Replies

1. 
   Rich14 | Jan 27, 2005 05:00am | #1

   Here's the deal.

   Manufacturers label their cans, "DO NOT THIN!!!!!!" They will not give advice regarding thinning.

   Yes you can thin a solvent product with anything that you can clean up with. No, same solvent will not affect the product after it has cured.

   Manufactureres take the position that you should not thin their product only because, as sold, the product meets VOC (Volatile Organic Compount) emission requirements. If you thin it, it will be out of compliance. If they have advised you to thin the product, they are responsible for haveing violated the standard.

   Most, but not all products will flow out and level more easily if they are thinned and it is good practice with most to use a very thin first coat for penetration, sealing  and adhesion and a thin final coat for final flow-out and film smoothness.

   A reactive finish like varnish and oils (linseed, tung, etc) which are thinned and cleaned with mineral spirits will not disolve in mineral spirts after they cure. Multiple coats do not "burn" into undercoats.

   An evaporative finish (lacquer, shellac) will redisolve in lacquer thinner, alcohol after they have dried. Multiple coats burn into undercoats and the entire multi-film thickness becomes one thick film.

   Rich

1. 
   Yogi | Jan 27, 2005 07:10am | #2

   Many thanks for the insight-  How thin is "thinned", i.e., how many parts polyeurethane vs thinner?  Is this half & half, or what?  Thanks again-

1. 
   Manchild | Jan 27, 2005 07:20am | #3

   Ive noticed that people in a hurry want fast build in a coating. they put it on as fast and as cheaply as posible. The problem is that the coating can lay on top of the wood and not adhere well. You'll notice it when you hit it with something even slightly. I like to seal wood first with something that penatrates a bit. I'm no expert but it makes sense to me.

2. 
   Rich14 | Jan 27, 2005 08:04am | #4

   Dave,You can use any ratio you want. It is not unusual to use a ratio of 1:1 stock material/mineral spirts as either a rubbing varnish or as the first coat of a several-coat finish. That thin, you can literally scrub the mixture on with a broom, in any direction, back and forth, across, every way, to work it into the wood for good adhesion. Then stand back and let it self level. Every brush stroke and bubble will flow out and disappear very nicely. It will also dry faster than will a thick layer. Sand lightly, but evenly and completely after 24-48 hours.Then apply full-strength using standard brushing-tipping techniques for one or two more coats. Or apply these coats thinned about 25% (3 parts poly to 1 part thinner). Use 3 coats of this thinned mixture. The mixture will brush more easily and flow out a little easier than the full-strength stuff. However, it is not at all hard to learn to apply full-strength oil-based poly that will flow out like honey.Sand between every coat and try to apply each coat within 48 hours of the previous.The last coat can be thinned as much as a 1:1 ratio again for very easy flow out. But again, after a few varnish jobs with a good brush and you won't worry too much any more about using lots of thinner to make the work easier.Give it at least 2 weeks to cure before using or trying to rub. I've never had good results rubbing a poly finish. I just leave it alone.Rich

   Edited 1/27/2005 12:05 am ET by Rich14

1. 
   Yogi | Jan 27, 2005 08:07am | #5

   Thanks again Rich-

1. 
   Rich14 | Jan 27, 2005 10:12am | #6

   Da nada.One last thing. If you use mineral spirits, use the "odorless" variety. Even with ventilation, the standard kind has an awful smell that will melt your brain and give you the worst headace you've ever experienced. Even worse than lacquer thinner.Naphtha is OK also. It evaporates faster than mineral spirits.Use LOTS of ventilation with any of these solvents. Wear a ventilator if you can, with the right filter. Wear gloves.Don't trifle with these things. They eat organic material. That's what we're made of.

2. 
   Gretchen | Jan 27, 2005 03:21pm | #7

   You can apply your entire finish film using coats of 50/50 thinned varnish. You do not need to brush any full strength.  There is a very large advantage to applying the 50/50 thinned varnish--you wipe it on with a rag.  It will dry to the touch within a few hours and you can re-apply.  It requires about 8 applications of the thinned product for your final finish.  Using this technique, there are not any drips or sags, and the drying time is so fast that dust nibs, etc. do not get into your finish.Gretchen

3. 
   Rich14 | Jan 27, 2005 06:50pm | #8

   Gretchen,Yeah, but then you miss the pleasure of having that nice viscous varnish flow out from the tip of your expensive brush and lay down exactly where you want it. Once it knows that you know how to do it, it doesn't dare disobey. But until then, as long as it knows you don't know, then you got trouble.Rich

4. 
   Yogi | Jan 27, 2005 07:30pm | #9

   I think it knows- 

5. 
   Yogi | Jan 27, 2005 08:27pm | #11

   Thanks for your thoughts, Gretchen-  Thinner seems better to me- 

3. 
   HowardAcheson | Jan 27, 2005 07:43pm | #10

   In most cases, thinning 10-15% is about right for brushing. The first seal coat can be thinned about 30-50% for better penetration and fast drying so you can sand it flat sooner.The new "fast dry" poly varnishes should not be thinned with naphtha as it will cause the finish to dry too fast and minimizing flow out or leveling.To make a wiping varnish, thin your varnish 50/50 with mineral spirits.Howie.........

1. 
   Yogi | Jan 27, 2005 08:29pm | #12

   Thanks Howie-  How broad is the range of thinners I could reasonably use with polyeurethane in your experience?

1. 
   HowardAcheson | Jan 28, 2005 04:54am | #15

   For oil based finishes there are really only two. Mineral spirits and naphtha. Mineral spirits comes in two flavors--standard and low odor. The low odor is the slowest to evaporate, the mineral spirits is in the middle and the naphtha is the fastest. Stuff called "Paint Thinner" is either regular or low odor mineral spirits.Howie.........

2. 
   user-75966 | Jan 27, 2005 11:09pm | #13

   Thanks Rich, very good explanation.   Does the same hold true for water based paints etc. 

   Thanks, Cliff

1. 
   Rich14 | Jan 27, 2005 11:23pm | #14

   Cliff,

   I am hardly an authority on this. I have thinned latex flat and semi-gloss paint to get them to spray out of all manner of spray guns from very inexpensive models to professional-level equipment. Most paints are too thick out of the can. I've had absolutely no problem with them, ever. Once they are thin enough to spray, they just work beautifully. They are more forgiving than any other material I've ever used. They go down seamlessly and dry to absolute perfection. Smooth, level, hard.

   I think that some of the more exotic water based products (varnishes, lacquers, etc)may not tolerate thinning as well, but I am not sure, and only experience will tell you that. They foam and do all sorts of weird things. It's easy enough to thin any product you want and give it a shot.

   I've always used plain tap water to thin latex paint, but it might be smart to use distilled water with the more exotic mixtures.

   Rich

1. 
   Gretchen | Jan 28, 2005 04:06pm | #16

   You cannot thin waterbased varnishes.Gretchen

1. 
   HowardAcheson | Jan 28, 2005 08:26pm | #17

   "You cannot thin waterbased varnishes".....more than specified on the label. If it doesn't specify, don't thin. Water is not really a thinner in waterborne technology.Howie.........