Polyurethane

[Matt88s]

I had a can of the spray on poly that I'd been using for misc projects, and I hadn't had any trouble with it drying.

I'd made something out of cocobolo with a secret compartment in it, and wanted a quick finish to put on it and seal it all up as all of my cocobolo has a history of moving around, so I shot a quick coat of poly on it thinking it would seal it up and give it a decent finish quickly. That was Sunday, it still hasn't dried. Whats worse, is even though I'd had this block of cocobolo sitting around for the better part of a year, it has still moved and developed some hairline cracks on the top. My perfectly fitting hidden seam is not so perfect nor hidden any more.

I don't know why but periodically I have issues with poly drying. Has anyone else ever had this and is there any way to make it dry faster?

I know with cars, certain finishes and putties we would pour a bit of thinner or the like on a rag and wipe it on and it would help it flash off and dry.

I need to just swear off poly, I've messed up enough projects to sour me on it. I keep it in the house, I don't let it get cold or hot, temperature has been in the 60-70's all week anyhow.

Any ideas?

[Master Splinter]

Cocobolo is an oily timber - this oil can interfere with the drying process of some finishes giving a very long drying time (if it dries at all..sometimes you luck out and drying stops altogether and you end up with a gluggy mess..also stuffs up glues, too).

Usually giving a wipe down with a rag wet with thinners immediately before you finish knocks off enough of the natural timber oil to give your finish time to set.

Its also possible that whatever is in the can has passed its use by date and has gone funny. (give a quick spray on something else to see how it dries).

Being an impatient so-and-so, my instinct would be to chuck it outside in the sun...and if the nice harsh Aussie UV doesn't prompt it to set after a day, I'd clean off the finish with thinners and rags and try something else like shellac! (remember to do the solvent wipe just before finishing)

[old_picker]

that will be tricky getting the good old aussie sun to shine in the USA

hehehe

[Matt88s]

that will be tricky getting the good old aussie sun to shine in the USA

hehehe

Meh, only about as hard as it would be to get the good old american sun to shine in austrailia.



Can of poly is good, I just bought it a couple weeks ago, been using it to seal up some pen blanks, hadn't had any trouble with it drying at all, in fact, it would dry up in a couple hours.

It may well just be the cocobolo, it is an oily bugger.

I put it outside on Mon, the weather was nice and sunny, I left it in the house on tue, I put it in the car today. Lets see if we can't bake that sucker on there. I also, and this is horrible, but I buffed it a bit with a cloth, it seemed to knock a bit of the sticky layer off. It's now a bit tacky, but not as bad, I think it will go ahead and cure out now. I'll need to go back, probably hit it with some 400-600 paper to knock the bits of fiber and whatnot out of the finish, and put another coat of something on it to bring the shine back, but I would have probably had to do that anyway. If it will go ahead and cure out though, then I'll at least be able to.

Cheers!
Matthew

[rgoossens]

Hi, I wonder if it dried eventually as I am having the same problem on a previously oiled dining room table. I sanded it off thoroughly and then applied a thin coat of exterior PU varnish (new can) with a cloth. 24 hours later it still felt slightly tacky but I applied another coat in the same way. Now 48 hours later still not dry. Should I put it out in the hot South African sun and will it eventually dry?

Cheers

Rudi

[Harry72]

Hi, I wonder if it dried eventually as I am having the same problem on a previously oiled dining room table. I sanded it off thoroughly and then applied a thin coat of exterior PU varnish (new can) with a cloth. 24 hours later it still felt slightly tacky but I applied another coat in the same way. Now 48 hours later still not dry. Should I put it out in the hot South African sun and will it eventually dry?

Cheers

Rudi

Could be several reasons,
What type of wood?
Even though you brought a new can it might still be old stock or opened by someone(it happens).
Very high humidity can effect it, it should be set off within 24hrs, it still will feel soft and indent easily for several days while it fumes off.
What did you thin it out with, how much did you thin it?
Did you dewax it before sanding?(may cause adhesion problems)

[Chipman]

This problem (finish not drying) happens with lots of different finishes, not only poly and in my experience, it is almost always the timber!

I have got into the habit of wiping it down with several applications of acetone first and as soon as it is dry, apply the finish. Oily timbers need to have this treatment before gluing too. It is quite a simple and inexpensive step but saves lots of problems later on.

If the surface has already been waxed/oiled, it can be quite difficult getting it out of the wood. I would be inclined to stay with the same finish!

Cheers,
Chipman

[rgoossens]

Thanks for the reply, it is encouraging to know it could take a few days.
Let me answer your questions.
The table is made of Rhodesian teak (or is it Zimbabwe teak these days?) salvaged from the treads of a flight of stairs in a demolished bank in Port Elizabeth 35 years ago. It is extremely dense, hard and heavy. During this time it had the occasional polish either with furniture wax or oil.
Two weeks ago the top got badly stained when we manufactured our own Christmas cards and glue penetrated through the newspapers. I then sanded with a belt sander starting with grit 40 and finishing off with 320 and decided to rather have a PU finish. I got recommended Rystix exterior (a locally manufactured brand) by an experienced furniture restorer.
As instructed on the tin I thinned the first coat down with 25% mineral turps and put it on quite heavy with a brush. When still very tacky after 24 hours I phoned the manufacturers helpline and got an earful that I had it done all wrong, I should not have thinned it and I should have have scrubbed the top with water and dish washing liquid before applying a very thin coat of PU. So I removed the first coat with plenty of steel wool (what a job), did the dish washing trick twice, let it dry out and then rubbed the PU on using an old hankey.
I do not suspect the tin to be old stock, the humidity has been very high (above 80%). This morning it feels a little better although still very soft but I will have to put it back soon as it needs to be ready for Christmas dinner.

Now back to the cricket in Perth.

[Harry72]

The dish washing trick is to try and remove any residues. A proper dewaxer is better(see a automotive paint shop for prep wash)
Try the polyU on some scrap wood of a different species, see what happens.
80% moisture should be fine, the only times I've had weather problems is when its too cold(>10°c) or raining on a warmer day.