White Flaky Spots After Polyurethane


jadedj
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Hi Guys - new to woodwork but really enjoying it!

I bought this antique table a few months ago and have been working on it ever since. I went through the laborious process of stripping, sanding, stripping some more, etc. Well after 3 or 4 coats of oil-base stain (it was summer in NY so pretty humid) it looked like it was time to add the polyurethane and I thought I'd be eating on it in a few weeks!

Not so fast. I started with the legs (thank God) and after applying a coat of poly and letting it dry, there were odd white flakes that showed up. I've attached what they look like, I've also attached a side-by-side comparison of the one leg that just has stain, compared with the poly leg. It's very odd and I don't understand what's happening.

Does anyone know what that is? Not sure how old the table is, any advise would be much appreciated!

flakes.jpg

flakes1.jpg

flakes2.jpg

sidebyside.jpg

withpoly.jpg

non poly.jpg

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Looks like eczema to me. I've got no idea how an antique table gets a skin condition <grin>

Could be something left on the legs , did you rinse or neutralize any stripper /chemicals  before you started with the stain?  I haven't done any refinishing in years but it seems like something wasn't compatible with a residue left behind. Not sure what do do except start over .

 

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A few questions to help (hopefully) narrow down the root issue-

How long did the last coat of stain cure before applying the poly?

You mentioned that the stain was oil-based, was the poly water- or oil-based?

How was the poly applied?

Were the stain and poly purchased for this project or left over from previous projects. If left over, how old are they, and have they been exposed to extreme temperatures?

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Unfortunately, there really isn't anywhere I can "test" the poly or the satin as the underside isn't finished; the only option I think I have is trying a corner but as the inlays are different pieces of wood (there are at least 5 on the ends; the two sleeves have 3 each), the stain nor the poly will be uniform.

2 minutes ago, JohnG said:

A few questions to help (hopefully) narrow down the root issue-

How long did the last coat of stain cure before applying the poly? - about a week, maybe less

You mentioned that the stain was oil-based, was the poly water- or oil-based? - oil

How was the poly applied? - brush

Were the stain and poly purchased for this project or left over from previous projects. If left over, how old are they, and have they been exposed to extreme temperatures? - both newly purchased

 

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I think i got it.

You brushed on the poly, what was your technique like? Did you slather it on like paint? If so that's not a good way to get poly applies especially the thick brushing type. I've found poly needs a good brush that is tailored to the finish. Sadly the brushes i used when i brushed poly cost more than the finish, which leads to clean your brush well.

My technique for applying brushing poly is very slow even strokes like 1 inch a second, with a brush that isn't soaking in finish because runs will form. If your brushing and a bubble forms on the finish you need a way to pop it, they don't pop on their own. I never figured that out other than trying to empty the brush and doing very light slow swipes to make sure i didn't leave any other bubbles behind, which worked about 50% of the time the other 50% it caused more bubbles. This leads to stirring the finish you need to stir slowly so you don't put bubbles in the can. Shaking is a HUGE no no for the poly. Does this sound complicated? It should brushing poly sucks, why i switched to wiping poly.

My suggestion is to sand back your finish. If the bubbles are from application you shouldn't have to go back to bare wood only enough to remove the defect. Second I'd consider diluting the finish or look into the home made wiping poly. I never bothered making my own homemade wiping poly (google has good results). I instead went out and purchased it because I'd rather spend more time doing wood working then playing chemist. For wiping poly I apply it with a clean lint free piece of cotton t-shirt or specifically bought cotton rags. I've even started to use the Scott shop towels for 2nd coats, on the 1st coat the wood tears the paper towel up. When applying make sure to have a dry cloth/towel handy to grab any drips or runs on edges or vertical faces. It's easier to remove excess when the finish will still self level than trying to sand it away later, it never really sands away as nicely.

Always sand between coats. I like to use 320 or finer. My latest choice has been 400 grit and I've started to use my random orbit sander on speed 2 of 6. I like this because the vac pulls the dust away so there is leas to clean up. sanding should be fairly quick, the goal isn't to remove finish but to hack off the dust numbs or remove small defects like a tiny ridge ect. If the surface isn't smooth that should be addressed at the wood level not the finish level. Wiping poly needs more coats for heavily touched surfaces i go 4-5. Other surfaces get 3, this is open to preference.

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Thanks for the advise Chestunt, that helps a lot. Few questions though:

Sand between ploy coats? I though that was a no-no; are you supposed to sand between stain coats too? And did when you say, "sand back your finish" - that pertains to the poly coat I'm assuming. Is that right?

Also, does it make a difference that even though I let it dry for at least 2-4 days, there are areas in the stain where it still looks wet (kinda sticky to the touch too)? Why doesn't it dry? Do you have to wait 7+ days for oil-based stain to completely dry? Maybe I jumped the gun in adding the poly coat.

Lastly, if the other spots on the leg look OK, is it fine to refinish just the areas with bubbles that I've "cleaned up" or do I have to do the entire leg again?

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2 hours ago, jadedj said:

Thanks for the advise Chestunt, that helps a lot. Few questions though:

Sand between ploy coats? I though that was a no-no; are you supposed to sand between stain coats too?

Sand between coats of poly not stain. It says on the minwax cans i use you don't have to if you recoat before 4 hours otherwise wait 24 hours and sand and recoat.

And did when you say, "sand back your finish" - that pertains to the poly coat I'm assuming. Is that right? Yes

Also, does it make a difference that even though I let it dry for at least 2-4 days, there are areas in the stain where it still looks wet (kinda sticky to the touch too)? Why doesn't it dry? Do you have to wait 7+ days for oil-based stain to completely dry? Maybe I jumped the gun in adding the poly coat.

So not sure how you applied the stain but i never allow it to pool and use the wipe on wipe off method. If it still feels tacky or wet after that long put a fan on it because it shouldn't. If it feels wet at all it will effect the poly on top of it.

Lastly, if the other spots on the leg look OK, is it fine to refinish just the areas with bubbles that I've "cleaned up" or do I have to do the entire leg again?

I suggest lightly scuffing the places that look ok and have an uniform coat over the entire piece. You only need to scuff the surface to help for adhesion if there are no defects. I suggest a uniform coat because i tried the spot fix and had poor results with a very obvious finish line. Finish has a thickness and if you stop in the middle of a flat area you'll see the line of thickness change.

See red above.

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  • 4 weeks later...

Legs seem to be OK, but now the table top is acting up. I've restripped it AGAIN and even after sanding it back, restaining and poly, I get white spots. Here are some pics of what it looks like with no stain or poly. And below it are the legs - which I've been able to fix.

top3.jpg

top2.jpg

top1.jpg

sidebyside.jpg

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6 minutes ago, Steve B Anderson said:

I’m not an expert at finishing but from my experience the white spots are from either moisture or the underlying finish still evaporating off. 

Yup. I think the problem is not in the poly, it is what’s underneath. What stripper did you use? Did you wash the stripper away with water? Some strippers have to neutralized. How long did it dry before staining? 

If there is moisture or stripper still in the wood it’s a problem.

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Usually when refinishing, the wood itself is not holding enough moisture to effect any refinishing stains or top coats. The problem is usually with the chemical stripper. After chemically and scraping the old finish off, the surfaces should be cleaned using denatured alcohol or mineral sprites. I’m not sure what the minimum wait time is but I will let it sit for a week before finish sanding and applying the finish coats. I don’t have a favorite stripper just whatever the big box store has.

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12 hours ago, Isaac said:

Yup. I think the problem is not in the poly, it is what’s underneath. What stripper did you use? Did you wash the stripper away with water? Some strippers have to neutralized. How long did it dry before staining? 

If there is moisture or stripper still in the wood it’s a problem.

I used this for stripping:

https://www.google.com/search?q=wood+stripper&amp;client=firefox-b-1-ab&amp;source=lnms&amp;tbm=shop&amp;sa=X&amp;ved=0ahUKEwjUiO6U2JLeAhXoTN8KHVF_CmgQ_AUIDigB&amp;biw=1534&amp;bih=701#spd=5620507950530168119

And then followed with denatured alcohol, using steel wool to clean off what the stripper didn't. I let it dry for about 3-4 days but when I did, it was warmer and humid. Only after stripping a 2nd time did I notice those lighter spots in the wood, before staining. Maybe I need a different type of poly? Should I keep sanding?

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Disclaimer: I did not read all posts thoroughly on my phone.

If this is veneer, you run the risk of sanding to the glue layer. If this is solid, I would sand the whole thing through the grits. If you are into glue, try a barrier coat of shellac before poly. This can help bond where you have some incompatibility issues. Honestly, with the value of the table a new container of poly is something I would consider just to limit variables. 

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25 minutes ago, Tpt life said:

Disclaimer: I did not read all posts thoroughly on my phone.

If this is veneer, you run the risk of sanding to the glue layer. If this is solid, I would sand the whole thing through the grits. If you are into glue, try a barrier coat of shellac before poly. This can help bond where you have some incompatibility issues. Honestly, with the value of the table a new container of poly is something I would consider just to limit variables. 

It's a table that's at least 50 years old if not older so I don't think it's veneer. But as you can see from the pics, there are various pieces of wood very cleanly stuck together so perhaps the different wood reacts differently when I add the poly.

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5 hours ago, jadedj said:

It's a table that's at least 50 years old if not older so I don't think it's veneer. But as you can see from the pics, there are various pieces of wood very cleanly stuck together so perhaps the different wood reacts differently when I add the poly.

It may not have any veneer. I am primarily looking at the last images of the top. Do not assume that 50 years old means no veneer though. Veneer as a product is much older than that. 

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8 minutes ago, drzaius said:

This is a mystery. Almost looks like a bleaching agent was at work.

Right?? So odd, I'm not sure what to do. Thinking about staining and poly just those spots to see what comes of it. Someone suggested trying different stains and poly combos.

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  • 2 years later...

I’m curious, therefore reviving this thread... I am running into a similar problem, and am puzzled.  Not much to find on the web.

 

  • i made about 20 coasters today. Two have this white in the finish.  The others do not. All were made and finished in the exact same way at the exact same time. First coat was lacquer, all following coats oil based poly, everything was sprayed, all at the same time...
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