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Polyurethane on top of latex paint?

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Forum topic by jasoncarpentry posted 1100 days ago 8395 views 0 times favorited 7 replies Add to Favorites Watch
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jasoncarpentry

111 posts in 1251 days


1100 days ago

Jusy when I thought I knew how to do the simple stuff …

I’m making a bookshelf from a 38” x 9” x 3/4” piece of top-quality, seasoned pine (from Home Depot). First I used one coat of Kilz 2 primer, then two coats of regular water-based latex paint (beige). Things were going according to plan until the next step. To protect my books from paint ruboff, I decided to add a final coat of polyurethane. I made up a solution of 1 part satin poly and 1 part mineral spirits, which I wiped on. I waited about 45 min., at which time the surface was dry to the touch. Then I rubbed it down w/ 00 steel wool in preparation for the next coat of poly. NOT GOOD!! Now I have a combination of beige and gray blotches where the steel wool seems to have embedded itself into the finish. I used a tack cloth, then 150-grit sandpaper, but I still have the blotches.

This isn’t the end of the world; I’ll just re-paint to cover up the blotches. But what then? Should I wait longer for the poly to cure? Should I not use steel wool, or at least use 000 or 0000 steel wool instead of 00?

Thanks in advance for your help.

-- Jim in Tennessee


7 replies so far

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Loren

7223 posts in 2244 days


#1 posted 1100 days ago

Poly takes awhile to firm up enough to take steel wool.

I rarely use real steel wool anymore, because the fibers come off
and cause problems like you experienced. The synthetic steel wool
is much better – more like a scrubbing pad.

Between coats I usually use stearated sandpaper. 150 or 180 grit
works well for most finishing jobs. You can remove the stearate
left behind by brushing or blowing with air, then a tack cloth. You
can also just brush the stearate off and re-coat. In my experience
the white stearate dust seems to dissolve into the next coat.

-- http://lawoodworking.com

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BobTheFish

361 posts in 1148 days


#2 posted 1100 days ago

Seconded on the “do not use real steel wool” bit. It’s kind of a think of the past, always leaves fibers, and even when they aren’t visible, they tend to rust over time.

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Cosmicsniper

2199 posts in 1755 days


#3 posted 1100 days ago

Jim:

Be aware that the poly might impart a slight yellowish tint. This might be an issue with your beige colored latex depending on how light it is. Trust me though, it really uglies up white paint! Don’t ask me how I know that! :>)

-- jay, www.allaboutastro.com

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gfadvm

10533 posts in 1286 days


#4 posted 1099 days ago

I have used Min Wax Polyacrylic [water base] over white latex to give it more durability on my shop counter tops. I had no problems with application or discoloring. Perhaps the water based is a better choice over latex?

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

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Earlextech

901 posts in 1287 days


#5 posted 1099 days ago

Important to let the latex paint cure for a few days before putting a top coat over it.
Then let the poly cure before rubbing it out with… scotchbrite pads. Steel wool is for maintaining your tools not for applying finishes anymore.
And yes the waterbased poly shouldn’t discolor the paint any more than water will.

-- Sam Hamory - The project is never finished until its "finished"!

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Cosmicsniper

2199 posts in 1755 days


#6 posted 1099 days ago

That’s an awesome point! I only recently started using the water-borne poly so I have yet to have had that experience. Good to know!

-- jay, www.allaboutastro.com

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SteveN

21 posts in 2839 days


#7 posted 1099 days ago

Polyurethane is not used for top coating. It builds well over itself but not other finishes. Sometimes you may get away with using it over sealers like shellac or vinyl sealer. With other finishes you run the risk of adhesion problems.

Latex can be top coated with shellac, lacquers, vinyl and acrylics. Acrylics and non-yellowing lacquers are best to preserve color. Others will shift color or yellow with time.

-- Steve Nearman, FurnitureRepair.net, ProRestorers.org, Fredericksburg, VA

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