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30 year old Bondo?

Nov 7, 2012
678
1978 Catalina 30 Wilbur-by-the-Sea
As I posted in an earlier thread I am removing and patching 2 transducers thru hulls.

As I was grinding away I came to realize that in the early 80s when they put the waste treatment system in they moved the 1.5" thru hull forward and filled the old hole with green glass impregnated bondo. Attached are 2 pictures previous to my removal and grinding the thru hulls. The dark blob is about 1/2 " of bondo lump now gray in color. The edges are pretty friable, I can peal it with my fingernail.


My concern is for the center, I did not probe it but I am concerned about it popping out in the future. Is this actually a good repair?

Heck, it has lasted 30 years but with the motor out it is a good time to fix it right.
 
Sep 25, 2008
5,542
Alden 50 Sarasota, Florida
Bonds is the worst thing anyone could use on a boat as it absorbs water, rots and serves as a source of moisture for the surrounding glass laminate. Remove every bit of it at your earliest opportunity and while cursing the idiot for using it.

Regardless of how long you theorize it has been there, it is the wrong fix to a potentially bad problem.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
bondo is a polyester filler... its made of polyester just like the resin used in laying up "fiberglass"... if the repair has lasted 30 years its probably been done right by someone who knows their stuff...
bondo has been being used on boats for a long time, and if you know the tricks to using it, as anyone who has worked with it very much does, it can be a perfectly safe to use below the waterline and to repair a hole...

so whether you grind it out and refill it your own way, or leave it as it is, which is someone elses way of doing it, is your decision in how much better you think you can make it, how much better you think it needs to be and how much work you want to put into it....
if its a nice clean job that has lasted 30 years, it will probably last another 30.... but if it looks like sloppy work, it should be redone on that count alone....
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
Bonds is the worst thing anyone could use on a boat as it absorbs water, rots and serves as a source of moisture for the surrounding glass laminate. Remove every bit of it at your earliest opportunity and while cursing the idiot for using it.
seriously, you must have been thinking of WOOD when you typed this:D
 
Sep 25, 2008
5,542
Alden 50 Sarasota, Florida
If there is any doubt, check out the discussion of "big bad bondo" on the wooden boat forum. Particularly the numerous examples of what goes wrong with some pretty vivid pictures.
Every reputable marine surveyor will agree but like some other myths such as the one about fuel tank condensation, they die hard.
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
If there is any doubt, check out the discussion of "big bad bondo" on the wooden boat forum. Particularly the numerous examples of what goes wrong with some pretty vivid pictures.
Every reputable marine surveyor will agree but like some other myths such as the one about fuel tank condensation, they die hard.
we arent talking about wooden boats here... but if we were I would agree with you. bondo against wood in a wet environment is a bad idea.

bondo, like regular polyester resin, and all other plastics, does absorb a small amount of water.... but when it is used properly and with reinforcment against more polyester, its as safe as polyester can be....

I dont mean to say you can just slap it on the hull like it were a car fender, what I DO mean to say is using it properly for the job that it is being used on..

do you think that all the modifications to the fiberglass structure of a boat comes out perfect and without blems?.. do you think they just roll some more glass and resin over it to fill in a bit of a low spot?... the answer is no... they use bondo or some other off brand of fairing compound to make it perfect and presentable...

like almost all other types of repair products, its not so much the product that is the problem, but its the user not knowing how to use it that causes problems and then starts bad rumors about an otherwise decent product....
 

Squidd

.
Sep 26, 2011
890
AMF Alcort Paceship PY26 Washburn Wi. Apostle Islands
They do make a "Marine" bondo... I don't know if it is a different formula than the "regular" bondo, but it has a picture of a boat on it and it costs more...
 
Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
They do make a "Marine" bondo... I don't know if it is a different formula than the "regular" bondo, but it has a picture of a boat on it and it costs more...
its a different color but not a different formulation. its all marketing, and of course it costs more,.. it says marine on it:D...
 
Sep 25, 2008
5,542
Alden 50 Sarasota, Florida
You can focus on the venue of the wood boat forum or you can focus on the substance of their experience with bondo. Bondo under water is bondo under water. Your choice Centerline.
 
Dec 11, 2008
1,338
catalina C27 stillwater
Don as a sailor who also does wood boat work I disagree. The problem with Bondo and wood is the same as any other synthetic "structure replacement" and wood: they are incompatible.

Wood boats have a different bending modulus, different "prooer" moisture, different everything. Bondo is bad In a wood boat JUST LIKE fiberglass and vinyl or epoxy resin is bad in a wood boat. It's not bad product, it's bad application, like substituting wheel grease for jelly on your PBJ sandwich. It just doesn't work.

To make the leap and say you can't use Bondo on a glass boat based on the experience of wood boat restorers is like telling your friend that chocolate is bad for you based on your dog getting sick from it. Again, great product, wrong application.

Wood boats are repaired with wood. Oh and glue. And Silicon Bronze fasteners, not stainless. Synthetic products trap moisture and cause rot. Synthetic products bend differently. Synthetic products come loose unexpectedly at bad times. They fail for either reason and often both at the same time. I know horror stories of synthetic bottoms applied to wood boats to "fix" the hull, only to peel away at high speed sinking the boat.

It's for these reasons that Bondo is bad in a wood boat. Not bad product, bad application. Same can be said for glass in a wood boat.

Don't make the leap suggesting that since Bondo is bad in wood that it must be bad in fiberglass. I don't buy that argument... I know better.
 
Oct 28, 2013
114
Catalina 30 1978 #980 Catalina 30 1978 #980 Mission beach, California
They do make a "Marine" bondo... I don't know if it is a different formula than the "regular" bondo, but it has a picture of a boat on it and it costs more...
I've been using PC-11 Epoxy-The mixing ratio is 50-50 and I use a gram scale when mixing. Like any epoxy you must mixing thoroughly.
 
Nov 7, 2012
678
1978 Catalina 30 Wilbur-by-the-Sea
Thanks for the input guys.

After much deliberation and as I am now pressed for time I have decided the bondo stays til the next haul out. I will just keep a nerf football close at hand in case the worst happens.

Look for a story titled "40 Year old sailboat sinks at Fort Jefferson" this July, you will know what happened. ;)