Gel Coat Blisters

[tgrass462]

Bucket List, a 2008 Catalina 320 MK II (Hull Number 1135) has just completed the LOOP. We have now pulled her at Charlevoix, Michigan for winter storage. All was well until it was noticed numerous small (about the size of a pencil eraser (see attached photo) circular marks on the hull near the water line. The first thought was Blisters! I then read that Catalina started installing, on later model boats (1996 or so and later) a 3/16" thick layer of water impervious Vinyl ester from rub rail to rub rail.

The recommendations here at our boat service shop was to sand blast the hull, put two coats of epoxy barrier paint and then two coats of bottom paint. I would love to hear any ideas or suggestions from other Catalina owners on this topic.

Tom and Tracy Grass
S/V Bucket List

 

[JK_Boston_Catalina310]

Are you sure those blisters are in the gelcoat? Have you explored one with a utility knife?

My first guess is that it's a blister between the gelcoat and an epoxy barrier coat that was put on as a primer for bottom paint.

 

[KD3PC]

sand blast the hull? I would get a second opinion on that as the first option. And I would look for someone doing media blast (walnut shells, etc) rather than sand.

I would also investigate those blisters, and if they do contain water, you need to abrade them or puncture them and let things dry out - before you do any painting or barrier coat...else you will just be trapping more moisture.

More pictures may help, but those don't look like they are any deeper than the antifoul paint...???

Lastly Catalina is low on the list of makers' whose boats end up with blistering, so I would check thoroughly with them and see what kind of failures they have seen.

 

[centerline]

the type of blisters you mention are not really a problem and will disappear on their own if left to dry out for about three months, with no real need to pop them... then sand and barrier coat to prevent them from getting wet again.
NO SANDING BEFORE DRYING! unless you are going to strip the gelcoat completely.

almost all plastics (some types more then others) will absorb water, and when it does it swells just like wood will do, and in the case of gelcoat, it will swell similar to what a wood veneer will do if it can come loose from the base layer...
a thin layer of overlayed plastic "or wood" can bubble up so that there is some place for the swell/expansion to go, and if its not adhered well, it will keep pulling loose from the base layer until the bubble grows large enough that the dome shape of it can absorb all the expansion.... and as the dome rises away from the base layer water will fill in the void behind it....
the small bubbles you are referring to form when the gel coat is very absorbent but well adhered.....
large bubble DO need to be opened and drained and probably ground out and filled, but the small ones you mention do not.

you should consider letting that small issue with your hull have the proper time to dry out rather than stripping the gelcoat... the money it costs to sit in the yard will be a LOT cheaper than the cost of stripping no matter how its done, and afterwards its only a reasonably simple matter of sanding and barrier coating.

or just not worry about it anymore... its a rare boat that if it hasnt developed a case of real blisters in 20 years, that it ever will, and even though what you have isnt a problem, it can still hurt the resale of the boat. Notice that I didnt say resale "value", because by the time you spend 5-10G or more on a full strip/barrier coat job, it is highly unlikely that you will ever recoup the money when selling it.... but it can help it to sell quicker.
Larger boats in the 40' and up range, or the expensive ones, may benefit much more...

 

[tahomathundr]

I have a 2006 C309 that has what looks like blisters that are hard and dry and about the size of a dime. I have a fin keel and I found 2 blisters that were wet about 2 ft from the bottom of the keel. I think Catalina used some fairing compound over the lead and that is what blistered. I haven't heard back from Catalina yet as to what they think is going on.

 

[bawlmer]

This may be a dumb reply but wait for a few days before you bust out your wallet. When I hauled my boat 2 years ago the yard guy said "you have a lot of blisters and you need a 500.00/ft bottom job. 48 hours later the blisters were gone (except for the ones he dug out) and everything was fine. They were between the barrier and the bottom paint.