Another painting question, primer after block sanding Options

[bbrock]

Okay, I'm about halfway through my first cut of block sanding the PPG K36 surfacer on my car. So far I'm very pleased. I have a few (not too many so far) high spot where I sanded through to bare metal. My plan is to seal the whole car with a coat of reduced PPG DPLF epoxy primer before spraying color. My assumption is that this will also suffice to re-prime those few shiny spots of bare metal, but my combination of paranoia, and lack of experience make me think it wise to make sure the brain trust agrees with this. Here's a couple examples of the spots I'm talking about - gray patches are DP50LF primer base coat but you can see two roughly dime-sized shiny spots.

[Superhawk996]

Coming along nicely! (IMG:style_emoticons/default/biggrin.gif)

[roblav1]

All bare metal should have DP epoxy. I would not put that over the K36 and then color. The DP is not a sanding primer.
If I went through, I recoated with both DP then K36. A pain. It taught me NOT to sand through to bare metal!

[bbrock]

All bare metal should have DP epoxy. I would not put that over the K36 and then color. The DP is not a sanding primer.
If I went through, I recoated with both DP then K36. A pain. It taught me NOT to sand through to bare metal!

This isn't quite making sense to me. The DPLF tech sheet says it can be used as a sealer if it is reduced with acetone. It also says it can be used as a primer with or without acetone reducer. That's why I thought it would be okay because the reduced DP is going to be the last coat before base coat regardless. I definately want a gray seal coat under my base coat to get the right color. Also, the K36 tech sheet lists DPLF as a suitable top coat so I don't see there would be any compatibility issues. I'm more concerned about whether a single coat of reduced DPLF will provide enough protection

[roblav1]

Brent, agree it's feasible according to the K36 tech sheet. But the DPLF tech sheet specifies a minimum thickness over metal. One thin reduced coat probably won't do it.

I personally prefer the nicely sanding smooth K36 directly under color, at least for exterior bodywork. On the other hand, in my engine compartment, I sprayed color directly over DPLF, and it came out OK. Sooo... maybe try it.

[bbrock]

But the DPLF tech sheet specifies a minimum thickness over metal. One thin reduced coat probably won't do it.

That's really the crux of the question. I know it will be a little thin on those spots, but they are tiny areas so I go back and forth. The issues are probably moot because I've got a few low spots that aren't going to block out so I'm going to have to reshoot some K36 anyway. I'm thinking I'll spot primer the bare metal spots with DP beforehand. Then when I reblock the K36, they'll get leveled.

BTW, I'm not sure if you've shot the DP reduced to a sealer, but it lays down almost like glass. I sprayed it over my sound deadener mats because acetone is also the flexiblizer. I couldn't believe how different it laid down. No roughness when it dried at all. Also, when I sprayed single stage on the interior, I just wet sanded the DP down to 600 grit and then sprayed color. The color laid down beautifully and the gray primer underneath really makes the silver metallic pop.

[roblav1]

I think that's the way to go... spot DPLF then add a bit more K-36. You're right on adding reducer to K-36. I've been using reducer with it on most of my progress so far, and it lays down really well... minimal sanding - and 600 grit was enough. Today, I sprayed K-36 on the exterior sides of the doors, but I didn't have enough reducer, so I added it only to the 2nd coat. Didn't come out nearly as well. I'm almost done with paint... exterior doors are last. Time to run back to the paint store... need gray and black DPLF as well as more reducer. Reducer in DP90LF (black) gives it more of a sheen... close enough for me to the original semi-gloss paint. The DPLF gray is real close to the original color of the headlight mechanisms, and I still need to DPLF black the rear suspension (after doing the 911 E-Brake conversion). Good luck with yours.

[andrewpsnow]

That would be ok to do but spot priming would be better. What grit did you block sand with? If it was 320 or finer then you need to go over it with at least 500 before sealing

[bbrock]

That would be ok to do but spot priming would be better. What grit did you block sand with? If it was 320 or finer then you need to go over it with at least 500 before sealing

Right now I'm just on the first cut at 220 but I will take it to 600 before the sealer goes on.

[andrewpsnow]

K36 can go over bare metal spots that are smaller than a silver dollar as I was told at the ppg painting school. I personally would reprime the whole car and final sand it with a very good da with a 3/32 pattern and interface pad. Or wet sand it with 600 and a soft sided block.

[doug_b_928]

Dumb question from a noob who has yet to do this (but will be if I ever get the rust repair done). At this stage where you reveal small high spots do you gently tap them down with a hammer or does the next coat of surfacer build up enough that re-sanding the entire panel levels it?

[bbrock]

Dumb question from a noob who has yet to do this (but will be if I ever get the rust repair done). At this stage where you reveal small high spots do you gently tap them down with a hammer or does the next coat of surfacer build up enough that re-sanding the entire panel levels it?

Those are level with the rest of the surface now so everything will be done with primer or primer surface from this point forward. Others might do it different but if I start tapping these spots down now, it will open a bigger can of worms.

Here is my plan now. I'm going to spot spray the bare metal spots just to make sure I have DP over all bare metal before spraying more K36 to bring up the few remaining low spots. The if I can complete sanding to a perfect surface without exposing any metal, I'll go with a DP sealer coat as originally planned. If not, I'll shoot a full DP primer coat and wet sand down to 600 before shooting base color. The only issue I have with the full primer coat option is the time needed for the additional sanding since I don't know how much more painting weather I am going to have this year.