Primer problems

Printable View

05-13-2006, 03:53 PM
Henry Rifle

Primer problems

Today, I was spraying Sherwin Williams 21 catalyzed polyester primer thinned with 1 oz acetone per pint. (SW recommends thinning up to 2 oz per pint to extend pot life) I use a DeVilbiss Finishline HVLP gun with a 1.8 tip. The gun is clean. The temperature was about 72 F, and very low humidity. It turned out like crap. Coverage wasn't good, the surface is somewhat orange peeled, and didn't flow out.

I don't have a pressure gauge at the cap, so I varied the input at the gun from about 10 psi up to about 20 psi. Didn't seem to help.

When I had trouble like this before, it was due to feeding too much paint, or the paint was too thick. It took a quart to spray my '34 hood, trunklid (inside and out) and one door. I should get about 200 sq. ft. from a quart, and there can't be more than 50 sq. ft. in those three parts. However, if I turned the fluid control in much farther than I had it, the spray would get really misty, and it started to look like a dust coat.

This primer is supposed to spray right out of the can, but I'm starting to think that it's too thick.

Another clue I noticed is that I had a difficult time getting a nice wide fan. With only thinner, I got a nice 8-9" fan. With the primer, it narrowed down to 6" or less. Sounds like another hint that the paint is too thick.

I sprayed the body a couple of weeks ago with Transtar 6541, which is virtually identical. I got pretty good coverage, with only a slight orange peel. I attributed that problem to the cool weather, since it was 60 F or a little less.

Any comments or helpful hints from you paint wizards?
05-13-2006, 04:37 PM
Henry Rifle

I may have figured it out. Not enough air pressure at the gun. The instruction sheet says it takes 23 psi at the gun inlet to get 10 psi at the cap. I wasn't running it nearly that high. Not enough air to atomize the paint, hence, a cruddy finish.

Sound right?
05-13-2006, 05:09 PM
pat mccarthy

sound like you have it to thick or your thinner may be drying to fast and not letting it to flow out ?i never used acetone? the guns i use for the two parts were gravity guns sharp and some german make that work very good can think of the name . still have it a small gun but it was a joy to use . i had a devibiss hvlp gun 15 years ago and it was junk .i thru it out . but all way like there guns and use many JGA and mbc and like them but there first try with there hvlp was bad set up
05-14-2006, 05:26 PM
Henry Rifle

Another issue. Will clearcoat hardener set up by itself? I have a can of Sherwin Williams UH-70 that I only used 1/4 of. It's been sitting for about a year. When I opened it today to check it, there was a hard surface about 1/8" thick across the top. I had to break it up with a punch. I'm guessing that the rest of it is still good, but I won't have enough to catalyze the remaining 3/4 gallon of clearcoat that I have, and it's a little over $100 per quart.

This has not been my best weekend for painting.
05-14-2006, 05:43 PM
pat mccarthy

what will happen his moister/ air get in the can space and it will be no good some time s it will dry fast or looks like it as sand in it when it drys best thing as to do a test panel and see if it good
05-14-2006, 06:26 PM
SprayTech

Most hardners / catalysts have a 30 day shelf life , depending on area temp. , humidity ect........
I wouldnt trust it , throw it away and get new .
05-14-2006, 07:22 PM
pat mccarthy

Quote:

Originally Posted by SprayTech

Most hardners / catalysts have a 30 day shelf life , depending on area temp. , humidity ect........
I wouldnt trust it , throw it away and get new .

yes this is the best thing to do. but have you worked with some cheap people ? so try it and use it on stuff that does not make up the out side of the finsh of the car
05-14-2006, 07:30 PM
Henry Rifle

Quote:

Originally Posted by SprayTech

Most hardners / catalysts have a 30 day shelf life , depending on area temp. , humidity ect........
I wouldnt trust it , throw it away and get new .

30 Days after opening, I assume. Otherwise, they wouldn't be able to stock it. Makes sense. Out it goes.
05-14-2006, 07:40 PM
pat mccarthy

if sealed it is good for a very long time but when you open it like i said air/ moister 1/2 filled with air / moister. no good. i work out of shops that it went bad faster than that if the lid is on off all the time when five guys are working out of the same can like in july at 90 humidity
05-14-2006, 08:05 PM
SprayTech

Quote:

Originally Posted by Henry Rifle

30 Days after opening, I assume. Otherwise, they wouldn't be able to stock it. Makes sense. Out it goes.

Yes , after its been opened , Sorry for not clarifying that :)