Originally Posted by Cthoops
Our new-to-us Bristol 29.9 has very likely spent her whole life in the northeast. She currently does not have a barrier coat, and she doesn't have any blisters.
The plan is to cut the lines and head for warmer climates in May 2021, so we'll definitely want to put on a barrier coat before we leave.
The bottom paint job by the prior owner's yard left a lot to be desired with patches that are flaking off down to the gelcoat, so it seems like a logical time for us to remove the existing bottom paint and put on a proper barrier coat before repainting.
How long can we expect a barrier coat to last? 10 years? Longer? I don't want to undertake this big DIY job too soon only to be hauled out in who-knows-where having to sand everything down to the fiberglass again.
I get asked this, at least 20 times per year.
We use Interlux
bottom products pretty much exclusively.
My recommendation is, if the boat is more than 20 years old, and is not showing any signs of blisters, a barrier coat won't hurt, but it won't really do anything either. If water isn't getting through the gelcoat, barrier coat can't do anything, as that is what it's for.
If the boats estimate value is over $100K, a barrier coat is a worthwhile investment.
If the boat does have an osmosis
problem (blisters), definitely do a barrier coat.
That being said, when we encounter anti-fouling
paint that is failing, or that fails an adhesion test, we will not overcoat.
So here is our process:
1. Remove anti-fouling
paint (sand or sandblast) in the fall to allow to dry all fall, winter, and spring.
2. If there are any blisters, grind them out.
3. In the spring, solvent wash the bottom.
4. If there is any exposed FRP, apply 1 coat of Epiglass epoxy
, sand, and apply another coat.
5. After a weak, wash with warm soapy water to remove amine blush, and rinse.
6. Key sand.
7. Vacuum off dust and solvent wash again.
8. Apply 1 coat of Interprotect 2000 E barrier coat (as a primer).
9. If there is damage or blister divets to be repaired, fill and fair with epoxy
filler and spot prime.
10. If owner wants to add barrier coat, apply 3 more coats, all within specified cure times (thumb print test).
12. After the last coat cures hard, sand smooth, vacuum, solvent wash, and apply last coat of Interprotect. (This reduces orange peel.)
13. Within specified cure time, apply anti-fouling.
For Micron CSC, we apply a base coat of contrasting colour, and then the desired colour, followed by a recoat of desired colour of high wear areas (leading underwater edges, and from top of waterline, down about 6".
While the Micron CSC job has a high initial cost, the life-cycle cost is actually least. Annual maintenance
is limited to just recoating any spots that the base coat colour shows through. (On a 40 foot power boat
that would take 2 gallons of Bottomkote to recover, we only use about 2 quarts of CSC.
Since the CSC does not build up over time, the need for complete anti-fouling removal
(due to failure) down the road, is postponed and minimized, or completely avoided.
For sailboats (and some power boats that are used infrequently) in freshwater, we recommend VC17m instead of CSC.
Regarding blisters, check the boat immediately on haul out
for blisters. Small surface blisters will disappear as the hull
drys. Some small blisters will eventually become bigger blisters if left unchecked, so they are worth addressing if the cost is less than the value retention.