Hull blister restoration with Bondo Fiberglass Jelly? Big Mistake?

[lakeboater008]

Hello, I recently have taken up restoring a old sailboat (CM 32, a hull over 50 years old) with the intention of sailing her on a inland freshwater lake. I apoligize in advance for any critical mistakes, as I live in the middle of Texas (not the biggest sailing community) and I am learning as I go. (Young and making mistakes)

As she had numerous blisters on her hull, (small in size, maybe the size of my pinky), I decided to grind out the blisters to clean fiberglass, pressure wash them and fill them. In searching for what to fill with, I came upon the Bondo Fiberglass Resin Jelly. I know regular Bondo is not waterproof due to the gypsum absorbing water but the fiberglass jelly uses a polyester polymer that has milled glass fiber and is rated for boat use and also stated it is waterproof. I know I should have just used West systems epoxy but it was all out locally and I did not have enough time to get it in on the weekend my friend was able to help me. (I know I know)

After the fiberglass jelly cured, we left overnight to make sure it was solid (cure time is only 20 minutes for reference), sanded over any big bulges with 80 grit, pressure washed any residue off, let the hull dry again, then applied two layers of pettit protect 4700, a barrier coat, and let it dry. After the barrier coat was done, I added 2 coats of Trinidad HD hard bottom paint.

The pictures below highlight my process. (identifying blisters, grinding out to fiberglass, filled bondo fiberglass resin, pic 2, and finished project after bottom paint pic 3)

I am now worried that using the Bondo fiberglass jelly instead of waiting for the west systems was a mistake. She is just going to sit in a lake, freshwater, and I was planning to keep her there for 3 years at least before hauling out due to the limited infastructure in the lake (no crane but I do have a trailer). (Hence the pettit protect and the Trinidad.)

Any feedback would be greatly appreciated. Would the Bondo fiberglass Resin hold up on the hull if it is sealed with pettit protect and Trinidad hd? Am I causing any potential to damage the hull? There are no hull cracks or structural damage. All blisters were just ground to fresh fiberglass. I am not looking to go fast with a smooth finish, I just want the boat out on the water to enjoy. Or am I making a critical mistake (please go easy on me if so, still learning.) I am very nervous since if I am in need of a redo, this will most likely delay my project by many months.

Thank you all in advance!

 

[lakeboater008]

Any feedback would be greatly appreciated by this rookie.

 

[matt167]

Your boat is made with polyester resin. Epoxy wouldn't be the right thing to use anyway.

Bondo jelly still has talc in it.. I used it for filletting the inside on a small boat I built but screwed up on, finishing it in a way to just get a little use out of it.. Not saying you should redo it, but it might need redone sooner than you expect.

 

[Scott Danforth]

first, that hull was no where clean enough when you started. you still had growth and goo on the exterior of the gel

second, bondo anything should not be used. for exterior of the hull, poly is correct, however bondo is bottom of the barrel garbage resin, and the bondo fillers use talc

there are fiberglass places everywhere. you should have mixed up your own filler using poly resin, cabosil, glass spheres and chopped glass.

blisters are from water getting under the gel coat

you just ground holes in the gel coat and patched with talc which absorbs water and you hit it with a pressure washer vs wiping with acetone.

as Matt stated, it may last a while, however the blisters will be back

 

[Chris1956]

OK, you applied an epoxy barrier coat. That is designed for hulls that tend to blister, so it should protect your hull.

I expect your repair to last quite a while, maybe as long as you need it to last.

However, next time use some marine polyester putty for your repair, and be sure to wipe the area with acetone, before applying the putty, and again after final sanding.

 

[lakeboater008]

Thanks everyone for the feedback so far. As far as acetone goes, this boat has been dry for over a year. I read that acetone was supposed to be applied for any deep blisters that still had the acidic liquid in it. I did apply acetone on the blistered spots on the very bottom of the boat. Only one blister had a little bit of liquid left when we punctured it. But I will make sure to use acetone next time for the whole thing.

On hindsight, I should have also made sure the hull was cleaned more. We sanded/used about 4 layers of an eco paint stripper to get the old bottom paint off, after all that we sanded more and also hit with a pressure washer with a narrow edge 2-3 times making sure to let the hull dry. Rookie mistake to think that the remaining was just discoloration. Thanks for that feedback. Next time I will make sure to be even more thorough!



With the consensus, would this be something you guys think I should just strip off the new bottom paint and pettit protect epoxy and the bondo fiberglass jelly and start over? It seems like you guys think it should last at least as long as I am looking for, at which time I can redo the hull properly again.... Itching to go sailing....

I also have a whole other gallon of trinidad HD. It already has two coats. Would layering more coats of hard bottom paint over the hull help seal it in?

 

[lakeboater008]

Thanks everyone for the feedback so far. As far as acetone goes, this boat has been dry for over a year. I read that acetone was supposed to be applied for any deep blisters that still had the acidic liquid in it. I did apply acetone on the blistered spots on the very bottom of the boat. Only one blister had a little bit of liquid left when we punctured it. But I will make sure to use acetone next time for the whole thing.

On hindsight, I should have also made sure the hull was cleaned more. We sanded/used about 4 layers of an eco paint stripper to get the old bottom paint off, after all that we sanded more and also hit with a pressure washer with a narrow edge 2-3 times making sure to let the hull dry. Rookie mistake to think that the remaining was just discoloration. Thanks for that feedback. Next time I will make sure to be even more thorough!



With the consensus, would this be something you guys think I should just strip off the new bottom paint and pettit protect epoxy and the bondo fiberglass jelly and start over? It seems like you guys think it should last at least as long as I am looking for, at which time I can redo the hull properly again.... Itching to go sailing....

I also have a whole other gallon of trinidad HD. It already has two coats. Would layering more coats of hard bottom paint over the hull help seal it in?

 

[Scott Danforth]

I would run it as is, then when you look at the hull again in a year or two to re-do the bottom paint, address it then.

 

[lakeboater008]

Just for fun, I decided to reach out to 3M and ask to speak with a bondo representative. I know that they must stand by their product so I am not taking them at face value, but was interesting to see what they said.....

 

[lakeboater008]

For anyone interested, since I did see lots of questions on Bondo when I was going through the forum, I did reach out to 3M over the phone as well, and pestered them enough till they let me speak with an application engineer for Bondo.

I raised my concerns with him with the Talc and using their "waterproof" product in a marine setting.

The application engineer explained to me that the fiberglass resin jelly does not contain a high amount of talc (not sure if this is true since it is listed as the second ingredient on the tub), but that even before you use the hardener cream, and the jelly sets, the glass and the talc mix with the resin to create that jelly like paste. As the resin is already saturating the talc, it is already waterproof "as is", and even more strong when the hardener is applied and it sets.

He did seem to know his way around fiberglass as he understood the reason for blisters and fiberglass, etc but he did say that it would hold up on the hull for the usage I applied it for. He confirmed multiple times that the jelly was waterproof when cured. I was pretty surprised that they would back the marine application since typically companies will try to be ambiguous or stay away from grey areas so they cannot take any blame, etc if used now how it was intended for.

I know that Bondo Fiberglass resin jelly is still not what I would use next time I am working on a hull, ill go straight to west systems, but maybe its not as dire as everyone has always said for all bondo products to be.