adhesion of new GRP to old

[catalac08]

I know this is going to sound like a reallly numb question but here goes...
I have a second hand wheelhouse that has had the bottom flanges cut off both sides as part of the removal process and needs new flanges fitting to both sides before mounting on the boat.. Laminating new flanges is not a problem but I am unsure of the best way to fix them. One option is to make them in GRP using polyester resin/matt laminate and then cured bond them to the wheelhouse using epoxy resin/laminate for max adhesion, using about a 1 inch "scarf" on both the wheel house and the new flange (would have a bigger joint but 1" is all there is remaining at the bottom of the wheelhouse). An easier way would be to mould the flange with the mould attached to the wheelhouse side and just continue laminating the mould and the joint over the "scarf" as one operation.
Done a fair bit of fibreglass work making things with polyester GRP and hull repairs/ reinforcement w ith epoxy so this uncertainty surprises me but I am interested to hear some views. Making the new flanges in epoxy GRP would be relatively expensive compared to polyester.
My question is how well new polyester GRP adhers to aged GRP, with old surface properly roughened and solvent cleaned..
It would be embarrasing/dangerous to have to the wheelhouse take off, although according to my calculations wind pressure alone does not amount to a great load but a wave would of course be different.

 

[moody1]

In the overlap of lamination you apply, drill holes in original moulding. When laminating new to old, making sure that a good amount of acetone has been used to clean up and soften surface of old after good wire-brushing, you force resing and matt to key through the holes as well - giving a physical bond as well as chemical.
This is in addition to any other ideas / methods to join.
I would still be wary of this though, as the force of wind is actually significant and could prove over-powering.

 

[William_H]

Yes I am inclined to think the polyester bonded to old polyester should be OK. Try to get the largest boding surface possible and try tp get a scarf joint and as suggested holes for resin to bond though might help.
Yes wind forces can be great but then you will have a pretty big bond area. olewill

 

[oldsaltoz]

G'day Keith,

I know this is going to sound like a really numb question but here goes...
What is the wheel house made of? I'm assuming it's fibreglass.

you have a second hand wheelhouse that has had the bottom flanges cut off both sides. So can I assume you have a slab of fibreglass and are looking for a way to secure this to your existing deck?

And it needs new flanges fitted to both sides before mounting. I'm not too sure what you mean by 'flanges'. Are we talking about a flat section to be fixed to the slab? like an inverted 'T' or a fillet rounded between deck and side of wheelhouse.

You say "Laminating new flanges is not a problem but I am unsure of the best way to fix them". One option is to make them in GRP using polyester resin/matt laminate and then cured bond them to the wheelhouse using epoxy resin/laminate for max adhesion, using about a 1 inch "scarf" on both the wheel house and the new flange (would have a bigger joint but 1" is all there is remaining at the bottom of the wheelhouse).

And go on to say "An easier way would be to mould the flange with the mould attached to the wheelhouse side and just continue laminating the mould and the joint over the "scarf" as one operation. Done a fair bit of fibreglass work with GRP and hull repairs/ reinforcement with epoxy. Making the new flanges in epoxy GRP would be relatively expensive compared to polyester".

And your question is how well new polyester GRP adheres to aged GRP, with old surface properly roughened and solvent cleaned.

Epoxy will give you a stronger bond than polyester resins, but if the stress is only compression it will make little or no difference what resin you use.

For this application I think I would giving both the joint areas a good grinding to produce a good clean key, then remove any dust with Acetone and white cloth.

Mix some epoxy resin and add Micro fibres and form a gusset with a small glass jar as a rounding tool, let this go tacky and apply 3 layers of 300 gram bi-directional cloth overlapped by 30 mm each, then one layer of 50 gram roving's to give a smooth and no ends exposed finish, let this go tacky and add 2 coats of resin wet on tacky to avoid sanding between coats.

Having done work with epoxy you will know that it is important to roll out any excess resin, you are looking for a 1 to 1 ratio by wieght of cloth and resin. Not 3 to 1 as for polyester resin to mat ratio.

I hope this helps.

Avagoodweekend......

 

[sailorman]

polyester doesnt really bond well to old polyester
use epoxy & f/g matt