# Polyurethane turning white



## Sandro (Oct 25, 2008)

I am painting an old wooden handrail. I gave a couple of coats of stain and a couple of coats of polyurethane. I waited at least 24 hours between each two coats. Everything went well until I decided to give yet another coat of polyurethane. That polyurethane immediately turned white in several places.

I have read that humidity causes polyurethane to turn white. However I didn't use any water, and I believe the humidity level in my garage is pretty normal. I used one brush for the stain and a different brush for the polyurethane. I clean the brush with thinner each time and save it inside a zip-locked plastic bag wrapped in a paper towel moistened with thinner, so it doesn't dry.

Could the thinner remaining in the brush have caused the problem? Or is water the only thing that makes polyurethane turn white? And why did this happen only once?

Thanks!


----------



## SnowyRiver (Nov 14, 2008)

Yes, water and thinner will cause the poly to turn white. It could be that the brush was getting more saturated with thinner as you did each coat and it finally showed up. When I clean the brush with mineral spirits I always snap the brush a few times at the ground (outside of course) after cleaning it to throw off any residue and I leave it out in the open so the thinner evaporates off the brush.


----------



## Sandro (Oct 25, 2008)

Thanks, Wayne.

Now I am wondering how I can get the white polyurethane back to its normal state.


----------



## Bureaucrat (May 26, 2008)

The only way I know of to get rid of the white is sanding, bummer.


----------



## SnowyRiver (Nov 14, 2008)

Sanding may be the best way although depending on how deep the white is, sanding could be quite a job. The only other thing I could think of would be to use a paint stripper and see if that will remove all of the poly, then start over.


----------



## Sandro (Oct 25, 2008)

Fortunately the white was very shallow, and it went away with just a little sanding. Thanks guys!


----------



## Smooth (Sep 14, 2017)

EASY fix!! Just take a standard blow dryer to it. It takes a little time, but works like magic and stays fixed. Mixwax really needs to add this tip to their label and save people a lot of extra, unnecessary work.


----------



## Smooth (Sep 14, 2017)

*Note on my previous comment - I did this outside (in the shade) when the temp was in the 90s. It didn't work so well when temp was in the mid 70s.


----------

