Thinning 2-part polyurethane for brushing

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Old 10-06-16, 02:03 AM
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Question Thinning 2-part polyurethane for brushing

Hi all

I'm having trouble with air bubbles always being trapped in my coats that are brushed on no matter what brush cheap or expensive varnish style. Even if thinly brushed. I have tried the advice given about typical can varnish like don't drag the brush in jar, just tap on side wall. And brush slowly in only one direction & then Tip off etc. But I always get air bubbles & they go down deep into the coat requiring alot of sanding to get them out.
The last line of advice it seems is usually thin your clear. Straight out of the can this product has a consistency of typical hardware oil based poly thinned by 15%.

I did thin my 2-part by an additional 10% & it helped level out, but still these air bubble defects were still significant. It's clear I will have to thin my poly to around at least 35-40%.

My question is does thinning this much affect the durability & chemical/scratch resistance of the clear? Imo with wood you need all the durability you can get with projects like table tops etc.

Thanks
 
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Old 10-06-16, 04:03 AM
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The protection by any coating relies in part to the film build up. When you thin the coating you may need to apply an extra coat to get that film build up.

Often air bubbles are introduced into a coating by shaking or boxing the coating back and forth. It's best to stir [and not aggressively] poly or varnish.
 
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Old 10-11-16, 12:57 AM
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Thanks marksr.

I get air bubbles trapped that seem to cause pinholes no matter what I do. Seems to be the nature of brushing the 2-part due to the chemical curing process i think. Thinning by 20% seems to reduce their depth, but not prevent them.
 
 

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