Grinded tons of blisters. Now what?

[Souzag818]

Originally Posted by Dark Horse

Do not do this. You must first repair with vinylester or the repairs will fall out.



So this is a area where I unfortunately have a ton of experience. We got a bad survey on a boat and subsequently found it had very bad osmosis. We ended up peeling the hull, washing it down for 30 days with a hot water pressure washer to dry it out and then putting 6 layers of fiberglass mat on it using vinylester resin. I was explicitly told by a yard in the Chesapeake that does this work not to use epoxy. Instead fix the blisters with vinylester or they will just come back.



In order to know how to fix it you need to understand the problem.

• Polyester resin is made by putting together a bunch of different chemicals and collecting the resulting solids. Glycol and phthalic acid are 2 of those chemicals.
• Polyester resin is not stable in water. If you take a solid block of polyester and put it in water it will over time start to dissolve.
• Water is able to migrate through the gel coat and into the polyester and when it does that it breaks down the polyester into its constituent components, glycol and acid. The process is called hydrolization. I am not sure why it does not dissolve the gel coat which is only thickened polyester.
• This process results in the hull becoming acidic.
• When you open a big blister it stinks , thats the acid, and it has green in it and it is sweet to the taste. This is the glycol.
• Because the boat is sitting in water there is pressure on the hull and these compounds ( glycol and acid) migrate into the threads of the fiber glass and it is in the thread under the pressure of the water that was supporting the boat. On a badly hydrolized hull with cracks in the gel coat or missing gelcoat the glycol and acid oozes out of the hull. Glycol and acid are both water soluble and so can be washed off with warm water.

Now you know what happened.

A Note On High Moisture Readings

• We measure the boat with a moisture meter and if it measures high we say the hull is wet but it is not wet with water. It is wet with glycol.
• If you take a hull that measures high and core that hull and then split the layers you will find no moisture.
• Take a badly hydrolized hull and expose the fiberglass under the gel coat and on warm days the exposed glass will get coca cola like brown stains on it and they correspond to places the glass fiber end is exposed. The hull is in essence depressurizing. This can be washed out and over the course of 30 days washing every day for 1 hour with 210 degree hot water at 4000 psi we brought the moisture readings down from 25 to 5..

How to fix.

• Epoxy has no resistance to phthalic acid so you don't want to us it to fix the holes. Depending of course on how bad it was the hull will continue to ooze glycol and acid at the damaged places. So you don't want to use epoxy to fix those holes. The acid will keep oozing out and damage the epoxy bond to the hull and the patch will fall out.
  • The yard that told me how to fix it said they peeled a hull and then used epoxy to put new fiberglass bottom on. 18 months latter sitting at the dock the entire bottom fell off the boat like it has been unzipped. ( his words)
• If you need to put glass back on, then use fiberglass mat and vinylester resin. This all depends on how much you have taken out of the hull. If you have ground half way through you need to put some mat glass back in.
• If you only need to fill the holes for fairing use 3M Premium Filler which is vinylester based. Cures and is sand
• Once all the damage is repaired you can use Interlux or Petite epoxy barrier coat.

Since I fixed my boat 6 years ago now, we have not had a single break through and the hull measures dry. A year after we did our hull there was another boat in the yard with the same problem. The blisters were ground and filled with epoxy. 2 years later that boat was hauled and found to be badly blistered. Again it was fixed with epoxy and bottom coated and launched and 2 years later was again found to be badly blistered.



Finally... you can put epoxy on vinylester or polyester but you can not put the esters on epoxy. It will not bond and will fall off.

Mat/chop strand doesn't really add any strength to the hull. Just provides a barrier. BTW, My first sailboat had a serious blister problem. Some were dinner plate size. After grinding them out, rinsing and letting the hull dry, I repaired the blisters with bi-axial cloth and epoxy. That was 28 years ago, and I haven't had any peeling/unzipping at all. I think the problem lay else were if they had layers falling off.

[Fore and Aft]

Last week I surveyed a yacht that I had last surveyed in 2014. Back then the yacht had around 200 blisters ground out, glassed with epoxy and double bias cloth, then filled with microballoons. The owner had never glassed/faired before and was in a rush so the whole job took less than two weeks. 5 years later when I surveyed her again there was maybe 7 or 8 small blisters. Not bad I thought for a rush job.
Cheers

[Suijin]

I agree that 3m premium filler or West system with microballons is adequate.

As Sean said, no boat ever sank from blisters. They are not structurally significant. So, an easy sanding filler is preferable IF you put 6-8 coats of barrier coat on.

The key will be surface prep. I’ve seen hockey pucks of epoxy filler pop off a hull because of bad prep. I’ve seen sheets of marine filler peel off a hull as well.

Clean it well, fill and fair. Put your first coat of barrier on and every flaw you missed will jump out at you. Fill and fair again. Let it cure then sand the barrier well getting ALL the sheen off it and giving it proper tooth. Hot coat on all the remaining coats of barrier and your first coat of antifouling.

[jakkum]

you really have to neutralize the acid ad afterwards dry the hull. the acid is hugroscopic so it will keep it wet.
To neutralize we use a mix of old fashioned soft soap and wallpaperglue. paint it wide over the affected areas and keep it a bit moist. you can give the boat a skirt pn the eaterline so rain will not wash it off.
There are eays to read the acid content with some chemical paper
lakmoes. do not know the english name.
Can take some months.
Pressire wash, not too high . I would not use epoxy because it encloses bad stuff that is always left.
Use a good polyester. my ifea is that the osmoses is cused bu the gelcoat andepixy does the dame or better
I have a big cat here and it never had a gelcoat
more tha 15 years in the eater and no blisters ever. was a diy job

[Montanan]

Wow, that is a lot of blisters, makes me doubt the quality of the original wetting out of the chopped strand mat.

Reference for expert guidance.

https://www.yachtsurvey.com/BlisterRepairFail.htm

Snipet at the end:

The bottom line to blister repairs is that there are far too many people in the business who don't know what they're doing. They apparently are not aware that for the repair to be successful, they must eliminate the defects that caused the blisters in the first place. Yet it is not possible to determine all of the factors that cause blistering, especially the cause of water getting into the laminate. The buzzword is "osmosis," as if permeability of coatings is the only means of water saturation. The reality is that we can identify a half-dozen ways that water can get into a laminate that have nothing to do with exterior coatings. So even if there were a totally effective, non-permeable coating, it would not solve the problem, for you can't prevent the absorption of water from the interior of the hull, or around through hull fittings and so on.

But the one method that offers the greatest possibility of a cure is to eliminate the voids within the outer laminations where blisters commonly form. And if that means stripping the chopped strand mat from the hull, then that is what has to be done. Otherwise, its just money down the drain.

Good luck.

[Tillsbury]

Have a watch of the appropriate episodes of Sail Life where he grinds, dries out, and refinishes his hull to what looks like a very good standard.

[gmakhs]

If the blister hole are not deep , fill with hardened polyester resin , there is no reason to spent money.
If they are deep do fiberglass repair with polyester resin .
Once you finish and fair you can add an epoxy barrier.
There are a lot of reason I don't recommend epoxy , and if we discuss it here will take forever but I will give you 3 :
Epoxy is only 15% stronger than. Polyester resin
Epoxy is stiffer than polyester so it can create hard spots on big repairs
Epoxy is super expensive .

[flyingfin]

After taking Fore&Afts advice and letting the hull dry out, clean the holes with MEK, then fill with 2part AwlGrip fairing compound. And dont waste your time sanding after filling, just practice getting it reasonably smooth. The fish dont care if your bottom looks like the hood of a new car.

[Montanan]

[QUOTE=flyingfin;2828075]After taking Fore&Afts advice and letting the hull dry out, clean the holes with MEK, then fill with 2part AwlGrip fairing compound. And dont waste your time sanding after filling, just practice getting it reasonably smooth. The fish dont care if your bottom looks like the hood of a new car.[/QUOTE]

Don't worry about appearances. Exactly, the osmosis typically occurs in the chopped glass mat that was applied over the gel coat. The chopped matting was applied to hide the appearance of the structural woven glass. But the chopped mat is difficult to wet out completely and each of the millions of ends become an entry point for water to wick the entire distance of the strand of glass fiber. If the mat appears to be white then it was not fully wetted during original production and will become a location that will infuse with water and blister. Removing all the chopped mat if it was not wetted properly is a solution but requires a lot of removal. Using a carbide planer works well.

[Spot]

I am seeing mention of all three resin types: polyester, vinylester, and epoxy.
I have heard it said gel coats will not stick to epoxies underneath as well as vinylester. My experience is mostly with epoxy, then poly, and so far none with vinylester which I understand to be styrenated epoxides.


Is this true? If poly gel coat is in the future then no straight epoxy underneath?


I am not a fan of the harsher chemicals: actetone, styrenes, MEK, and even TSP...but I also believe that doing something once right safe as possible is better big-picture than twice done over.

[bstreep]

I'm going to jump in here, and relate our experience. When we bought our boat, there were several hundred blisters. I was going to stop the sale because of them. Our surveyor, who has an underserved reputation for killing deals, told us to do this:


When you have your bottom done, have them grind out 1-200, fill them, and put a hard bottom on the boat. Repeat it each time you do the bottom. In a few years, your problem won't exist. He was EXACTLY right. 11 years later, we just did a bottom job - our 4th. ONE blister. Just one.



Interestingly, after our hurricane damage a year and a half ago, I talked to the surveyor just a few weeks ago (to set up an "after repairs" survey), and related the story to him. His comment? "Yeah, I was pretty sure that was the solution".



FWIW.

[mark Sobel]

First consider how you intend to use the boat and the term. If you intend to cross, sail over a number of years and keep the boat in the water expect more significant osmosis problems. The hull composition, thickness and overall condition are all important. Substantial cruising and custom built sailboats are less likely to show damage over the years. In Europe and Asia Hotvac extraction system are used to draw the byproducts of osmosis out of the hull.The process involves the use of large heated mats with vacuume pumps creating significant suction to adhere the mat to the hull and slowly draw out contamination. Gelplaning is a smart choice as the barrier works both ways reducing drying time. Considering that osmosis is a continual ongoing process today’s damage should be considered as a baseline to be tracked with a moisture
meter. Regardless of a sellers position, the brokers or inspectors assurances suggest you require a hull inspection with a Quality moisture meter before purchasing. Casually ask if they have a meter. If they do not have a meter consider carefully exactly what that means.

[Dougtiff]

A few year's ago, i was visiting a friend on the east coast, who was a surveyor, a call came in to survey a Taiwan built sail boat, she was hanging in the slings when we arrived, and the potential buyer was there,Now i do not exaggerate, but the osmosis was so extensive, the outer layer of glass was delaminated from the water line, all the way around, under the keel, you could push on the hull, and the outer layer would move, you could hear the water moving around, the potential buyer just got in his car and left, the boat went back in the drink, and back to the slip, afterwards, thinking about it, i reasoned that maybe it could have been a good deal, as the outer layer could have been cut off at the water line and the hull dried out. who knows.

[chowdan]

I agree with most - fix it right and be done with it(until next haul). Eventually you'll get to a point where none will exist.

Your already down to glass on them. It's not hard to build up the layers and then barrier coat the bottom. Do 7-8 layers of interlux and you'll be grateful you spent 1-2 days doing the repair.

[stargate]

I have used every different variety of filler for blisters. The best and easiest to use is Total Boat epoxy fairing compound. Comes two part , yellow and green, mixes blue, so easy. Great product and end result. You buy it at Jamestown Distributors. You will be happy you bought it.
I have used a heat gun as I filled to ensure the blister pockets are dry.

One thing I know about blisters, is you will never get them all unless you peel the fiberglass completely and reapply how ever many layers you removed.

In saying that, I have never seen a boat with blister damage that caused anything more than cosmetic problems.

Don't let any one take a disc grinder to your bottom. I have seen too much damage caused by guys digging holes in a bottom with an aggressive disc grinder and cutting through too many layers of the hull.
Fill the blisters, epoxy the bottom, enjoy your boat.
Good luck