How many woven roving cloth layers????

[Fire99]

Evening one and all,

I've just bonded in a new plywood (18mm) transom into the well of my boat and now it's time for the 'fibreglassing'
The transom has been well treated in SP300 Epoxy but I'm going to coat it in woven roving to blend it into the 'plastic' well and protect it from 'dinks' when lowering in the mighty Honda.

Any recommended number of layers? I was thinking Three but to be honest, I made that up

Any suggestions would be appreciated.

cheers,


Nik

PS - It's 300gm material

 

[maxcampbell]

I wouldn't start here

Sorry to say this, but it would have been better to do the whole lay-up at the same time as you epoxied the wood, to get primary bonding between layers.

At least do the rest in one go - after first washing the now-existing epoxy to remove the amine blush (what brand epoxy? - West is one of the worst for this (OK, just re-read SP, just as bad as West)) you'll know you've got it if the sandpaper you'll need to use vigorously clogs up.

After washing, with hot water, detergent and steel wool, then the vigorous sanding with, say, 60 or 80 grit paper.

Then consolidate one layer at a time, minutely going over every millimetre with a paddle wheel or other consolidating roller, just getting the cloth wet (doesn't matter what proportion of epoxy you roll on before the cloth and what proportion after, but not too much. The cloth should just go transparent, with no epoxy tending to run. As soon as you've got one layer down, get the next one on.

No idea about how many layers, but I'd guess 3, too.

 

[Fire99]

Thanks for the reply. The epoxy I used on the wood was Epoxy Sealer (CPES) with about half a dozen coats.. Unfortunately it wasn't practical to lay the cloth at the same time.. Hey ho, the cloth is only there to protect the wood from dinks from the O/B when fitting each season. I don't think it'll hut too much..


So the layers of cloth should be laid all at the same time?? For some reason I assumed (wrongly it seems) that you had to let each layer cure between coats.. On the positive side, the job will get done quicker.

 

[maxcampbell]

Not too serious.

If it really is just to prevent the dinks, and not adding structurally, then I'd have thought one layer was enough. Still needs the washing & sanding, I'm afraid.

 

[Fire99]

Still needs the washing & sanding, I'm afraid.

Me or the wood? No probs. It's not the largest piece of wood in the world so won't take me too long. I also have some neat acetone for the clean-up operation.

Many thanks for the info.

 

[William_H]

Epoxy on plywood

Much depends on how long since you applied the epoxy. A few days could enable a chemical bond but any longer then treat as said.
Just how much f/g depends on your engineering design. Thin layers of fibreglass will tend to peel off more easily whilst really thick f/g will have strength in itself so even delamination from the plywood will mean the f./g is strong enough to stand alone there for delamination doesn't matter so much. The wood if it gets mosture in it will deteriorate.
I think if it were me I would go for at least 3 layers of woven rovings. good luck olewill

 

[Fire99]

Thanks a lot OleWill. I think i'll go with at least 3 layers, since I have an abundance of cloth, and see how it goes.

 

[status]

Back to the original question.

What weight of rovings do you have?

My opinion would be that the new wooden transom is designed to take most of the load bearing so the woven rovings become irrelevant to strength as such one layer would be sufficient.

My suggestion would also be to use chopped strand mat (CSM) as it is much easier to work into corners and over the edge of the transom smoothly to give a good finish, but then the combination rovings we use are 1.2kg glass per square meter and as stiff as cardboard!

 

[PuffTheMagicDragon]

My suggestion would also be to use chopped strand mat (CSM) as it is much easier to work into corners and over the edge of the transom smoothly to give a good finish,

Not with Epoxy resin. The binder in CSM is not dissolved by Epoxy as it is by Polyester.

 

[Fire99]

Thanks for the comments.
I ended up using 300gm woven roving, which was quite easy to work with, other than the edge of the cut section liked to unravel itself.

Transom got 3 layers and the other areas of the well which were already part of the original grp moulding, got 2 or so.

Whole lot will be tidied up, primed and antifouled.

I'll let you know the outcome.

 

[VicS]

Not with Epoxy resin. The binder in CSM is not dissolved by Epoxy as it is by Polyester.

I think there is a CSM for use with epoxy. I think it may not be all that easy to work with, presumably because there is no binder.