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GRP to aluminium

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Is it worth it?

 

I’ve read conflicting opinions, but it seems if you get the aluminium  back to metal and very clean, it’ll bond very well.

 

the aluminium and GRP will be sprayed at a later date

 

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@miketomcat is the man to ask :)

Lotus glued the Elise aluminium chassis together with some form of epoxy, so I don't see why you can't get a decent result. Getting it clean will be key, for sure. Break the oxide off with a stainless wire brush that's never been used for anything else, rubbing only one direction (no power tools), clean with acetone until a fresh rag comes up spotless would how how I'd approach it. Same as prep for TIG welding really. I'm sure Mike will have more to add, though. 

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As the roof is currently finished paint, would a chemical stripper be a no no do you think?

i don’t like the idea of sanding down the paint job by hand if I’m honest 
 

the entire roof will need to be prepped for spraying eventually

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Polyester doesn't stick to aluminium very well and epoxy isn't much better. You can laminate over it with either to encapsulate it and if you put some big holes in it to push the glass down into it works well. The best products to stick aluminium to a fibreglass substrate are plexus (an acrylic glue from memory) or sikaflex with the correct primer. I have successfully used both products. Feel free to prod me for more info.

Mike

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googling about abit more with your info Mike, i'v found a few porducts that may help.

 

The issue seems to be that the aluminium begins to oxidise, thus weakening the resin's ability to stick to it.

 

The glue you mentioned, and others, coat the aluminium and put a barrier between it and good ol' air and this stop the oxidization ( is that a word?!).

I can't go making holes in the roof to bond it, so i'll go with the either the glue base or work quickly after initial rub down and clean.

 

Or, what would the result be if i used resin on the painted surface? 

 

If i keyed it in first, this is already a barrier to the aluminium.

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The resin would either pickle the paint or not stick to it any better than bare Ali. I glued two strips of Ali (6mm x 50mm x 1200mm) to the inside of my tomcat rear roof to stiffen the sides in way of the struts with sikaflex. It worked very well and never came apart in the 6 years I had the car.

Mike

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I've decided against using resin at the joint. 

There is a possibility of flex in the roof combined with the prep which will be disturbed when the roof is prepped and sprayed at a later time, the joint is likelyto fail at some point in the future.

 

 

 

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