Wednesday, November 28, 2007

Blocking Out A Guide Coat

Tonight I blocked out the MR2. Here's the process. Back a few days ago I shot the first two coats of plain K36 primer surfacer. In it's natural state K36 is very light gray - almost white. Then I shot another coat that was tinted with black base coat (DCC). I also reduced that mixture and shot it very thin and dry. Mixed this way, it sands off very easily.

This is a 'guide coat' that will expoose all of the hidden defects on the body. It will find all imperfections that are thicker than a layer of paint! It's almost impossible to see small imperfections, scratches, and waves in the primer - UNTIL the surface is glossy and reflecting light. Then they are glaring obvious. That's the last painting step, so we can't wait until then to fix them, without starting over completely.

Luckily, this is much easier sanding than stripping off the old paint. I simply loaded up some P180 grit paper in my blocks and went to town. Sanding leaves two different colors on the body, kind of like before with the yellow/red!

Because there are two contrasting colors, we can identify any high or low spots on the body. The block will simply pass over the low spots, leaving the darker primer. The dark primer gets taken off on high spots. They show up as white areas. Parts that are just right, end up speckled with both colors. Here's an example:

There are two low spots. One behind the wheel and another on the front of the door. These "bullseyes" are real obvious, aren't they? Spots that immediately turn white are too high, and need to be tapped down with a hammer, and then filled back to level with filler.

Finding the spots are easy. What can be difficult is deciding what to do with them. In some cases the filler has filled the defect. Here's a sample on the roof, where the dark coat of primer filled the defects. This looks rough, but it's completely smooth when passing the fingers over.

If the defects are still too low, they need to be filled with glazing putty before applying another guide coat. Then repeat.

My guide coat found lots of defects, but less than I had anticipated! My goal was to have the body flat in two guide coats. It's going to be close.

I have no regret about stripping the existing paint, as it was very uneven. If I hadn't, I'd be doing as much sanding NOW chasing down the defects as I did THEN. Work wise, it was a wash. But now I've built up the new paint on a good base.

One more note. I noticed something unexpected. My panel edges have been looking ragged and unsharp. The belt line break along the side looked really bad. But after blocking out, it's sharpened up! That's a relief. I was worried they were going to take a bunch of work to get looking sharp and defined.