Polyester primer question

M

mike r

Being that Im half way thru my second paint job, (ever) I had a hand full of questions about Polyester primer. after some searching on the forum I have found the answer to most of them. except:

Just shot my truck with feather fill G2 yesterday, now im ready for the blocking process. I have read on here that the goal is to get to 320. What I cant seam to find is the way in which to get there. Im thinking 180 to 320 or is it better to 180-220-320 or just start and end with 320. I have heard some say that its harder to sand Poly, so im confused on where to start.

my other question is: once its at 320 the "perfect paint job states to add 2 shot glasses (3 oz or) of reducer to the epoxy for a sealer. I have also read some guys mix 20% and others do 1:1:1 what are the deciding factors that determine which way to mix it?

Thanks mike
 
There are a lot of pros here that use this stuff all the time and may have so better ideas.
Myself, I block with 100 then go to 2K primer and block with 180, then re-prime and finish with 320-600 depending on paint and color.

I would hate to try and bock that stuff with 320, not sure it would even be possible but I never tried.
 
Barry is right on.

I usually use 120 though, then buzz over it with a da and soft pad with 180. then urethane prime. You have to remember, poly primer is like sprayable filler/glaze putty. You want to sand it pretty much like you would a final skim coat of filler or glaze. Anything more than 180, you are pretty much just polishing the waves in a sense. Cut it flat and use good paper. Change the paper often.

I will usually cut the poly down, and fix any other issues then spot primer with more poly. Block that down then apply the primer and block it once more. It's a process, and you will find more things here and there through the various stages (depending on how picky you are.)

I use gray epoxy as a sealer at 1:1:1. You just want a thin wet coat. If there is a sand through or 2 after the final sand before sealer, hit those spots first...let it flash for about 20-30 minutes then proceed with 1 thin, wet coat.
 
I wasn't expecting those answers. but thats why I asked, you guys are the pros. what do you think about blocking to 180 then epoxy full strength then blocking to 320 or 400. It was going to be black.
 
That will work just fine. I dot the poly+epoxy thing all the time.
 
I guess thats pretty much what Barry just said. Right? Except the epoxy part. I have plenty of epoxy on hand but no 2k
 
If you want to take the poly primer from 180 to 320 it does block just fine with 320. The epoxy will fill 180 grit scratches fine though.
 
Thats what I was thinking I was gonna do 180-320. but I was unsure. Here is where I am. All my filler work is done and over 2 coats of epoxy. I just shot two coats of poly or G2 feather fill over all panels except the two front fender and the roof. Those are in 2k because they didnt need any filler work. After this round of blocking it should be nice and flat and ready for color. (black) If I can get it to 320. what is my next step when it comes to the epoxy?

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Use guidecoat. For the best long term results I like to get a few good unreduced coats of epoxy on over the poly, use the epoxy for the final sanding, then seal and paint. I like the added strength and solvent barrier the epoxy provides. But there are a lot of people that final sand the poly then shoot a sealer then paint. The epoxy below and above the poly is what provides the durability and corrosion resistance.
 
Question For you Bob, I did all my sanding on the poly and its time to hit it with 320. I shot two coats of epoxy on the truck one coat yesterday and one coat today with a 1.8 tip. I split up one coat per day cause I was thinking I should put 3 coats before the 320 and the temp around here dropped to 68-70. though it would help in the curing process. I read on here that 3 coats of epoxy equal 2 coats of 2k. Well after the 2 coats of epoxy, I can still see all the scratches and the "soak in" on a few small spots where I had to add a little filler. My question is should I continue with the 3rd coat or sand these 2 coats and then shoot more epoxy after that. What do you think? Thanks
 
mike r;24225 said:
Well after the 2 coats of epoxy, I can still see all the scratches and the "soak in" on a few small spots where I had to add a little filler.
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Was the epoxy reduced? Keep in mind just because you can see dry areas and sandscratches doesn't mean there isn't enough on there to final sand-you can pick your worst looking area and sand it with some 320 to see if it final sands to perfection then determine from that if it indeed needs more build or not. Even if you get a few small cut throughs here and there it's really no big deal if you're shooting a sealer coat of epoxy before color.
 
When you sand surfacer primers like the poly and step your grits down it's important to shoot guidecoat between grits so you can verify the prior sanding scratches are removed, otherwise it's just a guessing game when to stop or if the coarse scratches are gone. I have sanded poly with 80, then 180, then 320 spraying guidecoat between sandings and never had any mystery scratches to worry about.
 
I did not reduce the epoxy and I induced over night. Half the truck was sanded with 180 and guide coat. by the time I got to the other side ( a week later) it was harder to sand either that or i was getting tired. so i switch to 120 laid on some more guide coat and then back to the 180. Im not sure how or if its just my imagination but the side i did with 120 then 180 looks to be heavier with sandscratches. If there is 120 scratches still showing will that be a problem for the epoxy to cover? I will do what you suggested and 320 the worst looking sections and see what happens.
 
It sounds like some of the 120 scratch didn't get removed. The epoxy will handle filling 120 scratches with 2 coats usually but 180 would be better for sure. What are you using for guidecoat?
 
Cheap lacquer spray paint? :( I know, I will never do it again! I swear!
 
mike r;24238 said:
Cheap lacquer spray paint? :( I know, I will never do it again! I swear!
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Some guys hate it but I find the 3M Dry Guide Coat an excellent product that can be used wet or dry. If you have scratches they WILL show with this stuff.
 
I went to my local paint supply store. They had the 3m dry stuff but it was only in black. i didn't figure the black on black would work to well. What do you guys use for black primer if not spray paint which is what they suggested to me. I know the first round of sanding I can do with out any guild coat due to the semi gloss but what about the second or does everyone just spray more epoxy.
 
When using black primer, we use grey spray can lacquer primer as guide coat rather than paint. The primer will not gum the paper nearly as bad as some paints will.
 
I use over reduced lacquer primer for guidecoat all the time-works great IMO! I've been bitten by the dry guidecoat a few times when final sanding jumping from 320 to 600 grit-found scratches that were missed. I still use it now and then though.
 
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