blisters on hull of 28' chris craft

[delle]

I have a 28' chris craft with a LOT of blisters on the hull. I'm looking at removing the gelcoat from the waterline down. Let me give a history of what I did in the past. 4 years ago, when I got the boat there was a lot of blisters on the hull. I soda blasted the hull to remove the antifouling paint but not the gelcoat. After about 9months of the boat out of the water I painted the hull with an industrial marine Ameron 400 epoxy primer then Ameron PU 450HS then applied antifouling over the 450HS. I did not fill in the pits that the blisters left with any fillers before painting. The Ameron coating held up fairly well, however it is time to re-apply antifouling. I started pressure washing with 3700psi to remove the antifouling paint and the pits are a soar eye. I would like to redo the hull right this time since I have the boat out of the water.
If i remove all the paint and gelcoat from the hull do I go back with gelcoat? trust me there is enough blister that i would have to remove all the gelcoat. or
Can I remove the gelcoat and apply an epoxy than antifouling to give me protection I need. The boat stays in fresh water all year round.
Sorry for the long story just wanted to get as much information out there as I can. Thanks for anyone who can help. I have attached a picture of what the hull looks like.

 

[ondarvr]

Re: blisters on hull of 28' chris craft

The short answer is blister repair is an all or nothing project, you either remove all of the gel coat AND all of the blistered laminate down to good glass, then rebuild it with epoxy, epoxy barrier coat, then paint, or do nothing. In between or half hearted attemps don't last very long.

 

[delle]

Re: blisters on hull of 28' chris craft

so after repairing the blisters, so should I re-apply gelcoat or just an epoxy barrier then paint?

 

[ondarvr]

Re: blisters on hull of 28' chris craft

Gel coat is not and option, it's epoxy all the way.

When I say removed the effected laminate I mean you need to grind off all the gel coat and glass down to the level of the deepest blister, not just the blister itself. They make gel coat peelers just for this purpose.

 

[surlyjoe]

Re: blisters on hull of 28' chris craft

Gel coat is not and option, it's epoxy all the way.

When I say removed the effected laminate I mean you need to grind off all the gel coat and glass down to the level of the deepest blister, not just the blister itself. They make gel coat peelers just for this purpose.

like he said, a gelcoat plane makes getting it off much easier, back before the gel planes were invented we used a regular elecric plane and a shop-vac and disc grinders for the curves. once you get the gelcoat off you will have a better idea of how much damage the osmosis has caused. be sure to plane off just the gel coat at first or you may have to add glass back to it.

if its not too bad, it can be dried out and epoxy coated /re-wetted then faired out again (the planing isnt all that smooth) before finishing it. If its really bad, expect to do some more passes with the plane and re-glassing back what you planed off.


oh! and can't see the pictures =/

 

[delle]

Re: blisters on hull of 28' chris craft

Sorry for the bad pics. I have attached a few pics. Some areas its as if I can just peel the gelcoat off. the laminate under the gelcoat looks good in the areas I can see, but I know I will have to remove all of it to see everything. I have one picture that it seems the laminate is going to need to be sanded down and repaired. that is the picture where you can see the white fibers of the glass, oh and the 3700psi pressure washer did that. If I'm wrong please let me know. I've never done this before. Also any recommendations on products to use. Thank you for the feedback!

 

[surlyjoe]

Re: blisters on hull of 28' chris craft

hard to get a sense of scale but it doesn't looks bad at all. are there any "zit" blisters in the glass that will squirt out water if you push on em? or small wet spots that haven't dried out and are weeping? I dont see a lot of osmosis damage.

It looks like the old epoxy is doing its job and just got blown off by the pressure washer in a few spots. I wish you were in my area so I could stop by and see it, but if there are only a few (like 20 or so) deep/weeping blisters I would just spot fix em, give it a qwick blast and fair out the pits before epoxy coating it like you did last time.

 

[delle]

Re: blisters on hull of 28' chris craft

there is absolutely no blisters that are weeping or any "zit" blisters. they are all dried out. as for as spot fixing, there are a lot throughout the hull. I was I could get a good picture of how many there are. If I fix one it will go into another then another. I guess I'll remove as much as I can. So I guess I should go with an epoxy barrier first then after an epoxy paint?
thanks for the help

 

[ondarvr]

Re: blisters on hull of 28' chris craft

In the bare areas you can see small white spots in the laminate, these are what you need to be concerned about, they are spots where either blisters have formed, or are forming. This entire layer is what needs to be removed, it means water has already damaged it and is breaking down the resin. The spots you see are just the ones that have progressed to that point, the area around those spots will be following close behind.

This is where many people make the mistake of only repairing blisters they can see and then coating it with epoxy. This layer has been weakened and any moisture left in the laminate will continue the blister processes under the new epoxy layer, resulting in a hull full of blisters a few years down the road.

 

[surlyjoe]

Re: blisters on hull of 28' chris craft

in freshwater i am a lot less woorried about those pits in the mat if they are already dry, its really just to prevent print through. How was the paint when you hauled it, was it the still intact or was there more blister damage this time. more a maintenace thing at this point I think.

 

[surlyjoe]

Re: blisters on hull of 28' chris craft

read these ...

boatstasmania.com.au | Tasmania's Boating Hub

Mustang Island Yachts (Rockport, TX)

 

[ondarvr]

Re: blisters on hull of 28' chris craft

Fresh water is typically worse for blistering than salt water, and those white spots are key to getting it repaired correctly.

 

[surlyjoe]

Re: blisters on hull of 28' chris craft

thats right fresh water is more viscous and penetrates the laminate easier, but also weeps out easier, and he says its all dry, so it makes me think that the glass is OK. thats why I asked about progression since the last haul out. bad gelcoat doesnt always mean bad glass..

 

[ondarvr]

Re: blisters on hull of 28' chris craft

Quote from your link

"To release this 'osmotic fluid' the gel coat has to be removed as it is impermeable to these large molecule chemical solutions. They then have to be diluted and extracted. Simply drying the surface out simply leaves an even more concentrated solution in the laminate ready to 'suck' water back in when the vessel is relaunched."

Removing the compromised layer is the only sure (most reliable) way to avoid future problems. The white spots indicate the depth of damage to the laminate.

 

[surlyjoe]

Re: blisters on hull of 28' chris craft

I think we have established the gel coat should come off.. whether he needs to remove the mat that was used to prevent the roving from printing through is what we are trying to determine I believe. if it did not absorb any water in the last 4 years and is not in to the roving, there shouldn't be any structural damage. and if it is properly sealed with epoxy, how is it going to "suck water back in" ?

like I said I wish you were in the bay area so I could see it for myself, do you have a straight line sander or a DA that you could knock off the gel over what you consider to be a bad spot in like a 3' x 3' area? that will tell a lot more .

 

[surlyjoe]

Re: blisters on hull of 28' chris craft

Oops!!!

 

[ondarvr]

Re: blisters on hull of 28' chris craft

The mat has absorbed water over the years and the white spots are areas where there is a visible indicator of damage, the area surrounding them just hasn't gotten to the point of it being visible yet, but is still compromised. It takes a very long time for a laminate to dry out, so to just strip the gel coat and cover it with epoxy is a huge mistake, and made by many because it seems like it should work.

People make the mistake of thinking blisters are a gel coat issue, when most of the time they aren't, it is a resin and/or glass (entire laminate) issue. To just remove the gel coat is like changing the bed spread to remove an infestation of bed bugs, the bed looks better but the problem is still right under the surface.

Epoxy isn't waterproof, nothing is, it is only more water resistant than polyester, so there is a very good chance that with this boat being left in the water some moisture will find its way back into that layer of compromised glass, which has blister pockets already in place to speed any future outbreak. And that's if he was actually able to dry it out completely prior to applying epoxy, if it isn't dry the blister process will continue on under the epoxy, just slowed down slightly and more blisters will show up later.

 

[surlyjoe]

Re: blisters on hull of 28' chris craft

you say... "People make the mistake of thinking blisters are a gel coat issue, when most of the time they aren't, it is a resin and/or glass (entire laminate) issue"

I say .... many times it IS a gelcoat problem that may have damaged the surface of the print through mat but has done no structual damage to the laminate.

the diffence is thousands (perhaps tens of thousands on a large boat) of dollars and the chance comprimising the original plug as it was laid by the builders.

If you are at the boat its fairly easy to tell which has occured by digging / tapping around , with photos not so much. removing a larger patch of gelcoat for better visual refrence isn't going to hurt anything.. perhaps we should wait till he exposes more area ...

If you want to do more reading, it seems the aerospace industry has done more research on this than than the boating industry, check out some of their studies on water immersion ..

 

[ondarvr]

Re: blisters on hull of 28' chris craft

I started working on the blister issue in the 70's and since then have done a great deal of testing and consulting, also as an expert whiteness in court cases. We currently do blister testing on all of our products and for our customers (boat builders) to see what will work for them.

Blister repair is a well know process now, there are specific guidelines on what needs to be done for a repair to reliably hold up long term.

There are specific indicators of blisters that are only in the gel coat, and these pics don't show those defects, at least not that you can see. They do show the signs of laminate blisters though, which are far more common than gel coat only blisters.

Examining the laminate up close would yield more information, but in the pics I can clearly see white spots in the glass, this is what dictates at what level the problem is, and the repair process.

We also work with the aerospace industry, we will be speaking at an Advanced Composites class targeting the aerospace segment this coming week. Two weeks ago we co-sponsored a school for a combination of market segments including aerospace and marine.

 

[delle]

Re: blisters on hull of 28' chris craft

I was thinking of Soda blasting the gelcoat off instead of sanding, any thoughts on that. Once I get the gelcoat off I was going to post some pictures of the laminate. Also, can someone suggestion what kind of epoxy barrier should I go with?