Seacast Transom Repair

[drj]

HI again.
I know you all may be tired of me changing my mind on this transom =) but I have finally decided I am going to do a full traditional transom replacement using coosa board. I am going to do it from the inside. A friend of my dad's that now manufactures boats with what used to be the manatee boat molds had a chance to come and look at it for me and this is what he recommended. He said there wouldn't have been any way for me to remove all the wood from the top because it was only rotted in a small place and the other wood had been bonded well. Also because I wanted to make it a full 25 inch transom the pour method wasn't the best method in this situation. I hope I will have an opportunity to begin this weekend. I'll take some good pictures as soon as I begin =).
I was wondering. When cutting fiberglass with a cutoff wheel of grinding it with a grinding wheel do you use metal cutting wheels or masonry wheels. I had been using metal but I though maybe someone may have tried both. thanks guys.