Bubbles in spar varnish?
#10
  
I'm throwing together a rough kick up rudder for my boat. It won't be the final iteration, so I'm not worried about pretty. I just want water tight.

Helmsman spar varnish applied by brush. No thinning. Five hours between coats. Sanding with 220 between coats. This is the third coat. Three pieces done, only bubbling on one.

I'm not terribly concerned; I'll just sand these down and recoat it. I'm just curious why it happened here.

Thoughts?


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Semper fi,
Brad

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#11
  Re: Bubbles in spar varnish? by ®smpr_fi_mac® (I'm throwing togethe...)
My only guess is some sort of contamination.  

John
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#12
  Re: Bubbles in spar varnish? by ®smpr_fi_mac® (I'm throwing togethe...)
John, that might be likely--the bubbles formed in two rows, about the width of the brush apart. I used a fresh brush each coat.

Weird.
Semper fi,
Brad

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#13
  Re: Bubbles in spar varnish? by ®smpr_fi_mac® (I'm throwing togethe...)
If this is oil based spar varnish, then make sure you gently stir it and not use a drill mixer or shake the can. 

I get bubbles in oil based finish, but if it is not too hot the bubbles work their way to the top and pop on their own.  Applying the finish in the sun would prevent that from happening. 

Use a good brush or a foam brush.  The foam breaks down from the oil based finish's solvent.  It is not a problem on small jobs, but plan on more than one foam brush for larger jobs.
No animals were injured or killed in the production of this post.
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#14
  Re: Bubbles in spar varnish? by ®smpr_fi_mac® (I'm throwing togethe...)
was this in water before?
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#15
  Re: Bubbles in spar varnish? by ®smpr_fi_mac® (I'm throwing togethe...)
No, this is fresh wood, stored in my shop for a few years. It's a new build.

The application was done in the sun. After popping the bubbles and recoating, they didn't show up again. It's ugly, but it's sealed. I'm happy.
Semper fi,
Brad

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#16
  Re: Bubbles in spar varnish? by ®smpr_fi_mac® (I'm throwing togethe...)
It does look like contamination. Bubbles everywhere + finish issue. Bubbles random = contamination. In my experience anyway.
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#17
  Re: RE: Bubbles in spar varnish? by ®smpr_fi_mac® (No, this is fresh wo...)
(06-09-2020, 07:18 PM)®smpr_fi_mac® Wrote: No, this is fresh wood, stored in my shop for a few years.  It's a new build.

The application was done in the sun.  After popping the bubbles and recoating, they didn't show up again.  It's ugly, but it's sealed.  I'm happy.

The sun is probably the culprit.  Bubbles will generally rise and pop by themselves if the varnish does not  dry too quickly.  The sun probably accelerated the dry time and it dried before the  bubbles could rise to the top and pop on their own. 

I applied paint in the sun and got horrible  brush marks.  The heat from the sun dried the paint before it could self-level.  Now I wait for shade before painting.  It if is on a boat, that might not be an option.
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#18
  Re: Bubbles in spar varnish? by ®smpr_fi_mac® (I'm throwing togethe...)
The oil in the finish absorbed into the pores of the wood while the finish cured. The finish was not fully cured before you applied the next coat. The previous finished heated up and expanded creating the bubbles as it off gassed.
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