I have had to do a lot of touch-ups on a place that was a photography studio. There are close to 100 nail holes on every wall and most of the walls are 20 feet by 12 feet. The nail holes are all sizes. The owner did not want to use a primer, figuring that the majority of the spots were so small that it would not be a problem, so we decided to use 20-minute mud for patching, then we sanded and painted almost as soon as the mud dried.

The problem is that all of these little spots are flashing through the walls. The larger patches show through because of differences in the texture of the surrounding wall, which has had several coats of paint applied over the years. So you have roller texture and smooth drywall patches. I also noticed that the 20-minute mud seems to sand to a...

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