TheSamba.com :: View topic - how many coats of filler primer before it's too thick

Mon Aug 20, 2007 7:27 am

I'm block sanding the last few low spots out of the panels on a split window bus and I'm starting to wonder if some of the low spots I'm blocking out are too low to use filler primer...

the problem is actually that there are high spots along the spotwelded ribs behind the panels...I'm not going to undo the welding, beat on the metal along the ribs or try and hammer and dolly "up" the low spots

I'm laying three medium wet coats then blocking out with a 30" or 24" durablock with 320 grit (I would use 220 grit...if I had any left)...I sand down until metal high spots start to show...some areas are not touched by the sandpaper...the areas are about 4"widex6"long

I'm on my third round of high build and I can still feel some areas that I doubt will block out...

How many more hi-build coats am I safe to use or should I remove all primer and use metal filler? Should I use the more sandable glaze filler or good old Evercoat Gold?

All help is appreciated...Mark

Mon Aug 20, 2007 7:30 pm

Mark, here is what i would do. Get ahold of some more 220 paper, put a nice even guide coat over the areas that you feel are bad and block them down even if you see some metal showing. The areas that show up as low, fill with some polyester putty and block them down even with the primer or metal depending on where the low spots are.

If you highs feel fairly high you may need to tap them down lightly with a body hammer prior to putting on more primer.

This is my general rules that apply to bodywork. I always try to fix as much of the bodywork and straighten the panels and sand the body filler straight prior to the primer. When i feel that i have the area nice i will put 3 coats of high build primer on and let it set out in the sun for a day or so to really shrink into the bodywork. Then i will block sand with 220 and fill my slight lows with polyester putty and tap the highs back into place.

Then 3 more coats of primer, this should really get me into the ball park as far as straightness is concerned. After block sanding i will know whether or not i need to prime one last time or finish the primer in a paintable grit..............400 dry or 500 wet.

Mon Aug 20, 2007 7:41 pm

when the last three coats of primer are applied, is this the high build primer? and is this primer paintable? can the color be applied directly over the high build? thanks.

Mon Aug 20, 2007 9:52 pm

ZODIAC wrote: when the last three coats of primer are applied, is this the high build primer? and is this primer paintable? can the color be applied directly over the high build? thanks.
Your question is more of a "sealer" question. Most all primers are are paintable, after properly prepped and cleaned. There are a few out there that need a lil extra care (only one I know off the top of my head is PPG's DCP21). If you wet sand these primers they need to be coated within 3 hours or they "case harden" and need to be re scuffed with a red scotch brite. This is only on a few. The R-M DP200 I use, in the "p sheets" say no more than 3 coats (this does depend on how heavy your coats are). This can crack like a dry river bed if it goes on too heavy.

Mark how big is the block your using? This can make a huge difference, I would figure especially on a bus.

I agree with Matt.
If I know Im going to reprime something I'll block it with 180'. Reprime it, give it a lite blocking with 180' just to knock any texture down. Re guide coat with 3m powder guide (basically powered printers ink) Block with 240' reguide coat block with 320-400 depending on the color Hi-metallic or not. I do all this dry, I havent wet sanded a car in 10+ years. Even cutting for polish. Once in a while I'll use some Aberlon's 2000 and 4000 sponge discs with water.

Tue Aug 21, 2007 7:57 am

ZODIAC wrote: when the last three coats of primer are applied, is this the high build primer? and is this primer paintable? can the color be applied directly over the high build? thanks.

color "can" be applied over high-build...but you really should put a seal coat between the highbuild and the paint within an hour of doing the paint...it aids in paint adhesion, gives a uniform base color and comes in a couple different colors to help the paint get coverage over darker/lighter primers...several brands just use their hi-build primer with extra reducer for the recomended sealer coat

I'm dry sanding everything...wet sanding isn't worth the risk of getting fillers wet in my opinion (and my first body job has lots of filler areas)...

So three applications of high build is all I should use :? ...guess I need to do extra blocking down on the remaining low spots and apply filler...this flattening work is getting old...

Tue Aug 21, 2007 4:48 pm

[quote="Naked"] ZODIAC wrote: when the last three coats of primer are applied, is this the high build primer? and is this primer paintable? can the color be applied directly over the high build? thanks.
Your question is more of a "sealer" question. Most all primers are are paintable, after properly prepped and cleaned. There are a few out there that need a lil extra care (only one I know off the top of my head is PPG's DCP21). If you wet sand these primers they need to be coated within 3 hours or they "case harden" and need to be re scuffed with a red scotch brite. This is only on a few.

is the dcp21 a primer or a sealer? I am confused. are you saying that after shooting that primer surfacer you have 3 hours to block, wet sand and shoot color? or are you saying that you can shoot this primer and do nothing until you do the final wet sand, but then after final wet sand you have to seal then top coat?
confused because i am not familiar with PPG

Tue Aug 21, 2007 8:07 pm

DCP21 can be used as a primer or wet on wet sealer. Depends on reduction. After wet sanding this product it is supposed to be coated with a basecoat or single stage within 3hrs. If you don't you just give it a quick scuff with red scotch brite is all before painting, not a big deal if you know.