Replies

1. 
   _mj_ | Mar 10, 2022 03:16pm | #1

   You can thin anything, but the quoted coverage and protections listed on the can go out the window. Manufacturers don't want their reputations dinged by people altering their goods, so they tell you not to.

   As long as you choose the right thinner you should be fine. I'd test any new concoction on something that did not matter before I used it on a project.

2. 
   Go_Bills | Mar 12, 2022 08:40am | #2

   Hal Taylor promotes a 50/50 mix with a wipe on - wipe off application on his rocking chairs. Hal is obviously a creditable resource.

3. 
   john_c2 | Mar 12, 2022 09:23am | #3

   Instructions on the can are wrong more often than not. Thinning is fine.

4. 
   StevenH01 | Mar 12, 2022 12:07pm | #4

   I alway thin poly with VM&P Naphtha, and not mineral spirits. You can get it at your local hardware store. Solvents used in mineral spirits vary by manufacturer and what's readily available. Sometimes adding mineral spirits to thin your poly will prolong drying time. The longer your poly stays tacky, the more likely you are to pick up dust particles and the like, and if you plan to lightly sand between coats, you'll be waiting longer for the poly to completely dry. Naphtha thins nicely, lets the poly level more easily and does not prolong the drying time.

5. 
   oxmach | Mar 12, 2022 04:29pm | #5

   +1 StevenH01. I’ve done a few kitchen cupboards, and misc tables etc. with a 50/50 mix of poly and naphtha. No bubbles, quick dry, level etc. it takes a number of coats to build, but you can gauge as you go to avoid a plastic look.

6. 
   EdWeber | Mar 12, 2022 05:33pm | #6

   Yes you can thin polyurethane. I suggest using matching solvent.
   Yes it will take longer to dry, as there is more solvent to evaporate before the polymerization starts and the finish begins to cure. To be safe, you should always sand polyurethane between coats, it may not bond properly without etching the previous coat for a mechanical connection.
   Wipe on poly is nothing more than standard thinned out.

7. 
   mikaol | Mar 13, 2022 08:20pm | #7

   What kind of wood? oily woods are a pain. Now - ignore label instructions. but before you jump to naphtha(which I agree with,) try acetone. It dries quickly but stinks during application. And IMHO, skip the foam brushes. oil-based finishes cause minor foam melting and sticking to the finish. Trust me, I've ruined too many finishes.
   Oh, if you're dealing with oily wood, a good wash coat with shellac should dry it out some.

8. 
   mlindy | Mar 14, 2022 12:38pm | #8

   I've used Zar polyurethane varnish (semi gloss) thinned 50:50 with mineral spirits, wiped on, with good success on multiple occasions. For a good while it was my go-to finish. Now my hardware store is carrying Arm-R-Seal, which also has worked well. I could swear there was a FWW article advocating this approach in the past few years, but I can't locate it in a search. I usually use a seal-coat of Zinser Bulls-Eye shellac diluted 50:50 with ethanol. It dries to the touch in a few hours and can be recoated in 12 or so. Since it is diluted, 5-6 coats are necessary, but results are good.