Sharing here some findings while testing film thickness.
Background: I spray UV cured polyester from Cardinal. Typical schedule that I think most people use is to spray two overlapping coats, cure, and then spray two more.
What this results in is a 2-3 mil base layer and a 2-3 mil top layer totaling 5-6 mils of finish before leveling & buffing. This depends a little on the brand of material and if using any reducers. In my case I’m using Cardinal U4PA-CLE22 polyester which is 65% solids.
Using the above two coat approach also requires sanding between coats at 220 / maroon scotchbrite. This is critical because the material is all mechanical bond and failing to properly tooth the surface between coats can lead to adhesion failure (ex: Taylor horror stories).
This also creates a concern about going through the top layer and having witness lines from the 220 scratches between coats. How to solve this?
My thought has been to wet stack three coats rather than “two - cure - two.”. The obvious concerns are:
- Getting it to hang properly with no runs or sags
- Spraying three “lighter” coats may result in excessive orange peel.
- Curing the thicker material properly
Using a sprayout card I sprayed three wet stacked coats of around 4 wet mils which created a dry film of around 6.8-7.4 mils (measured in various places on the card). Note that the 1.4 mil second layer is the sealant on the card.
The images below are measurements of a specific area at each step of leveling and buffing. You might ask why I would go from 400 grit paper backward to 360 grit Assilex. I’ve found that the 600 grit Assilex on a ROS cannot get hand sanded 400 grit Cubitron scratches out.
Was quite surprised too by the amount of film removed by the medium cut Menzerna. This was all focused on a small area so the buffer may have removed more than typical.
Any feedback / recommendations / etc… appreciated!
Brad
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For now I have to level at 400 and go up. 