Will two-part paint lift varnish?

[MJT]

I'm about to tape off about 200 feet of varnish where the rails and house teak meet the deck and roof. The image gives you some idea of my situation.

I'll be painting with a two-part system like Interlux Perfection. Am I worried the two-part paint will lift any varnish not covered by the tape? Thanks in advance.

I hope this thread is not inappropriate for this forum, but I know there is deep knowledge here.

 

[Mr Efficiency]

Is it a 1-pack polyurethane varnish ? I don't quite understand why you are worried about the varnish lifting, it will be taped off ? But I am fairly confident that epoxy won't lift PU, it didn't when I used it over what I assumed was 1 pack PU. But your primer may not be epoxy. I think the solvent used with 2-pack PU will aggressively attack most, if not all one-pack finishes, from memory.

 

[fallguy]

Use the reducer for the paint and do a surface compatability test first. Put a bit of the reducer on a rag and tape it to varnish somewhere inconspicuous overnite. If it peels or blisters; the whole job probably will.

 

[Mr Efficiency]

Use the reducer for the paint and do a surface compatability test first. Put a bit of the reducer on a rag and tape it to varnish somewhere inconspicuous overnite. If it peels or blisters; the whole job probably will.

How silly of me to not suggest this ! In my experience the thinner for 2 part PU ( I assume this is what he is using ?) will soften and wrinkle one-pack paints, but bearing in mind a thin application of the thinner as a test, will need to allow that is warm conditions, it will flash off quickly, before it has a chance to act upon the old coating. With paint, that won't happen so quickly.

 

[fallguy]

I get your concerns. You are worried about the intersection where the paint will touch the edge of the varnish. I would probably plan to use a flexible sealant there like Sikaflex. Then, when you paint, you could actually keep the paint just away from the very edge either by steady hands or masking it off on the intersection about 1/16th" onto the deck. Otherwise, you could try to find a more suitable paint that is less likely to lift your varnish.

I would most definitely test things on non-boat samples. If you find the test I recommended above fails, it might still not fail on simple edge contact, or it may, for example. But, for sure, remove the masking tape right away and use a very good quality masking tape that will not bleed and test test test.