Refinishing and pinhole problems

How to prevent and fix those pesky pinholes. January 16, 2002

I am refinishing a couple of small red oak tabletops for a customer. I stripped off the old finish and applied the stain that I had color matched. I applied a coat of MLC water white vinyl sealer and then 2 coats of MLC clear acrylic modified lacquer. It was then that I discovered dozens of pinholes over the darker portions of the wood grain. I let the stain dry for more than 48 hours. It has linseed oil in it. Is there a way to get rid of the pinholes or do I have to strip everything down and start from scratch?

Forum Responses
If you are not sure whether or not the customer uses something like Pledge to clean her furniture, always clean the piece with denatured alcohol after you first strip, but before refinishing. Stripping will get out most of the contamination, but not always will it get the oils and waxes out of the furniture left by those type products. MLC is best used in a 2-coat application of WWVS, then 1 coat of the Acrylic Mod. If you had used 2 WWVS it would have blocked more of the contamination between the wood and the finish. If you don't want to re-strip, sand the acrylic back down, leaving only a little of the sealer on, without damaging the stain underneath, then reapply WWVS 2 coats and then finish it again with 1 coat of the acrylic. Sand in between coats with 220-320 grit alum. oxide paper. 3m makes the gray Tri-Mite paper that works great.

Lisa Gilbert, forum technical advisor

From contributor D:
Pinholes are a pain. I've spent many a day sanding back and re-coating, trying to beat them, only to eventually give up and start over.

I think paste filling open grain tops will go a long way toward eliminating them, especially on red oak. I rarely see pinholes since I started paste filling all my open-grain tops. Make sure your paste filler is dry before you overcoat, or guess what... pinholes.

I do think vinyl sealer helps prevent the scourge of pinholes too, but I don't know if I can explain why. I know vinyl is sensitive to any moisture in your line, though--leaves little miniscule bumps that look like grit. Anyone else ever notice that? I use a disposable in-line filter at the gun when I use vinyl sealer and that seems to take care of the problem.

A lot of cabinet shops out there tack with compressed air. Be careful when doing this over open-grained woods such as oak. Let the wood relax for at least 10 minutes prior to shooting on a coat of finish after tacking with air. Also, don't forget to check and bleed your lines for excess moisture. If you should tack with solvent, let the solvent fully evaporate prior to finishing, so you don't trap it. The further the solvent penetrates, the longer it takes to work itself out.

Do a slight reduction of your initial coat by no more than 15% - 20% with the recommended solvent. Try to apply your finish in thinner, more even coats.

Talk with your spray equipment manufacturer and see what adjustments can be made to achieve better atomization of your material. A different air cap just might help. Before you call your equipment manufacturer, know the viscosity of the material you will be applying. Viscosities stated on technical data sheets from manufacturers are typically stated by having the finish at 77 F degrees. Make sure the material and the substrate are at the same temperature prior to spraying.

From the original questioner:
Lisa, you recommend one coat acrylic. I was told that you could build acrylic, unlike conversion varnish or pre-cat. Any truth to this rumor?

Contributor D, I haven't used any paste fillers. Can you point me in the right direction?

I usually tack with a vacuum and a tack cloth. Reducing the initial coat sounds good. I am pretty consistent at about 4+ mil per coat. Are you talking thinner than that?

From contributor D:
I prefer an oil base filler and lately I've been using Lilly's filler from I order it pre-tinted to the color I need--a darkish walnut most of the time. You can tint it yourself and they have the tints you need.

If you've never used paste filler before your first impression may be negative. This is one of those tasks most finishers do not enjoy, but the result is worth the hassle.

Typically, I stain first, then put down a thin washcoat of my sealer. The washcoat locks color in, so then the filler will only penetrate and lodge into the open pores. After the washcoat dries, apply paste filler liberally, working it into the grain in a circular motion using an old scotch brite pad or piece of burlap (some like a rubber squeegee here). Then rub it off in alternating 45 degree angles to the grain with fresh burlap. Keep changing it out as if fills up. When you think you've got most of it off, rub with clean burlap, almost in line with the grain. Avoid rubbing hard with the grain, as this tends to pull the filler out of the pores. Allow more than ample time to dry, then lightly block sand to remove any residue. Then remove the dust, run another sealer coat (I like a vinyl sealer) and follow through with your topcoats.

There is a lot you can vary with this procedure, depending on the goal. Generally I am not going for a full-filled look--only an evenly filled appearance (without pinholes!) that still shows grain texture. So I don't fuss with my fill routine that much--just get it on, get it off and go. If you're going for full fill, it is a different approach and some finishers will go through the fill routine twice to achieve a full-fill.

Jeff Jewitt's book, Great Wood Finishes, covers this subject in very good detail with illustrations.

You can use more than 1 coat of acrylic, sanding the 1st coat before adding another coat, but where you get the most protection is building with the sealer coats. This allows you to block more of the contaminants from furniture polishes used by the homeowner before you get projects to refinish. WWVS, when used in a 2 coat application, will help with those pinholes. It will let the air trapped inside the grain escape before you put the finish coat on, making a smoother topcoat. Make sure each coat is dry. About 45 minutes between coats is enough, and sand between each coat.

MLC makes a paste filler. It comes in a clear base so you can get it tinted (844 colorants). This product does need to dry very well before putting on a seal coat as well. The darker the color, the more colorant is used. More colorant means more pigment added, so you will need a little more dry time. Don't rush through this process if you've never done it and you'll be okay.

Lisa Gilbert, forum technical advisor