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Repairing GRP


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Last race, I had a little - er -  meeting, with a crash barrier.   Nothing serious but it damaged my Vitesse's bonnet.    Some cracks, fractures and joint disruptions, that should need mending with resin and layer(s) of random mat.    Several hours with prep and letting it go off.

Well, no more!   Gorilla Glue!   This stuff is really good!   Wet the surfaces (!) Spread the Glue and clamp up.   It FOAMS as it sets, penetrates voids and fibrous surfaces, grips like, well,  a gorilla, and doesn't go rigid and brittle.  Very useful stuff!  I recommend it.

John

Edited by JohnD
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Hello All

              That,s the stuff I used to glue the veneer on to the dashboard.

I read its only worth buying a bottle big enough for the job as it starts to go off once opened(damp air) water is the activating agent.

But on saying that just looked at the bottle in the garage and it is still liquid inside(did not take the top off) but whether it is any good still?

Roger

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It foams as well when setting, so not ideal for gluing veneer?  If you got the same sort?

That action is ideal for GRP repair as it penetrates the matt, and as I said before fills voids.

I had one nasty crack, no significant gel coat loss, but still completely detatched, so I ground out a 'V' of gel, sprayed water, put Glue in and covered it with a strip of plastic bag, taped down with masking.   The result is almost a perfect repair!   It's ready for painting (if you're not fussy - this is a race car; war wounds are allowed), and the Glue has penetrated behind as it swelled, unable to get forwards, locking the sides of the crack togther.

John

Edited by JohnD
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It's PU glue isn't it?  I've heard many good things about it.

My top tip with fibreglass gelcoat or epoxy repairs is to use plastic (acetate) sheet and/or tape to cover the repair.  Essentially making part of a mould.

Works like you did with the plastic bag, but as it's got a bit more structure it allows better filling of concave sections.  Saves a load of sanding and polishing after the job.

 

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Yes, it is polyurethane.    I used that before, in the form of builder's space filler, when making the roof for Silverback.   That was a thin, outer skin of a tissue layer plus half a glass matt, with a layer of paper honeycomb inside and an inner skin of tissue.      Bonding the paper honeycomb to the outer skin in the mould was the problem, and the builder's expansion foam did a splendid job.   I spread the inner skin of tissue over the honeycomb, and wetted it with resin, which stiffened it and did the bonding as well.   I didn't think then of PolyU as a glue, until Gorilla came along! 

I'd use Builder's foam again for  a roof job, as getting a bead of GG onto all the edges of the honeycomb would take too long!    I just spread the foam inside the outer skin, laid the honeycomb on top and weighed it down.  You can see the irregular expansion of foam in the honeycomb cells below, where I got the foam thickness uneven.

 Gorilla Glue must be a different formulation, as it comes from the bottle as a syrup, that takes hours to expand and set.   The old builders foam expands instantly - it's in an aerosol can - but sets as slowly as Glue.    And the Glue advises to wet the parts to be bonded, while the builder's foam doesn't.

 

John

Honeycomb-tissue.jpg

Edited by JohnD
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Wow!  That's well beyond what I've ever got up to.  I've seen people claim serious penetration depths into wood when PU glue is used properly so wetting surfaces probably encourages a good bond.

The extent of my work has been smaller re-fairing of foils on boats and patching up the odd small hole.  I've got some gelcoat repair work lined up this winter on my current boat, but again, just sorting out some minor dings, not even close to the stuff in your picture!  

Pics attached of foils from my last boat that I repaired if interested. 

IMAG2438.jpg

IMAG1701.jpg

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