Marine - Bondo

[Spence]

Has anyone used regular car body filler on the topsides of their boats? I'm re-bedding all my stanchions and fixing the crazing while I'm at it. It looks like nothing was done since it was made in 1980.
From inside the cabin, I'm thinking of filling in the convex mounds under the stantion posts, then redrilling. With wide washers under the nuts, the torque applied to the stantions would in this arrangement be better distributed to the full mound area instead of the screw area. After filling with filler, I'd flatten the bottom of it, and apply a couple 4" circle layers of glass for extra strength.
Doing a google of "bondo & Marine" I get the home page with splash page and a boat and "Marine" mentioned, then I go to fillers. When I do a product description on Bondo, no mention of use on boats. Looks like a come-on and deceiving.
Also, has anyone used auto glazing compound for pinholes on topsides before painting?
These products are cheap and don't add a mechanical necessity to the boat,so they should be safe.
Thanks

 

[Don S/V ILLusion]

Thickened epoxy wouldbe stronger, specially used with glass layers when you flare out the area. Bondo should never be used on a boat.

 

[rardiH36]

Several years ago upon FedEx receiving a replacement strut that was supposed to be identical, it was ... except that the base had a slightly different angle than needed to match the prop shaft vs hull "slope". Therefore wouldn't mate correctly with the hull. The yard's recommended solution: Use marine Bondo to create a new bed. The day after the installation, I torqued the bolts quite hard. The bed was rock solid. Advantages of the marine bondo for my project: It set up in just a few minutes. Then stayed pliable in a hard-gel like state for a while. So a razor knife can be used to cut away the squeeze out and then sculpt close to the desired end shape. Saves a lot of fairing sanding later. Thickened epoxy can behave the same, but depending on the hardener, can take quite sometime before it begins to set.

I can't comment on whether standard Bondo and marine Bondo are interchangeable. The thought did occur to me at the time of my project since auto store bondo can be had for a lot less $'s. But my application was for high stress underwater duty. So not worth the risk of the experiment.

Here is a link to the product that the yard recommended.

http://www.marine-products.com/3m-m...40e62f&gdfms=E4313394DE344DB98B19A7A9BDE3E832

 

[Bill Roosa]

Yes, use it all the time to "fix" gelcoat issues. If you have ever mixed gelcoat you will know the smell of it setting up is identical to bondo. Now if it only came in white! Bondo holds up well above the water. I can not testify to how it works submerged and subject to marine environs.

 

[Benny17441]

Thickened epoxy wouldbe stronger, specially used with glass layers when you flare out the area. Bondo should never be used on a boat.

I agree with the preference for the use of epoxy, but is there a specific reason why Bondo could not be used? Something about duct tape and Bondo being a good fix for almost everything.

 

[Don S/V ILLusion]

I agree with the preference for the use of epoxy, but is there a specific reason why Bondo could not be used? Something about duct tape and Bondo being a good fix for almost everything.

"Fixed" a lot of cars with that combination.
The problem with Bondo is that it's formulation will absorb moisture, particularly underwater and will do so on deck in places where it is often wet while sailing, raining, etc. Cars are better at shedding water and therefore less prone to issues.

 

[FastOlson]

One reason Bondo (r) is inexpensive to buy is that it's inexpensive to make. Instead of using a stronger and more costly filler like micro balloons or chopped glass (like some the thickeners used with epoxy), they use clay.
Clay absorbs moisture -- not good for anything underwater.
Also, it is formulated from the less-expensive poly resin base and not $ epoxy resin.

If they have changed the type of filler material, I stand corrected.
In the 80's I saw some boats with keels faired with Bondo and it was spalling off later. Kind of a mess. It's good to save some $, but this is probably not the place to go cheap.
Just another opinion... and, YMMV.
Loren

 

[Charlie Jones s/v Tehani]

"Also, has anyone used auto glazing compound for pinholes on topsides before painting?"

Yes sir. I used it all the time when building boats, and still do when the need arises. Comes in big tubes.. I use dark color under dark paint and white under light paint. Tube it in, use a credit card or squeegee to spread, then sand.

But understand- this is for pinholes and minor scratches. DON'T depend on it for large gouges- for those, Epoxy is the ticket

 

[Spence]

Thanks everyone.
The consensus here seems like it's not reliable in staying power and reliability. I just thought that in a car repair the salty air and flooding and water exposure and such during a car's life would exceed dampness and conditions inside the boat cabin. I'm basically looking for a hard mass that will stay intact in all conditions and crushing pressures that a stanchion base would receive.
I guess I'll need to go epoxy, but all prices get you when you try to buy the larger size cans, which I'll need.
I was actually toying with the idea of sealing off the area I want to fill under the stanchion with a flat piece of 14 gauge galv tin sheet and duct tape, and pouring epoxy in a screw hole on the outside.
But what is puzzling is that Bondo in their internet advertizing implies the reg bondo is also good for marine use.

FWIW: I discovered that one stachion base had the drain channels mounted uphill, allowing water to collect above the crazing, like a glass of water with a crack in the glass. Also the bedding compound was very flimsy and just around the screws.

 

[Spence]

Update:

Got the answer. "Bondo Glass" is the marine product for filling. Description says it's waterproof. The application for boats is to clean and remove waxes and dirt then roughen with 80 grit of a file and basically go to laminate level. I guess that means remove gel coat too.layer.
Says "Use on fiberglass truck,cabs,boats,etc."
I do know that by law a manufacturer can't say it's waterproof unless it is. Up here water restistant is not the same as waterproof. Strict laws on that. Don't know about the US laws though.

 

[Bill Roosa]

While bondo may not be water proof if you paint it with a good marine paint it will last at least 7 years. Never tired it as a base material and my spidy sense tells me that it would fail in that application

 

[Don S/V ILLusion]

Update:

Got the answer. "Bondo Glass" is the marine product for filling. Description says it's waterproof. The application for boats is to clean and remove waxes and dirt then roughen with 80 grit of a file and basically go to laminate level. I guess that means remove gel coat too.layer.
Says "Use on fiberglass truck,cabs,boats,etc."
I do know that by law a manufacturer can't say it's waterproof unless it is. Up here water restistant is not the same as waterproof. Strict laws on that. Don't know about the US laws though.

From whom did you get that answer?

 

[My Mistress]

My Mac has several patches on her undersides where PO's applied Bondo. On some patches' it's breaking away, on others, it is still holding. It seems to be a matter of how the surface was prepared and how the product was applied, vs it's contact with water.

Now, what I don't know is how long those patches have been in place (I bought my Mac last November) and how long the boat was in the water vs being a trailer queen.

What I can say is that polyester resin with filler has been used in the medical profession. I once observed and assisted a total knee replacement where the teflon wear plate was glued to the S/S appliance using a polyester resin product.
That having been said, epoxy will make for a stronger patch on our older boats. I use epoxy filler to fill the myriad of small holes in my boat.

 

[woodster]

thickened epoxy works very well ..automotive bondo is for autos not boats ...you can use some of the polyester fillers that have kitty hair in them...but i have to recommend above the water line only.....

 

[Spence]

From whom did you get that answer?

Right off the can.

 

[Guts1236]

PC 11 Is what I've been using I mix it with a scale 50-50 weight in grams
http://www.thepaintstore.com/PC_11_Epoxy_p/02011.htm

 

[spukistiles]

Of course an epoxy compond is the preferable option, but I don't see why it couldn't be used for mostly cosmetic repairs above the waterline. The auto body filler used for the same purpose on vehicles is not waterproof until it is primed and painted. It would be a mistake to rely on it for a repair where structural strength is needed. Why wouldn't the prefered repair material be the same as what your boat is made of?

 

[Dennis Kitchen]

Apples vs oranges:
Guys, "Bondo" is a brand, not a product. However, most of us know of it as an auto body filler, ie a product. Auto body filler has no place on a boat. Chopped strand fiber glass in a polyester resin will do fine, whether it is made by "Bondo" or anyone else, if it is properly installed and suited to the task. It is thick and heavy and will not penetrate cracks well, the crazing will need to be ground open enough to let the filler fair in. And there must still be structure it's applied to as it's strength is far less than laminates.
Dennis

 

[John23883]

I used "Bondo Glass" which is approved for boats to re-bond the the hull to deck joint at the transom of my Hunter 26. It required removing about 4 to 5 feet of the original bonding material that was no longer attached. Then I put gelcoat over the top. That was 10 years ago and it is working perfectly.

 

[Guts1236]

I have used PC 11 from the engine room too topside repairs the only thing is it will not accept gelcoat you have to use resin over the PC 11 before you use gelcoat. I have areas of my boat where there used to be vents on the Stern that I filled in with PC 11 and has been exposed for at least 3 years now and has not cracked weathered or deteriorated in any way. I can take pictures of these if you don't believe me. You can't really knock this product if you have never used it! So if you have never used it don't knock it. It is a great product for Marine use. Another thing that it is good for, if you want to bed something to your haul butter the each side and put it in place then run your finger around the outside to wipe up any extra and it leaves a nice fillet when you go to glass the object. Again I have done this many places on my boat and gel coded over it after glassing. This is a great product.

Regular auto body bondo will absorb water and is not preferred in Marine use.