Conversion Varnish and Sanding Sealer

Advice on switching to a clear conversion varnish over a vinyl sanding sealer for a simple, quick two-coat system. April 15, 2013

We are seriously considering changing our spray to Sherwin-Williams Sherwood Water-White CV for our clears. Our goal is a two coat system and we are hoping to find someone who has successfully used their vinyl sealer topped with the Sherwood CV. Right now I'm doing a stain job using the Sherwood as self-sealing, and it's working fine (looks great) but obviously is a bit of a hassle to sand compared to a good sanding sealer.

Is anyone able to get a good build in two coats using their vinyl sealer? Also, how does Sherwood behave in the heat (90-100F) or in colder weather (50F or so in the spray shop, cured overnight around 60-70F). Do you need a bunch of different solvents/thinner, or does it behave well with any one particular thinner? We are using MAK as a slow thinner.

Forum Responses
(Finishing Forum)
From contributor N:
I use the SW Water White CV for sealing and topcoat, so no vinyl sealer comment. Regarding the temperature, 70 plus works best for spraying and curing, and when very warm it has always behaved very well for me. It seems that the ďhotter the better."

For dead-o-winter I try to prime my finish room and do not run the blower for any longer than absolutely necessary. The room recovers relatively quickly. If I can get back up to 68 or so in the first 30 minutes of drying/curing I feel pretty good about it. Also, I'll pull air through the shop rather than directly from outside when I am trying to warm the finish room back up.

From the original questioner:
Unfortunately our shop is small enough such that we almost have to run that dust hood the whole day while we have curing finish, otherwise we get gassed to death. Fortunately though, we spray our items vertical and we hang them on a 4x8 grid that hangs just overhead, and we set our torpedo heater on a cart blowing down the gridwork. Should I keep the temp at least above 70 in that one localized spot? I may even see about hanging a 1/4" sheet of material on front and back to act as a baffle to keep the heat channeling through it. Thanks for sharing about spraying in the heat. It was about 90 in our area this past week (55% humidity) and it sprayed quite nicely. Do you thin with M.A.K?

From contributor G:

We use it as a self-sealer and two top coats all reduced to 15% with butyl acetate. In the last top coat I add 2% xylene for better flow and smoother finish. When I tried the fast drying vinyl sealer with one top coat it didnít come out the same final quality Iím getting now. As a self-sealer you can add some lacquer thinner in winter or more butyl in warm weather to help it dry harder, but always scuff normal. The best way for us is to let the sealer coat dry overnight, scuff, and apply two reduced top coats.

From contributor N:
I'm a one-man show in Illinois - yay for small shops! I don't know what MAK, or M.A.K. is, actually. I have always reduced with xylene, two ounces per two quarts of CV. Temperature (one way or the other) has never seemed to make any difference in application or performance. No adverse effects, anyway. I use a turbine HVLP for application, so the air coming going through the gun gets very warm. That may help in cooler temps. I should have added, when I am warming the finish room ahead of spraying, the project is warming too. Not that heat retention is one of wood's properties, but I do what I can.

Regarding sanding, not knowing any different, I've never thought the first coat of CV difficult to sand. Also, I've read elsewhere here on WOODWEB that two coats of CV is considered an economy finish, but premium when using vinyl sealer first. I don't know. I would be interested to hear from others in this regard.

From the original questioner:
MAK is Methyl amyl Ketone. Smells like ML Campbell Flow #2 solvent, similar results. I've sprayed a lot of ML Campbell's Level Sealer and it sands like butter and leaves a very nice smooth surface for your topcoat. So I'm a bit spoiled. I'm not able to do the overnight-cure for sanding. We spray one dayís work at a time so that the next day we have doors to hang on our cabinets which can be wrapped and stored away. We are a small shop although surprisingly high production for two guys.

I have never had an issue with using CV as a self-sealer. I've sprayed all of my own personal furniture (including stands for saltwater aquariums) with CV as self-sealing and it stands up quite wonderfully to the abuse. I can't personally see the advantage of using vinyl sealer when I'm getting these kinds of results, except that maybe it's a touch easier to sand.

From contributor M:
I use SW fast dry vinyl sealer and then clear coat with SW water white CV. I'm happy with the results. Make sure you catalyze your vinyl sealer when you're using a conversion varnish over it.

From the original questioner:
For those who have responded here I'm spraying this clear right now as self-sealer. I'm thinning with 10-15% butyl acetate. Even after curing for two hours at 70-80 I'm still not seeing the finish harden as much as I'd like for sanding the first coat. It sands and powders ok but I have to spend three times the amount of time sanding the door to make sure I get it looking right and I get all the surface pips off of it. Otherwise, I get rough spots that show to the eye more than they do with the hand. If I sand any harder (using either a super-fine sponge or 320 hand paper), I burn through. Anyone else have this issue?

From contributor N:
I only ever use, or have ever used xylene to reduce. Is butyl acetate as hot? Two hours seems like a long time. Why so much - does it spray better for you? Iím just curious, not argumentative at all.

Here is my ratio for SW ww CV, which is very close to the spec: 1 qt CV, 1 oz catalyst (which is a visual estimate of 1/2 of a quarter cup measure), and 1 oz of xylene.

I don't sand within one hour of spraying the last piece, so if I started a bunch of doors at 1 and finished at 2:15, even though the first doors have been done for an hour and fifteen minutes, I still won't start sanding until 3:15. That's just me. You ought to be able to sand in an hour.

If it's unstained, I sand with reckless abandon! Okay, not quite like that, but I don't worry about sanding through, and I use 320 in an ROS. If stained I pay much closer attention to de-nibbing and smoothing. Yes, it's more tedious. Two coats, sometimes three depending on the intended use, and done. I think it's awesome, too and can't imagine vinyl sealer providing any better product. I don't know what the trick is though, if any. Just make sure you're getting enough on in the first place. It's been a very straightforward finishing schedule for me for about 11 years.

From the original questioner:
I cannot speak to the evaporation of butyl acetate compared to xylene, but butyl is a medium-road in terms of flash. It's the main ingredient in several standard reducers. It's neither very hot nor very slow. I am using 10-15% in the finish because that gives me the best flow after spraying. I could perhaps use 5% on some days, but I have to spend time making sure it's flowing just right when I could just start with 10% knowing it will flow nicely 99% of the time.

Glad to know you've had 11 years of success with it. I do not know why I'm having the hassle with it that I am. I know ML Campbell's clears never cured this slow for me, but their white paints are a pain compared to what SW gives us. Thanks for your help, your finish schedule gives me a good comparison to my own. We are quite similar.