bottom paint - lots of questions

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rapscallion

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Looking for advice on bottom paint and painting process. The boat I'm buying is a 1982 30ft Carver aft cabin. It needs full prep and recovering. There is little marine growth, but the surveyor pointed out about 20 blisters on each side, all of them 'cosmetic', hull laminates still fully intact.

I understand the process is roughly thus:
- pressure wash entire hull bottom;
- grind out blisters just down to hard, dry surface;
- fill blister areas with bonding material;
- fair smooth;
- sand entire bottom;
- apply paint.

Now, about the specifics:

- what grinder discs to use on blisters?
- what bonding material to use?
- what grits of sandpaper? wet or dry?
- random orbit sander?
- what brand of bottom paint?
- how many coats?
- how many gallons to properly cover 30 footer hull bottom?
- how long should that last (mooring in fresh water, or fresh-ish - tidal area of the Fraser River in BC - and boating in salt water).

Advice would be appreciated.
 
After the blisters are opened, you need to apply the correct thickness of barrier coat like Interlux Interprotect before you apply any anti-fouling paint or you're going to have blister pfroblems again. If the blister problem is significant, you may be better off having this job done professionally. Lots of older Carvers have blister problems. When the blisters are opened, you need to pay attention to what comes out of them. If it's water, OK, but if its gooey fluid, you're into the laminate.
 
Any grinding disc will work. I use a small 36 grit palm grinder.
I would fill them with fiberglass matt instead of bondo.
STart with 120 to get things level enough for gelcoat. Once gelcoated, 180 grit to smooth enough for barrier coat.
Brand: Your choice. Ask around your local docks to see what everyone else in your area is using.
2 coats on bottom, 3 at the waterline.
4 to five
My Ablative in non moving water lasted 4 years before showing thru.
 
Great info; thanks.

I was present when the surveyor cut into several of the blisters. Only water came out; nothing gooey. He also scraped some of the blisters out and tapped the hull underneath them. It rang solid like the rest of the hull.

I'm curious: fill blisters with fiberglass mat? The blisters are mostly the size of a quarter or a dollar coin. Is that right fix?
 
If they are just into gel coat, then they can be filled with a compund like 3M Marine Fairing compound,sanded, then apply the barrier coat, then the anti-fouling coats. Still think you should let a Pro look at this and give you advice so you aren't doing a bandaid fix only to lead to bigger problems down the road.
 
The guy at my marina uses WEST System to repair blisters that are going to be covered by bottom paint.
 
Agree with the advice provided.
Would highly recommend you allow time for open blister to dry out thoroughly before resealing. Best time I found is during (heated) winter storage...
 
I prefer to fill with fiberglass. Although I reckon a fiber reinforced epoxy would do well.
 
quote:
Originally posted by KiDa

The guy at my marina uses WEST System to repair blisters that are going to be covered by bottom paint.

Click to expand...


Same here. The little hand pumps they sell make mixing pretty fool-proof. I think that's the PROPER way to fix blisters.

As far as a barrier coat, the old bottom paint should be removed to assure proper adhesion. I just did my Silverton with InterProtect 2000e. They recommended 5 coats to create the proper (10 mil) thickness. The stuff is pretty easy to apply but skins over very quickly, so when rolling you need to limit "wet re-coating". They say up to 2 weeks between re-coats but I was able to do all 5 in 1 week.

Mine turned out so well I almost hated to cover it with antifouling paint, but I did- 3 coats of Pettit Ultima ll.
 
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