Rubbing Out Conversion Varnish

Can the same method be used as for pre-cat lacquers? January 29, 2004

Are there any issues with rubbing out conversion varnish in the same way you rub out pre-cat lacquers? I figure you need to let it cure for a few days first, but I wanted to make sure I didn't screw up the finish by trying to rub it out and polish it.

Forum Responses
(Finishing Forum)
From contributor A:
I have done it with success. I think that it is fairly common practice though I am not sure of that.

From contributor B:
There is definitely one issue that you want to be aware of, and that is witness lines. Like most waterbornes, post-cats don't burn into previous coats, so unless you're very careful with your leveling and polishing you run the risk of burning through one layer into the next, leaving visible boundary lines.

From the original questioner:
I would expect that if the conversion varnish (which is still basically a lacquer, from my understanding) says there is no critical recoat time, that it is designed to burn in to the previous coat.

I am not sure that is the case, but that's what I would expect. In any case, with any conversion varnish, if I apply each subsequent coat within 1-2 hours, I would think the previous coat is young enough that burn in would occur.

Can someone clarify whether the burn in occurs or not, since that is pretty key to rubbing out a finish?

From contributor C:
CV does not burn in to the previous coat. The last coat does not melt into the previous coat. They are separate and distinct layers.

From contributor D:
If you recoat within an hour, the next coat will melt into the previous one. I usually shoot another coat as soon as the previous coat skins over. If you don't think it will melt in, try putting some fresh finish on a coat of cv that is less than an hour old, then wipe it with a rag; it will dissolve the previous coat.

From the original questioner:
Seems like a conflict of opinions in the responses. Is there a consensus on this? I guess I could try the test of putting some new CV over "young" CV and see if it does indeed melt the finish.

I generally use pre-cat lacquer and of course don't have any issues, but I was wanting something even more durable and wanted to shoot CV but still be able to rub it out if necessary to create a glass smooth finish.

From contributor E:
When I have used conversion varnishes and rubbed them out, the final coat was sprayed quite carefully and very close to an acceptable gloss so that the needed abrasion was minimal and we had no problems with witness lines. I am sure that we could not have cut through the top layers without encountering problems. In any case the undercoating should be quite well leveled before a final coat is applied and if the top coat is skillfully and carefully done, there should be no need to cut through more than the top ten percent of its thickness, leaving reasonable room for error. I like to use damp rags and soft scrub cleansers for the rough polishing and finish with appropriately finer polishing creams. This system removes very fine amounts of material from the surfaces and does it quickly and evenly. Power buffing will get you some trouble and you will really earn your money.

From contributor B:
Given the variety of experiences reflected here, the smartest thing for you to do is to call the technical assistance hotline for the product you actually sprayed, and ask them about this. Then you won't be flirting with a gruesome learning experience.

From contributor F:
Don't know about conversion varnish, burning in, and witness lines, but do know about wb's, conversion varnish, and witness lines.

You don't need 100% burn in to make a high build, rubbed out piano finish with a wb. Partial burn in is enough. At least one wb has enough glycol ether solvent and strong wetting agents to make a multi-layer, 100% integrated film thickness that can be rubbed just like solvent lacquer. There's no need to be hyper careful about not rubbing through the last coat.

However, it's important to learn the difference between witness lines and trapped solvent. These gylcol ethers can become embedded deep inside the film thickness, and become visible as they slowly work themselves up and out of the coating. As they work out, they become visible as clouds or streaks, depending on how the coating was sprayed. It's easy to assume these are "witness lines".

There are two ways to avoid this problem. Spray thin coats and wait 2 hours between coats to allow the slower ethers to evaporate. You can also subject the dry-to-touch surface to warm, circulating air. This will accelerate the removal of the solvents.

If you end up with streaks, and they aren't real witness lines, then you can just wait for the solvents to come out, or subject the entire object to warm circulating air. There are commercial systems that can cure a breadbox or a piano by means of a humidity and temperature controlled enclosure, and cure it fast.

From the original questioner:
Just got off the phone with Gemini Coatings and the guy there told me there is some burn in between coats if done within an hour, and rubbing the finish out shouldn't be an issue but to still be careful of sanding too deep just in case.

However, they also have a new water clear catalyzed product called Ultra Solids and it is a finish that will burn in and is as durable and hard as conversion varnish. Apparently they have gotten "fantastic results when rubbed out" as long as it is done within 3 days. After that it gets too hard (so I was told).