Did a Boston whaler 14' transom about 10 years ago with Seacast pour foam. Took awhile to dig out the wet plywood between the two skins but was very easy to pour. no issues beating it through LI sound chop.

 

The entire idea is a fail from the start. Wood is rotten, essentially is wet cardboard, possibly dried out after. Would you feel good about a transom made of that material and glue kinda sorta holding it together?

Really the fix is, put what was originally in there back to restore it.

 

The key is will it last. I would take it apart, re-core, re-glass.

 

I agree , it will be like an investment to repair it right , over the years I have tried shortcuts and it does not pay

 

Any move like that can make it considerably more difficult to do a proper repair down the line, if that matters....

 

Is it a propulsion transom like sterndrive or outboard? big difference in the load on it.
My Dad was a huge fan of git rot and other ways of fixing stuff with out really replacing it. My son got a Whaler years ago because the transom was rotten and the owner wanted out. Cut it out and made an exterior mold with plywood braces supporting Formica. It came out pretty well with plywood and foam in the layup and as far as I know it's still going.

 

You want to hog out the rotted wood then use a product like this.
Ceramic Transom Pour Putty

 

Or this one
CarbonBond Transom Compound - Carbon-Core Corporation

 

Or this one
CarbonBond Transom Compound - Carbon-Core Corporation

I never knew there was such a product strictly for rebuilding a boat transom. Looks like a great product for the right application.

 

Its usually a much faster and certainly more robust repair to leave the exterior skin in place , cut out the interior skin and rotted core, layup the new core of your choice while bonding the new to the old skin with thickened epoxy resin or hull and deck. Finish the layup on the interior . If you have access to the interior. Same can be done from the exterior leaving a 12-1 tapered bonding surface on the transom perimeter with the same layup.

 

Hardest part of that pour transom is getting the old wood out and making a form to hold the skin in shape. Like any job the preparation is 90% of the job. I’ve yet to use the product myself but I know a few that have and it worked well. It sealed everything up so it’ll never need replacing again.

 

You can't make chicken salad out of chicken shit. Get rid of the rotten core. It is mush. Moisture trapped inside will not end well in the long run. Just my opinion.

 

I agree. This pour repair will only work if you remove all the wasted/ rotted wood .

 

2 friends used the pourable (was nidapour now Arjay I believe) about 10 years ago. One has a 250 on the transom, one a 300 and both fished hard with no issues, rock solid. As stated, lots of importance in prepping for a good bond.

 

I have heard a lot of good reports with pourable transoms but I don’t have any personal experience yet. As stated above, the key is getting all of the rotten core out first

 

Practical Sailor tested different products for repairing rotten deck core like epoxy & InjectADeck. As I recall Gorilla Glue worked the best because it actually needs moisture to cure & adheres well to wet surfaces. Epoxy & moisture was a fail. However, there's a big difference between a deck & a transom with an outboard hanging from it.

 

I gave inject a deck a try. It did stiffen up the deck, balsa core deck on a sailboat. It wasn’t anywhere as solid as if the coring was replaced. I also noticed that the deck was not flat the product caused the deck to bulge upwards. If I ever have to do it again I’ll make sure to have a cover board and some cement blocks to prevent bulging. I wouldn’t call the patch a failure. Just not a long term repair. Nothing is going to beat removing rotted coring and replacing.

 

Like what LuSea said - often outboard transom coring does not even go full width and height on the inside - you can basically see where the core starts, cut right around, tear the skin off, and expose what's in there. Rip the bad stuff off, prep, get your new core in there, laminate and tab it back onto the hull. Yes you will need to cut some deck back to get to it completely, but it's not that complicated. And on the inside the cosmetics are partly buried and a lot less work to get to an acceptable level.

Generally, talking just a transom without complicating factors, isn't really that big of a job. It's easier than say replacing a deck.