What are these defects in my Polyurethane?


  #1  
Old 09-15-16, 12:57 AM
M
Member
Thread Starter
Join Date: Sep 2016
Posts: 11
Received 0 Votes on 0 Posts
What are these defects in my Polyurethane?

Hello all.
I'm getting defects in my coats but they are not dust or debris from the air.
It happens when ever using a brush even a fine varnish brush I get these types of defects in my coatings. I think it's just the nature of using a brush & can't be avoided. I have tried thinning my clear a bit but they still form to some degree.

Here are some pictures I took to show what I mean.

After coat dries there is fine dust like defects.


After a moderate sand you can see these defects go deep into coat.


They always have a round base shape to them.


Just curious as to what these are & how to reduce them.

thank you.
 
  #2  
Old 09-15-16, 03:30 AM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 48,238
Received 426 Votes on 381 Posts
The 1st pic looks like air bubbles in the poly. Poly/varnish should never be shook, only stirred and not aggressively.
 
  #3  
Old 09-15-16, 07:07 AM
S
Group Moderator
Join Date: Oct 2004
Location: WI/MN
Posts: 19,641
Received 98 Votes on 86 Posts
Do you know what tipping-off is?
 
  #4  
Old 09-16-16, 12:18 AM
M
Member
Thread Starter
Join Date: Sep 2016
Posts: 11
Received 0 Votes on 0 Posts
Hi marksr,

I can't avoid these I never shake my cans & when I pour a small amount into a see through container I let it sit for a while & there is no air bubbles in it.

Is this just what brushes do?

thanks
 
  #5  
Old 09-16-16, 12:22 AM
M
Member
Thread Starter
Join Date: Sep 2016
Posts: 11
Received 0 Votes on 0 Posts
Hi stick****

I will read up on tipping off, I still have a lot to learn about varnish.

thanks
 
  #6  
Old 09-16-16, 03:11 AM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 48,238
Received 426 Votes on 381 Posts
They sure look like air bubbles. I suppose it's possible to introduce the air while you are brushing or loading the brush but I've never had that happen to me with a brush. Another possibility is a containment on the surface you are applying the poly to. You might try wiping the surface down with a clean rag damp with mineral spirits [paint thinner] prior to applying the poly.
 
  #7  
Old 09-16-16, 05:10 AM
J
Member
Join Date: Sep 2014
Location: USA
Posts: 486
Received 0 Votes on 0 Posts
Is the wood red oak? If so, oak is a porous wood and unless you fill the pores first the poly kind of runs/sinks in to create this look. If you keep adding coats these will eventually fill in and you will get a smooth surface. It may take many coats.
 
  #8  
Old 09-16-16, 05:22 AM
pugsl's Avatar
Forum Topic Moderator
Join Date: Mar 2008
Location: United States
Posts: 9,029
Received 76 Votes on 69 Posts
I always use water based poly, 1st couple of coats I use 50 / 50 with water. It spreads easier and few defects (less sanding) Works with oil base but I hate cleaning brushes.
 
  #9  
Old 09-16-16, 05:26 AM
M
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 48,238
Received 426 Votes on 381 Posts
The only times I've thinned poly/varnish 50% or more was when the wood needed a wash coat - similar to wood conditioner, prior to applying the stain. Thinning the poly a little [about 10%] does help it to flow and level off better.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: