibers and seals the surface. One coat, a light sanding, and you're ready to topcoat. This stuff even preps PVC to accept regular paints, so, if you have PVC duct collection piping that you need painted, this is what you will want to use.

[Lex Boegen]

I use dewaxed shellac. It's frequently sold as "sanding sealer". Any type of film finish can be applied over it (paint, varnish, etc.).

[Alex Borshov]

I ended up getting Zinsser Sealcoat and the cheapie spray gun from Harbor Freight. Both are working great so far. I need to work on the ventilation in my garage, though. I got the heater cranked up so the sealcoat dries properly but then have to open the garage door a few feet to vent the over spray and all the heat escapes. Oh well, it'll get done. I don't think I should be spraying that stuff with the heater on anyway...

[Alex Borshov]

Have you guys had a problem with sand paper gumming up when sanding shellac? The little gummy spots on the wood are about impossible to remove. My best luck has been to use 150 grit paper, instead of 220 like I wanted, and to blow the surface clean after each pass, but it's still not great. I'm using an electric sander. I'll try hand sanding in the morning but that's going to take a looong time. The shellac dried for at least a couple hours before I started sanding so I don't think that's the issue.