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why does polyurethane pull away from growth rings?

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Forum topic by strandedpirate posted 06-08-2014 05:55 PM 538 views 0 times favorited 11 replies Add to Favorites Watch
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strandedpirate

8 posts in 137 days


06-08-2014 05:55 PM

Topic tags/keywords: oak finishing polyurethane

I’ve applied several coats of polyurethane to a stained oak seat. When first applied the poly is smooth and even, then as it dries it pulls away from the growth rings.

Have I applied it incorrectly or is this normal? Any way to get a perfectly smooth finish?

I stained the seat then put two layers of sanding sealer on it followed by four layers of the poly but it still pulls away from the growth rings no matter how many layers of poly I apply.


11 replies so far

View johnstoneb's profile

johnstoneb

727 posts in 859 days


#1 posted 06-08-2014 05:59 PM

It’s not pulling away from the growth rings it is going into to fill the voids. You will need many more coats and sand between each coat until everything is filled. Open grain woods require a filler before the finish. if you don’t want to put on many coats of finish to act as a filler.

-- Bruce, Boise, ID

View bondogaposis's profile

bondogaposis

2590 posts in 1037 days


#2 posted 06-08-2014 07:10 PM

It is not pulling away from the pores it is being sucked inside them. They are like straws. You need to fill them before they will stop doing that. One way to do that is to take some 0000 steel wool and load it with tung oil and polish the wood with it to form a slurry, then wipe it off and let dry. Then apply your finish over that. This is a micro photograph to help you understand what you are dealing with at the cellular level.

-- Bondo Gaposis

View gfadvm's profile

gfadvm

11226 posts in 1376 days


#3 posted 06-09-2014 12:42 AM

Great explanation and pic Bondo!

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

View strandedpirate's profile

strandedpirate

8 posts in 137 days


#4 posted 06-09-2014 04:07 PM

Thanks, do I need to strip the existing poly off or can I apply tung oil over it?

View TCCcabinetmaker's profile

TCCcabinetmaker

925 posts in 1041 days


#5 posted 06-09-2014 04:48 PM

I do not think you can add the tung oil now, unfortunately, it would have bade effects.

-- The mark of a good carpenter is not how few mistakes he makes, but rather how well he fixes them.

View b2rtch's profile

b2rtch

4341 posts in 1735 days


#6 posted 06-09-2014 04:55 PM

You could buy and apply a filler but normally you apply the filler before finishing.
Back home we had a product named ” fond dur” which was filler and finisher as the same time. In the USA , I do not know of one.
http://www.blanchon.com/produits-bois/distribution-pro-du-bois/produit-pro-interieur/couche-primaires-pro/fond-dur-preplast.html

-- Bert

View bondogaposis's profile

bondogaposis

2590 posts in 1037 days


#7 posted 06-09-2014 04:57 PM

Thanks, do I need to strip the existing poly off or can I apply tung oil over it?

It is probably too late for the tung oil treatment at this point. If you really want a level surface you will have to strip and start over I’m afraid. Your seat doesn’t look that bad to me and if it were mine I would probably give it a few more coats and then top it with some paste wax and call it good. It depends entirely on the look you want. Another way to go is to enhance the look of the pores by using a colored wax to bring them out, black bison wax comes to mind. It will darken all of the pores and really make them stand out, kind of an antique effect.

-- Bondo Gaposis

View TCCcabinetmaker's profile

TCCcabinetmaker

925 posts in 1041 days


#8 posted 06-09-2014 05:08 PM

Rather than strip it, just sand the finish coat heavily and reapply, if the pores are still very noticeable, then repeat, each time sanding a little heavier with 220 grit sand paper. Make sure to wipe away all dust as it will not melt back into the finish with polyeurathane.

You are only supposed to let most finishes get so thick, so a lot of coats without sanding can cause the poly to crack and peel, well most finishes will do that if you get them too thick, except maybe laytex.

-- The mark of a good carpenter is not how few mistakes he makes, but rather how well he fixes them.

View ChefHDAN's profile

ChefHDAN

371 posts in 1536 days


#9 posted 06-09-2014 06:57 PM

I learned this same lesson the hard way refinishing a QS oak table, I spent weeks trying to get a flat surface, stripper, sanding, cursing, screaming, all to no avail, the finish never seemed to “flatten out”, rottenstone was probably the only thing I didn’t try, and finally resigned myself to liking the table the way it was. For my next project with oak I used Famowood filler and got great results after the first coat.

-- Sssshhhh, I'm pretending to be working

View strandedpirate's profile

strandedpirate

8 posts in 137 days


#10 posted 06-09-2014 11:53 PM

I went ahead and heavily sanded to level the surface out. Looks much smoother now with a few stubborn areas refusing to fill up with poly. It’s definitely smoother when viewed at an angle with the light casting on it, but more than smooth enough to the touch so I’ stopping here and moving to the next project.

View lateralus819's profile

lateralus819

1444 posts in 576 days


#11 posted 06-10-2014 12:01 AM

I think that looked awesome!

-- Never confuse mistakes with failure. Kevin

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