'Nuther Polyurethane Question

[Barefoot]

An area about 2'x3' of my clear polyurethane on 5.2 mm luan (real wood) is still tacky after more than a week. Why, or better yet, what might fix it for another coat if waiting still longer doesn't? Thanks.

[doug hodder]

What's underneath it...any stain, epoxy etc...if so, were the stains or colorants fully dry and any epoxy fully cured?....Doug

[kennyrayandersen]

sounds like an unplanned chemical reaction -- sounds like something underneath wasn't dry, or wasn't compatible. If it's epoxy, was it hard already? (maybe too much hardener in the epoxy will cause that, or when it is not mixed well). The polyurethane doesn't usually suffer from the same problems unless something is messing with it...

[wannabefree]

Sorry, a lot of these things happen because we don't know what's in the stuff we're using. I swore off poly 30 years ago in part because I had adhesion problems. I also didn't like the look. Poly has improved but I still won't use the stuff. Burned once; won't be burned again. Can't tell you what's wrong, but here's a way to fix it.

Clean off the gooey poly with whatever will cut it. If you have a stain under it this may also lighten the stain. If so, restain with a thinned coat. Let it dry thoroughly. That usually means a week or more if oil based, a couple days for water base and a good day for alcohol soluble dyes. Get a can of super-blond shellac and cut it 2:1 with denatured alcohol. Brush that over your problem area. One light coat will do. Give it at least a day to dry; preferrably 3 or more. Then reapply your poly.

I suggest experimenting on a piece of scrap so you know how much stain to apply to get a color match. If you can't get a match with the stain, add a little dye to your shellac. Transtint is what I use. Get it at a Woodcraft store. The nice thing about using the shellac seal coat to match color is if you get it wrong you just strip it off with alcohol and redo it.

This works because shellac sticks to anything and anything sticks to shellac. The shellac seals in any bad stuff that is interfering with your poly.

A side note - poly still has adhesion problems on oil based stains. To test adhesion, stick a piece of the regular brown masking tape to your poly. Rub it down good and go away for half an hour or so. Then rip up the tape. Hopefully the poly will stay stuck to your wood, not the tape. If it comes up with the tape you have a bigger problem. But you might not want to know that

[kennyrayandersen]

Sorry, a lot of these things happen because we don't know what's in the stuff we're using. I swore off poly 30 years ago in part because I had adhesion problems. I also didn't like the look. Poly has improved but I still won't use the stuff. Burned once; won't be burned again. Can't tell you what's wrong, but here's a way to fix it.

Clean off the gooey poly with whatever will cut it. If you have a stain under it this may also lighten the stain. If so, restain with a thinned coat. Let it dry thoroughly. That usually means a week or more if oil based, a couple days for water base and a good day for alcohol soluble dyes. Get a can of super-blond shellac and cut it 2:1 with denatured alcohol. Brush that over your problem area. One light coat will do. Give it at least a day to dry; preferrably 3 or more. Then reapply your poly.

I suggest experimenting on a piece of scrap so you know how much stain to apply to get a color match. If you can't get a match with the stain, add a little dye to your shellac. Transtint is what I use. Get it at a Woodcraft store. The nice thing about using the shellac seal coat to match color is if you get it wrong you just strip it off with alcohol and redo it.

This works because shellac sticks to anything and anything sticks to shellac. The shellac seals in any bad stuff that is interfering with your poly.

A side note - poly still has adhesion problems on oil based stains. To test adhesion, stick a piece of the regular brown masking tape to your poly. Rub it down good and go away for half an hour or so. Then rip up the tape. Hopefully the poly will stay stuck to your wood, not the tape. If it comes up with the tape you have a bigger problem. But you might not want to know that

Sorry you had trouble with poly -- While you've been avoiding it, I've been using it and never once had a problem. I REALLY wish I had it on my kitchen cabinets instead of the lacquer (they shoot lacquer because it dries fast, and really for no other reason). My 4 kids absolutely abused their bunk beds and the stuff never came off and never cracked even though the wood (hardwood at that) took a ding (like the lacquer on my load speakers cracked) and it never got gummy on a hot day like shellac can. Shellac is a natural product, but gets so soft with elevated temperatures (say outside on a tear) that you can put a thumb print in it. It's OK if you want to French polish an indoor piece of furniture, but I'd never use it outdoors. Maybe it will work as a flash coat as you suggest, but one manufacture I saw says not to apply their poly over shellac:

DURA SEAL™ Polyurethane will have an ambering effect when applied over light colored surfaces. Do not apply DURA SEAL™ Polyurethane over floors previously finished with wax, shellac, lacquer, or stains containing wax or stearates. Allow extra drying time when applying over floors that have been stained. Do not steel wool or burnish the surface before applying DURA SEAL™ Polyurethane. Do not apply DURA SEAL™ Polyurethane during extremely cold or humid weather. Do not close off ventilation after applying DURA SEAL™ Polyurethane. Always screen lightly between coats.

That's just one manufacturer, but since it's the first poly to pop up I thought maybe it's not so uncommon. I've never had to wait more than a day for any stain to dry, including oil-based stains (I never do finish work in less than 68 degree temps), and the finish should be hard in 24 hours and about as hard as it will ever get in 48 hours.

Seems to me the biggest problem is one of reading the directions and following them to the letter. Also, and call me paranoid, but most manufacturers make there products to work well together, and they really have no control over what others are putting into their formulations etc; so, how would they know exactly what is compatible with what. I usually do is pick a brand and use their stain and finish together. It's probably not necessary in all cases, but I figure why risk it.

[aggie79]

I like the water-based polyurethanes BUT like a water based stain or tint they can raise the grain on some woods. To counter this, either raise the grain by misting the wood prior to staining, and then sand the "nubbies" away or use a sanding sealer before the water-based poly is applied.

[Barefoot]

Oh boy. I failed to mention a few things that are givens on this build, so I never though to mention them. The feedback has helped with that.

This is clear (slightly amber) oil-based poly over no stain nor other finish but what came on the factory 5.2 luan exactly like all the rest, which set up long ago. Of course something may have gotten on that one section at Lowe's or even here. Also, maybe that one bit of poly didn't stay mixed.

Becaue I'll not recoat until the heat and humidity fall enough to have the garage door open, I'll be waiting a while longer anyway, so it may dry yet. I can also try sanding the tacky poly off that area but must be careful not to cut into the oriiginal finish, revealing nearly pure white!

Any other ideas now that you have better information?

[48Rob]

Are you running fans when applying the varnish to keep cool, or hasten drying time?

Too much breeze can flash dry the surface and prevent the solvents from evaporating.

High humidity can also lengthen drying times.

I've had on occassion to wait 3-5 days for varnish to dry, especially if I was in a hurry, and should have waited another day for stain to dry, or other coats to dry.

If the varnish is still very sticky to the touch, wipe gently with a very clean lint free rag and mineral spirits to remove "excess" varnish.
If it is just a little soft and tacky, gently rub with 220 grit sandpaper, with the grain, just a couple passes (GENTLY) to break the surface, then allow to dry further.
You're only sanding the varnish, not the original finish under it.

Setting a fan in the room to blow air over the panels will help too.
Never blow air on the panels, just over them, as in keep the air in the room moving around.
Of course this is only done after the finish has hardened to the point dust will no longer stick...

On another note, when applying finish to "new" panels from the store, or where ever, it is wise to first sweep away and dust, then gently clean the surface with mineral spirits, then lightly sand after the solvent has dried.
Then remove dust, and thin the first coat of varnish between 25 and 50% with mineral spirits.
Then sand with 220 between coats.
Depending on the project 2-6 coats may be needed.
It usually takes 3-4 coats to seal a plywood panel, but 5-6 is much better.
Generally 24 hrs drying time is required per coat, plus sanding and cleanup time beteen coats.
"Varnishing" a panel, correctly, so it will last, is not something that can be done on a Sunday afternoon...

You may well know all this, but for someone just learning, it is important to not assume that because it is brand new at the store, that it is clean and or ready for finish...

Rob

[Barefoot]

I'm not brand new at this but no way a pro either, so thanks to you all and to Rob for "the rest of the story", as Paul Harvey used to say. This is steam bath season in Florida but the humidity is no worse right there than on the rest of the trailer, which dried two weeks ago. I did have a fan going out of human necessity, and it could have been blowing mostly on that area. I did not think to wipe down with solvent first, just a light sanding, so my guess is that something foreign was on that part of that one panel. I did sand the whole trailer with 220 between coats and now again for the next coats when the weather improves, but it didn't help that one area, so will now try wiping that down with solvent. Interesting puzzle. More to follow on and off for the next couple of months.

[48Rob]

Barefoot,

Sounds like you did it right.

If there was "something" on the panel that should have been removed (wax, oil, dirt, etc) it could have caused adhesion problems at worst, and a mark or stain under the finish at best, but it is unlikely that it would cause an extra long dry time...unless some odd chemical reaction occurred.

Most likely, the area that didn't dry properly had a previous coat that had not fully dried when another coat was applied.
I realize you said the rest of the panels cured properly, so it is difficult to pinpoint, but it is easy to apply varnish thick in one spot, and thin in another...

Another long shot possibility was that the varnish applied to that area was the unstirred "stuff" on the bottom of the can.

If wiping the area with solvent doesn't help, brealing the surface with sandpaper to allow the solvents trapped underneath to escape, along with a few more days should do it.

If after another 3-4 days it is still very sticky and wet, flood the area with solvent (use a heavily soaked rag) and then a scraper to just remove the uncured varnish.
The scraper should be a real wood scraper, designed to scrape wood, it must be very sharp.
A scraper is pulled towards you, and gives you very good control over depth.
It can easily take off the varnish, without damage to the panel.

Rob

[Barefoot]

At my age I think very slowly but very thoroughly (I hope), and eventually recalled where that panel was in the stack and that it probably got a fine mist of Fresh Care fabric freshener and/or Windex window cleaner on the one corner, which surely would have upset the cure. Duh.

Plan A just as suggested: wait, sand again, light solvent or heavy solvent, maybe with scraping, refinish. If all else fails, well, then it will just stay sticky and attract dust and insects. I don't like most "learning experiences" but like having what I've learned.

Your ideas have been moist helpful and jogged my memory, too.

[Barefoot]

This should be the end of this thread. My guess is that the stuff that likely got misted on to parts of the one panel also rose to the surface, because wiping it down with solvent WORKED! It's dry to the touch and the color is unchanged. A bonus is that now it's as smooth as a baby's bottom, better than the rest of the panels. When the weather allows, I may just wipe them down too! Thank you all.

[48Rob]

Glad to hear it worked out for you!



Rob