Touching up conversion varnish

Problems related to conversion varnish touchup. (From WOODWEB's Finishing Forum) January 21, 2003

Why do people say it is difficult to touch up conversion varnish? In most cases, lacquer touchups adhere well enough. It's easier to do burn-ins on CV because the hot knife doesn't mar the finish as readily as it will mar a lacquer finish. It seems to me that CV is at least as easy to touch up as lacquer. Furthermore, when a job is finished with CV it doesn't get damaged as easily as a lacquer finish, thereby reducing the number of necessary repairs. If you're dealing with major damage, you have to recoat the entire area, whether it's lacquer or CV. Why not just use CV?

Forum Responses
I agree. Beats me as to why other people think this is an issue.

From contributor M:
It is an issue when you go through layers and try to blend it in. When you're sanding or compounding and you go through the topcoat down into a shading stain, or into the seal coat, it is very difficult to feather these damages in. Naturally, it will depend on the finish that is being repaired - if it is opaque, transparent or translucent, the level of challenge can change.

As stated, it is an issue when you rub through coats but you can still recoat the entire surface. Burn-ins are much easier to do on CV. I think most people consider doing spot repairs with CV versus lacquer due to the fact that you have to recoat the entire piece with CV and don't with lacquer. Although, I have had some success with some CV spot repair techniques when working with customers.

From contributor M:
No repairs are pieces of cake, as you know. There are three types of repairs - one in the clear coats, the color (shading stain, glaze, stain) and the substrate (wood, veneer, MDF, etc.).

As the effect of the damage goes further down into the substrate, the repairs get more difficult, the transparent finishes being the hardest of the repairs.

Yes, when you can re-coat the whole surface after the repair is made with compatible and equal material, you have a good repair. When a lacquer or even a pre-cat is used in the repairs, it changes the whole integrity of the repair and the finish, and then it becomes a cosmetic repair.

The ultimate repairs are where no coating is used, only a clear filler and at times some color added, and then sanding/polishing pads are used to level and polish up the filler, and then compounding is done to complete the repairs. These are the most difficult repairs of all.

Being able to do the repairs in your shop where you have time is the way to go, but when you go out into the homes and offices where you cannot spray, I don't think you can call any of these catalyzed repairs a piece of cake.

When we have to do a touchup on CV at the job site, we use a brush, let it dry, recoat, then sand out the patch to the right luster. If the damage is caused by someone besides ourselves, we charge from the time we leave the shop to the time we return and have the brush cleaned up.

Has anyone used an air brush? Will it work on CV? I have thought about trying one for small touchups.

From contributor J:
I've always heard a repair to CV will not blend in around the edges even after it's rubbed out. Is this true?

From contributor M:
It would depend on the damage and the finish, and the method of doing the repair. I think we better mention and explain the types of repairs we're talking about. There are damages, and there are damages; a surface scratch in an opaque black finish is not the same repair as a scratch down into stain or substrate.

From contributor M:
I'm talking clear finish dings and scratches.

From contributor M:
Are these defects surface scratches or are they deep into the clear coat? If they are surface scratches, you have two options depending on the sheen of the finish. You can sand them out, or compound them out. If the defects are too deep to remove by sanding or polishing because you would create a cupping problem in the coating, filling will be needed.

First you need to evaluate the defects. Are all the edges smooth or ragged; is the bottom of the defect also smooth? If not, sand them all to a polished edge. Blow off any dust, and prepare to do your filling.

From contributor M:
I call small dents "dings," so they would have smooth edges. I hate repairing damage - I leave most wear from usage (character) under the new finish. I am a repair and refinish type, and of course restorer when indicated. I'm going to use CV in the future because some modern tabletops need a tough film. I need to know how to repair it or I could really screw myself on a callback years later.

From contributor R:
I just had to do a touchup on this cabinet door. Cross grain scratches caused by scaffolding being run into the cabinet. Door is radiused and right next to an exterior door with a *lot* of sunlight. I got it fixed, but it was difficult.

From contributor M:
Contributor R, I know what you mean - I don't consider any repair a piece of cake. A lot has to do with the types of damage, and how the finish was made up. In my opinion, the biggest factor in doing repairs is the refraction of the lighting on the pieces you're repairing, which can really make a big difference in the end results.

Contributor R, those cross-grain scratches are terrible - always the most difficult I do, especially when they are at eye level.

I find if I severely limit my repair to just around the scratch and carefully fill/sand/color just that area, I do better on the repairs. It's when I get aggressive and sand too far out into surrounding areas that I compound my problems.

I do high-end entry door repairs and these cross-grain scratches combined with a level finish and 40 sheen or higher are incredibly difficult for me. Fortunately I have a high hourly rate that begins when I leave the shop!

Each repair is different and a lot depends on where the damage is and the lighting, sunlight, time of day and if the customer has seen the damaged area.

I try to avoid rubbing out any scratches in conversion varnish and frankly, most damages are not scratches that can be rubbed out. The catalyzed conversion varnish does not scratch easily (as noted in the previous discussions).

I find most touchups to be easiest using a set of touchup markers for color. Each can be used individually or mixed to match the desired color in a puddle of topcoat, conversion varnish, and applied with a fine artist's brush or the edge of a small piece of paper.

Deeper gouges and scratches should be filled with a putty stick, especially those out of the way places and nail holes, but larger and more obvious gouges and scratches should be filled with a burn-in stick.

For severe damage a total refinish of the surface may be necessary, either in the shop or on site. Most of the time a refinish can be done on site if the damaged area can be sanded to breaking lines in the piece, such as the whole edge of a door, or the face of a raised panel. Small Preval spray cartridges can be used on site to spray conversion varnish. They work great.

Any other problem, bring larger equipment or get it back to the shop.

From contributor J:
Let's say you scrape out a chunk of topcoat and you need to fix it real quick, so you puddle on some finish, say CV, with a Q-tip. You wait for it to cure, then block sand it with 400 grit, and maybe 600 or higher, then you rub it out with pumice or whatever… Will there be witness lines or a discernable edge around the repair? Normally, I'd learn about this by doing a job, but I haven't had the opportunity yet. The only clean repairs I know of like this happen only with finishes that melt into each layer like shellac or lacquer. Can CV blend in?

From contributor M:
The key to doing all touchup repairs is not to make it worse by sanding through the color when sanding down the filler, or not to paint out the wood's character when coloring out your repairs.

There is nothing written in stone about how to do every type of repair. Options, alternatives and adjustments are a very important part of completing your repairs.

I will pass on one more technique on doing repairs that was not mentioned. If the damages are in the clear coat, polish off the edges in the clear coat, and if the damage is down into the substrate, here is what you must do to get good repairs:

1) There must not be any ragged edges. Use a razor blade to cut the damage into an oval shape.
2) Sand and polish the entire damage, including the edges.
3) Fill the defect only up to the wood line, and on your clear finishes use a gold base color for reflectivity, then add in any stain/toner colors and any grain lines.
4) Sand the coating in an inconspicuous spot and look at the sanding powder to see the color of the coating (water clear, amber).
5) Apply the same type of coating, then adjust the sheen.

This is a condensed version - add in the options for your types of repairs.

An addendum: Whenever you're repairing damages that are down into the substrate in any of the solid opaque colored finishes, you will find many of these finishes are first color coated and then clear coated. You must follow this same process when you're doing the repairs.

It is very important to fill only up to the wood line (to the color coats). You must allow some space for your clear filler. Otherwise you will never get a good color match in the repairs.

You also must be sure to check if the topcoats were amber or water clear. As I mentioned, test for this sand in an inconspicuous spot and check the sanded powder for color. It will tell you what the final coat was. It may be the same color or it may be an amber or water clear coat.

Finish off your repairs the same as was originally done.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor O:
I agree that doing a touchup is not a piece of cake. Touching up is a skill which is a part of a top-notch finisher's job. Finishers with a background in art have an eye for colors and are very sensitive to details. Touching up is like restoration of an antique painting. This is what I normally do with a cross grain scratch.

1) Lightly sand the topcoat of the item.

2) Fill up the deep scratch with filler or putty stick.
3) Lightly seal the affected area so you can see the original colour of the wood/grain.
4) Mix a color tint with sealer and match it with the color of the wood. (Please note that the grain of the wood has a diferent tone than the color of the wood itself.)
5) Use a fine brush to apply the mixture to the scratch matching the colour of the wood.
6) Try to mix a color tint to obtain the tone of the grain and blend it in using a fine brush.
7) Spray topcoat.

Usually finishers use the same toner to touch up the scratch, but most often it will not match, especially on a cross grain scratch.

Comment from contributor D:
In on-site touchup of conversion varnish, I explain clearly to the client that vestiges of the damage may remain, and offer the option of removing the piece to a shop for stripping and refinishing.

If they choose to keep the piece on site, I write in my work order that the client understands and accepts that traces of the original damage may remain visible, and have them sign it. So far (28 years) I've had only one complaint after signing, by a difficult and unreasonable client.