Cleaning Urethane from Brushes

I was doing a project with urathane, and after applying it to several large pieces, I had a very messy brush. I spent twenty minutes plus trying to clean it using paint thinner, and running water. I thought I was successful, but when the brush dried, it was hard enough to be unusable. Is there a trick to cleaning urathane off brushes that I'm missing, or do I just have to use more paint thinner and time?
John
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Hmmm...I never would have used water, but that doesn't mean it's incorrect. Unless you're using soap and water after really cleaning it out with the thinner to get the thinner out of the brush (mineral spirits I assume when you say thinner).
I've accidentally under cleaned a brush before and it was tacky the next day (fortunately I caught the problem before it had cured fully). I recleaned it in twice the amount of spirits and was able to get all the varnish (poly) out.
I guess I'd try more mineral spirits is what I'm kind of rambling on about...
Good luck, Mike

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Try acetone. I use acetone to clean up Polyurethane glue.

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Two suggestions; Preload the brush with the proper solvent, mineral spirits for oil based and water for WB, prior to dipping in the finish. Stops the drying of the finish near the ferrule which keeps bristles limber and makes brush MUCH easier to clean. I used CitriStrip to clean a stiffened brush based on a suggestion from Jeff Jewitt and it worked. Soaked it overnight if memory serves.
On Wed, 4 Feb 2004 11:01:57 -0500, "John Smith"

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Uncured urethane is best removed with xylene of toluene. After it cures (polymerizes) it's difficult to remove but you might try NMP (n-methylpyrrolidone) which I have found in HD on occasion.
RB
John Smith wrote:

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Paint thinner and running water are worthless if the urethane has either partially or completely cured. You have to essentially use some form of finish stripper. There are several brush cleaning liquids available. Try one that indicates it can clean cured finishes like polyurethane. You can also use finish stripper but it may be a bit harsh on the brush.
Some people make it a point to completely clean their brushes, minus soapy water, between large pieces just to avoid partial curing.
Good Luck.

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I use laquer thinner, just be sure you have good ventilation and no sparks.
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