Poly Finish Problems - some white spots


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Old 01-31-15, 09:25 AM
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Poly Finish Problems - some white spots

Hi,

I am refinishing some 90 y.o. stairs.

After sanding, staining (minwax w/VOC), and the primer coat (water-based) of Sanding Sealer (for floors), six treads had small to medium sized spots of white. Kinda clashes with that darker stain!

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Am currently spot-sanding, restaining, getting ready to recoat those areas - but put my question here to see if there's a good answer or a better fix.

Thx -

Bardi
 
  #2  
Old 01-31-15, 09:43 AM
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Am I reading right that you used oil based stain and water based sanding sealer?
 
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Old 01-31-15, 09:50 AM
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It's ok to go over oil base stain with a waterbased sealer BUT the oil stain needs to be good and dry!
How long was time period between the oil stain and water based sealer? what were the temp and humidity conditions? Do the white spots feel good and dry?
 
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Old 01-31-15, 11:35 AM
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Yeah, I'd also say that maybe there wasn't adequate dry time after staining. Especially since one of those spots conforms perfectly to the grain of the wood.
 
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Old 01-31-15, 01:20 PM
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I recommend doing the entire tread over. What you are doing is not going to look good.

Minwax stains take FOREVER to dry.
 
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Old 01-31-15, 02:11 PM
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I thought it might be something that had soaked into the treads over its 90 year life and I just hadn't sanded deeply enough to get it out.

Yes, oil based stain - which was dry to the touch and then another 8 hours passed before water-based seal coat. For the stain, I waited a total of about 48 hours; 68 degrees with 20-30% relative humidity.

The Sanding Sealer dried within 30 minutes with the same conditions, even though it says 2 hours on the label.

----

I agree it would be better to sand the entire tread, restain, etc. But I am experimenting with one of the spotted treads first as this staircase is not well-lit.

I patch sanded 3 days ago and then stained it, then added a 2nd coat of stain that same day to match the darkness. Today I used mineral spirits to remove the stain that was over the sealed portions for a more even transition. I'll wait another day and then apply sealer - to see if it will even out.
 
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Old 02-02-15, 08:27 AM
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The patches on one tread has been restained and primered. The white stains have not returned. The spots ARE pretty obvious, though.

I think I will do a test on a clean piece of wood, just to see if a not-fully-dried (ie, slightly tacky) stained surface would produce white spots. Just to be sure.
 
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Old 02-02-15, 10:08 AM
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The stain itself shouldn't turn white but uncured water based poly/varnish can.
 
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Old 02-02-15, 01:40 PM
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I don't think it is the varnish/poly. It has long since dried and you can see the white stains.
 
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Old 02-02-15, 02:36 PM
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The white indicates the finish has lifted and is not bonding. Its a sealer/poly adhesion issue.
 
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Old 02-02-15, 06:09 PM
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I don't think the poly itself is drying white. There does not seem to be any bubbling or gap between the finish and the wood. The poly dries clear and the poly is definitely dry.
 
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Old 02-03-15, 03:44 AM
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Most clear latex coatings and sealants go on milky and then dry clear. Some will return to the milky look when they get wet. I believe those spots are where the water based poly didn't fully dry .... even though it may be dry on top.
 
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Old 02-03-15, 07:49 PM
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I sure do appreciate everyone's responses.

The white spots showed up after the Sanding Sealer (water-based primer for the poly) was dry to the touch.

The treads were long dry from the stain - over two days - before I applied the Sealer coat.

The parts during staining that didn't dry as quickly were tacky (after 24 hours on some parts of some treads, but most were dry) on the wider patches between rings where the stain does not soak in much. But they were dry after 48 hours and I waited an additional 8 hours after that.

Note that the white spots did not pop up where the stain was tacky after 24 hours.

So far, I have only spot-treated one tread. The other treads show the same white spots. I'm sure they're long dry, and the spots won't go away on their own, even though "full curing" does take more time. The white spots did not return after re-staining and re-sealing.

So, I think it is a different chemical reaction that causes the finish to turn white.

To test this, the next tread I work on - I will also take a clean piece of pine, stain it, then apply the primer after 24 hours to see if a tacky stain will cause the poly to turn white when it cures. But I'll let the tread dry, again, at least 48 hours.

Pictures to follow, too.
 
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Old 02-04-15, 04:27 AM
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Just to be clear - the stain doesn't turn white but water based clear coatings can.
 
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Old 02-04-15, 07:34 AM
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The Sanding Sealer dried within 30 minutes with the same conditions, even though it says 2 hours on the label.
Latex coatings may be dry to the touch (which is normal) but the 2 hrs on the label usually refers to the time to recoat. If you put poly over a sealer too soon, the water becomes trapped before it has time to completely evaporate. This would be especially true in areas where the sealer was thicker... or any areas that just had not fully cured.

The dry times on the can vary based on conditions and on how thick you put the finish on. You also don't usually want to back brush latex coatings, since they dry so quickly.
 
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Old 02-04-15, 09:14 AM
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marksr, I think you're right - it is the Sanding Sealer that has turned white, not the stain.

But this primer coat wouldn't just turn white by itself.

And I seriously doubt it is trapped water. It is a water based finish, water would mix with it, not get trapped under an impervious layer.

I did not sit and watch it dry, but I applied it, cleaned up, went back and the sealer was dry to the touch - and there were no white spots - and the milky look of the sealer was gone.

It was the next day - I put the finish on in the evening - that the white spots were seen. So, sometime in the curing between "dry to touch" and 12 hours those white spots developed.
 
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Old 02-04-15, 10:18 AM
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It is trapped moisture. I don't know exactly why but clear latex coatings and sealants can turn milky when they get wet but generally go back to being clear once they dry back out. Somehow the sealer got damp [evidenced by the white spots] and the next coat of poly trapped the moisture. It is possible that if for some reason the 1st coat of water based didn't cure completely that the water in the 2nd coat of water based poly can bring on the problem.
 
 

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