How to use polyurethane

[zenwood]

I've just finished a side table in oregon with a polyurethane finish, which looks pretty crappy, after 4 coats with a minimum of 24 hrs drying time and sanding in between. Apart from the mozzies and other bits and pieces that seem to land on top, the surface is wrinkly (brush marks) and the verticals have some drip/run marks.

I used a brush, and applied it as thinly as I could, yet it looks like it's been laid on with a trowel.

Am I doing something wrong? Should I thin the PU (gloss) way down with turps? Should I be applying it with a pad/rubber, in the manner of shellac?

I wanted a hard-wearing, fairly waterproof finish. Would there be something else I could've used?

[Skew ChiDAMN!!]

I hate poly, but there've been times I've had to apply it to small turned items. I won't use it on larger furniture.

But I was taught it should be sprayed on. I wouldn't rate as a spray-painter's seatfiller but at least my small items turn out OK.

[Harry72]

I used a brush, and applied it as thinly as I could

There's yer problem!
The thicker you can get it on the flatter it goes, just like enamel paint! Even when Im spraying it on I put very little thinners in maybe 5% and absolutely flood it on horizontal surfaces.
You can apply it with a pad/rubber like your saying but dont expect a high gloss level... unless you're using a proper wipe on poly.

Both these photo's are only 2 coats 1st is brushed on and the second is sprayed

[Richardwoodhead]

Like Harry said, you just have to spray on pure poly's and also lacquers to get that great smooth / even finish.

[zenwood]

Wow Harry: those look a million times better than mine. Maybe you can give me a lesson if you make it to the barbie. Can you get a finish like that with a brush? (I haven't got a sprayer.) For some reason I had this thing in my brain that thin coats and lots of 'em were the go for high shine finishes. Don't know where I got that from.

The things that annoy me are a bit hard to see in the photos. Maybe daylight would be better.

[NewLou]

Gidday Zenwood

Have a squiz at these I think you'll find them Handy:

http://www.woodworkforums.ubeaut.com...ad.php?t=19175
http://www.woodworkforums.ubeaut.com...ad.php?t=19173

REgards Lou

[barryr]

to me using poly is like using shellac - build it up nice n thick and cut it back flat with wet n dry .

[zenwood]

Thanks for those links Lou. The spitpolish one is the reverse of what's recommended on the can, which says to lay down a thinned coat first, then full strength. The spitpolish method is the other way around.

Haven't read the other one yet, it quite long...

[Harry72]

Zen the 1st pic is brushed on, all up its prob about 1-1.5mm thick!
Yep I can see from you're pic's the "Ol'not enough paint trick 99", The first coat can be thin if spraying.

[JB]

you just have to spray on pure poly's and also lacquers to get that great smooth / even finish.

What's all this talk about spraying lacquers and polys unthinned to get the best results? I thought the consensus of the recent discussion at http://www.woodworkforums.ubeaut.com...ad.php?t=19490 was great results came from thinning big time, ie 10 parts lacquer to 6 parts thinner, or more? I for one like a very thin mixture, but that's with lacquer; I have no experience with poly. Richard, didn't you advocate a thin lacquer mixture in the link above?

Getting back to the original post here, my experience with brushing estapols (clears and paints) unthinned is they leave brush marks as they are simply too thick to 'smooth out' before they dry. Obviously from the above posts this isn't everyone's experience, so I must have been doing something wrong.

[Harry72]

You are correct most nc lacquers must be thinned a lot(except pre-cat), but for high gloss/plastic look applications in poly very little thinning is needed while spraying and you dont thin it at all if brushing it on.
Are you using very old stock poly?(how long has it been on the shelf?)Was the weather cold and dry?
Did you rebrush over it while its at the gel stage?

[Richardwoodhead]

JB, my reference to "pure" poly's was to distinguish between oil/poly mixes (like Danish) and not to suggest you can spray poly's and lacquers "pure" - without adding thinners - which in my experience you cannot. All the poly's and lacquers I've used need to be thinned. The recommended amount of thinning seems vary with the technique / preference of the operator (lots of thin coats versus fewer thicker coats. Thinner coats seem to give fewer spraying "problems" like runs, orange peel, etc)

With less "pure" poly's - like oil poly mixes - you can get away without spraying. That was the point I was trying (badly) to make. Hope this is clearer.

Richard

[JB]

1. lacquers must be thinned a lot(except pre-cat)
2. Was the weather cold and dry?

1. I thin pre-cat lacquer up to 50% with no problems Harry. Have you had problems thnning it a lot?

2. Yeah it possibly was.

[Harry72]

Yeah you still can thin pc nc heaps, but I find you get a much better build with it thicker(ameron/croda brand) only takes 2 double header coats to get a nice thickness a whole cabinet is done in under 2 hours start 2 finished... love it!

[Toymaker Len]

I've just done my new bluegum kitchen benchtops from raw with Intergrain brand so called Tung Oil finish which I suspect is more poly than tung. Sanded raw to 320 grit brushed the TO on, left it for ten minutes, wiped it off with a clean cloth. Next day lightly sanded with 400 grit to knock off the raised grain ,dust, insects etc, wipe down with tac cloth (yesterdays wipeoff cloth stored in a plastic bag) then brushed on the TO, wiped off after ten minutes. The third coat went on the same way the next day. Finally a light go over with 600 grit and a touch of EEE Ultra Shine buffed up with a clean cloth and the whole lot looks a treat. That was about two weeks ago and its wearing well so far. It has made a nice waterproof seal but you can still feel the wood.