Bottom Painting

[gettinthere]

Old boat with many layers of bottom paint. Sanding off all loose paint. In some places getting down to gell coat.
New ablative bottom paint manufacturer says it will adhere fine to the bare gell coat.
Besides adhesion, are there any other concerns with paint over the bare spots?
I'm not doing a complete peal of the bottom. Out of the question. Wondering if I should consider some sort of primer or sealer on the bare spots?
I don't have a blister problem.
I suspect it was never barrier coated but cannot be sure.
All recent paint has been ablative.

 

[Chris Patterson]

Yes, I would. The epoxy barrier coat is also marketed as an epoxy primer, and is good stuff. Ablative paint is not water proof, and the primer will help with future water mitigation problems. The mix can be done a little at a time without mixing a whole gallon and trying to get it on quickly. I would recommend it.

 

[Prime Time]

If you are removing all the paint down to the gelcoat, I would consider a barrier coat. If not, why bother. Just follow paint instructions. Use surface prep as directed. Use what silver that is recommended to remove mold wax, sand with recommended grit, wipe with solvent then paint.

 

[victorhoisington]

Having done bottoms on 2 boats (1981 Hunter 25 & 1989 Hunter 28), I would highly recommend the epoxy barrier coating. Older gel coats are subject to blistering, even when no problem exist today.

I didn't do the barrier coat on the 25 and it developed small blisters. I barrier coated the hunter 28 and after 3 seasons, no blisters. The barrier coat provides both a barrier against water intrusion into the gel coat (blisters) as well as acts as an excellent primer for the final barrier coat.

My experience was one of sanding to gel coat and then deciding what was the next step. I didn't know much about barrier coats the first time around but, after reading this forum and doing some research I decided the barrier coat was worth the effort when I got to the 2nd boat. Since putting it on, I have had very little flaking of bottom paint - much less than on bare gel coat and no blisters.

Just my experience, I'm sure others have more details and better info

Have fun,

Victor

 

[Gunni]

I've been there - sanded flaking paint for several years, spot primed, rinsed and repeated every year. You'll buy yourself some time, but tons more effort. Next time you will have more flaking paint...In the end I sanded the entire bottom of all paint and epoxy barrier coated. You can't be certain whether the sanding/scraping has compromised the gel coat, and you likely don't have the vinylester barrier coat in your hull laminate. If I had to do it again I would pay a contractor to soda blast my hull and then DIY the rest. Make sure he has a full-proof compressor oil preventer. Good luck, this is sucky job.