this is part of the response from P21S corporation when I asked them about layering. Sounds like a sales person response, not an engineer. "...We do know of successful instances where layering has worked for people, at least a second layer, not sure beyond that. Some say it is good to wait 24 hours between coats and do a cold water wash, rinse and dry before the second application, but we have not verified this, so maybe you should try yourself.
The most detailed info about the P21S line can be found at p21s.com..."
The most detailed info about the P21S line can be found at p21s.com..."