Epoxy resin over fiberglass bondo repair?

[SteveO]

I just completed a repair on the bottom edge of a 15' fiberglass boat that the previous owner had botched up pretty badly. The previous repair was entirely on the outside. I went inside and ground down a larger area, wiped it down good and and laid down four layers of heavy fiberglass cloth with epoxy resin. It's dry now and and looks and feels very strong. The previous outside repair was a "fiberglass patch" of sorts. It had high and low spots everywhere, really thin where the strength mattered most (it had actually cracked and was leaking water into the boat on the first trip to the lake). they had also globbed up a bunch of repair resin on the bottom really thick. I removed the patch with a grinder down to the gelcoat. I then took fiberglass stranded bondo and leveled the entire area out. It looks great now but here is my question.

Would it be a good idea to put a layer or two of epoxy resin over the repaired area on the outside to add strength/waterproof it? I have heard polyester resins soak up water and this repair is on the joint between the vertical and horizonal surfaces. I was thinking of two layers of brushed on epoxy (no cloth) then sand everything down prior to paint.
Does this sound feasable? Will the epoxy stick ok to the bondo? I'm experienced in aircraft and car repair but have never ventured into the marine world before now.
Thanks for your help,
SteveO

 

[Solittle]

Re: Epoxy resin over fiberglass bondo repair?

Most guys here will advise that bondo is fine for cars but should be kept away from boats. Do a Search - -

 

[bassboy1]

Re: Epoxy resin over fiberglass bondo repair?

Bondo is not good in boats. Go to the boating forum and check out my question entitled "What is bondo." At this point it should still be on the first page.

 

[andy6374]

Re: Epoxy resin over fiberglass bondo repair?

I am having a hard time picturing what you mean.

From what I understand:
You repaired the damaged glass from the inside (the best way 8) ). And now you've grinded all the crap that the previous owner gobbled on from the outside. You leveled it out with bondo....

Grind off the bondo, get some polyester glazing putty and use that to fill in some low spots. If the low spots are >1/8" (1/16" would be better) you can't use the putty yet but rather you should fill with some glass and then grind fair. If the area being filled is to "low" the putty will crack when the hull flexes, so make sure you adhere to the 1/16" to 1/8" rule.

The name of the game is glass, grind, glass, grind until your surface is ~ fair, then apply the polyester glazing putty and sand fair.

Remember you can apply the putty over roughed up gelcoat but for glassing you should need to grind off the gelcoat first. Then just apply some gelcoat over the repair.

Also, applying a few additional coats of epoxy will add little to no strength to the repair but it will increase the waterproofness of the repair.

 

[imported_TheMan]

Re: Epoxy resin over fiberglass bondo repair?

along with solittle and bassboy,
bondo isn't designed for a flexing hull. Need elasticity, which is whyh you should go with the polyester like andy said.

 

[SteveO]

Re: Epoxy resin over fiberglass bondo repair?

Thanks for the info guys. The bondo I put on the boat is a polyester gel resin with fiberglass strands. It's around 1/8" in the deepest areas. I guess I should grind it back off and start over. Where can I get poylester putty (a brand name maybe)? I've never seen it before? I thought polyester filler is what bondo is made of?

I was looking over the bottom of the boat late last night and it's pretty gouged/scatched up. Especially down the
center. It has some deep gouges/chunks nearly up to the wood reinforcement in an area around 4" long. There is no access from the back side since it's below the wood keel piece. What is the best way to repair that area? I'm guesssing several layers of epoxy and glass to bring it to the level of the rest of the keel? Then feather the area out?

Refinshing the exterior is a subject that seems to have lots of different opinions across the internet (Google search). Some say Gelcoat (seems like lots and lots of work to get the finish right), some two part paints (seems like you need a spray booth/special spray equipment/respirators to get the job right), some one part urethane paint (like Brightsides-seems the easiest with decent results) and I've read where some people use exterior latex paint(above the water line of course).

This boat is going to be used maybe once a week on a freshwater lake and only on the water maybe 8 hours at a time. The rest of the time it'll be kept in a garage. I'm not looking for it to look perfect, just a a structurally sound, decent looking boat to enjoy.

I want to tthank each of you for taking the time to respond. I really like learning from others ahead of time than from my own mistakes.
SteveO

 

[andy6374]

Re: Epoxy resin over fiberglass bondo repair?

Evercoat makes Polyester glazing putty. It's not structural at all so it should only be used when trying to fair out an area. Resins mixed with milled fibers and cabosil make sound putties, but are very hard to sand.

If you just have scratches in the gelcoat you can mix up a batch of gelcoat and cabosil to a ketchup or peanut butter consistency and spread over the scratch. Course sand it fair, then go through 1000grit followed by compounding and polishing.


Your idea about grinding the glass back on the keel and then laying overlapping peices of glass and feathering out seems good. Glass mat is the weakest but absorbs the most resin and hence is a good waterproof barrier. Biaxeles and woven roven are the strongest glasses. I would lay at least one layer of 1708 or 1808 to ensure a strong repair (then of course followed by mat until the surface is ~ fair).

 

[seven up]

Re: Epoxy resin over fiberglass bondo repair?

You can make an epoxy putty too...with the fiberglass strands. Very Strong stuff. Many additives are available to add to your epoxy.

The fact that there are other spots that need attention...it may be a good time to stick to the same products and avoid lots of half used products for this or that.

Epoxies cure to a stiffer product as the ratio to one goes up. 1:1 more flexible than 4:1 after full cure.

You may have noted from past experience that polyesters will still be curing years from now.


Enjoy !

 

[Chris1956]

Re: Epoxy resin over fiberglass bondo repair?

SteveO, Bondo is made of talc mixed with Polyester resin. The talc will absorb water, which is why it should not be used on boats. It sounds like the stuff you used was fiberglass strands and poly resin. If so, it is acceptable to use on boats. You can brush a coat of poly or epoxy over it, to fill in any voids. Both poly and epoxy are waterproof enough for your needs. Remember, gel coat is simply thickened polyester resin, and forms the surface of many boats.

 

[Paul Moir]

Re: Epoxy resin over fiberglass bondo repair?

I don't know a whole lot about gelcoat, but it used to be that you could not gelcoat over an epoxied area. Just poly based materials. I really don't know for sure if this is still true as some epoxy makers claim it isn't.

What I'm getting at is you should plan your finish before you start the patch.

A good quality single part boat paint makes a fine, easily repaired finish. Two part urethanes are tougher, but sometimes spraying isn't an option. Good boat paint lays down nicely with the roll & tip method of painting. Gelcoat saves you from painting the whole boat if you've only got a few repair spots. It's not user friendly like paint though so it's a lot more work to get it to come out nice.

 

[flashback]

Re: Epoxy resin over fiberglass bondo repair?

I look at it like this, and I may get blasted for it, but the polyester works fine above the waterline.. never use it below... I always use a 2 part epoxy below the waterline..and fair it out as best I can.. then wash the blush off of it and apply the gelcoat.. after sanding.. Above the waterline I like the poly fillers.....they sand down at the same rate as the gelcoat so they fair better...think about it.. if you take a sheet of lead and fill the hole in it with a diamond you will sand and sand on the diamond and you might cut it down some but the surrounding lead will be ground down much faster... very hard to fair.. on the other hand the epoxy is much more waterproof than anything else and should always be used below the waterline..IMHO...d

 

[SteveO]

Re: Epoxy resin over fiberglass bondo repair?

Excellent advice...I will head to West Marine (here in San Antonio) tomorrow for some supples.

I started sanding the upper/interior section of the boat yesterday. All the interior is removed (seats, cushions, side bolsters, carpet, top, along with all the cleats and hardware). Not going to remove the motor since I have no way to get it off and store it. I also can't figure out how to get the windshield off. I can see some long screws coming down through the frame from under the dash but no access to them from the top? I'm removing the rub rail and hopefully can find a better replacement for it some where. Mine has several "crunched" areas and is looking pretty sad.

This quick "spruce up" is turning into a major renovation. I'm still on a budget of $1000 for parts and supplies. Of course my labor is free. Thanks again for everyone's support!
SteveO

 

[andy6374]

Re: Epoxy resin over fiberglass bondo repair?

www.fgci.com
www.mertons.com
http://www.fiberglasssupply.com/
www.uscomposites.com
www.compositesone.com

Don't pay out the #$@ for fiberglass materials at West Marine.

 

[Chinewalker]

Re: Epoxy resin over fiberglass bondo repair?

My local hardware store beats West Marine by $8 a quart for the West System #206 hardener and about $12.00 a gallon for the #105 resin. I doubt most hardware stores carry it (mine is Ace affiliated), but if you live near a large body of water it's worth it to shop around...
- Scott

 

[jtexas]

Re: Epoxy resin over fiberglass bondo repair?

I was looking over the bottom of the boat late last night and it's pretty gouged/scatched up. Especially down the
center. It has some deep gouges/chunks nearly up to the wood reinforcement in an area around 4" long. There is no access from the back side since it's below the wood keel piece. What is the best way to repair that area?

While you're at west marine, get some Marine-Tex for those gouges & scratches.

 

[turtlem1969]

Re: Epoxy resin over fiberglass bondo repair?

OK, time for me to post my two cents worth, I have been in the boat repair and building field for several years and I just cant hold back any more. You all are giving good advice, and each is entitled to his/her own opinion. First thing I have to say is that the majority of your production boats are made using a polyester resin due to the cost, so it is perfectly fine to use below the water line. Bondo is not to be used any where that water might come in contact with it. It can be used very sparingly above the water line, in a very thin layer. The best way to fill in cracks or deep gouges is to grind down to the glass, past any visible cracking, clean the area with a mild detergent and water then wipe down with a clean rag with acetone or denatured alcohol, then cut paces of mat to fill in the gouge and apply one layer at a time sanding each layer until you have almost built up to the same level as the original glass and finish with a layer of 1708. Then sand smooth with 60-80 grit paper and apply gel-coat. Another point I have is why waste your time with a two part polyurethane instead of gel-coat? Its just as hard to apply as the gel-coat, doing just as many steps in the prep and have just about the same working time. The boat came from the factory with gel-coat above and below the water line, so why change a good thing? The last thing I'm going to mention is don't waste your money going to West-Marine for your supplies, they cater to the people that have more money then sense and dont opperate their own boats. Sorry for such a long reply but just had to put in my two cents worth, good luck on your project and hope everything turns out well. Happy boating to all.

 

[ondarvr]

Re: Epoxy resin over fiberglass bondo repair?

Good post turtlem.

 

[Labman]

Re: Epoxy resin over fiberglass bondo repair?

2 year old topic, but the info seems valid.
That's why I love this site, lot's to learn, lot's to read!