Shellac Under Conversion Varnish in a Fisheye Repair Situation

This discussion digs into the issue of applying CV over shellac, with other considerations involving fisheye. April 16, 2010

I recently posted some photos of wicked fisheye on red oak tables. The problem has much improved, but we're not up to quality standards yet. I'm debating whether to use Smoothie II or unwaxed shellac. It turns out the bottle says to use Smoothie II for catalyzing finishes (I'm using catalyzing sealer and conversion varnish, both from Sherwin Williams). I'm concerned about the effect on catalyzation and contamination of my equipment with silicone. Unwaxed shellac makes me concerned about adhesion with the conversion varnish topcoat. Can anyone address these issues? I don't want to see these tables ever again after they leave our shop.

Forum Responses
(Finishing Forum)
From contributor G:
Opinions are divided on shellac under CV. Some say it's okay, as long as your first applications of CV are light. Here are a couple of comments from others...

"What you want to avoid is getting too much wet product on the shellac. I find spraying a light first coat with a little heavier second coat works well. Scuff first."

"I would not use shellac under conversion varnish; I'd only use a catalyzed vinyl sealer or clear conversion varnish. Otherwise, wrinkling of the finish would be a real concern."

From contributor D:
I've used seal coat under CV and 2K with no problems, adhesion or otherwise.

From contributor R:

If you use the shellac under the CV, you are on your own. No finish manufacturer will warranty their finish with that schedule, so why risk it? Smoothie will do the job and spraying it on just one job will not cause any problems. In the good old days we sprayed that stuff on everything. Just clean your equipment and the shop real well after you are done. You can also check with SW - they probably have their own fisheye eliminator you can buy for their product. (It will still be silicone of some kind.) The silicone fear is a little silly to me. Silicone is an additive in many metallic automotive paints and they don't seem to have many fisheye problems with it.

From contributor B:
The most important coating in the finishing schedule is the very first coat. That said, I'd be real concerned with moisture since shellac isn't a good barrier against moisture.

From contributor A:
"Silicone is an additive in many metallic automotive paints and they don't seem to have many fisheye problems with it."

They add the Smoothie for you, hence no fisheye.

The manufacturer's warranty is bogus anyway. They will pay for more product, no labor. If things go bad, who cares about the cost of a few gallons of product? When the shingles fail on my roof, the least of my concern will be the expense of buying new shingles.

From contributor R:
They don't add smoothie; they add silicone, which enhances the metal flake. Smoothie is a Marson brand fisheye additive flow and gloss enhancer.

I don't know which manufacturer you buy your coatings from, but many years ago Sherwin Williams paid our company a substantial amount of money to strip and refinish a huge job that went bad as a result of their mistake. They didn't just pay for the replacement of the coating. If we had used other products they wouldn't have done anything.

I do many things as a finisher that I am not supposed to do, but there is a risk involved every time and it is my responsibility to understand the risk and do everything to minimize the chance of failure. I am just saying using shellac under CV is an unacceptable risk in my opinion. If I needed a sealer to seal off the contamination I would use a 2k isolante, otherwise I would just use Smoothie.

From the original questioner:
Good to hear about Sherwin Williams. I had my local SW manager check for a fisheye additive. He said they didn't have any such thing (from SW). I'd prefer to use their brand to eliminate as many possible chances of problems.

Where can I get the 2K isolates (2k polyurethane?)? Anyone know about Smoothie I versus Smoothie II?

From contributor T:
I believe if you do a little research at the SW automotive finishes web site you'll find that they discuss fisheye in their tech helps section and recommend adding the fisheye eliminator designed for that topcoat which they also market.

A little more research on Marston Smoothie will show you that Smoothie is a combination of solvent and Poly-Dimethylsiloxane (AKA silicone). Smoothie II has more complex chemistry but I don't think it contains silicone.

It's interesting that any time there are fisheyes we jump to the conclusion of silicone contamination, and if we add a silicone product to our finish we think everything is contaminated. Neither is always true.

Fisheye can be caused by little spots of oil or wax or almost anything that can be called a lubricant. This probably includes dandruff from the head of someone that uses a shampoo which includes a surfactant. Adding silicone to your finish puts it in a homogeneous solution. There are no little spots to cause fisheye.

So I would be suspicious of a lot of recommendations that seem to be based on superstition. In my opinion, you'll probably be okay with either dewaxed shellac or Smoothie II. That is provided your source of contamination is not something like dandruff.

Please forgive me for adding a bit of trivia. There is a common belief that overspray or contamination of WD40 causes fisheye because it contains silicone. WD40 will cause fisheye, but it contains no silicone. Its principal ingredient (believe it or not) is fish oil. Nuf said.

From contributor Y:
WD-40's principle ingredients are petrochemicals/hydrocarbons, not fish oil. If there is any fish oil, it's only 2% max!

3 - Composition/Information on Ingredients
Weight Percent
Aliphatic Hydrocarbon

Petroleum Base Oil
LVP Aliphatic Hydrocarbon
Non-Hazardous Ingredients

From contributor W:
The two Smoothies are indeed different, but both contain siloxanes (AKA silicone).

From the MSDS for Smoothie:
Ingredient C.A.S. No. % by Wt
POLY(DIMETHYLSILOXANE) 63148-62-9 30 - 60
From the MSDS for Smoothie II:
Ingredient C.A.S. No. % by Wt
XYLENE 1330-20-7 30 - 60
ETHYLBENZENE 100-41-4 10 - 30
2-BUTOXYETHANOL 111-76-2 7 - 13

27306-78-1 3 - 7
ACRYLATE COPOLYMER (NJ TSRN: 800963-5156) Trade Secret 1 - 5
TOLUENE 108-88-3

Interesting that they have gone to such a complicated formulation.

From contributor T:
Thanks for disabusing me of the fish oil thing. I have no doubt that you are correct. I was told that by someone who should have known and never checked it. Bad practice. Do you think the 2% surfactant may be silicone? I should think they would have to list it if it were, but it doesn't take much to do the job. Perhaps the non-hazardous ingredients include fish oil? I think it remains that there's a lot of oil, no silicone that is identified, and it can still cause fisheye.

From contributor R:
In my experience it's when the silicone is atomized that it is a real problem. In one of the shops I used to work, they used silicone spray on the saw tables to make things slide easier. One day they were spraying that crap 100 feet from where I was spraying finish coat on a top and I swear it got there at light speed. You could just see the fisheyes forming in a wave.

From contributor Y:
I'm not sure it's the surfactant, but it could be, since they don't say it is something non-toxic. I don't have the samples anymore of the test I did with WD-40 for a man I used to work for in Florida, but he too was under the impression that it caused fisheye or contained silicone (siloxanes) also. So since I didn't know for sure, I put WD-40 on a piece of bare maple and sprayed it with Delta's acrylic sealer - no fisheye. Then I sprayed the sealer when it dried with more of it and wiped the excess off with paper towels and sprayed a second coat of sealer - no fisheye. I took the board to my boss and showed him the results and then had him watch while I ran the test from scratch on a new board
(this was all done outside the shop just in case). The results were the same. This was in 2005 around November.

The only test I have not done is to spray a light particle coat where only a little of it forms droplets on the surface so that the whole board is not covered with it, and let it dry out before sealing. Maybe this is the problem, if any. I'll leave that test for you guys to do.