Dealing with Shallow Blisters ... Pics Enclosed

[sharpey]

Hi All,

Am looking for a bit of guidance here... My dad and I have spent the last week grinding all the gelcoat off our (new to us) Moody 376... you can see the blistering in the pictures...

Below the gelcoat is a thick-ish layer of resin before you get to the layer of fibreglass matt. It would appear that the vast majority of the blisters (which cover about 70% of the hull below the waterline) are occuring between this layer of resin and the mat beneath it...

I'm thinkning of just sanding down the resin using an orbital sander to both a) get rid of the blistering, and b) help keep the hull fair.... It's pretty wavy at the moment after all the grinding you see...

Any opinions much appreciated... "expert" advice is often thin on the ground here

James


https://plus.google.com/u/0/100259384424719169654/posts

[justwaiting]

Ask minaret, thats what i would do
However taking all the gel coat of with a grinder - rather you than me
With 70% blisters i would have looked at peeling rather than grinding, less dust, easier to fair the hull ....
You are going to have to ensure that the hull has dried out before you recoat - moisture meters and more than likely enhanced drying or you may be waiting a while

[sharpey]

Fair point... but a peeler was an expense we weren't too keen on...


Quite right on the drying... we're not planning to spalsh for a good few months (trust me, there are plenty of other jobs to be getting on with!) With the humidty we get here (typically 70% plus) I'm looking at tenting and having dehumidifiers... but that can wait... want to spend the next few months giving regular dousings to the ground/sanded blisters first...

Cheers.

[CharlieCobra]

Take a look at the "Old Warhorse in the Shop for a Makeover" thread to see how we handled the same issue. We did hit all of the blisters that had popped up with a grinder to make sure we got all of the water/acid mix out.

[capn_billl]

It sounds like a pretty bad case. Sorry to hear it.

[David_Old_Jersey]

Never done that job - and hope never to!

Certainly I would use the oribital sander to fair the hull (post the grinding you have already done) - and maybe after / instead a belt sander.

For the blisters I would favour (careful!) use of the angle grinder (I suspect you are getting quite handy with that by now!) - might want to consider going down a size on that, if not done so already.......as an intermedite between grinder and orbital sander maybe give a wire brush attachment a go (various shapes and sizes) - they do shift fibreglass a bit more controllably than a grinder, albeit a tad slower - and also cheaper than sandpaper.....finish can be a bit rough - but you will be filling anyway.

Have fun........

[minaret]

That's a pretty good effort with the grinder there, doesn't look like you hacked it up too bad! You should have bought the peeler though, it would have paid for itself on this job. What you are seeing there is classic. When you build a boat with a chopper gun this is what happens, the operator lays down a coat of resin against the gel coat for tack, then he comes back with the cutterhead trigger on and blows CSM onto the layer of resin he just shot. The air roller crew behind him has to keep up and roll the matt into the resin and get all the air out before the resin kicks. But most chopper guns are external mix, which means the catalyst is blown into the fan out of a separate nozzle. This means getting precise rates of catalyzation can be tricky, and it's easy to spray a little hotter than you want. Combine this with the fact that many of these boats are built in hot humid places without full on environmental control, and you can see why this happens. The guys with the air rollers can't quite keep up, and the result is a layer of straight resin backed up with a porous substandard matt laminate. It's extra porous because it's full of air bubbles that were not properly rolled out.
When I see this in the boatyard, the usual answer for us is the double or even triple peel. The first peel removes the gelcoat while keeping the hull dead fair. The second and/or third peels remove the layer of resin which should never have been there and the bad matt backing it. When we get to good laminate, then we glass the whole bottom back up before fairing and barrier coating. It's a big job and not cheap.
You can of course acheive the same effect by grinding, but it's very difficult even for experienced pros to remove that much material and keep the hull fair. The peeler does it perfectly every time with minimal effort. At your present stage of the job I would still consider getting one. Sometimes you can find one on E-Bay for cheap, people buy them for a single job and then sell. Also some people operate as traveling peelers who do only that. They travel around subcontracting for yards and owners. You might get lucky and hire it out. Otherwise it'll be a lot of grinding to get off the resin layer and bad matt, and even more work fairing out your grinding, all of it overhead under the boat.
If that process sounds like too much for you, and that wouldn't be surprising, the best you can do is get that resin layer off, dry it out if you can (it wont dry easily with all that porous matt), and fair and coat it. It may or may not blister again. We are one of the only yards around that gives a ten year warranty on our blister jobs, and we would not warranty this unless it was done as I describe. Good luck!

[Sailmonkey]

I will say only this.
Your hand at the grinder is impressive

[Bash]

Heartbreaking.

We hauled last week, and when I was looking at sharpey's photos just now my wife looked over my shoulder, gasped, and asked, "Oh my god! Is that our boat?"

Hard to go with a full diagnosis just by looking at photos. That said, were this my boat, I'd be inclined to go with a full peel. Otherwise, the chances of repeat blistering are just too high.

[minaret]

By the way I really feel for you on this one. That is some truly insufficient safety gear, you must have been miserably itchy and coughing up bottom paint dust.

[Cheechako]

Nice job! Smooth 'er out and fill anything deeper after drying. Roll 2 coats of real epoxy resin on there...

[sharpey]

My sincere thanks for all the positive replies.

It was a crappy job to do... and although I still have very itchy hands... the n95 face masks did keep the dust out of my lungs (went through a box of them though!).... My dad claims not to have had any itching from the fibreglass... some magic skin he must have!

Part of the reason for the better than awful grinding (perhaps) was that we used 40 grit flap discs on a 4" grinder... they gummed up within an hour, and would need changing... but we found you could wash and dry the discs and have them as good as new for the next day... Am sure something more abrasive would have been faster though... all this took us somewhere in the region of 30 man hours each.... over the course of 5 days.

Understanding how the bottom was put together gives me a clear view of what caused the blisters... and what could cause them again...

Just need to weigh the options now... whether to get a peeler, and peel that mat off, and then re-glass (all stuff that will be new to me).... or just grind off the resin layer and hope for the best...

Decisions decisions... Having done all this work, I do want to finish the job properly... I'll admit that!

[delmarrey]

Peelers can be rented in most port cities. But what ever you decide, I'd recommend a full epoxy barrier coat over the bottom to prevent any more saturation.

[CharlieCobra]

Originally Posted by minaret

By the way I really feel for you on this one. That is some truly insufficient safety gear, you must have been miserably itchy and coughing up bottom paint dust.

No doubt. Full face respirators are the minimum. Fresh air suits are better.

[minaret]

Originally Posted by sharpey

My sincere thanks for all the positive replies.


Always happy to help if possible!

It was a crappy job to do... and although I still have very itchy hands... the n95 face masks did keep the dust out of my lungs (went through a box of them though!).... My dad claims not to have had any itching from the fibreglass... some magic skin he must have!

I've worked with a bunch of guys who make this claim. I've noticed a correlation between skin tone and susceptibility to itch. It seems to me that darker skinned hairier people don't itch as much as those of us who have fair skin. I itch like crazy myself, one of the reasons I'm very careful with suiting up well.


Part of the reason for the better than awful grinding (perhaps) was that we used 40 grit flap discs on a 4" grinder... they gummed up within an hour, and would need changing... but we found you could wash and dry the discs and have them as good as new for the next day... Am sure something more abrasive would have been faster though... all this took us somewhere in the region of 30 man hours each.... over the course of 5 days.

Go out and buy a 8" softpad sander now. You must have one for this job and it would have saved you countless hours already if you were using one instead of the flapper wheels you did use. You would also have gotten a much fairer result. Do a search on this forum, I have done several posts here with lots of info and links. You want to be using 8" 36 grit for almost all work on the bottom.

Understanding how the bottom was put together gives me a clear view of what caused the blisters... and what could cause them again...

Glad you understood and it helped. This is very common. We do a double or triple peel on about 50% of the blister jobs that come in.

Just need to weigh the options now... whether to get a peeler, and peel that mat off, and then re-glass (all stuff that will be new to me).... or just grind off the resin layer and hope for the best...

A few points here. If you don't peel and just gring, either just the resin or the matt as well, the thing to keep in mind is that the natural inclination when grinding it will be to "chase out" the resin layer or the bad matt. In other words the operator will want to keep grinding until he sees good glass on a given area, because this is his only visual cue on how much material he has removed. However, the layer of resin/matt will not have been applied at a uniform thickness, nor anything like it. Quite the opposite, the nature of the problem will insure that it is not a uniform thickness. Hence if you just chase out the bad stuff you will end up with a very unfair bottom. This is one reason the multiple peel can really help if you start with a fair surface, ie the original gel.
For us, it usually works out to one layer of 10 oz. CSM per extra peel. We usually do two extra peels, so we glass back up two layers of new matt. You don't need to use cloth of any sort, just matt. That is what you are replacing after all.We like to use vinylester resin for this, as you cant glass matt with epoxy and the vinylester acts as an added barrier coat under the 2000. We have never done any warranty work whatsoever on a bottom done this way, and as I said we give a ten year warranty. Don't overlap the matt, butt it instead. Rip all the edges first with a straight edge and they will fair right into each other when you air roll it. Stagger the buts if you do two layers. After the glass cures knock it down and provide tooth with the 36 grit softpad. Then we slick the whole bottom with WEST epoxy and 407 and fair it out using flexible "misery boards" and once again the 36 grit softpad. Once it's fair and the waterline has been blocked in dead fair by hand you're ready to barrier coat and bottom paint!


Decisions decisions... Having done all this work, I do want to finish the job properly... I'll admit that!

Nice to see someone who realizes theres no way out of the hard work involved! All of this is absolutely doable by the amateur, it just requires some planning and intelligence and loads of hard work. Experience really helps too! Feel free to ask any questions.