Bondo-Glass To Fix Hull?

Has anyone ever used Bondo-Glass to fix a fiberglass Hobie hull? I've got a couple of small cracks in the bottom of the hull which allow the boat to take on a minor amount of water and was wondering if this Bondo product would work. It appears to be easier to work with than a fiberglass repair kit.

We're repairing seven Sabots that have been used for a junior sailing program. They've been abused for about four years and have lots of damage.

We've found that using a tube of one part Bondo works great for scratches. We are applying paint over the Bondo.

For damage where the hull has been dented or punctured we're using two-part Bondo or two-part Bondo with fiber in it.

We had a couple of places where the damage had been bad enough that we removed what foam was left and used Great Stuff insulating foam to fill the void. After it set we shaped it, filled in the small holes with Bondo and glassed over it. After sanding and paint it looked just like new.

IIRC all or most of the Bondo Products use polyester as a resine. Better adhesion and durability is probabely provided when you use somekind of epoxy material. In some cases you might be better up using a gel coat. Check the west systems website.

It is probably worth mentioning that polyester resin dissolves foam quite aggressively. So, if you are patching over foam, be sure to use epoxy.


Yes, epoxy is tougher and adheres better. But, it is a lot more expensive, has a much longer cure time, and is generally harder to use.

Personally, I use both. My general rules of thumb are;

- Structural damage = epoxy
- Foam exposed = epoxy
- Big cosmetic damage (gouges,dings) = vinyl ester (preference) or polyester
- Minor cosmetic damage (scratches, small gouges) = vinyl ester or polyester
- High wear spots in need of build-up (keel) = vinyl ester or epoxy with an appropriate filler and/or glass cloth


...Moral of the story - a crack letting in water would generally be classified as a structural issue and would benefit from the use of epoxy. You will need to thoroughly dry, and then clean out the crack. Then your best choice would be non-thickened epoxy followed by some thickened epoxy to fill the void. Without seeing the damage, I cannot advise whether glass cloth should be included in the repair.




Dave <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Thanks for the advice. We tried the Bondo and it didn't work. We're now going to go back and try a traditional fiberglass repair. So much for the easy way! <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

I had typical beach dragging type damage to my boat from years of beach trips before Cat-Trax. I used a product recomended to me by car mechanic he had used on a corvette. It was a fiberglass resin GEL. The thicker product helped to build up the edge and repair the hull profile. It wasn't pretty, but serve the purpose until I sold the boat. Good prep makes the repair.
I sanded the repair area with a fairly couase grit automotive type sandpaper, to make a good maiing surface and get is clean. I layed on a couple of layers of cloth more out of precaution than anything and then rebuilt the hull shape using the thicker gel. It took tons of sanding and I ended up using an "Air File" (pnuematic inline sander) to work down the high areas. Agin this was not a pretty or professional job, but I was back sailing in a week with lots less water in the hulls.

I am currently repairing my stingray with West System and have found it extremely easy to use. Spend the extra on the instruction book and you will do a fantastic job, I have watched the experts do it roughly and it looked rough not to mention all the beer bottles etc stuck everywhere around the workshop. It sands easily for a pleasing tough finish.
regards

Using Formula 27 for the cosmetic repairs (thanks Matt B for that tip), it is poly based and very easy to shape and sand.

Now that the weather is warm enough for repairs (and warm enough to sail too <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />) I've experienced a very, very, short window of working time with this product. I've reduced the hardener significantly and see not much difference in set up time (and when it starts to go hard it's gone in a flash) and I'm wasting a lot of product.

Has any one tried mixing in a plastic cup and setting that in ice? Looking for, or will try any suggestions. I has to be better than what I'm doing.

I had a similar experience with West System epoxy. I had mixed a batch of 200 grams: after several minutes, the mixture began to smoke, became very hot, and then turned solid within a few seconds.

Nothing to say against West System! I reread the manual and found that there's "weight limit": I wasn't supposed to mix batches bigger than 100 grams.

Possibly your batch size caused you having the short window of working time?

H77

No, I least I don't think so. My scientific measurement is a pool about 3 to 4" diameter. Don't know how many grams.

One way to help out with this problem is using a different hardener for higher temp environments. Also, instead of mixing in a cup or other small container, mix on a board and spread out the epoxy. This will allow the heat of the chemical reaction to disperse more. When the epoxy cures, it creates heat. Heat adds more energy to the mixture causing it to catalyze faster. It's a snowball effect.

If you are going to chill the mixture, chill the parts before you mix them. I keep a resin and hardener in my fridge for summer repairs.

For more detailed information on epoxy check out these guys.

CLC Boats

They really know thier stuff. Though most of thier problems are dealing with the epoxy being too cold during the winter.

This sounds like a lot less than what I was messing with. 200 grams of mixed epoxy was about fist size. Can't be the batch size, then.

H77

Both polyester (Formula 27) and epoxy resins cure via an exothermic reation (they give off heat). The shape of the curing resin can affect the rate of cure. Spread in a thin film (lots of surface area), the heat dissipates and doesn't affect the rate that much. Contained in a cup (small surface area), the heat builds up and accelerates the reaction.

Formula 27 does go off quickly, but you can adjust the rate of cure by using less catylst (use 5 drops/oz vs. 10). Keep it out of the sun and spread thin on a plastic mixing palette. Once it stops spreading smoothly, toss it. It's done.

You cannot adjust the cure rate of epoxy by adjusting the resin/hardener ratio. You can use different hardners (205 / 206 for WEST System), but changing the ratio will give you a sticky mess that will never cure completely.

I've had West System epoxy get hot and cure quickly also when mixed in a cup. Bill Mattson in California had extreme problems with epoxy heating up when repairing his Hobie. Luckily, he has photos to show the carnage.
http://www.catsail.com/crap/epoxy.html

I have seen the cup melt and gear going everywhere and was wary about using it myself, but I purchased the west system manual for $11 read it then did it exactly as per the book which included buying the pump dispensers and never got any excess heat for a very pleasing job. I mixed it in a plastic drink cup for each batch stirring with a piece of broken steel tape measure and recoated the entire decks using a small foam roller.