At this time I do not recommend painting BilgeKote over 3M 4200–they appear to be incompatible.
Preparation was as follows:
- Apply 3M 4200
- Let cure 72 hours (cure time is given as 3/16 inches per 24 hours)
- Scrub with Scotchbrite pad and water; allow to dry
- Sand 220 grit
- Brush away sanding dust w/ toothbrush
- Clean with acetone; allow to dry
However, the paint over the 3M 4200 has not cured after a week and is still tacky.
On every other surface that is not 4200 and was equivalently prepared, the BilgeKote has dry within 24 hours.
According to Jamestown Distributors, “it is paintable and sandable.”
3M has multiple pieces of literature for the same product, some marketing and some technical. I’m now unable to find the item that led me to believe the two would be compatible.
However, reading the data sheet again, I see in the fine print:
Some one part solvent-based Marine paints may not cure on top of cured Fast Cure 4200. It is strongly recommended to test all desired paints for suitability.
So technically it’s “my bad.” But still highly annoying. And there appears to be no clear, definitive information about this combination anywhere on the internet, although I can’t possibly be the first person who’s attempted this and run into trouble.
I contacted Interlux (the makers of BilgeKote) technical support, and they appear to be unaware of this incompatibility.
Finally, in the category of anecdotal evidence, there is the forum thread 3M chemists say that 4200 is not paintable.