finish problem

Refinishing old table for MIL. Table is small coffee table made of white hard wood with walnut veneer on top everything stained with a med dark stain. Cleaned the table with denatured alcohol and cleaned up 80% of finish problems, on top used a finish remover, sanded, cleaned with denatured alcohol. sprayed on water based poly this afternoon and the table has turned white, looks like a poor paint job. Sprayed box made of oak and maple yesterday and it looks good, same can of finish, Finish has been on table about 5 hours and is still tacky, temp is 70 deg F and falling, humidity is 79% with rain coming in. any suggestions on what went wrong (my fault I'm sure) and what corrective measures to take.
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wrote:

Uh ohhhhh.....

You will get a lot of opinions here, so here's mine. You have some contamination that has worked its way under your poly that isn't compatible.
You may have loosened up or dissolved some of the old finish when you cleaned the surface with the alcohol and it remains on the top (under your finish). There may have been something spilled on the table (who knows when) that was fine with the old solvent based finish, but without 100% removal, will not allow your new water based poly to dry.
If the alcohol bath didn't outright dissolve the original finish, then it was probably one of the 1,000 different blends of lacquer. What you did with the alcohol was simply clean the grime off the surface.
My solution to this would be what my solution always is on these problems... start over. Go buy a good stripper, strip off ALL the finish to make sure you leave no contaminates behind. Sand lightly as needed to take off the remaining resins that redissisolved with the stripper. Clean off the surface with lacquer thinner and really clean rags. Apply final finish.
If the wood is really clean, you shouldn't need a barrier coat of anything like shellac. If you have your doubts, a quick spit coat of sanding sealer only takes a few minutes to apply, and it is compatible with anything you want to put on top of it.
For me personally, my experience has been that when finishing/ refinishing wood that has a chance of contamination, I get better results with a solvent based top coat.
YMMV.
Robert
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I'm just seeing this thread for the first time and didn't bother to look up the original post, so I may be a bit off base. So, what's new huh?
I'm not sure this sounds like contamination to me Robert. I'm not seeing him complain about adhesion problems or any other indicators of contamination or incompatibilites between finishes. This sounds like a problem with the finish at hand. I'd like to know how heavy the finish was sprayed on. Humidity level is high so I'd expect a water based poly to be pretty slow under those conditions. Temp is fine, but it's more about humidity with water based stuff.
I'd like to hear a little more detail from the OP on how he sprayed this. What type of gun, how many coats, how long between coats, how heavy were the coats? Was the OP seeing tack between coats or was this drying problem evident throughout the spraying process? Any other incidentals like tendency to run (indicating a way thin product), etc.

I too resort to this approach, but in this case I think I'd wait 24-48 hours and see what the situation is. I'd probably throw a light at it too, in attempt to encourage drying.

Solvent based smells so much better too...
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Tue, Dec 11, 2007, 5:31pm (EST-1) snipped-for-privacy@bellsouth.net (sweet sawdust) 'did' ssayeth: <snip> cleaned with denatured alcohol. <snip>
Dunno if it figured in, but thou did 'not' sayeth how long thou let it dry.
JOAT I do things I don't know how to do, so that I might learn how to do them. - Picasso
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sweet sawdust wrote:

Sounds to me like an oil/water reaction. Whether it was old finish partially dissolved but not completely removed, or something in the finish remover you were using, I don't know. But there was something on the surface keeping that water based poly from drying like it should.
You can try starting over again, but you might have a problem getting all the old finish off without sanding right through the veneer.
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He's not reporting any adhesion problems which would be expected with an oil/water reaction. No blisters, no lifting, no fisheye, nothing that sounds like a contamination of any sort. I'm curious what you may have experienced with water based poly that causes you to suggest this. One never stops learning ya know.
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Mike Marlow wrote:

I've never had that reaction with water based poly, but then I never put it on over an old oil based finish I had tried to remove. Based on the fact that he said he used the same batch of poly on another project without problems, I ruled out problems with the finish itself or his application. Simple deductive reasoning tells me it must be a problem with something on the surface. I confess that oil/water reaction was a guess. <g> The only other thing I could think of is that maybe he put the poly on before the alcohol had dried.
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Ah. Thanks. From his reply I'm thinking it is more a combination of his application of light coats (before each coat cures) and the sorta high humidity. It's not killer humidity and I've certainly sprayed a lot of stuff at that level, but he did say rain was moving in and that'll hurt the drying time.
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Mike Marlow wrote:

I agree with you about thicker coats.
For those of you like me, without spray equipment, I've had very good success with the following technique if I want a really glass-smooth surface: Apply several thick coats, allowing to dry completely and with a light scuffing in between. Then sand this buildup down through 400 or so, and apply the last coat carefully with a foam brush.
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"In answer to the questions in the replays to my query: The Alcohol did soften and remove most of the old finish but not all, the finish acted like Shellac. The adhension of the new finish was good except in one or two spots on the part that was washed only, I have since sealed those spots. There was no tack between the first and second coats, finish was soft but not tacky to the touch, you could dent it (barely) with a fingernail but it would not stick to your hand or leave an imprint. Run was slight to none the product had not been cut and was straight out of the can. I used a HVLP spray gun on a light setting, I prefer several coats to one or two heavy coats. From the final sanding after the last wash to spraying was in excess of 24 hours, time between first spray and seconed spray was about 4 hours. The veneer is getting thin and I would hate to resand the top, probably be eaiser to make a new top.
After 14 hours of drying I checked the finish, it had gone from milky white to crystal clear, still not a hard finish, can be dented with a fingernail but not tacky. I sanded the finish and it sanded with out pills or loading the sandpaper (220 grit). Surface of table was wavey not smooth, it looked like the finish did not flow properly, the sanding gave it a smooth surface. I resprayed and within 5 minutes the new finish was again the color of milk. I am going to put a spot light on it to try to heat is slightly and see if that helps. I am wondering if it is a combination of high humidity and cold?

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I don't spray water based poly so you'll have to correct me if the manufacturer suggests something different, but I don't initially like the idea of the first coat being soft when you shoot the second coat. If I'm correct, this finish cures by evaporation - right? In that case you'd want to put on a heavier coat and let it dry thoroughly. Scruff it and put on a second coat. Poly does not burn in to the coats below it so when you apply coats - even light coats over coats that are not fully cured, you are trapping the carrier in there. It will make its way up and out but that is going to delay the curing time of the subsequent coats.
As a rule, spraying light coats is not a preferred technique. Of course, we all have our definitions of what is light and what is heavy, but a heavy coat covers more evenly, and with less surface distortion caused by the sprayed particles.
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Hey Mike, how ya doin'? Don't see you around much anymore.

idea of the first coat being soft when you shoot the second >coat. If I'm correct, this finish cures by evaporation - right?
In my personal experience, a tack or soft coat can be good for solvent based finishes, but don't know anyone using that technique for water based. (PING - Barry...) And of course, NONE of the manufacturers endorse a tack coat for any of their final finishes.
I have read how some of the newer, more sophisticated water borne finishes cure, and I'll tell you, you have to be a Chinese mathmetician to understand the science of the the cobination of curing polymers. I think in this case it actually depends on the type of finish you use whether it is MLC, Target, Fuhr, etc.

trapping the carrier in there. It will make its way up and out >but that is going to delay the curing time of the subsequent coats.
Nicely said. There is no reason to put on thin coats of poly unless you can't control the finish texture. Put it on the manufacturer's receommendation and follow up coats as directed. It sounds like you were >right on the money< with this as he does say that it did cure out later... so it seems this would be at least a large part of the problem.
And check this out. One of the boys on WoodWeb described the hole he fell into by using some of the new water based finishes with multiple thin coats. After he put on one coat, he waited until it was tack dry, then applied another, then another. In effect, what he did was build a sandwich of layers that made it impossible (after the very top of each coat dried) for the product to off gas and cure. Since the first of four coats was down so deep, the solvents in the finish (see below) may have discolored the wood! His project was sticky for some time (couple of days?) as he screwed up the manufacturer's instructions. Luckily, it cured out while he was frantically trying to find out ways to keep from having to strip and start over.
A common mistake is to think that these water based products are "safe". NOT SO. They are filled with different poisons, not much better than the old solvent based stuff. Formaldhyde, ammonia(s), alcohols, stereates, and all kinds of other nasty stuff are in these mixtures. That's one reason I am not on water based stuff now.
Besides, I agree with Mike. The solvent based stuff does smell better! I got a laugh out of that one! I am just thinking of a day of spraying with a leaky mask.... YIPEEE!
I STILL think there was something left on the table top, even if it was just some left over moisture held in the old finish. Cool weather, mild temps, and the use of alcohol may have been a contributor. After all, even though the alcohol was at 80%, that means it was still 20% water he was washing with.
I didn't originally go to the contaminated finish/gun road as my personal experience with contaminated finishes is that they are erratic, and don't follow a pattern. A -uniform-, cloudy finish seemed to point somewhere else.
Robert
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snipped-for-privacy@aol.com wrote:

Full, wet coats for MLC Ultrastar. No tacking, and don't build too many coats. Once I'm happy with color, I'll usually go one coat of Zinnser Seal Coat and two coats of Ultrastar. If I want a deeper build, I'll use a second coat of shellac or add a coat of Ultrastar Sanding Sealer.
For solvent stuff, I flow-coat the last coat, but don't tack it. I've really come to like the Kwick-Kleen "Fast Dry Poly" when I need more durability than NC lacquer.

Very true.
The big attraction for WB is no fire hazard, easy cleanup, and excellent durability.
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Ahhhhh, yes. There's just nothing like those paint trails up your nostrils after a good day of spraying... They almost look like they were air brushed there.

I agree. Nothing in what the OP posted suggested contamination to me.
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