Osmotic Blisters

Face · Post by **Face** » Apr 24th, '10, 13:07

I know this has probably been discussed many times here but I am having trouble finding a good thread. I took a break from restoring my B28 due to lack of funds/time but I'm getting back into it now.

I had my hull blasted with "black magic" (glass?) and it has since sat in my yard to dry out. I know there are arguments for walnut or soda blasting but we don't need to go there. I do have numerous dime-sized blisters on the hull. My question is as follows:

Can I apply two coats of epoxy barrier, then fill and fair, then follow up with more coats of epoxy barrier. It seems to me the barrier would adhere to and fill these blisters allowing for less filling/fairing. I would rather not grind these small blisters and apply mat glass to large portions of the hull.

Does this short cut make any sense? Will it bite me in the ass?
-Joe

TailhookTom · Post by **TailhookTom** » Apr 24th, '10, 16:01

For what it is worth, I ground out the 10,000 or so blisters I had in Tailhook's bottom. Some were the size of dimes, a few were the size of half dollars, the majority were somewhere in between. After grinding the biggest and deepest received several layers of new glass. The majority were just filled and faired. After that was done I applied 5 coats of 2001 barrier coat. It was not fun, it was not easy, but from what I was told, it was the right way to do it.

Ed Curry · Post by **Ed Curry** » Apr 24th, '10, 16:13

I don't think you'll get much fill into those dime sized blisters with the barrier coat and the barrier coat will be a bear to sand, besides what would the difference be between filling and fairing a thousand quarter sized holes as opposed to a thousand dime sized holes. I filled mine with polyester putty and barrier coated 12 years ago and I've had no issues since. Then again 12 years of bottom paint hides an awful lot.
I'd open up all the blisters, fill with an easily sanded compound and then apply the barrier coat to the faired hull.

Face · Post by **Face** » Apr 24th, '10, 16:26

I figured the barrier would be like a "high-build" primer. Maybe it would not fill small blisters, I don't know. I guess my next question is should I grind/open every dime-size blister?

Secondly, would filling with an epoxy based mud, rather than a polyester mud/filler be advantageous in any way? I will definitely epoxy barrier either way and of course an epoxy based filler will be a pain to sand. Marginally advantageous? Not at all? Thinking strength and water proof.

scot · Post by **scot** » Apr 24th, '10, 22:39

I'd open up all the blisters, fill with an easily sanded compound and then apply the barrier coat to the faired hull.

Ditto.

Tony Meola · Post by **Tony Meola** » Apr 25th, '10, 18:43

Did our in 1986. Sand blasted (never let them use sand again) filled every opening and pin hole I cold with the Interlux fairing coumpound. Where it had just exposed the mat used the interlux sealer, (don't remember the number) then 5 coats of interprotect.

23 years later, not a problem and still going strong.

Face · Post by **Face** » Apr 26th, '10, 10:18

Sounds like I need to just suck it up and get into it again. Grind, fill, fair, barrier. After replacing strut pads and rudder shelves I hoped to be done grinding...one day.

gplume · Post by **gplume** » Apr 27th, '10, 20:31

No one has mention the importance of drying yet, so I figure I better. In my opinion, you need to dry the boat out real well for a successful job. I blasted mine, and let it dryout for about 6 months. Shrink wrapped with the bilge sponged dry. Not a drop of water inside for at least 6 months (my boat), I am sure you can get away with less. Open up the pock marks blisteres ect....After blasting I sanded the whole hull down with a RA sander. Wet first with unfilled epoxy then fill the blisters /pock marks /ect with epoxy and fairing compound (I used west system and 410...I am sure there are other combinations that will work,,,you will get many differing opinions for sure). Now sand it all down fair again. 4 coats of interprotect 2000 and 3 coats of bottom paint (one marker, and 2 top coats). Bottom still looks like a new boat 3 years after doing the job. This is waht worked for me. I beleive the key to success is starting with a dry boat. I also belive the good adhesion is promoted by wetting with unfilled epoxy and then applying the filled material before it drys.

My 2 cents,,,,, got some pix if you are interested.

Face · Post by **Face** » Apr 30th, '10, 12:08

Gplume, I hadn't thought about the bilge side of the hull-glass. I just might follow your advice on wetting out the surface with epoxy before filling (after opening the blisters up). I hadn't thought about that but it would make a true "barrier". Of course if I do this I will then have to use an epoxy-based filler. Harder to sand but probably the best way to do the job in the long-run.

In Memory Walter K · Post by **In Memory Walter K** » Apr 30th, '10, 15:01

If you use the West System's 401 mixed to peanut butter consistency, it sands down OK.

Charlie J · Post by **Charlie J** » Apr 30th, '10, 15:46

giff is right let the hull dry out , i have been trying to get to mine for the past 3 seasons, just cant bring my self around to pull it during the fall run. maybe this year. at least let it sit for 4 months

Face · Post by **Face** » May 1st, '10, 15:19

Fortunately/unfortunately, it has sat plenty long enough to dry.

CaptPatrick · Post by **CaptPatrick** » May 1st, '10, 15:46

Face wrote:Fortunately/unfortunately, it has sat plenty long enough to dry.

Not if the blisters weren't opened up.... The only way for the blisters to dry out is FIRST grind them out, THEN let them sit open to the air for several months. And only then fill and sand 'em down.

Face · Post by **Face** » May 1st, '10, 16:45

Touche

bertram31.com

Osmotic Blisters

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