Transom Replacement - resin problem

[Waterskipper]

While replacing the transom on my 1976 Aluminum Starcraft I read that it's best to drill oversize holes through the transom, fill with epoxy resin and then drill actual size when reassembling. I did do that. However, upon filling the holes with resin/wood flour mix, the resin cracked in some of the holes. I am wondering if I didn't use enough of the wood flour in the mixture or missed some other step. Do I need to redrill and put a different mixture in or can I give another coat of epoxy and assemble it using some type of marine caulking? I have included a picture of one of the cracked fills for observation. Any help would be appreciated.

 

[ondarvr]

Re: Transom Replacement - resin problem

Resins get hot, change shape and shrink when curing and in a thick mass normally crack. The cracked area needs to be removed and refilled.
Wood flour doesn't really add any strength, it just thickens the epoxy, to add strength you need to add milled fibers (short strands of glass) to it.

When drilling an oversized hole, then filling it and redrilling, you don't need to drill the first hole that big, it only needs to be slightly larger than the bolt that goes through it. If the washers don't cover the hole completely and overlap onto the area around the epoxied hole, then you're depending on the strength of just the epoxy to hold your motor, or whatever you bolted on, in place.

 

[Waterskipper]

Re: Transom Replacement - resin problem

Thanks for the tip. The picture is of the drains for the back splash area.
Can you tell me where to get the milled fibers? Also is there a difference between epoxy resin and fiberglass resin? Thanks!

 

[oops!]

Re: Transom Replacement - resin problem

Thanks for the tip. The picture is of the drains for the back splash area.
Can you tell me where to get the milled fibers? Also is there a difference between epoxy resin and fiberglass resin? Thanks!

any fiberglass or composite store....(not wall mart)....look in your phone book, youll be suprised.

what is generally considered to be fiberglass resin, is called polyester resin...all fiberglass boats are made from it.

epoxy resin.....sometimes called "the glue", is a more high end fiberglass resin. much stronger than polyester, it also has better water proofing qualities, bonds very tenaciously to wood, and can be used with composite materials,

however it costs double the price of polyester resin......

because of the cost and polyesters ability to control cure times, polyester resin is the industry standard

 

[iwombat]

Re: Transom Replacement - resin problem

That being said, if you're using polyester you need to use some glass mat at the very least. Polyester is too brittle to use on its own.