[SV Siren]

I had the same problem with Schooner varnish. It was most obvious trying to get that last perfect coat on. If I used it full strength it was too thick and I got brush strokes. It also seemed to start curing almost immediately and get even thicker as I applied it, even on relatively small areas.

Starting inspecting the work very closely and I swear it looks like the bubbles were appearing in the varnish after I applied it, just like bubbles appearing in a soda. It's like the varnish was generating the bubbles. My theory is the thinner was causing some kind of reaction that generated the bubbles and I tried every kind of thinner I could think of: Schooner brushing thinner, mineral spirits, generic thinner and a couple more that I can't recall. All had the same result.

I even called tech support to ask but they couldn't come up with a solution.

One thing that I tried that helped a little. I warmed the varnish before applying (without thinner) to reduce the viscosity and slow the curing.
.

I tried warming the varnish and going full strength, and like you, had the bubbles seem to form out of nowhere in 15 seconds. I will try thinning with a little 333, which is a slowing agent for high temps, and if need be, I will bust out a hairdryer and a heat gun. In progressive steps if it doesn't work.

If all else fails, I will go with a different top coat.

 

[skipmac]

I tried warming the varnish and going full strength, and like you, had the bubbles seem to form out of nowhere in 15 seconds. I will try thinning with a little 333, which is a slowing agent for high temps, and if need be, I will bust out a hairdryer and a heat gun. In progressive steps if it doesn't work.

If all else fails, I will go with a different top coat.

I had one other idea I had but didn't try due to running out of time and motivation to put yet another coat on my project.

Since the bubbles seemed to appear from within the varnish but only when I used thinner I was speculating that some kind of reaction or dissipation of the VOCs might be the causse. So what if I mix the thinner and varnish then let it sit for some time in hopes that the bubble forming process will complete and then the varnish could be applied without the bubbles.

Feel free to try this out and let me know if it works. :smile

 

[RichH]

Just a little off topic, but it concerns schooner varnish. I am getting persistent bubbles. I have been very careful about stirring, and I am on the 6th coat, and still getting them, the first couple of thinned coats I did not get them. The last couple coats I have been using non thinned varnish. Any suggestions???

Several problems will cause bubbles.

1. Not using a 'spit coat' on the first coat which soaks deeply into the wood and 'seals' it. A 'spit coat' is typically 50% varnish and 50% thinner/reducer.

2. Using a dirty brush. If your brush isn't cleaned perfectly, it may develop bristles that become 'non-wettable'; hence, trap air. Once cleaned its usually best to keep the brush wetted in sealed container partly filled with thinner ... and with the working end of the brush held off of the bottom of the container.
For repetitive coats and to keep the brush wetted, consider not to clean the brush between coats .... just load the brush with varnish, put it into a plastic bag, and put the whole works into a FREEZER. Allow it to fully come up to ambient temperature before using.
2a. If you're using foam brushes .... switch to JEN foam brushes (Amazon) and/or SLOW DOWN your brush strokes. Consider to soak the foam brushes in your 'spit coat' to wet them out; then gently squeeze out the spit coat before using 100% varnish.
The slower you lay down the varnish, the better the 'flow' of the varnish 'from' the brush - for the least amount of bubbles.

3. Dont ever apply varnish to a hot surface or a surface the will 'become' heated. Such will/can cause aggressive outgassing of the thinner and/or varnish, etc.

 

[MastUndSchotbruch]

Yes, it worked for me. I did the saloon table in a 2 pack resin. Worked like magic. 1 breath and they would pop.

Cool! Thanks for the tip.

 

[skipmac]

Hi Rich,

Know this wasn't specifically addressed to me but since I'm having the same problems I took the liberty to reply.

Several problems will cause bubbles.

1. Not using a 'spit coat' on the first coat which soaks deeply into the wood and 'seals' it. A 'spit coat' is typically 50% varnish and 50% thinner/reducer.

I did do the initial thinned coat on all part so don't think this was my problem.

2. Using a dirty brush. If your brush isn't cleaned perfectly, it may develop bristles that become 'non-wettable'; hence, trap air. Once cleaned its usually best to keep the brush wetted in sealed container partly filled with thinner ... and with the working end of the brush held off of the bottom of the container.
For repetitive coats and to keep the brush wetted, consider not to clean the brush between coats .... just load the brush with varnish, put it into a plastic bag, and put the whole works into a FREEZER. Allow it to fully come up to ambient temperature before using.
2a. If you're using foam brushes .... switch to JEN foam brushes (Amazon) and/or SLOW DOWN your brush strokes. Consider to soak the foam brushes in your 'spit coat' to wet them out; then gently squeeze out the spit coat before using 100% varnish.
The slower you lay down the varnish, the better the 'flow' of the varnish 'from' the brush - for the least amount of bubbles.

Have tried every combination of badger, synthetic and always new foam brushes (not Jen, thanks for the recommendation) and still have the bubbles. I am 99% certain the bubbles are NOT from brushes or brushing technique. I can put on a coat, it's perfect, then I look very closely and see bubbles forming. Forming and not floating to the surface but appearing from clear varnish.

3. Dont ever apply varnish to a hot surface or a surface the will 'become' heated. Such will/can cause aggressive outgassing of the thinner and/or varnish, etc.

I kept the work inside my garage where it was cool, max about 70 F.

I think that my problem is definitely outgassing, just don't know why. Another thought I had, maybe the underlying coats were not fully cured and the thinner in the new coat caused outgassing from the underlying coat, even though it was cool. I did typically wait 24 hours or more between coats. Long enough that I could sand the previous coat before applying the new and yes, I did wipe and clean with a new tack cloth. Maybe the tack cloth was reacting?

 

[SV Siren]

I just did a little of experimentation of one practice door, and here is what I found.

Parameters:
Air: 68F
Hand sanded one side, Ro sanded the other, 320 grit for both
Two new foam brushes, 1" Jen
Strained Schooner 96 into both, into small plastic cups, and covered, let sit 5 minutes.
Cup 1 I thinned 25% or so with 333 brushing liquid.
Cup 2 I thinned 25-30% with Mineral spirits.

I let both cups rest for 5 minutes after a gentle swirling motion.

Findings:
The cup with the 333 thinner actually flowed out nicely, very very few bubbles, like glass. I tried a gentle hair dryer after a minute, and that made things a little worse, and it skinned over, don't do....

The cup with the mineral spirits flowed well, but a couple of bubbles appeared, not many but more than the 333.

Additional suggestion, to me and others that I noticed. Do not press the foam brush into the bottom of the container, as I did the first time, bubbles came out of the foam...bad news... The 333 thinner is a thinner for higher ambient temps, and REALLY slows the curing process when used in cold temps, as it is still tacky for a long while..I have a clean room which helps.

 

[Minnewaska]

Minor point and should be unrelated to the bubbles, but I use 220 sandpaper between coats.

Can't help but wonder if your experience would be better with the manufacturers recommended thinner.

 

[Tanski]

Odd I get a few bubbles after brushing that go away without doing a thing. Maybe it's a schooner varnish thing. My experience with Epiphanes with mineral spirits has been nothing but positive.
Anybody tried Le Tonkinois? Read good things about it as well.

 

[skipmac]

Minor point and should be unrelated to the bubbles, but I use 220 sandpaper between coats.

Can't help but wonder if your experience would be better with the manufacturers recommended thinner.

I tried the recommended thinner and got about the same bubbling as I did using mineral spirits and generic thinner.

However I did not try the thin and let sit method that SV Siren tried.