Bondo putty filler for underwater repair

[tuntini31]

Hi I was wondering how bondo filler putty would hold up underwater. Im doing a repair on the keel and am at the fairing stage and need to use bondo for a car project anyway. I know its a polyester filler, but I used polyester resin for the glassing so they should bond together right?

I wouldn't need to paint afterward correct?

I also have this epoxy pool putty made by atlas at my house. The kind where you cut off equal parts resin and hardener and mix them together. Its moldable before it dries, then its sandable. It cures underwater. Looks this this




Otherwise I'd have to order fairing compound online and wait for it to ship and deliver such as quikfair. I only need a small amount really so I didnt want to have to buy really expensive stuff.

I also wish they sold gelcoat in smaller quantities other than the small repair tubes. I dont need that much of it, and I could use it over the bondo wich i beleive would be fine

[GreenLake]

There are marine fillers, made by 3M, that are vinylester and work under water. The High Strength Marine Filler is the one to use for deeper or wider gouges - it's amazingly tough, but still sandable (just not the thing to use for fine leveling of large surfaces).

For that, my go-to product is QuickFair by System Three. It's epoxy based, but a real pleasure to work with. Just don't eat any by mistake, it has the color and consistency (but not the temperature) of chocolate flavored soft ice cream.

If you plan on painting, there's no need to stick with polyester for any reason, but, if a spot calls for the 3M high strength product, also no reason not to use it if it works.

(Some car putties are not safe for under the waterline if you wet sail your boat and the manufacturer may not bother to tell you this. All marine products will tell you in the product description whether or not they will work).

[nota]

micro balloons
little tiny balls you mix with resin poly or epox
light and eazy to sand
that is what the pro's use

always paint over poly or any filler

the epox is much harder to sand smooth
stronger and a better bond
but cost more and harder to smooth

[GreenLake]

You can mix your own, or get it pre-mixed. I'm happy to accept the convenience of the latter, and have made very good experience with QuickFair(systemthree.com).

It's super easy to work and sands well (it's epoxy based, so it can be used below the waterline, but that doesn't compromise the sandability). Like all fairing compounds, this is not something you want to use for structural purposes.