Rule of thumb for cloth, thickened epoxy or just fairing in abundant blister repairs?

[PANorth]

We are in the midst of a major hull repair job after finding abundant blisters under the bottom paint on our new-to-us 1982 E38. I posted about this in the fall before we removed the bottom paint. It didn't look quite so bad then.
Less than a dozen blisters reached the laminate, and none seemed to penetrate. 90%+ were into the chop layer, and the rest are tiny and just below the gelcoat. The biggest is about 6 inches across, though before we are done grinding I am sure many will blend together. Is there a rule of thumb about filling these groundout voids? I assume some will require layers of cloth, some just thickened epoxy and (dare I hope) some just fairing. How do I decide which gets what?
Are there any other things to consider when there are abundant blisters below the water line? See photo.

 

[KS Dave]

West System has a pretty thorough guide published on this: Gelcoat Blister Diagnosis, Repair & Prevention

It seems to indicate that you'll want to use cloth when you have a large inter-laminate void. For most cavities you've ground out, filling with thickened epoxy seems to be sufficient for the repair. Have you thumped around with a plastic hammer to listen for voids? They also describe how to test how dry your laminate is using condensation tests (if you don't have access to a moisture meter)

I haven't actually had to deal with blisters; some others who have actually done this repair might have more to offer.

 

[PANorth]

We are thumping around as we go to make sure that we are getting all the voids. I just bought a moisture meter, but I am familiar with the plastic sheet method. I'll probably do both. The boat is under cover and well ventilated. We plan to leave the boat sitting well into the summer so it has ample time to dry out. There appears to be a lot of water in the hull.
Thanks for the reminder of the West System guide. I will read through it.

 

[KS Dave]

There appears to be a lot of water in the hull.

Ugh. Sounds like more quantity of work than anything. Best wishes. Kick up some blog posts and show us how it's done.

 

[Pete the Cat]

West System has a pretty thorough guide published on this: Gelcoat Blister Diagnosis, Repair & Prevention

It seems to indicate that you'll want to use cloth when you have a large inter-laminate void. For most cavities you've ground out, filling with thickened epoxy seems to be sufficient for the repair. Have you thumped around with a plastic hammer to listen for voids? They also describe how to test how dry your laminate is using condensation tests (if you don't have access to a moisture meter)

I haven't actually had to deal with blisters; some others who have actually done this repair might have more to offer.

I have dealt with blisters and generally agree with Dave. I went too far an peeled my hull and added 3 layers of cloth. I really think this is overkill. If you have identified the voids and filled them. In most of the Ericsons, the hull is to keep the water out. The structure for stress is in the TAFG if that is the way the boat is built. You do have some laminate damage, but I cannot really assess it from the pictures. Most surveyors these days are useless for these matters, but you might ask the boatyard. Most of the boatyards are not as blister crazy as they were a couple decades ago.

 

[Nick J]

I have dealt with blisters and generally agree with Dave. I went too far an peeled my hull and added 3 layers of cloth. I really think this is overkill. If you have identified the voids and filled them. In most of the Ericsons, the hull is to keep the water out. The structure for stress is in the TAFG if that is the way the boat is built. You do have some laminate damage, but I cannot really assess it from the pictures. Most surveyors these days are useless for these matters, but you might ask the boatyard. Most of the boatyards are not as blister crazy as they were a couple decades ago.

I dont think blisters affect the structural integrity of the hull for the most part, but saying the hull only keeps the water out may be taking it a little too far. The fore stay and back stay connect directly to the hull and there are plenty of boats out there, including quite a few Ericsons, still floating and supporting their rigs without a TAFG. The TAFG strengthens and stiffens the hull, it doesn't take 100% of the loads from it.

 

[Mark David]

No doubt that West System makes great products, but they are primarily 'adhesives' that require the user to thicken them for fairing or filling work.

Another approach is to use a pre-mixed fairing compound. It is easier to work with and way more consistent. It also greatly reduces the chance of failure due to incompatible layers of fillers, with different densities, 'flaking' off when the hull flexes.

I am not affiliated with the company, but this is the preferred brand around here..... https://masepoxies.com/product/fairing-compound

 

[KS Dave]

Another approach is to use a pre-mixed fairing compound. It is easier to work with and way more consistent. It also greatly reduces the chance of failure due to incompatible layers of fillers, with different densities, 'flaking' off when the hull flexes.

Have to agree, here. I have used the equivalent TotalBoat product with great success. Consistencies are perfect, it's easy to work with, and you know when you have it mixed right. TotalBoat also has some thickened epoxy in a tube that I have found handy for many things, but also more of an "adhesive" product.

 

[PANorth]

I don't know what TAFG is. The boat is not in a yard. We are lucky enough to have a free space to work on the boat under a shelter.
I had not heard of the premixed fairing compounds. Thanks for that, its good to know about.
The great majority of the blisters are in the chop layer and did not get down into the woven laminate. But here is a picture from when I was exploring the blisters. I'll take a picture of it now that it is ground out.

 

[PANorth]

I agree about the surveyors. I sent our surveyor these pictures. He maintained that they were not worth the trouble to fix.

 

[KS Dave]

I don't know what TAFG is.

Life's a bilge and then you dry (E381....with images)

Hey, folks I'll likely turn this into a blog post at some point, but wanted to share some ongoing bilge/keel bolt work and check with the hive mind on a few things. First up, we all know that a clean bilge is a happy bilge. Respira did not come with a clean bilge. She's been sitting on the...

ericsonyachts.org

 

[PANorth]

Lots of good information in these posts, thank you. I am also getting information for work in other parts of the boat that I have not yet started. Here are pictures of ground out blisters. In a video by a famous cruiser about repairing boat pox on their boat after 40 years he made the comment that the boat was stronger than new. I keep wondering about that. Is there enough history for these kinds of wide spread repairs to demonstrate that the added materials don't eventually fall off (assuming its all done correctly)?
Here are pictures of lots of ground out blisters. These are all blisters that sounded hollow. Any white spots that sounded solid were not ground. The site of the photo above after grinding. You can also see places that I interpret a previous blister repairs (much smaller). We are about 1/5 of the way around the hull. The whole thing has about this density of blisters. After grinding we will let it sit well into the summer so it will dry out as much as possible. We also plan to drop the keel to inspect the keel bolts. I wonder if that will be another exit point for water in the hull.

 

[Christian Williams]

Department of Why We do this Work:

Yard bill for my PO to have bottom prepared and barrier coated in 2015: $15K.

 

[tenders]

Is this red substrate we're looking at, around the ground-down blisters, bottom paint? You're going to be a lot happier hiring somebody with a soda blaster to take a day to exfoliate all the old bottom paint. It simply isn't possible to get a good outcome trying to fill and fair around dozens of blisters, hundreds/thousands of little pockmarks, and residual bottom paint.

I think you're on the right track with applying cloth and epoxy over the deepest blisters. But you absolutely need fairing compound on the outer layer, and in the irregularities that aren't deep enough to warrant the cloth treatment, because you can't sand and fair the boundary between gelcoat and epoxy/cloth. They have extremely different hardnesses, and you'll always end up with a valley in the softer material and a bump in the harder material.

Don't worry about the fairing popping out. Epoxy is extremely good at sticking as long as it's sticking to something solid, like gelcoat and fiberglass...which is another reason for the soda blast.

My experience: did my own bottom job last year with my long-suffering boat partner. No blisters, but we had probably 50 years of old bottom paint sloughing off and not allowing the top coat to do its job. A pro did the soda blast ($1350), removing all of the bottom paint and revealing an absolute moonscape of degraded gelcoat. We used plastic scrapers and popsicle sticks to put on what felt like innumeral batches of premixed epoxy fairing compound (Watertite and System 3, both easy to use). Using this fairing compound instead of West System + DIY additives is absolutely critical, because you cannot get a good hardness match between the West System and the surrounding gelcoat, and as you sand you will end up with random divots and proud spots. This is why you've got to get the bottom paint off too - it's far softer than gelcoat or fairing compound. After sanding the fairing, we coated the bottom with Interprotect HS (high solids) epoxy primer, which looks like liquid metal. This, appallingly, highlighted tons of remaining irregularities, which were again sanded, faired, and recoated. We did this four or five times, each time getting the bottom looking exponentially smoother, and eventually switched over to coats of Interprotect 2000E. The first coat of bottom paint was put on over still-tacky Interprotect.

This was quite a lot of effort but the pro who did my soda blast did the same project on another boat in the yard at significant cost, and I know we did far better work. Total cost was about $2k including the $1350 soda blast. The other costs were just sandpaper, masks, fairing compound, the epoxy primer and Interprotect, and bottom paint.

 

[PANorth]

This is really helpful. I will dissect your advice and make sure that I heed it all. Except that I think I'm past the point of needing a soda blast job.
I've been trying to figure out if the red is bottom paint. I don't think it is. If you look at the sides of the divots you can see red, white, then the same color red. So I think this is a layer that was put down during layup. It doesn't act like bottom paint either. It is very smooth and consistent across the entire bottom, there is no flaking, unlike the layers on top of it. So maybe a little more cleanup of the darker stuff, which I think is a very old layer of bottom paint.

 

[tenders]

I see, that red stuff seems to make a sandwich with gelcoat in between. And I guess the darker splotches of red are residual bottom paint. If you’re confident you can get all that bottom paint off, perhaps the soda blasting is unnecessary. But I’d want somebody’s knowledgeable opinion on the red layer’s stability and fitness for epoxy primer. It obviously wasn’t an effective moisture barrier.

 

[Loren Beach]

I recall that red is the color of old "Bondo" filler, from back in the 80's and earlier. Lots of yards used it for cheap fairing material, even tho it absorbs water over time and cracks and chips. Really not recommended for underwater use, but really cheep. (sigh...)
I hope that's not what you are finding now.

 

[PANorth]

Today the whole family, including the son-in-law, will do a marathon grinding effort to get all the blisters opened. Maybe we'll get through it all. Then we will leave it to dry into the summer. After that we will move inside to replace the soft wood around the portlights. Then...

As Mr. Rat in Wind In The Willows said "“there is nothing – absolutely nothing – half so much worth doing as simply messing about in boats.” Though I am sure he meant being on the water, I think it applies on the hard too. But we'll get there.

 

[frick]

I have help friends fix hull blisters.
Little ones we cleaned out and filled with two part vinal puddy. Big one ground out filled with glass and resin. Use fairing compound to smooth it out. Remember it's easy to sand fairing not so easy to Dane glass.

 

[frick]

Sand glass not dane