Need some help with primer/paint finish trouble

[Goodwrench3]

Hi all: 

I've got a few builds in process after taking a 25+ year break .. lol long break. 

Anyway.. in the past, I never used primer -- I just brushed or sprayed rattle cans over bare plastic. This worked pretty well -- for a chassis, I'd spray Model Master gloss gull gray and I'd get a really nice smooth wet glossy finish on the chassis pan. 

Wanting to "step up" my skills, I've started to take the advice of most here and use primer on everything. So far, this has been a "plus" as it has helped with brush painting engine parts, etc. 

Tonight, I got a chance to spray the chassis for the #52 Butch Miller Revell ASA Camaro I'm working on. After spraying it (Tamiya rattle can), I can see a fine "pebbly" finish in some areas which looks like the surface finish of the primer (Tamiya fine light gray spray primer) that the paint is showing. 

I'll post a pic here after the paint has had a day or so to dry. 

Here are the steps I used in painting it: 

1) Sanded, filled, etc. all pin marks, flash, holes, divots, etc. 

2) Sprayed 1 coat of Tamiya fine light gray spray primer on the chassis. 

3) After the primer dried for about a week (that being today), I sprayed 1 light "mist" coat of Tamiya TS-49 bright red and waited about 10 minutes. Then I sprayed another heavier coat over it. 

So -- I'm wondering -- in order to get that nice even, smooth, wet finish what I might be doing wrong? 
-- maybe not enough primer ?? 
-- do I need more coats of spray color over the primer ? I didn't want to get the paint on too thick. 

Thanks for any help.

[espo]

Getting a paint finish wright is almost the most difficult part of modeling.  A couple of suggestions, and there will be many others with additional suggestions . Since your in Wisconsin, not sure how far north but I spent a year one winter in Eagle River, ambient temperature and humidity play a heavy roll in the paint finish. The pebbly finish you mentioned sounds as if you might have been holding the spray to far from what you were painting allowing the paint to start drying before it reached what you were spraying. This can become worse if it is cold also. Tamiya primer can usually be sanded very shortly after spraying. Many have different ideas on this, but I have had good luck spraying primer go have lunch and then  start sanding. Besides better finish paint adhesion the primer will show you any other body imperfections you need to work on before using your final color coat.    

[Snake45]

A picture would be VERY helpful in diagnosing your problem, if you can swing it.

[Jhedir6]

What David said is spot on. Temp and humidity play a big role in quality of finish. Are you spraying inside the house with a paint booth where its warmer, or in the garage/outside in the open air where its much cooler? Also, distance. If you're getting a "pebbly" finish you're likely spraying from too far away and the primer is drying mid air before landing on the body. Check the manufacture specs on distance. I usually go 4-6" away. Start spraying infront of the body and go all the way across to the other side dont start and stop the stream over the part. Usually after an hour or less you can sand and recoat as needed. I'd say you can probably do 1 coat with most primers from a rattle can, unless you find imperfections in your prep work then fix and respray. For sanding, if there's no touch ups I'll sand it out with some 600 or 800 grit then maybe up to as much as 1200-2000, depends on the brand of primer, Tamiya, should be fine with 600-800 as Tamiya paints level out nicely on their own. Once you paint, mist coat or two, let them dry a few minutes before going onto heavier coats. And again, watch your distance. TBH, its all about experience. The more you do the more you'll learn. I suggest getting some Isopropyl alcohol and some Castrol Super Clean, or other stripper, cause you're gonna mess a paint job or two up and its nice to have those on hand for when you do. Check this sub section for tips on the paint stripping too. Good luck and Happy New Year.

David

[Goodwrench3]

HI -- thanks for the replies.

I was spraying in my basement in an Artograph paint booth.  

Here is where the problem is -- with the NASCAR floor pans, it's not possible to sand them after spraying primer.  There is so much detail and recesses, etc. that you really can't practically sand them (in my opinion).   So if you have something like that where you are not able to sand the primer, it seems like you are then at the mercy of the smoothness of the primer coat -- and then how do you get that nice and smooth ?

Again, 25+ years ago I was using Model Master spray enamel -- so it seemed easier as we just sprayed directly on the bare plastic (after sanding out pin marks, etc.).

 

[Goodwrench3]

This is the next chassis i'm getting ready to paint. You can see the filler work I had to do to fill in the ditches, dents, holes, valleys, pin marks, etc. 

So are guys spraying the Tamiya primer and then actually sanding it on a piece like this with all that detail and the recesses etc. ?? 

Thanks

[drsnapper55]

I'm not much of an expert, but I certainly don't sand down something like you have pictured unless I'm sanding some easy, open flat areas or where I have filled with putty, etc.  One thing that might help on something like the part above is more than likely you have handled it quite a bit in your prep which leaves oils all over it - not good for paint to stick too.  Before painting the primer, wash it down good with some spray cleaner (like Purple Power) and a brush (like an old toothbrush).  In fact, I do this with all my parts before painting them.  Dry it out really good after.  I like to make sure my paint in the can is at a decent temp too and mixed very well.  I try not too push if it it seems too cold.  I also spray just a little out first before it hits the part just to make sure it gets a good flow.  As far as the finishing coat, I'm trying to practice more with just barely sanding the primer in order to get a smoother finish coat.  Hope this helps you out some.

[Goodwrench3]

Here are some pics of the chassis I was referring to.

Note in the first pic on the left side, you can see the "pebbly" finish reflected in the light that I was referring to.

In the second photo the round cross member bars look like they have a pretty decent smooth finish.

In the third photo, you can see the "pebbled" finish better in the light along that leftmost frame rail.

In the last photo, you can see that the front end area has a pretty decent finish too.  

Thanks for your help.

 

[935k3]

There is actually a way to smooth out primer on chassis with allot of detail. I run into this problem with rally cars I build. I use a toothbrush and Soft Scrub cleaner. You could use something like COMET. make sure it is rinsed thoroughly under running water.

[Jim N]

What you might have with the pebbly finish is orange peel.  I get that kind of finish when I am spraying too far away from the part.  I think it can sometimes happen when one applies an additional coat of paint before the prior coat has fully set up.  You can use 600 or 1000 grit sand paper and wet sand the areas to knock down the high spots.  You want to work slowly because the only thing you want to do is smooth the finish and not burn through to the primer.  The way I tell if I have smoothed the finish, is to run my finger over the sanded area.  If it feels smooth, I move on to the next area.