What is the goal of using 600 grit to start wet sanding clear coat? And why 600 and not other grits, like 800 or 1,000?
The only objective of the first grit used to sand clear coat is to get it completely flat, and nothing else. 600 grit is aggressive enough to sand it flat without doing any damage to the clear coat. Remember, it is plastic, so too coarse of sandpaper can get very difficult to remove scratches from.
Everything must be flat with 600!! Do not leave my texture left over to catch with the next step, it will not be flat enough. You will be able to feel the texture through while you’re sanding. It should feel completely flat. Also, when you squeegee the panel dry, sight down it and look carefully for remaining texture.
This step is massively important if you are looking for completely flat paint. Be very attentive to what is being sanded, and take a lot of pride in the work you are doing.
Of course I recommend the True Blox wet sanding blocks. No matter what block, they need to be hard blocks. That doesn’t mean they can’t flex, the material just has to be hard, like acrylic.
Starting with 800 will work too, it just takes a lot more sanding, which can actually be worse, even though the grit is finer. The 600 just gets the job done fast and safely. (At least 5-6 coats of clear, depending on the solids content). 1,000 just won’t cut the texture completely out of the clear coat.
The second step will be 1,000 grit, which is only meant to remove the 600 grit scratches. If 600 doesn’t get it flat, 1,000 never will.
The front of the door is the transition into the fender, so these doors are supposed to have a reverse curve in them.