Primer, why is it doing this?

Hi everyone, i have not posted in sometime due to the fact that i have been veryyy busy with school; work on my masters. Anyway I have been working on my M, trying to get it ready for next weekend. I primed it yesterday and for some reason it did not come out well a good portion of the frame came out with a "grainy" surface, its almost like there is dust or debris stuck in the paint. Can i sand this down and just apply the top coat of paint, and what caused this happen; not enough thinner ? or to much ?

Thanks everyone!

Andrew

could be a number of things that caused it, also depends on what type of primer you used. sounds tho like the primer either wasnt reduced enough, or too fast of a reducer. did you run the primer thru a paint filter when you loaded the gun? i would sand the primer down and shoot another coat over to even it out, block it again and then shoot it. i am assuming you used the right gun pressure .

Likely 90% of those posting around here know paint better than I, but I have had that exact symptom with two different problems (though slightly different in look).

1. I didn't sweep the floor or curtain off the rest of the garage and didn't realize until nearly done: I was kicking dust into the air - I actually managed to get some large chuncks in that as well.

2. I'm not sure if thinner itself is the cause so much as the gun or perhaps way too fast of a thinner, but I've had paint "act like" it was partially atomizing in the air and hitting the surface part wet/part dry and leaving a grainy surface (again I didn't notice it right away, though I believe I caught that while it was wet). I believe I kept it about the same viscosity [assuming you're not too thick and starving your gun...done that too ] and opened the paint needle knob a bit further.

In the former, I think I lightly sanded and didn't see bare spots crop up so I just shot the top coat... did that one for a neighbor who later sold it, so no idea how it held up, but looked fine.

The latter was a horse trailer not a tractor and a "impact resistant" industrial coating [urethane, I believe] with a catylist rather than enamal; IIRC I had planned two coats of primer anyway, so a little sanding, second primer coat, came out fine, still holding up great. This was a "heavy" primer though and not intended for much reduction; infact I believe I had to to remove the cup screen too.

Of course the latter was probably 3 years ago, the former more than 10, so a bit rusty in the head if not the paint jobs......... let's see what the experts say!

thanks, yes i used the right pressure, prepping was good, and i used the right thinner. But i think i did not add enough thinner. I thought that the paint was pretty thin to start with so i did not add much. but i think that i should have added more to the mix i will have to try that again. Thank you for the thoughts.

Andrew

Did you use a paper strainer? Hal

Also, make double certain that your gun is clean. A tiny little speck of dust in the nozzle will create some very interesting effects.

It sounds like the surface was a little wet when you painted it. Was it humid out the day you painted it? I have had that happed me me before and it also looked "grainy". I would scuff it up with some 180 and shoot it again. Good Luck

I forgot to add that it is a must to use a dry in-line before your paint gun. This will trap any moisture coming thru the air line.

(quoted from post at 15:45:10 10/09/08) I forgot to add that it is a must to use a dry in-line before your paint gun. This will trap any moisture coming thru the air line.

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Good call! I've gotten so paranoid about water that last time I painted I had something like a 10 feet of black pipe making a J trap out of the tank, then a separator, then 50 of 1/2" hose (more for convenience than heat transfer), another separator and (IIRC some black pipe between) a coalescing, small hose, then a desicant right at the gun.

There is a reason mixing directions are on cans of paint/primer, you can't judge by "eye".

This has happened to me and the cause was that it was too cold in the shop. No one else mentioned this. Needs to be at least 70 degrees and 75 is better.