Rick,
I have three experiences with barrier coats. The initial contact was applying a West System
epoxy in 1988. It finally got tired in 2004. At the time of application, the popular wisdom was about 4-6 mils of thickness. Over the years of applying ablatives and sanding for prep, I am sure the thickness decreased, especially locally. The remnants were extremely tough to remove.
Went back on with an honest 8 to 10 mils of Interlux 2000. This has been followed with two coats of Micron CSC with Biolux. Can''t say enough about Interlux technical support and the anti-slime additive (Biolux). This is not a racing bottom. We did not burnish the barrier coat or the CSC. Many race bottoms don''t look as good!
The race boat had an Interlux 2000 barrier coat applied in the mid-90''s. Last spring we stripped an ablative and applied VC Offshore. We wet sanded to #600 grit. Fastest bottom in the fleet. It was a ton of work!! We considered VC17 but felt we could get multi-year service with the VC Offshore. Interlux said there were no compatibility issues with 2000 and VC Offshore or VC17.
Like I said, the Interlux response, either by phone, fax or e-mail has always been great. It has been well worth the cost premium over the store branded stuff.