Number of layers required on transom rebuild inside?

tank1949

Lieutenant Commander
Joined
Apr 4, 2013
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I have epoxied (2) 3/4" marine plywood pieces into place on my 270 Sea Ray AJ (dual MC I/Os) . I used turnbuckles and c clamps to secure plywood/epoxy (photo attached). Transom assembly cutouts and 8 1/2" bolt holes are all completed (not pictured.) I used outer skin holes as templets. Imperfections or spaces on inside where plywood fitted to transom have been filled with silica/epoxy "butter." No dips or voids (see photo attached) . I am ready to coat inside transom skin. I plan on wetting out plywood to soak in and semi-cure. Then, I plan on wetting out matt, for first layer with tabbing all around edges/seams. I will followed by covering the matt with 6 oz fabric, including 6 oz of tabbing around edges. Finally adding one layer of 1708. I will smooth out the 1708 with matt tabbing. If anyone thinks I need another layer of 1708, please advise. MC manual states that finished transom should not be thicker than 2.25." I am at 1.95" now. I suspect the three layers (matt, 6 oz and 1708 ) will take it to 2.25. I might be able to add another layer of 6 oz? Any suggestions:
 

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sheboyganjohn

Senior Chief Petty Officer
Joined
Aug 2, 2005
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753
I would not plan on using matt with epoxy unless you are absolutely sure it is compatible. Most matt has a binder that needs the styrene in poly to dissolve it so it will wet out properly. From what I have seen you should be ok with the 1708. See boatworks today on youtube, he has a good video on resin compatibility with demonstrations.

When I did my transom I built it up with extra glass around each cut-out to make overall thickness. The full transom does not need to be that thick, just where the transom assembly mounts. I then concentrated on tabbing it in to the sides of the hull well.
 

Redtruck12

Petty Officer 1st Class
Joined
Jan 25, 2018
Messages
344
Hey Tank
when I built my transom (3/4” plywood doubled up) I coated broth sides , edges everything with CSM for waterproofing and then1 layer of 1708 all around before installing then 2 layers of 1708 As tabbing and still undersized for thickness. I suppose your hull thickness may be larger (being a larger boat)
i used polyester resin and 1708 and I figure I gained less than 1/8” per layup.
you mentioned Epoxy???? From what I understand polyester will not bond to epoxy😳
IF you’re using epoxy then 1708 is NOT what you need.
1708 is for polyester resin.
i am not greatly experienced BUT learning from the great information and experience on this site forum.
hopefully some of the more experienced members will chip in with further discussion and advice.
best of luck with your project.
 

tank1949

Lieutenant Commander
Joined
Apr 4, 2013
Messages
1,911
Hey Tank
when I built my transom (3/4” plywood doubled up) I coated broth sides , edges everything with CSM for waterproofing and then1 layer of 1708 all around before installing then 2 layers of 1708 As tabbing and still undersized for thickness. I suppose your hull thickness may be larger (being a larger boat)
i used polyester resin and 1708 and I figure I gained less than 1/8” per layup.
you mentioned Epoxy???? From what I understand polyester will not bond to epoxy😳
IF you’re using epoxy then 1708 is NOT what you need.
1708 is for polyester resin.
i am not greatly experienced BUT learning from the great information and experience on this site forum.
hopefully some of the more experienced members will chip in with further discussion and advice.
best of luck with your project.

I have already used E-Bond epoxy on other glassing projects . It seems to work well with matt and 1708. E-Bond stuck well to existing polyester in my SR. And E-bond is very inexpensive. 120$ for 3 gallons 2 resin, 1 hardener.
 
Last edited:

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,930
Epoxy does adhere very well to poly resin. Poly does NOT adhere well to an Epoxy base. 1708 will work with epoxy but it's a waste of epoxy. the CSM sewn to the back of the cloth absorbs a LOT of epoxy and it adds very little to the mix. IMHO you should tab the edges of the transom to the hull with two layers of 8oz fabric and then a final layer over the entire transom extending 8" onto the hull sides and bottom.
 

tank1949

Lieutenant Commander
Joined
Apr 4, 2013
Messages
1,911
Epoxy does adhere very well to poly resin. Poly does NOT adhere well to an Epoxy base. 1708 will work with epoxy but it's a waste of epoxy. the CSM sewn to the back of the cloth absorbs a LOT of epoxy and it adds very little to the mix. IMHO you should tab the edges of the transom to the hull with two layers of 8oz fabric and then a final layer over the entire transom extending 8" onto the hull sides and bottom.

Thanks to all!
 
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