Ready to start final blocking...need advice

[chevynut]

I'm getting ready to start the final blocking of my Nomad to get ready for paint in a couple of months. So far after completing all the metalwork I prepped the metal, sprayed DP50LF, sprayed Slicksand and blocked it with 120 grit (I think), then when it was all blocked I sprayed a coat of PPG K36. It's sat like that for a couple years now.

I am now ready to go to the next step. I have a can of spray-on guide coat, rolls of 320 and 400 sandpaper, and sanding blocks of various lengths. My painter wants me to take it to 600.

I plan to start by blocking across the door gaps one more time. Then I'll disassemble the car and prime and sand each piece to the final finish. I need to end up with 600 grit with no sand-throughs on the primer.

So, should I start with the 320 grit (dry) now, or go back to the 120 or 180 first? My painter though the primer was pretty smooth but there are some "dry" spots of overspray.

Also, how do you use the guidecoat? I know you spray it on lightly, then sand. Do you have to sand until all of it is gone? What if you need more primer...do you remove the guidecoat in low spots?

I'm assuming the final 600 grit should be wet-sanded and long sanding blocks aren't that important at that point, since not much material is removed. Is the long sanding block still needed for wet-sanding?

Should I wait until just before painting to do the final 600 grit sanding?

I've never been here with this level of paint job, so this is all new to me.

[Rick_L]

If you are going to block across the doors, or block anything else for straightness - I would do that with 120 or 180 grit - no finer.

The reason to use a block for the fine grit sanding is just for uniformity of the finish, you already made it straight if blocked with the 120 or 180. In fact you can't really straighten with 240 or finer. So you don't need a long block. A short medium hardness block will do. You don't have to wet sand either. But either wet or dry, you have to manage the sanding debris and regularly get it out of the way. Take your pick.

Your guide coat question is a good one. I use the 3M powder because you can wipe it off with wax and grease remover. I quit using spray can lacquer primer surfacer because I didn't want any lacquer, no matter how little, sandwiched in my primer and filler.

[chevynut]

Well I hit the entire driver's side and hood today with 320 grit and a 16" semi-rigid board. I really didn't find any major high or low spots but I removed the little bit of orange peel I had. It sure seems straight, so I did okay 3 years ago when I blocked it out. ;)

I did sand through the K-36 in a few small spots. Now I'm not sure what to do about it. I guess I have to re-spray the whole panel or just those spots and feather it in. I always thought you wanted at least a couple of coats of primer so you can do the final blocking, and 180 seems pretty coarse. It seems like the 320 does a reasonably good job of smoothing the primer, and showing what few tiny irregularities I did find.

I'm really wondering how big of a deal it is for me to have some sand-thrus. We're planning to spray the entire body with white base before the orange. The white base is opaque so won't it cover anything just like the white sealer would? The reason we're using white base is to get the paint to "pop" more in sunlight and it goes down smoother than epoxy.

Thanks for the advice.

[chevynut]

Also, I find that it's hard to sand concave or convex surfaces like around the front of the hood. Do you do those by hand-sanding without any block? In comparison, the flat surfaces seem easy.

[Rick_L]

What are you sanding through into? I think that's the key question. If you're showing epoxy primer through the K36, probably OK except if it's a big dark spot. If you're showing filler or slick sand, I'd want some primer on that.

For the dark spot, once you go over the whole car you'll have a better idea whether you need a sealer coat or spot priming.

[chevynut]

Rick, I'm sanding into the Slicksand. It's hard to tell how much K36 you have left. If I got to epoxy, I went through the Slicksand too.

Maybe I'm not at the "final" blocking, and still need one more coat of primer to be there. But I'm really close. The 320 grit paper seems to flatten it nicely.

I guess I'll try to do the curved stuff with a sponge and sandpaper.

[Rick_L]

Forgot to add this on the last reply. On concave surfaces I use a piece of broom handle or something like that with pipe insulation over it. You can wrap PSA paper or wet/dry paper over that. The broom handle works for a lot of curves, but if the radius is big you can do the same with pvc pipe and pipe insulation of any appropriate size. Or for roughing filler, forget the pipe insulation. You probably have the materials for a lot of odd shape sanding blocks right in your shop, if not a trip to the hardware store or home improvement store will fix you up.

This stuff works on convex surfaces too with a cross hatch pattern. Or blends from convex to concave like you see on the 55-56 taillight area.

[MP&C]

The SS I'd want sealed before applying a basecoat. On the other hand, not knowing what the white base is that he will be spraying, it may not be needed. Ask your painter what he wants..

To add to Rick's selection of sanding blocks, I needed a small radius today, used some 1/2" ID heater hose with a rod inside and PSA paper wrapped around. Need flexible, remove the rod. I'm sure you have quite a few sanding blocks in your shop, you just don't know it yet :)

[chevynut]

Robert, we're going to be using white DBC base. I found a mis-mixed gallon of white DBC pretty cheap so I may buy it. Or we may use PPG DMD 1684 White tint base. I found that for $149 a gallon.

I have some hose sections and some paper tubes to use for blocks. I've been using K-blocks on the flat areas....I have a 9", 16", and 24". The 16" seems to be the best even for the flat areas. Some areas around the headlights and inside the taillight area I found handsanding works best.

It sure is slick with that 320 grit. I think I'm going to shoot one more coat on doors and fenders, then sand and call it good. Hopefully I won't sand through anywhere after that.

[markm]

Before the foam blocks which I really like an old painter told me he used balsa wood and radiator hose. I have a couple hundred dollars worth of foam blocks and still resort to these on occasion.

[Bihili]

Before you take it to your painter pay him to come look at it for his opinion.

[chevynut]

Bill, the painter came over and looked at the car before he committed to painting it. I am supplying the material, he's painting it and I'm helping with as much as I can. ;)

[smooth 56]

Chevy I got a feeling your going to have to prime again before you get to the finer grit that he is wanting you to get to.I have just started blocking the GMC the first priming I dry sanded with a coarse paper.The second coat I guide coat with the 3M powder using 220 paper and I sand all the guide coat off. The third coat I will guide coat again just because I want to make sure I have got every thing smooth with 320, after that I will prime one more time thinning the primer down so it goes on slick and then use the finer paper. May be over kill but that's just how I do it, so far I have turned out some good paint jobs.

[chevynut]

I have just started blocking the GMC the first priming I dry sanded with a coarse paper.

By "first priming" what do you mean? I already blocked the Slicksand (high build polyester primer) that I sprayed over the epoxy. That made the car really flat by the time I was finished with it. Then I sprayed the K36 over it just to cover the Slicksand with something.


The second coat I guide coat with the 3M powder using 220 paper and I sand all the guide coat off. The third coat I will guide coat again just because I want to make sure I have got every thing smooth with 320,

I think I'm already where you are with your third coat. It's looking really smooth and straight with the 320, I just have some light sand-thrus in some areas.


after that I will prime one more time thinning the primer down so it goes on slick and then use the finer paper.

That's sounds like what I need to do now, but I thought there was a limit to how much thinning you can do with primer. How much do you thin it? I thought too much thinner could cause problems.

I'm thinking I'll spray one more coat, sand with 400, then sand with 600 just before painting to clean it up and smooth everything. I'm hoping paint is only 3-4 months away.

[smooth 56]

First priming would be your slick sand. I don't thin it much just enough to where it don't look like it went on dry.I think your on the rite track with priming one more time. The thing should be one slick sob then.

[smooth 56]

Men't to ask have you guide coated?