How bad did I screw up?

[Sinewave]

I'm a newbe to body work and could use some advice.

I am restoring two doors for my '76 MGB. I stripped the doors with a 3", 60 grit disc on an angle grinder and filled the dents and dings with Rage Extreme. I shaped the filler with 80 grit on a long board.

After 2 coats of DuPont DTM epoxy primer, I sprayed 3 coats of Nason 2K high build.

Here is where I screwed up. I did not use a finer sandpaper on the filler or the bare metal before I sprayed primer. I can see ridges (sanding marks) in the primer, especially from the 60 grit.

Will blocking and re-priming fix this or will they eventually show in my finish coat?

[Len]

I'm a newbe to body work and could use some advice.

I am restoring two doors for my '76 MGB. I stripped the doors with a 3", 60 grit disc on an angle grinder and filled the dents and dings with Rage Extreme. I shaped the filler with 80 grit on a long board.

After 2 coats of DuPont DTM epoxy primer, I sprayed 3 coats of Nason 2K high build.

Here is where I screwed up. I did not use a finer sandpaper on the filler or the bare metal before I sprayed primer. I can see ridges (sanding marks) in the primer, especially from the 60 grit.

Will blocking and re-priming fix this or will they eventually show in my finish coat?

60 grit is pretty coarse and could come back to haunt you. The problem is that the primer may look great when it's blocked sanded and the paint may look great when it's applied but as the coatings cure they could shrink a little causing the scratches to appear in the finish. I usually recommend that filler be finished in 180 then primers applied and the primer is finished in 400 or 600 before painting.

If removing the 60 scratches is not an option then be sure to apply enough paint so that you can sand and polish it after a couple months of hot weather. This will insure that any shrinking is finished and you can remove any scratches in the top coats. However if you're planning on a metallic base/clear then polishing out the scratches in the clear may not remove the visible scratches that may remain in the base.

[Sinewave]

Thanks for the reply Len. I'll be using a single stage solid color final coat so I may be able to color sand and polish the marks out if they come through later.

[turbocobra]

Len,

Since he is still in the primer stage, can he do a skim coat of poly putty, or even shoot each door with slicksand, guide coat, block sand, and then go to paint?

[Len]

Len,

Since he is still in the primer stage, can he do a skim coat of poly putty, or even shoot each door with slicksand, guide coat, block sand, and then go to paint?

The problems come in the difference in the density of the filler versus the density of the primer. Because of this difference they tend to shrink at different rates AND can be effected by solvents in the top coats differently. This difference can cause scratches to reappear as the coatings shrink. Applying more material on top may or may not help depending on several factors like the quality of the materials, how hard they get and how porous they are etc.. You may get away with doing nothing but I'd still apply at least three or four coats of single stage paint or three or four coats of clear so that you have enough to sand and polish after the materials are fully cured.

[Sinewave]

So it sounds like the longer I wait before I finish coat, the better off I am.

[SamG]

You're right in thinking that waiting longer is better...however at the very least, find a way to expose the doors to some high temps (like a hot summer day in the sun) or even get them close to a space heater of some sort. Where they are very warm (almost hot) to the touch. Let 'em cool before proceeding, again, the longer the better.

Block sand your primer, being sure to 'use up' your primer with some ~180 grit. By 'use up' I mean to remove most, if not all, the primer that is not necessary. You should only have primer left in the deepest scratches. Primer left in deep low spots prob needs to be replaced with poly-putty or filler anyway. Problem is, when block sanding (if done properly), once you hit metal you're done...So as soon as you hit metal if there's still a lot of primer left adjacent to the now exposed metal, you've got to decide to live with it's depth or re-work.

Once you're satisfied that your door is both straight and properly blocked with ~180 grit, re-prime and your doors should be slick...

http://webpages.charter.net/sgilliam8850/MyProjectsPage2_files/image013.jpg

Hard to see in this picture, but you may can make out on the back edge of the door there is metal showing and green etch primer showing. You may can also make out the majority of the door is gray primer and there are a few spots of a lavender looking primer. This door got one coat of etch, 1 wet coat of straight 2K, one wet coat of tinted 2K (the lavender color, used as a guide coat). Block sanded with 180 (when the picture was taken), then followed with 2 med coats of 2K. 400-600 grit then paint.

[Henry]

Thanks for the reply Len. I'll be using a single stage solid color final coat so I may be able to color sand and polish the marks out if they come through later.

If you have 60 grit scratch way down then sanding and buffing the finished top coat will have no affect on those deep scratches.

Listen, in this field there are thousands of variables to make our lives miserable. This is one of YOUR big ones that was self-induced.

Consider it a learning thing that you won't let happen again and properly sand the affected panels down and start from a solid point the right way - the way you KNOW how to do. Take your time and it won't be as bad as it sounds. There are no shortcuts or easy fixes on the road to perfection. Youwill have more work after the finish paint to contend with when you have a fantastic gloss/glass like top surface showing all that mess below and magnifying it at that. Sorry. Henry

[recoatlift]

henry is right on [so are the other posters]. make a positive learning expeirence out of it. although, some folks make a habit of their doing body work with primer & could care less. len's right on that 60 grit scratch shrinking back due to primer bridging or whatever the proper word is. that's a big valley scratch. i've got a feeling you're gonna come out ok on this. good luck, keep posting.

[Steve g]

If you have 60 grit scratch way down then sanding and buffing the finished top coat will have no affect on those deep scratches.

Listen, in this field there are thousands of variables to make our lives miserable. This is one of YOUR big ones that was self-induced.

Consider it a learning thing that you won't let happen again and properly sand the affected panels down and start from a solid point the right way - the way you KNOW how to do. Take your time and it won't be as bad as it sounds. There are no shortcuts or easy fixes on the road to perfection. Youwill have more work after the finish paint to contend with when you have a fantastic gloss/glass like top surface showing all that mess below and magnifying it at that. Sorry. Henry

That's not always the case with today's high build urethane primers. Omni's 282 primer specifically says it it can be used as either a high build primer or a spray on filler depending on it's mix (no reducer when used as a filler). The other special instruction when using it as a filler is a longer cure time before sanding and top coating. Up to 4 coats allowed and with no reducer and a 1.8 - 2.0 tip that's a lot of build. They behave much the same as the sprayable polyesters and do create a very hard stable surface. It's certainly not the same as attempting to build the surface with a single stage old school primer.

I wouldn't remove it unless there was a caution about excess build amounts on the tech sheet for that product. I would ensure that it has cured adequately at correct temps, long board/block with 180-220, shoot one more coat and block with 400-600 wet. Works for me.

Steve g