spraying polyurethane

[james matthews]

I would like to know what ratio you cut your polyurethane when you spray it? This will be the first time i will try it. Thanks.

[Jim Becker]

Frankly, I do not recomment you spray polyurethane varnish or any other oil-based varnish. It dries too slow and you'll have a sticky mess from any overspray. But if you do want to spray, reducing by about 33% is a good place to start, depending on your gun and it's projector set size.

[nic obie]

I would like to know what ratio you cut your polyurethane when you spray it? This will be the first time i will try it. Thanks.

Don't thin it with mineral spirits, it will take forever to dry. Use naptha, or better yet use lacquer thinner.

[Jim Becker]

Don't thin it with mineral spirits, it will take forever to dry. Use naptha, or better yet use lacquer thinner.

Lacquer thinner is only for thinning lacquer and you don't want to be spraying anything with it in it, anyway, without a proper spray environment...very dangerious. Naptha is a good choice for a quicker flash off, but MS isn't going to be much different in this application since the coats are very thin. It flashes off nearly as quickly.

[jack duren]

first off only thin enough to get it through the gun properly. use mineral spirits. second if you use naptha you might as well get "fast dry" poly.

spraying poly will dry depending on air movement. spray outside if possible but beware on woods like oak that have been stained they tend to bleed from the heat....jack

[Bill Lewis]

If you do spray outside, don't do it in direct sun either. It can dry the poly surface and encapsulate uncured poly beneath it leading to fisheyes. Or, if the surface heats up too much before spraying, you can end up with a rough surface as the spray droplets dry too fast. DAMHIK

[Don Selke]

Frankly, I do not spray any oil based finishes or Lacquer any longer. I only spray water base finishes both inside and outside the shop. In this day and age, there are a number of water base finishes on the market including acrylics to take the place of the oil base products. I am probably opening up a can of worms as there are a lot who prefer oil to water base finishes. I prefer the water base due to the hazards associated with oil base products and the storage of hazardious material needed to thin them.
When spraying, I thin the material to meet the needs of the particular gun that I am using. I spray most of my stuff with a 1.2mm to 1.0mm gun to get good atamization of the product. I would prefer to spray one extra coat then glob the finish on. What ever you spray, make sure that you wear a good mask designed for hazardious vapors.
I am not a expert painter but have done my share of spraying finishes and this is what works for me. OK you oil base guys, give me a slam!!!!!!!!
I do add retarder to my finishes especially here in the desert south west and I also do all my spraying in the early morning before the temperature hits 115.

[jack duren]

Don.."In this day and age, there are a number of water base finishes on the market including acrylics to take the place of the oil base products."

its not that water base finishes dont work as expected, they just dont give the correct patina a oil base can. even i switched to pre-cat to get that amber tint. but... still not the same result as good ol oil base poly..

hopefully over time ill be able to mix enough old furniture with the new to break free from the poly, but aint there yet.....jack

[Ron Teti]

I use only W/B poly also. I use a LVLP and do not have to thin it. The person asking the question didnt specify if he wanted to spray O/B or W/B. So its hard to answer the question

[nic obie]

Lacquer thinner is only for thinning lacquer and you don't want to be spraying anything with it in it, anyway, without a proper spray environment...very dangerious. Naptha is a good choice for a quicker flash off, but MS isn't going to be much different in this application since the coats are very thin. It flashes off nearly as quickly.

Sorry Jim, but I think Lacquer thinner will thin anything that is oil based. I know people who use acetone to thin poly.

Probably the best thing to do is to ask Jeff at Homestead finishing.

[Don Selke]

You have to be extremly cautious when using acetone to thin a finish for spraying, the acetone can cause the finish to flash so fast that the material will not dry and form a guey mess. I think that this was pointed out earlier in the post. When I use to spray oil, I used a combination of thinner and Naptha to thin the material. I have used TransTint dyes to get some panta where needed with water base finishes. The dye is added to the first coat of finish.

[Tim Sproul]

Sorry Jim, but I think Lacquer thinner will thin anything that is oil based. I know people who use acetone to thin poly.

IIRC, acetone = lacquer thinner. My guess is lacquer thinner is just acetone that hasn't been as purified quite to 100% or 99.9% purity.

[nic obie]

IIRC, acetone = lacquer thinner. My guess is lacquer thinner is just acetone that hasn't been as purified quite to 100% or 99.9% purity.

That's interesting, I didn't know that.

[Steve Clardy]

I use lacquer thinner also. Dries faster than mineral spirits.

[Phil Phelps]

Sorry Jim, but I think Lacquer thinner will thin anything that is oil based. I know people who use acetone to thin poly.

Probably the best thing to do is to ask Jeff at Homestead finishing.

I wouldn't do it. I've seen lousy finishes from folks thinning oil base enamel with lacquer thinner. I don't think water base products will ever take the place of oil products, for the sheer durability, if nothing else. And to the post above about not reducing material because you use a HVLP? I don't understand that statement. A HVLP gun sprays more material than a siphon gun, but you still have to reduce the product.