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Crevasses/gaps in my polyurethane table top

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I just laid down my 7th coat of oil base polyurethane (applied with a brush) on a dinning room table made from 1x6’s of solid oak. I mistakenly didn’t put wood filler in the tiny cracks between the boards and still have crevasses in a few spots (see pic attached)...Can I thin my poly with mineral spirits, and use the homemade wipe-on poly to only fill the crevasses or will this make the table uneven? 

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Brush or wipe just the seams to fill them and let it cure well then sand or use a card scraper to flatten the excess off. Sand the entire surface with 320  or 400 grit to prep for a final complete top coat.

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I just laid down my 7th coat of oil base polyurethane (applied with a brush) on a dinning room table made from 1x6’s of solid oak. I mistakenly didn’t put wood filler in the tiny cracks between the boards before finishing and still have crevasses in a few spots (see pic attached)...Can I thin my poly with mineral spirits, and use the homemade wipe-on poly to only fill the crevasses or will this make the table permanently uneven? 

1EA3E120-11C2-4DC4-914A-F505C47718F4.jpeg

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1F4CA88E-563D-4465-A641-CA6525A31317.jpeg

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59 minutes ago, wdwerker said:

Brush or wipe just the seams to fill them and let it cure well then sand or use a card scraper to flatten the excess off. Sand the entire surface with 320  or 400 grit to prep for a final complete top coat.

Wdwerker, Could he use aquacoat, it dries a little thicker (but not much),  but it dries faster and might shorten the job?

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Yikes, 7 coats is a lot of coats, why so many? Are you trying to fill the cracks with finish? filling the voids with finish would take a lot of coats. with that many coats you could sand off a bunch of finish, and make a mixture of epoxy and sawdust to fill the cracks then when flat put on a last coat. red oak likes to chip on the edges espically when run they a table saw, a jointer works best for all edge joints but not everyone has one. a higher tooth count ( 40) on a very sharp blade helps with chipping. and welcome to the show glad to have you. 

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You're effectively pore filling with finish (it's a small crack, but it's acting the same as a pore).  I've done this successfully with wipe on poly.  However, I think you'll need to sand back the entire table some.  Not enough to burn through the finish and get to the wood; just enough to help level things out.  If you don't sand back the areas around the cracks, you'll be chasing flatness coat after coat.

 

When I did this method, i would lay on three coats, then sand back.  Then lay on three more and sand back.  Rinse and repeat until pores are filled and everything is flat.  Then go for your final coat.

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Is flatness really an issue?  

I would support Werker's approach - I think "cured enough" is "hard enough to work on with sandpaper or scraper."

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Wood filler will make it look worse. If it were my table I would rip it down the joints, joint the resulting boards and glue it back together. 

Assuming you have a tablesaw or tracksaw and a jointer (whether motorised or hand plane) you could do the same.

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I agree with @TerryMcK . Filler will stand out like a horse turd in a glass of milk. Filling those cracks with epoxy prior to finishing would be less obvious.

Cutting & reglueing  is the best solution.

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If the finish gums up the sandpaper wait a couple more days. A sharp Card scraper is a better approach but you have to learn how to sharpen it. Great tool to have if you plan to keep doing woodworking but use sandpaper if your projects will be few and far between. 

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Ultimately, you may have to do as suggested above; rip, re-joint, and re-glue. However, considering the amount of work you have already put into it, I would try to fill those depressions with more finish as you suggested. Keep in mind that it may not work, but I think it is worth a try. Also, it will be a tedious process. So, be patient.

Do not thin your finish. Use full strength and using a toothpick or very very small brush, put just enough poly into the depressions so that it fills it without overflowing. Let this thoroughly dry to the point that it can be sanded or scraped. The finish/filler may shrink some as it drys. So, you may need to apply a second or third coat before it is ready to scrape and sand. Once you think the finish/filler is built up enough, carefully scrape with a razor blade and sand with a very small block until you get it flush with the rest of the finish. If you are still left with depressions, add more and scrape/sand more. When done, you may want to add an additional coat over everything.

Good luck. Let us see your results

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Adding another thought. Creating a thick finish like this might increase it's tenancy to fail. I know poly is flexible but at a certain point your going to be pushing your luck with that.I know paint =/=  poly but i had an old house with THICK buildup of pain and that stuff chipped and flaked really easily. Removing some finish will accomplish 2 things. It will reduce the film thickness which might increase the durability, and it will decrease the number of additional coats you need to fill the cracks.

My last advice is to use high grit sand paper after you remove some finish. I touched up the finish on a coffee table and the lower grit paper i used left the finish slightly hazy so i had to let it cure and remove it back to correct the problem. I used 180 grit and found 400 grit works well for satin poly gloss might have to go higher.

 

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Card scraper (also called a cabinet scraper )would be at a woodworking store like Woodcraft, Rockler or Highland. Big box won't have them but a big hardware store might( doubtful)

You need a smooth metal file, a burnisher and a sharpening stone plus a vise to do a decent job sharpening a card scraper. Some come "presharpened" but it won't be good enough or last very long.

https://www.ptreeusa.com/hand_tools_scrapers.html

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I really appreciate your attention guys, here’s an update...I filled in the voids initially using an oversized toothpick, then on the fly switched to the tip of a 1" foam brush. Some voids/cracks still remained after drying, so my plan was to sand the excess flat then dab the voids a second time, but had a hard time getting things flat. Things seemed to get more jagged and uneven the more I sanded ( if there is a next time, I’ll buy a scraper). At this point I was ready to grab my 8’ step ladder and Jimmy “Superfly” Snuka [ jump] off the top rung onto the middle of the table...Luckily my wife was around to talk me outta that and I decided to just add another full coat then pray to the wood finishing Gods. That one coat turned into two after my beautiful assistant carried the brush over the table leaving two drops of poly on the freshly laid first coat...which may have been a blessing because 90% of the voids/cracks filled in and the jagged/uneven looking sand job dissipated after the 2nd coat. The table still has a couple small dimples along a couple seems, but improved a lot and is good enough for my personal use. My question now is if I applied, don’t laugh, 9 coats on the top side (I probably sanded at least one coat off thru the entire process) do I need to apply an equal amount on the bottom side? I only did four on the bottom side because that was my plan for the top...Thanks in advance for any comments

 

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Well first off, congratulations.

A bonus to all this is that since you made it you know how to fix it.

On finishing the bottom: I think you want to give it a coat or two so that you don't get uneven moisture absorption (and subsequent uneven wood movement - warpage!)  Not 9 coats.   (Being a still novice woodworker myself, the devious, mischievous guy on my shoulder says: yeah do exactly to the bottom what you did to the top; including sanding etc. ;-)

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No you have sufficient coats on the underside as it is never seen. It will be a waste of your time. Now go build something else and enjoy woodworking.

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2 hours ago, TerryMcK said:

No you have sufficient coats on the underside as it is never seen. It will be a waste of your time. Now go build something else and enjoy woodworking.

Oh, I missed the fact that there were 4 coats already!

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