Refinishing table - Polyurethane Flaking Off - Woodworking Talk - Woodworkers Forum
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post #1 of 19 Old 08-16-2019, 01:17 PM Thread Starter
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Question Refinishing table - Polyurethane Flaking Off

Hi everybody. I'm working on a round oak (veneer) table that I got used for $20 with chairs for our kitchen. We looked at buying new and I talked the wife into letting me fix up a cheap table so here we are. I've sanded the old finish off, used Varithane wood conditioner (probably bad idea), stained with Minwax oil based and could not get it dark enough, cleaned with Mineral Spirits and sanded again (ended with 150 grit going with grain) to start fresh, stained again with Minwax oil based stain... It was still too light so I read online that I could add oil based stain to oil based polyurethane to darken it further. So, about a week after staining, I used an HVLP sprayer to apply Minwax Wiping Polyurethane mixed with maybe 1/4 Minwax oil based stain. I did 3 coats and it looked very good at the time but a few days later my 18 month old daughter was doing what kids do and she ended up scraping up some of the tinted finish in a couple of spots. I'm able to scratch more of it off with my fingernail pretty easily so I don't think it has adhered to the wood very well. The table had been in my garage so it was a bit on the warm and humid side but not horrible here in Nebraska the past week. Any ideas what I've done wrong? Or is it just going to take longer than a few days for the finish to adhere and harden? The only thing I can think of is that I did not wait a full 2 hours between coats. Since I was spraying it on fairly thin I didn't see a reason to wait very long. Do I try to touch it up or start over again? Thanks in advance!!
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post #2 of 19 Old 08-16-2019, 01:28 PM
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Well, to begin with, polyurethane really needs to dry for about 24 hours between coats. Then you have to sand lightly to scuff the surface and give the subsequent coat some texture to adhere to. I don't know what the directions on the wiping poly can said, but 2 hours is not enough time to allow good adhesion between coats. It doesn't matter how thin the coat is.
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post #3 of 19 Old 08-16-2019, 02:02 PM Thread Starter
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Thanks for the information Mark. Here's a link to the wiping poly I used - it calls for 2-3 hours between coats and sanding between (which I did not do): https://www.minwax.com/wood-products...x-wipe-on-poly

I'm not sure how sanding between coats would help my first coat stick to the wood though. Where it has scratched off you can tell it is down to the wood since I added dark stain to the poly.
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post #4 of 19 Old 08-16-2019, 03:28 PM
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Polyurethane by nature has more adhesion problems than a lot of finishes. When ever you refinish wood it should start with a paint and varnish remover. Sanding tends to get just what is on the surface and leaves the wood penetrated with the old finish. Also if there is any foreign substance in the old finish sanding will just rub it into the wood. A lot of substances can cause a wide variety of problems with the new finish including adhesion. Suppose someone used pastewax a lot on the table and you ended up rubbing it into the wood. You couldn't expect polyurethane to adhere to waxed wood.

The next problem is the wood conditioner. The only time you use a wood conditioner is on certain types of wood that go blotchy when you stain it. None of the species of oak is prone to blotch. A wood conditioner is a sealer and what it did for you is make the wood hard to stain. Adding wood stain to polyurethane was not a good idea. Stain is incompatible with polyurethane. You could have added a universal tinting color to poly but there are finishes already tinted with color. Minwax makes Polyshades for one. Still in the end these types of finishes are kind of like mixing brown paint and varnish together. It has a muddy appearance to them. If I adjust a stain color I use a alcohol based dye stain to supplement the color. If you use it before you get very much finish on it's transparent so nobody can tell the color has been altered.

As far as the drying time on polyurethane occasionally in hot weather you can put two coats on in the same day if you use the fast dry polyurethane. Otherwise I would limit the coats to one a day.

As far as what to do now, it's as close to as impossible as it gets to try to color a spot which pealed off. Then you have to wonder what else might peal off. The only way to be confident the finish is good is to strip it off and start over. Using chemicals it shouldn't take but the slightest sanding this time around since the wood has been sanded before.
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post #5 of 19 Old 08-16-2019, 04:36 PM Thread Starter
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Thank you Steve. I am curious why I need to let Polyurethane dry so long between coats if I'm spraying it and not sanding. My understanding from this article (#7 Myth - https://www.popularwoodworking.com/e..._polyurethane/) is that sanding between coats is not necessary for adhesion and it is more for clearing off dust and imperfections. I also found this instruction on the Minwax Aerosol Spray Polyurethane "Apply thin coats to avoid runs and sags. Recoat within 2 hours. If unable to do so, wait a minimum of 72 hours, then lightly sand and recoat." https://www.minwax.com/wood-products...ethane#aerosol

Obviously I did something wrong so I'd like to figure it out before I try again. I'm new to all of this, I just google what I'm trying to figure out and run with it. Somewhere I read that I could mix oil based polyurethane and stain up to 50/50 so I guess there's a lot of false information out there. Is there a better/more durable finish you would recommend than the Minwax stuff? And compatible dye stain to tint it? Ideally I would spray it on because I had really good luck with the spray gun and the "fast drying" wipe on polyurethane - it turned out very smooth and I was able to even out the color as I went. I attached a photo, I think it looks pretty good(?).
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post #6 of 19 Old 08-16-2019, 06:23 PM
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Quote:
Originally Posted by Tyler33 View Post
Thank you Steve. I am curious why I need to let Polyurethane dry so long between coats if I'm spraying it and not sanding. My understanding from this article (#7 Myth - https://www.popularwoodworking.com/e..._polyurethane/) is that sanding between coats is not necessary for adhesion and it is more for clearing off dust and imperfections. I also found this instruction on the Minwax Aerosol Spray Polyurethane "Apply thin coats to avoid runs and sags. Recoat within 2 hours. If unable to do so, wait a minimum of 72 hours, then lightly sand and recoat." https://www.minwax.com/wood-products...ethane#aerosol

Obviously I did something wrong so I'd like to figure it out before I try again. I'm new to all of this, I just google what I'm trying to figure out and run with it. Somewhere I read that I could mix oil based polyurethane and stain up to 50/50 so I guess there's a lot of false information out there. Is there a better/more durable finish you would recommend than the Minwax stuff? And compatible dye stain to tint it? Ideally I would spray it on because I had really good luck with the spray gun and the "fast drying" wipe on polyurethane - it turned out very smooth and I was able to even out the color as I went. I attached a photo, I think it looks pretty good(?).
If you put one coat of poly on and then put another coat over the top before the first coat is dry the first coat will stop drying. The last coat will dry hard with the coats underneath still gooey. Over time the coats underneath will eventually dry and shrink as it dries but the last coat has gotten hard. This could easily cause the top coat to crack or if the finish is damaged before the undercoats dry it can just peal off like tape since the undercoats are still gooey. It's likely the scenario you had with the colored layer you put over the top which got damaged.

Despite what you have been reading sanding between coats on polyurethane is necessary. Some finishes like lacquer and shellac literally melt together when you put a coat over the top. On any varnishes every layer is just that a separate layer. It has to adhere to the previous coat like you were going to glue a piece of plastic on with epoxy. When you sand between coats the sandpaper makes scratches in the surface. These scratches greatly increase the finishes ability to adhere. It's called a mechanical bond.

Where you read about putting all the coats on within two hours or wait 72 hours is called a recoat window. It's a different kind of finish than I thought we were discussing. A lot of times they make a completely different finish and call it the same thing so customers will feel comfortable using it. The fast dry polyurethane and polyurethane and water based polyurethane are all very different finishes. I know it's confusing but that is marketing. Anyway the recoat window usually stems from the finish being thinned with acetone. The acetone is such a hot solvent that if the finish completely dried the acetone would lift the finish. It would wrinkle up like you put paint stripper on the finish. These type finishes you would apply faster than normal. Another note, the 72 hours they say is probably rushing it. Unless the weather is pretty warm I would let the finish dry a week when there is a recoat window like that.
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post #7 of 19 Old 08-17-2019, 11:17 AM Thread Starter
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Thank you Steve. All of my coats were tinted with stain but it sounds like either adding the stain or not waiting long enough was my issue. The top coat did not crack. The poly I used was "fast drying" but I don't think it has the hotter solvents in it like the aerosol stuff I referenced.

So I'm going to get some stripper and paint and varnish remover today and start there. How would you recommend that I achieve the darker color? I'm not too concerned with the "muddy" look because we are going fairly dark. And is there a more durable finish I should be getting than the Minwax Wiping Poly? I need to match the seats of the chairs to the top so I'd like to go as durable as possible.
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post #8 of 19 Old 08-17-2019, 12:04 PM
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For some reason when I wrote post 6 your picture in post 5 wasn't there. I'm not seeing the problem you are dealing with. If it's that minor you may be able to touch it up. I was visualizing a more dramatic color change. You may be able to put some of the tinted poly in your sprayer and gently shade the spot. You choke the sprayer down to where you can hardly see the finish coming out and kind of air brush the spot. If it's little spots you can use touch up markers. They are like a brown sharpie.

If it ends up you need to refinish the table I think you would have a lot better luck with the stain if you would omit the wood conditioner. If you still can't achieve the color you could spray some dye stain over the top of the stain and proceed with the finish. Then if when your first coat of finish you think it's still not dark enough you can put another coat of dye stain over your first coat. It's just you would need to do your between the coats sanding before using the dye and then another coat of clear. This is the dye stain I use. https://www.mohawkproducts.com/Mohaw...ain-p/m520.htm
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post #9 of 19 Old 08-17-2019, 01:10 PM Thread Starter
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Yea I didn't have a photo of the scratched area when I posted that. I've attached one with one of the scratched areas, I scratched a little more off to see how easily it peels. My daughter made two of these spots in a matter of minutes with just her fingernails so I don't think it is going to hold up. I scratched more today and it didn't seem any better - not any more difficult than a scratch off ticket. Obviously it stands out really bad since the finish is so much darker.

As for the wood conditioner, I had wiped off the excess stain with mineral spirits and re-sanded (after conditioner) so I don't know if there's any more I can do to remove it. As thin as the veneer is getting maybe it penetrated all the way through.

It looks like I'm out of luck for finding alcohol based dye stains anywhere around me so the wife will not be happy. Would have been nice to get it finished this weekend.
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post #10 of 19 Old 08-17-2019, 02:16 PM
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If the finish scratches off that easily then you do have adhesion issues and the finish needs to come off. You shouldn't have to do very much sanding since the table has been sanded before. Let the chemicals remove everything that was done. Soak it with remover for longer than the directions say. Recently the government has caused these companies to remove the methylene chloride that makes the remover effective. What is available now is a lot weaker and will take more elbow grease. You could use coarse steel wool or a brass brush to help it along. The main thing is to keep the finish wet with remover until it easily comes off clean. Then wash the residue off with lacquer thinner. Thoroughly wash it changing rags because removers contain wax to retard evaporation.
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post #11 of 19 Old 08-17-2019, 03:32 PM Thread Starter
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What do I gain by using the dye stain over Polyshades or similar stain+poly? If it's just appearance I will probably do the Polyshades because I can get that today and get a coat on. If the dye stain option is going to be more durable I will wait. I'm not super concerned with the murky appearance as long as I can get the color dark enough. I think the darkest parts of the grain will show through no matter what I concoct. Plus there are some scratches and thin spots so the table is far from perfect.

Is it possible to get too much dye stain on there and affect adhesion of the finish? I assume the dye stain will give me better adhesion than caking an oil based stain on there? Thanks for all the help! These DIY projects really test the marriage
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post #12 of 19 Old 08-17-2019, 04:13 PM
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What do I gain by using the dye stain over Polyshades or similar stain+poly? If it's just appearance I will probably do the Polyshades because I can get that today and get a coat on. If the dye stain option is going to be more durable I will wait. I'm not super concerned with the murky appearance as long as I can get the color dark enough. I think the darkest parts of the grain will show through no matter what I concoct. Plus there are some scratches and thin spots so the table is far from perfect.

Is it possible to get too much dye stain on there and affect adhesion of the finish? I assume the dye stain will give me better adhesion than caking an oil based stain on there? Thanks for all the help! These DIY projects really test the marriage
What I was proposing is use a clear polyurethane instead of polyshades. Even if you solve the adhesion problems any scratches you might still get would show white. Stain and clear coat is more durable. With polyshades it would be pointless using a dye. Each coat the finish will get darker. You would also benefit from using just a plain oil stain. It would give you some color before the polyshades.

The dark areas of the oak is places where the grain pores are bigger and absorb more stain. It's a normal characteristics of the wood.

As far as the dye stain it is very concentrated and normally doesn't interfere with adhesion but if a person used enough of it could interfere with adhesion. The reason it usually doesn't interfere with adhesion is it's more like ink than a stain. There isn't anything that can get into the grain and block the pores.
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post #13 of 19 Old 08-17-2019, 04:32 PM Thread Starter
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The stripper worked almost instantly, the finish was wrinkling up behind my brush as I went. I'm guessing that is indication of the poor adhesion.

My dilemma is that I can get Polyshades today and get 2 or 3 coats on this weekend. If I go with the dye stain I will have to order it online so I'm out of comission until that comes in. I've read that people don't like the poly shades but I was not sure if that was just due to blotchy color or other issues. I think i can minimize the blotchy color by spraying it.
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post #14 of 19 Old 08-17-2019, 07:34 PM
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The stripper worked almost instantly, the finish was wrinkling up behind my brush as I went. I'm guessing that is indication of the poor adhesion.

My dilemma is that I can get Polyshades today and get 2 or 3 coats on this weekend. If I go with the dye stain I will have to order it online so I'm out of comission until that comes in. I've read that people don't like the poly shades but I was not sure if that was just due to blotchy color or other issues. I think i can minimize the blotchy color by spraying it.
The dye stain may not be necessary. I only recommended that in case you had difficulty getting the color dark enough. You would be better off with a plain oil stain on raw wood.

The only thing I have against the polyshades is it muddies up the appearance of the wood. If you are happy with it that is all that matters.
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post #15 of 19 Old 08-22-2019, 09:04 PM Thread Starter
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Thanks again for the help. I ended up sanding down further than I had planned because there were some more scratches I wanted to get rid of. My 150 grit sandpaper gummed up a lot even after using the stripper so maybe that was why I had poor adhesion. Anyway I put two coats of the minwax stain on again and color was darker than before so I went to the Minwax wiping poly (no stain added!). I've sprayed two coats and wiped one coat and I think I prefer the spraying despite the mess as it gives a heavier, smoother coat. I think I may still get some polyshades so I can darken it a bit more and blend in the color - the areas I sanded more are a little darker and I think the muddy look will hide some of the flaws.

How would you recommend that I test the finish to make sure it is going to stick? At this point I may bring out the sledge hammer if it does not stick but I'd like to find out before I do the chairs.
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post #16 of 19 Old 08-22-2019, 09:54 PM
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It's generally not a good idea to use two coats of stain but minwax is more dye than stain so you might get away with it. I wouldn't test the finish, just assume it's going to work until you have reason to doubt it. It's important with a stain not to have any of it dry on the surface. Stains don't bond like paint. Anything left on the surface can cause adhesion problems.

The citristrip is pretty crummy remover. That is why you ended up having to sand the finish off. The government recently banned the sale of the chemical that makes removers work so the citristrip may be as good as it gets now. It takes methylene chloride to make a remover work and you have to be a professional refinisher now to get removers that contain it.
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post #17 of 19 Old 08-25-2019, 09:53 PM Thread Starter
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I checked the can of stripper I got (Savogran Strypeeze) and it does have Methylene Chloride in it. It worked really fast on my finish re-do but did not do very well on the matching Chairs I worked on yesterday (taking off original finish).

I ended up getting some Polyshades to darken and make the color more uniform. It sprayed on well with the HVLP but they didn't have the color I had been using for stain (Jacobean) so my color is a little more brown/red than I wanted. I also have a couple areas with more sheen to them because I got too heavy with the sprayer so I'm debating between one more coat of clear poly or trying brown paper bag sanding. I'm using a satin finish. I will say the finish now feels different and much stronger than what I had before. I think adding stain to the poly was my biggest mistake.
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post #18 of 19 Old 08-25-2019, 10:13 PM
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I checked the can of stripper I got (Savogran Strypeeze) and it does have Methylene Chloride in it. It worked really fast on my finish re-do but did not do very well on the matching Chairs I worked on yesterday (taking off original finish).

I ended up getting some Polyshades to darken and make the color more uniform. It sprayed on well with the HVLP but they didn't have the color I had been using for stain (Jacobean) so my color is a little more brown/red than I wanted. I also have a couple areas with more sheen to them because I got too heavy with the sprayer so I'm debating between one more coat of clear poly or trying brown paper bag sanding. I'm using a satin finish. I will say the finish now feels different and much stronger than what I had before. I think adding stain to the poly was my biggest mistake.
The color jackobean is mostly black. If you wish to try to counteract the reddish color in the finish you can mix a green alcohol based dye stain about the color of lime koolaid and spray a coat of that on between the coats. The finish would have to be scuff sanded with 220 or finer sandpaper first but it won't interfere with the adhesion. Then after you spray it spray a coat of clear over the top. If you do this don't pay attention to the color of the dye when you spray it. It looks like nothing until you put clear over the top. If you keep adding dye until it looks right it will be very green when you clear coat it. Of course test a little spot somewhere inconspicuous place before you shoot it. The dye can be cleaned off with alcohol to some extent but you can't wash it all off. It would be better to not put enough on and have to do it twice than to put too much on.
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post #19 of 19 Old 08-27-2019, 09:55 PM Thread Starter
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I tried sanding the polyshades a little and sprayed another coat of clear wiping poly over it. It toned down the reddish brown a hair and the sheen is uniform now so I'm going to leave it alone. Thanks again for all the help. I'll post some photos when I get it done.
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