Recoating polyurethene . . .

I've had a lot of trouble trying to coat a table-top with polyurethane.
I first applied regular Minwax polyurethane with a sponge brush, as the directions suggested. Inevitably I wound up with a certain amount of ugly "puddling" of the finish.
So I resanded, and used Minwax wipe-on. I put on half a dozen coats. The result: A poor finish. And even worse, it doesn't protect against water-rings when wet glasses are placed on the surface.
My question is, can I lightly sand the wipe-on finish, then put on more coats of the regular polyurethane?
I realize of course I'm likely to get "puddling" again, but I'm willing to try once more time. If it doesn't work I'll get a professional to do the refinishing, or just buy a new table.
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you need outdoor polyurethane its water resistant and sand thouroughly to bare wood
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IMO, poly shouldn't be used for anything that will be seen up close like a table-top. [maybe it has gotten better in the couple decades since I last used it-- but I gave up trying to make it withstand close scrutiny.]
I'd take it all off & go with either a lacquer or a solvent/wax rub-on finish depending on your level of patience and tolerance for future maintenance.
Jim
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Lacquer will absorb moisture like nothing else. I think it also softens with water. Ruined my car paint with a bra and rain.
Greg
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Ray wrote:

Yes, you can sand; in fact, you must. Poly doesn't stick well to itself so the sanding provides "tooth" for it.
--

dadiOH
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if first coat wasnt even it seperated you didnt prep the surface right, oils grease will penetrate old finishes, sometimes you have to strip but cleaning would have needed to be done with a strong solvent till table was clean like alcohol, laquer thinner, paint thinner, then sanded, so now you have a mess of finishes, maybe wait a few weeks and sand fully and try again or strip to wood
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I am going to assume "puddling" of the finish means that after drying, some areas looked dry and some looked as though there was finish. This is due to the wood surface absorbing less finish in same places and more in others. To minimize this in the future, sand the wood evenly and then apply a wash coat of shellac. The shellac will even out the absorption of the topcoats. You can lightly sand the wash coat if you like to create a very smooth surface. Polyurethane has its own set of tricks for applying a smooth finish. You do not describe what you mean by a "poor finish" so it is not clear what the symptoms actually are to your eye. As for water rings, all finishes with perhaps the exception of epoxy are susceptible to water stains. You can try using coasters, be really quick about cleaning up any water spills or condensation, or just remove the rings as they occur using heat or abrasion. You can definitely sand the existing finish and apply more polyurethane. In fact, you would want to sand anyway since polyurethane does not stick to itself by melting into the previous finish but rather by a mechanical bond. This means that the previous finish needs to be sanded to provide some "tooth". I suggest that you sand well until you can see "witness lines" or "spiderwebbing" or "lace". This shows up when you have sanded through the topmost layer into the previous layer. When you apply a new coat of polyurethane, it should go on smoothly, hide the webbing, and give you a very smooth finish.
Good Luck.
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On 11/8/2011 7:28 AM, Ray wrote:

What does the label say on the wipe-on? Oil or water base? If the finish "puddled", it likely was applied too thickly. Minwax has a "high build", which is intended to look thick and glassy. White rings on poly suggest the finish isn't thick enough (water gets into woodgrain) or the finish isn't cured....I've used poly, mainly solvent-based, a number of times and never had trouble with wet glasses...used it on kitchen table and could beat the hell out of the table.
To refinish, you want to make sure the finish is hard (no dents from finger nail) or it will turn into a gummy mess. When I apply more coats of poly, I rub it with very fine steel wool...never any trouble with it not adhering. Fine steel wool is also nice for rubbing down dust globbies or tiny bubbles.
Here is link to Minwax: http://www.minwax.com/wood-finishing-101/guide-to-clear-finishes /
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On Tue, 8 Nov 2011 07:28:58 -0500, "Ray"

A proper Poly coating takes some time. Sand to bare or nearly bare wood. Cut the first coat with 50% mineral spirits. Lightly sand with 220 grit. Cut the second coat with 10% mineral spirits. Sand again. Put on at least two but three coats is better with the sanding between.
Let it cure for four weeks. Yes, 4 weeks.
Very Lightly sand with 320 grit. Wet sand with 600 grit. Rub with pumice. Rub with rottenstone. Wax with paste wax. Admire.
I will look like a professional finish, not plastic poly.
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Bingo, in fact I keep with the 50% thinned. You really need to shoot it with a gun for a really good finish tho and shoot a lot of thin coats, allowing it to dry between them. You also want to sand a little between coats, particularly the first couple. The first coat will be real rough, you are really just sealing the wood. You want to get that smooth between coats before you shoot on another coat or you will keep transferring that roughness up through the finish.
If you do this outside in the sun it really does dry pretty fast.
I shot 16 coats on the maple tops we have in the kitchen and 5 years later they are still holding up with pretty hard use.
When they finally need it, I will hit them with some 400 grit and shoot a few more coats on.
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On 11/8/2011 9:25 PM, Ed Pawlowski wrote:

I don't know what the wax is for...you can beat the heck out of poly as long as the wood grain is sealed up. I had poly on a refinished antique oak table, used for dining, cutting cookies, all kinds of craft projects...took a beating, and refinished top about every five years just for appearances.
The secret to using most clear finishes is to thin first one or two coats (more that the label allows), which really gets the finish down into the wood grain to seal it up. Always worked for me :o) If a thick glassy finish is wanted, pile on two or three coats of shellac, and then the varnish of choice. Fine steel wool has always worked for adding tooth and getting out tiny bubbles or dust lumps.
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I use a spray poly spar varnish. No Problems.
Joe
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