Transom lay up process advice

Hi All,
I am relatively new to glass work. Been reading a bit, but couldn't find exactly the info I am looking for.

I am working to give new life to a 1979 Boston Whaler V-20. She has some wet foam in the lower keel area and transom was in bad shape. I know I am crazy, but I like a challenge...
To start I am focusing on the transom. I have removed the back skin and old transom wood, which was measured to be roughly 1 7/8" thick. I have left 4" around transom perimeter for tabbing. I have ground all internal transom cavity surfaces to fresh glass to achieve best chance for a good bond. I have templated the transom cavity and cut out 2 x 3/4" layers of Coosa Blue Water 26 for a total coosa thickness of 1 1/2", and have bonded those together with thickened West System 5:1 epoxy using the slow hardener. To make up the additional thickness of appox 3/8" or so to get back to original thickness, my plan is to laminate, on each side, 1 layer 1.5 oz CSM and 2 layers of 1708 using laminating VE resin. I have all of this material. After the VE hardens up, mix up some thickened epoxy and apply to old transom cavity / skin, as well as the mating surfaces on the new coosa transom and install and clamp the heck out of it looking for good squeeze out. Then grind hardened squeeze out away and prep for lamination to replace layers of outer transom skin using VE resin again. Followed by Gelcoat, thus the reason for VE at all...

Question 1: To bond new transom into old cavity with epoxy, should the new transom VE be fully cured with a waxed resin, PVA, or other means before attempting to secondary bond? Or can the tacky VE laminate be bonded via epoxy? I think the answer is it must be cured...

Question #2: I have peel ply I could use on layed up coosa transom. If used, will peel ply cure the the VE resin to non-tacky and ready to bond using epoxy? Should it still be ground after removal of peel ply?

Question#3: Should I try to get cute with peel ply to affect an epoxy bond in the areas on the back of the new transom to be bonded to inside of remaining 4" tabbing zone, while retaining a laminating (tacky area) in the center field of the back of transom to continue with a primary chemical bond?

Thanks in advance. Let me know if I missed any important details.

Cashinhand2

 

Why do you want epoxy ?

 

I guess I thought it would be the strongest secondary bond to original skin, from everything I have read...

 

You could clamp your coosaboard on to the glass you have left around the perimeter with epoxy "putty" I guess, but are you intending to, or already have applied glass/resin to the coosaboard slotted in ? I don't know that there is any need to be worrying about an epoxy bond to the VE unless you have done this already. You could use the VE direct to the old glass if cleaned up well.

 

Ok Thanks Mr Efficiency. Coosa in picture is just dry fit. I will remove again for further lamination to outer surfaces. I am Intending to apply glass/ resin to the coosa to build out to original thickness. Most information I have read kinda pointed me to using epoxy for best secondary bonding to old transom skin, with VE option in second place followed by least preferable PE. But I hear what you are saying... adding epoxy in to the situation, Just may not be worth the additional effort vs benefit given VE already in use?

 

If you are concerned that unwaxed VE may not bond properly with the epoxy, and I think that is your concern (member Ondarvr here is the best guide with that), don't glass it before installation, or glass it on the inside only. The outside will be glassed after installation. When you glass the inside of the new transom to the boat sides and bottom, the whole thing is trapped in there anyhow, I don't think the bond is that critical around that outside, between the outside face and what is left of the transom glass, you will soon be glassing that outside anyway, bridging over on to the old glass, if you want to thicken the panel by pre-glassing, I would just make a putty using VE to bed it in, clamped.

 

I am a bit confused by the approach.

First of all, you cannot add glass to the new transom only. This will create a hardspot or a concentration of strength. The glasswork on the outside must extend over the 4" area and it should be a bit staggered, although you can probably go to the edges with each, or wrap around the hull.

This is done by grinding away the paint and feathering the edges toward the new core.

You state the transom thickness was 1.875", and that the coosa you laminated is 1.540" done properly. This means you need 0.335", but you say you need it on each side?

If my measurements are not misinterpreted, you would not bond the epoxy side with vinylester at all. You would bond with epoxy. If you want bond strength of epoxy for the secondary bonding, why would you want a weaker ve bond on any glass on the inside? Makes no sense. Also, the bonding of the inside skin, with epoxy, could be done at the same time. Typically, these repairs are done by bolt holing. Glass on the inside skin side makes for a surer bond thickness, but it is more difficult to hole and bolt wetted glass, so the work is done on green glass, or overnite cure, or no glass on the inside and just thickened resins. Here, you can shim onto the tabbing area you left and get a fairly decent push, but you can't pack that space up woth glassed core ahead of time.

Honestly, I would not glass much on the inside. Trowel 1/8" thickened epoxy onto the inside skin (it will be a lot, keep the thickened resin on a flat board so it doesn't kick fast and tongue depresser into the edges for and aft and bed the core into it. Shim it well from the outside. Force thickened epoxy into the outside margin woth 4" trowel. It must be thick enough to not sag when built up on a pile. This is about 2.2:1 by volume cabosil to epoxy. I may have a weight measurement I can give you in the shop.

Then, grind the tabbing and epoxy down to a feather. (This can be done before adding the core, but shimming can break the edges). Then you have about 1/4" to make up, plus over the edge. This can be done a few different ways. Personally, I would use a combination of glass and fairing and g/c. But you could make a couple lifts with thickened epoxy, then sand it with 40 grit and glass over that and no feathering I suppose.

I would do all of the work with 1708 unless you need finer for g/c. The minimum amount of 1708 I would use would be 6 layers, not 2. And those layers must bond to the 4" tabbing you left, and they will hardpoint at the edge. I must admit, I am not a fan of the way you did the job. I would have told you to leave more tabbing or remove the inside skin only. The reason is you only have a 4" bond surface for what will probably be ?250hp hanging there?

Are the sides and bottom of the boat getting re-gelcoated? And alternative approach that is better would be to wrap some of the 1708 into tabbing reliefs ground on the bottom and edges.

@ondarvr is an expert on much of the esters work, but I don't think you ought to mess with ve on any inside core glass and I gave you my reasons..he may also give you some advice about dealing with your 4" tabbing..

Also, I'd do the entire job in epoxy and only use the ve at the end for the gelcoat. Then you get the bond strength of epoxy on your rather short tabbing area.

Make sure to finish the lower edge of the transom at a 90 and not radiuses if you decide to wrap some 1708 around the hull more. See what advice you get from others.

Also, please let everyone know the power plan. If you are hanging 250 hp off the transom, I doubt anyone will agree with 2 layers of 1708.

 

Also, I hope you used thickened resin on the coosa. Coosa is epoxy thirsty and a raw epoxy bond would be very weak.

 

Thanks for your feedback Fallguy, I am learning so I appreciate you taking the time. Sorry I wasn't very clear when describing my approach. My intent was to beef up the Coosa to original transom thickness by splitting the remaining 0.335" evenly and applying it in VE laminate on each side of Coosa. Just seemed like the right thing to do to balance the additional material on both sides of Coosa.

It was also my intent to bed and bond the beefed up core to forward skin with thickened epoxy. I will clamp, screw, as well as shim along tabbing to ensure good squeeze out and no voids.

It is also my intent to grind way the excess epoxy and feather the 4" tabbing (12:1) toward new core after epoxy is set.

Then my plan was to laminate over the whole arrangement on the aft of the new core and existing feathered tabbing with VE resin while staggering layers. I would need to do some of this on this inside too as the previous owner had already removed a small section of the inner transom skin when trying to determine condition of old transom. I had previously understood it was not a good idea to laminate esters or gel coat over Epoxy, so that is why I had chosen the VE resin, to kind of strike the balance. The rest of the hull gelcoat is in pretty good condition, so wasn't planning to gelcoat beyond the transom area. Can VE bond to epoxy for gel coating? It seems most of the available info I have found advises against esters bonding to epoxy, but I am just learning and It maybe just in structural bond situations that its a no no?

All lamination is planned in 1708 except I had planned to use 1 layer 1.5oz CSM next to Coosa as a tie layer. There is a light CSM backing on 1708, but wasn't sure it was enough and others had advised me to use the 1.5oz first...

I believe the boat was originally rated for a 180 HP outboard. Would like to go with a 4 stroke, so will look to see how close I can come to that considering the weight also...

I did use thickened Epoxy between the 2 sheets of Coosa. West 406.

Thanks again. Good to have multiple points of view!

 

Just use epoxy on the inside work. You don't want to get too thick and push all the troweled thickened resin down to the bottom, so do the thickness build on the open side.

 

Ok Thanks fallguy. I understand what your saying about scraping / pushing down the thickened epoxy as the new core is being inserted from the top. So will leave some space to allow the new core to drop in without piling up the epoxy. The ends shouldn't be too much of an issue as they are tapered and wont make contact until almost seated. But the back of the 4" tabbing area, while trying to prevent same on front skin, could be a challenge without the space you are recommending.

How challenging do you think it will be to force the thickened epoxy into the outside tabbing margin without voids? Do you think injecting a thickened epoxy like West Six10 into the gap would be an effective method? I am not so worried about the bottom margin as gravity will aid with that when it comes time, but the vertical margins, that's a different story. Too thin and it runs out. Too Thick and it may not be forced to the extent of the void...

 

Let's start over.

There is little to no advantage in using epoxy in this type of repair, it just over complicates the process. These boats held up to decades of abuse with the cheapest polyester and chop laminates that could be used. Repairing part of it with epoxy yields no advantage.

After saying that, you created a problem by cutting off the transom from the outside and leaving such small area to bond to. This is the only place the epoxy will be a benefit, it's a little more insurance that it stays put.

VE, will hold up, but you need to do it correctly, epoxy gives you some room to make "a not as good as it could be" laminate and still hold up.

It does complicate the finished cosmetic coating though, bouncing back and forth between resin types leaves many opportunities for errors/failures.

 

Pretty much my view completely.

only difference is, you are a much wiser owl

his mistake cutting the exterior skin is why I lean toward the better resin (epoxy)..

I have no experience with the others, save a bit of polyester, but I would use epoxy on the inside and skip the glass and then switch to ve for the balance.

 

Ok guys thank you for your insight. I will do inside work with epoxy and then switch to VE for outside skin replacement.
Will be sure to grind the well cured epoxy bond line when feathering the 4” tabbing and then wash with warm water and Scotch-Bright pad to minimize potential for amine blush in that narrow zone.

Thanks again.

Tony