Alumium boat wood transom repair

[SCD]

Hi

I have a 1977 14' Duranautic offshore with 9.8 Mercury. I removed the old plywood (I replaced about 15 years ago). The aluminum behind the plywood had about 6 small holes less than 1/4"diameter.The rest of the 18 x 20 section had some gouges eaten in and wasn't smooth.

The questions I have are these.

After I clean the area, can I use a skim coat of a fiberglass re-enforced body filler to fill the holes and smooth the area then paint?

I’m going to use 2 pieces of ¾ plywood glued together primed and painted.

I’m going to attach the plywood to the boat with stainless steel bolts.

I will sand and paint the outside of the boat also.

If I put a piece of rubber roofing between the plywood and aluminum will this keep this from happening again?

Does this sound like it will work?
I think this happened because I used pressure treated wood the last time.
Newbie to this forum
Steve

 

[ggoldy]

I'm not sure about the Fiberglas, but your other ideas are sound. A picture of the damaged areas would help.

 

[minuteman62-64]

Was the old plywood sealed? Based on my readings, unsealed plywood in transoms leaches chemicals from the resins that eat away the aluminum. You are on the right track painting the new stuff.

I have some pin holes on my transom skin. Sealed them from the outside with MarineTex. Holding strong going into year 4 now.

 

[Johnny]

okay, in MY opinion, it is not whether the transom wood is sealed or not.
or, a plastic or rubber film put between the wood and metal skin.

I am thinking of WATER ENTRAPMENT between the transom wood and the hull is the culprit.
Especially if you make any trips to salt or brackish water.

in MY world, I would take the transom metal down to bare shiny finish.
Remove all paint, corrosion, oil and all contaminants.
Sandblasting is the most efficient, but not everybody has access to a blaster.
Treat with OSPHO as per directions on the bottle.
Two or three thin coats of RustOleum Aluminum Primer. (or, what ever brand you prefer)
Then, a couple coats of an oil based paint. (all 24 hours apart)
So what you are doing is setting up a moisture barrier between the metal and other entrapment surfaces.
That should protect the transom hull skin for a few years.

This thread may shed a little more light on transom skin preservation.
https://forum.tinboats.net/viewtopic.php?f=3&t=37415

and :WELCOME:

 

[huntinfool]

I wouldn't use fiberglass, it won't bond well enough.
Epoxy would work better. But honestly small indentions aren't really a problem. You will have wood there. However if it is either from water or chemical leaching eating at the aluminum, make sure you get it real clean.
I agree with the sandblasting. Even a small one will do wonders. Once that is done you could just use a spreader and spread 3M 5200 in them. That will seal them if they continue to corrode and come through. For holes through the skin, use a piece of tape on the outside and wipe the 5200 in. This will seal them forever. I've got 2 1/4" holes from a previous owner's transducer at the bottom of my old hull. Its been maybe 5 years now and not one leak.
As for protecting the skin, I'd do as BF Johnny said.
But the main answer is, fiberglass relies on a chemical bond, which it won't get with aluminum. Epoxy is a physical bond.
3M 5200 is a physical bond also....but MUCH stronger. I've lifted 21' bay boats off of trailers while trying to take a motor off. With a pry bar and hammer I'll eventually get them off. But it rips the gel coat and glass off the boats. Its really strong stuff.

 

[SCD]

Hi

Thank you for all your info. Just finished the transom repair yesterday.
Sand blasted alumium,filled and bridged holes with epoxy putty, coated inside of transom with epoxy resin,applied two coats of paint. Fiberglass resined two sheets of 3/4 plywood and bolted with stainless steel bolts to transom.

Thank you very much for all your info:

Steve

 

[CMOS]

That very similar to what I did. I sanded the corroded areas, sprayed with Self-Etching Primer, then covered the entire inside face of the transom with one sheet of fiberglass material & resin. Then installed 2 sheets of 3/4" plywood after 3 full coats of Resin.

My only suggestion to you would be to be sure that the bolt hoes you drilled in the transom are pre-filled with either resin or 3M 5200 sealant, let dry, then drill the holes. This will seal the inside of the bolt holes so that over time, no water can seep into the inner layers of your new wood. FYI.

CMOS

Hi

Thank you for all your info. Just finished the transom repair yesterday.
Sand blasted alumium,filled and bridged holes with epoxy putty, coated inside of transom with epoxy resin,applied two coats of paint. Fiberglass resined two sheets of 3/4 plywood and bolted with stainless steel bolts to transom.

Thank you very much for all your info:

Steve