Adding layer of glass to new laminated ply transom core, before fitting. Advice?

[CW180]

Hi all

I'm at the stage where I have my new ply core cut to exactly the correct shape with the 3 layers of ply bonded well together.
I have treated the edge all round (so all the end grain, and overlapped round the sides by 2") with first one layer of neat epoxy, then with a slightly thickened coat on top to give a slightly thicker layer to smooth & fill, and give a better sealing barrier round the end grain.

So next, once that's set and sanded a bit, I want to wrap the new core with fibreglass as it needs a couple of extra mm that the original core had from the same, and as this seems to be the done thing, presumably to assist with bonding in the core and sealing off the plywood completely etc.

I'm not sure of best practise for wrapping the core though. If someone could answer the following I'd be most grateful so I can ensure it's done right.

1: Should I be using CSM, or roving, or biax for this, or a combination like normal layering up (ie csm first, then roving)? If nothing else I'm assuming it would NOT just be a layer of roving since it's not strong by itself or as a base layer.

2: how should the layer(s) be added in terms of practicality? What I mean by this is I can't think of a good way that I can wrap the whole panel and get the resin in while being able to handle it and keep the fibreglass medium in place and not moving it, or leaving it held/supported somehow without it sticking to something I don't want it to.

3. If I wrap the piece around the the sides and faces in one piece, what do I do for covering over the top & bottom edges?Should I - A: use a wide enough piece of cloth that it overlaps the top & bottom edges, or B: match the csm/cloth width to the height of the core then add a separate piece over the top and another over the bottom edges with an overlap on each? C: some other way that I haven't thought of?


Quite appreciate I might just get told "Don't worry - as long as it has a layer of glass to help it bond to the skins, and to thoroughly seal the ply, it doesn't matter how. Don't stress!" or suchlike, or alternatively, "Are you a moron?! Of course you don't do it like that, you need to...." but I'd rather ask now and ensure it's done right rather than make an assumption and find out I've wasted a lot of time & money by ballsing it up.

Appreciate input on this, thanks in advance!
Jim

 

[Woodonglass]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

If you truly mean epoxy and NOT polyester resin, then you do NOT use CSM. CSM requires styrene to break down the fibers and epoxy does not contain styrene. With epoxy you only use Cloth. I recommend using two layers of 17 oz biaxial cloth for your transom. I would pre cut the cloth 3" larger than the transom core. Wipe it down with acetone, then Coat the transom with a light coat of resin and then lay the cloth in place. Use a 6" short nap nylon roller (de fuzzed, I scrape mine with a hack saw blade) soaked in epoxy and roll the cloth smooth add more resin as needed to wet it out until it goes clear. Roll it over the edges and make every attempt to make sure and not get any air bubbles. If you don't have a bubble roller. Get one. A light to medium rolling pressure is all that's needed. Don't want to move the cloth or have it lift up on you. Less is best. Let it set over night, flip it, wipe it down with acetone and do the same on side 2. Let it dry. do a Light sanding with 60 grit wipe it down with acetone, and do another layer of the 17oz cloth. It should be ready to install in the boat.

 

[CW180]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

Thanks for the detailed reply but I should apologise at this point as on reading your post I realise I haven't given all the necessary details for the correct replies to be given.

Yes I've used epoxy (West stuff) for the sealing I've done around the edges/end grains of the core, but it's not epoxy that I'll be using for adding a glass layer. I should have clarified this at the point where I was saying that I wouldn't of course be using roving by itself but it didn't even occur to me for some reason sorry!!

I'm aware that historically there's been concerns at times about adding polyester onto epoxy layers rather than the other way around but to my knowledge that's been pretty much debunked these days and explained away as simply the base epoxy layer being stronger. Given that the whole core will be wrapped, there's no reason to worry about such issues, especially since it's only got the epoxy on the edges.

So it's polyester I'll be using, but I think your answer still is valid in some respects as it answers the question I had about trying to do the whole thing in one piece/one attempt, or else doing the 2 sides separately but with overlap. The answer you gave was just what I wanted to hear I must admit!

I'm assuming the only real difference in terms of using polyester is that the norm would be to use a layer of CSM and then a layer of roving, rather than just using biax (although I guess it wouldn't hurt to use biax anyway)?

Thanks - and sorry for not mentioning the particulars of the resin in the first place since it's kinda fundamental!:facepalm:

Yes I do have a bubble roller too.

 

[Woodonglass]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

So... Only the edges of the wood have been coated with epoxy and the rest of the wood is bare? If that is the case the read the first link in my signature and it will tell you exactly how to fabricate your transom. By the way it is still true that polyester resin does NOT adhere to epoxy. You can get it to do so with varied results by sanding and washing down with acetone etc but it is still not advisable to try to adhere poly over epoxy. Not sure where you're getting your info but the pro's on here will tell you it is not advisable to do so. If it's only the edges then you will be ok but if the entire surfaces of the wood are epoxy coated then I'd say you have a problem.

 

[CW180]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

Thanks

Yes it's only the end grain edges of the core with the epoxy currently. I did wonder about using epoxy across the entire surface but decided against it since it's not what was originally done, and I'd then have to spend a lot more as the amount of remaining epoxy I've got is not masses, but I do have about 13kg of poly left still!

Can't find the article in question now annoyingly, but it was an article where a series of tests had been done to demonstrate that with properly prepped epoxy surface you can still get a satisfactory bond with poly on top. All I can find when I look for this is an article on West's website concerning gelcoat to epoxy as being acceptable strength, but that's not the same thing as you'll know.

I've got the book written by the gougeon bros which has a lot of useful information so I'll have a look in case it was in that somewhere, but I don't think it was.

No matter though. That link is handy thanks, and I love the seat pods and simplicity of the clamps you've fabbed. Very good ideas indeed!

Excuse me for asking for reiteration here, but the diagram you have of the transom is I suppose slightly different to mine in that it's not a case of slotting in a new core between two existing skins, but rather adding it to one skin then fabbing a new inner one directly onto the core. In your diagram you've just got the wrapping around the core, without any roving as such, then peanut butter to the outer skin and biax directly onto the csm as the new inner.

For me, I'd have to guess it'd be csm then peanut butter on both faces of the core before clamping?

If that's the case is there any benefit in me adding a layer of roving as well over the csm? I've already got supplies of it, and presumably it'll give additional strength to the core itself, but I'm pondering whether it's possible that roving could prove detrimental as the bond between skin, peanut butter, and roving would be a weak point where peanut butter meets the roving, and thus better just to stick to csm?
I hope that makes sense - but basically I'm asking if it's worth bothering with roving as well as csm around the core, or leave it just as csm to give a better bond to the skins?

Sorry for all the questions

 

[Woodonglass]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

Forgive me for forgetting but are you saying you are going to be slipping your core between an existing outer and inner fiberglass skin? If that IS what you are doing then I would recommend two layers of 1.5 oz csm on the transom core and then PB between both the inner and outer skins. IMHO no need for the roving but you could use it if you wanted to. Your bond would be fine with just the CSM. It seems it will be a challenge to get a nice even coating of PB on the Core and the walls of both the inner and outer skins as well as even clamping. How are you planning on doing this?

 

[CW180]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

Forgive me for forgetting but are you saying you are going to be slipping your core between an existing outer and inner fiberglass skin?

Not quite like that no. You might not recall, but on my original topic I upset one or two people by doing an outer cut but later had it confirmed by one or two people on the topic that this was actually completely acceptable to do, if not what is normally recommended on this site.

BillP:

In Florida anyway, and at yards who make a living doing transom rebuilds, it's very normal to cut the outer skin off, insert the new transom from the back and glass the skin back on...without wrapping glass around the corners. Cosmetically it looks no different than before cutting. The exterior transom skin typically add very little structural value to the transom core anyway

Ondarvr:

The transom can be done from either side, the reason most people say to do it from the inside is the exact same reason you are planning to remove the cap now, more needs to be done than just the transom, so the inside needs to be gutted too

If a boat yard or glass shop is told to only replace the transom, then many would rather do it from the outside and avoid the possible issues of getting the boat apart and putting it back together, it takes more man hours to remove the cap.

It looks like you left a good sized lip on the outside of the transom, so you can glass to it and not need to wrap it around onto the hull, so you’re OK there.

So I have a complete outer skin (when I say complete, I mean intact in one piece, NOT the entire transom surface though as I left a 3 inch 'gutter' of outer skin to facilitate a strong outer repair without radiusing round the side of the hull).

What I am going to be doing is inserting the new wrapped core and bonding/clamping this to the inside skin first. The fact it's an outer cut makes it super easy to ensure a nice even coating of PB before doing so, and the clamping can focus purely on one single bond taking place rather than worrying about what you described.

Also, prior to installing the core (but after wrapping it), it's easy for me to ensure it fits in place perfectly against all of the inside structure, and the channel it sits inside around the whole edge. This means there is no guesswork of positioning, or excess of PB needed to fill gaps etc.

It seems it will be a challenge to get a nice even coating of PB on the Core and the walls of both the inner and outer skins as well as even clamping. How are you planning on doing this?

As above, this isn't going to be an issue due to the outer skin not being there at present.

The next stage once the core is bonded securely to the inner skin, will be making sure the outer skin is going to sit correctly before it is reapplied. As the outer side of the core is exposed at this point it will be a very easy (albeit probably tedious) task to offer up the outer skin, then apply a small amount more glass if necessary. Once I'm satisfied it's going to sit as level as I can reasonably get it to, it will be bonded and clamped. Again, I'll be able to ensure an good even layer of PB, and concentrate purely on clamping one individual join when this is done, so it gives me really good control without worries along the lines of "The other side isn't doing what I expected - what do I do now?!!".

Hope I've explained that ok.

Appreciate the input as usual.

 

[Woodonglass]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

Yeah, NOW I remember!!!! Yep You got it. CSM PB and clamp it to the inner skin. Then PB and clamp the Out skin piece that you cut out back in place. You can then grind, bevel and glass the 3" gutter back to the piece to obtain the bond and strength needed. You should be able to obtain excellent structural and cosmetic results using these methods.

 

[CW180]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

Phewww - glad what I'd written made some sense. Not easy sometimes to convey exactly what the intention is with things like this without images etc.

Also glad that the planned approach seems an agreeable one. The more I do on this rebuild the more excited and enthusiastic I get about doing more!

I have been a bit spendy as well in the last week or two:

Excuse the mess in the photo, but that's my lovely little new backup - it's a 2006 BF5A which has only about 3 hours on it, and a set of BF90 carbs to change my main Honda from 75-90hp since the carbs are the difference between the two engines.
The fuel use figures are apparently lower for the 90 engine, so if there's any truth in that then it's a plus.
The engine currently has a 13 x 19 prop, which is quite a bit of pitch, but with 90hp and barely any weight in the boat, hopefully it'll be good with that.

Also bought a bunch of stainless fittings like rod holders etc.

 

[Woodonglass]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

NICE!!!! Great Addition to your restore!!!

 

[CW180]

Re: Adding layer of glass to new laminated ply transom core, before fitting. Advice?

Thanks

I have a 5hp johnson 2 stroke that works just fine, but this is WAY newer, starts a lot easier, and was really good price.
I wanted a 4 stroke, and these things are meant to just run and run and run, so it's good peace of mind.
Plus, the 12L tank it has got fits perfectly into the forward seat locker too.

And no more pre-mix fuel for me!

*edit* just found out that the BF90 carbs that I bought a week or so back are actually not BF90 ones at all, but BF75 ones just like I already have. Am pretty angry about it as it means I now have to go through the rigmarole of returning them to the seller and obtaining a refund.
If it's a genuine mistake on his part them he'll presumably doubt what I'm saying, and I'd guess will be suspicious of what I'm telling him, and if it's deliberate then I presume he'll try to wriggle out of it, so I'm not enthusiastic about this process with ebay I must admit!!

But having told him from the moment I received them that the numbers stamped on the carbs weren't what I'd expect on a 90, I've now checked the jets in the bottom carb, and the jet numbers match the 75 spec and not the 90 spec at all.

What a ballache!