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Hull Blister Repairs

erikwfab

Member II
As the pround new owner of an E36C I have a few questions for this community of boatowners.
I have elected to have her bottom sandblasted due to the number of blisters I discovered after hauling her.
I would like to know what the best way to proceed is. She is east of San Francisco and the weather is dry and temperate. I am planning to do as much of the work as possible but I live and Work quite a distance away (6hrs), so i need to work efficiently.
I have been told that West System is the answer, there is a 45' Swan in the yard which was blasted and is having its entire bottom skim coated with 400 I think. I know the blast will make the gel-coat more pourious and I am wondering if i need to skim coat the entire hull as well. If so sanding her fair will be a big job.
 

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Emerald

Moderator
If you do a search on blisters on this board, you'll find a ton of discussion. Enough to make sure you're confused. For example, check this recent thread:

http://www.ericsonyachts.org/infoexchange/showthread.php?t=6547&highlight=blister

OK, now that's out of the way, from your pictures, it looks like you are a candidate for filling with West System and barrier coating the whole thing afterwards. I followed the advice of the marina that I was hauled at, and after filling with West System, used the Interlux Interprotect for the barrier coat. As I talked with everyone I could think of, this combination of West System followed by the Interlux Interprotect seemed common. If you haven't seen it, check this article from EpoxyWorks magazine (a West System publication):

http://www.westsystem.com/ewmag/17/repairinggelcoat.html

I took a hybrid approach on the filling. I initially did all the blisters with 406 for the basic fill. I then faired the blisters with 410. As the above article points out, if you do a barrier coat over the whole bottom, you can fill and fair with the lighter weight 410. I wanted as much density as possible, so I went for the 406 for the bulk of it.

Hope this helps. All of the above is, of course, just another blistered opinion, and perhaps not even worth the .02 you didn't pay for it. :egrin:
 

Brisdon

Inactive Member
Drying is the key to success. If you can let it bake in the sun for a couple of months until all the moisture is drawn out of the fiberglass, you will have a better chance of success. Also, painting the blister cavities out with plain epoxy before adding thickened epoxy will give a better seal and actually add some structural integrity to the damaged core, because it crawls into the fibers as the thickened stuff can't. Finally a barrier coat like Interlux Interprotect 2000E should top it off.
 

footrope

Contributing Partner
Blogs Author
Drying is the key to success. If you can let it bake in the sun for a couple of months until all the moisture is drawn out of the fiberglass, you will have a better chance of success. Also, painting the blister cavities out with plain epoxy before adding thickened epoxy will give a better seal and actually add some structural integrity to the damaged core, because it crawls into the fibers as the thickened stuff can't. Finally a barrier coat like Interlux Interprotect 2000E should top it off.

I hope you're right about the drying out. The 'Project has been out since May and I'm finally finished with the epoxy work on the blisters. There was a nice stretch of warm weather after I ground the areas out. The moisture readings dropped by several percent on all of the areas measured. Almost all were below 10% before I applied the penetrating epoxy seal to each area.

Good luck on the repairs. My method used West and 406 filler, cloth with West if I ground out bad cloth layup. I skipped the 2000 coating, but I did use 2000D a few years ago on 4 areas where the West barrier coat had holes in it. The 2000D seems to have worked ok. I'll let you know in a couple years if the West repairs worked out.
 

erikwfab

Member II
I have elected to use cavosil as the filler and skim the entire bottom. In speaking with a number of boatowners the biggest criticism i heard regarding cavolsil is that it is brittle. one other recomendation was to use dyco-pearl. Eventually you have to make a decision and go with it so i will keep you posted as to my findings.
 

Emerald

Moderator
My recollection is that Cab-O-Sil is colloidal silica and the MAS equivalent of West System 406. This is a reasonably high density filler. It would be good for blister fill, but I don't think I would want the sanding time if you skim the whole bottom - that's where 410 comes in as a lightweight fairing filler. On this note, I wouldn't skim the bottom at all. I'd fill the blisters, fair them in as smooth as possible, and then barrier coat. I wouldn't use an epoxy thickened with 406/410/Cab-O-Sil for the barrier coat. West System has special barrier coat additives, or you have the Interlux Interprotect 2000E, or I'm sure MAS has it's own additive that would be good for barrier coats. These additives have different properties that make them better suited for certain tasks than others. For example, if you read the product literature on the Interprotect 2000E, they have solids that are supposed to lay out like shingles on a roof to provide a physical barrier within the epoxy base. I believe it's quite a bit different than epoxy mixed with a standard thickener like 406. Finally, pure epoxy is brittle. Additives give it strength. The type of additive, colloidal silica, cloth, woving etc., is where the strength comes from, and why choosing the right additive is so important - you'll notice on the West System blister guide they have you put cloth or mat in a deep hole before putting epoxy mixed with 406 in to fair it. In the same guide they talk about 410 only when covering with a barrier coat, and using the 406 without a barrier coat because of the higher density (and water proofness that goes with it). If you feel like your eyes are crossing as you hear all the differing input, well, it's all part of the fun known as blister repair :egrin:
 

Brisdon

Inactive Member
If there is a lot to fair, as in a big blister job, something like 410 filler is going to give a much better result with much less work. But again, the key is to:

1. open it all up.
2. wash it thoroughly to get all the vinegar like compounds out.
3. Let the boat dry thoroughly
4. saturate the hull with un-thickened epoxy (which will draw up into all the open fibers by capillary action)
5. glass deep voids with stepped overlapping layers. (if you have a hull that was put together in two halves like an E 35-2, it's not a bad idea to add a layer of glass up the seam)
6. Fill all the recesses with thickened epoxy
7. apply a barrier coat (like 2000E).

Interlux 2000E has metal bits in it like tiny fish scales that lay flat and make a very permanent water proof membrane. I wouldn't want to try to blend something my self to compete with this fairly sophisticated product, when I can just go in and buy it ready to go.
 

larossa

Member II
Blister Repair

In looking at the picture attached, it looks like you have some blisters bigger than an inch. My experience with this type of repair, (3 of my own boats and worked professionally) I would recommend covering these with a layer of glass cloth. Filler in these larger blisters can eventually pop out. Neither the West Epoxy nor the Interprotect will not be enough to hold the filler in over time. I see this all too often up here in the North on boats every year. It would be shame to do all this work and then have the filler pop within a couple of years.


Good luck,

Brian
E 31 Nemo
 
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