David P Williams Posted December 6, 2021 Share Posted December 6, 2021 I have a large fibreglass cowling moulding that I want to modify. Is there an easy way to identify whether it's polyester or epoxy? I understand that they don't play well together. Is it easier to bodge it to how I want it then make a new mould and cast a new epoxy one? Any gotchas to watch out for? Thanks, David Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted December 6, 2021 Share Posted December 6, 2021 Sand the inside with some coarse glasspaper, say 120 or 180 grade. The smell of polyester will be very strong and "plasticky" - just like polyester resin. Epoxy frequently has a very faint smell or none at all. It's hard to comment on your proposed modifications without knowing what they are, but GRP moulded (regardless of the type of resin used) are simple to reshape, rework or repair. 1 Quote Link to comment Share on other sites More sharing options...
David P Williams Posted December 6, 2021 Author Share Posted December 6, 2021 Thanks Alan. I need to shorten the cowling, but of course it tapers, different angles all round. If I am reshaping or reworking it, can I use epoxy regardless of what it’s made from or must it be epoxy on epoxy, polyester on polyester? Quote Link to comment Share on other sites More sharing options...
flight1 Posted December 6, 2021 Share Posted December 6, 2021 If in doubt use epoxy as it will stick to itself or polyester will be lighter and stronger, just prep properly(degrease and roughen to key up) Quote Link to comment Share on other sites More sharing options...
Alan Hilton Posted December 6, 2021 Share Posted December 6, 2021 If it’s glass chop it’s got to be polyester ,epoxy won’t work with chop due to silicone which is used to hold the chop together . If it’s glass mat it could be ether so smell it Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted December 6, 2021 Share Posted December 6, 2021 That's not strictly true, powder bound chopped strand mat is perfectly compatible with epoxy resin. Quote Link to comment Share on other sites More sharing options...
Paul De Tourtoulon Posted December 6, 2021 Share Posted December 6, 2021 Polyester dust smells like marzipan,,, Don't forget Epoxy sticks to Polyester but Polyester won't stick to Epoxy. Quote Link to comment Share on other sites More sharing options...
Alan Hilton Posted December 6, 2021 Share Posted December 6, 2021 2 hours ago, Alan Gorham_ said: That's not strictly true, powder bound chopped strand mat is perfectly compatible with epoxy resin. Haven’t come across powder bonded chop is it common ? Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted December 7, 2021 Share Posted December 7, 2021 Just stick to epoxy for epoxy and polyester for polyester then you won't have to worry about silicone or powder bound chopped mat. With either type , clean ,degrease and abrade thoroughly any areas to be bonded prior to starting work. 2 Quote Link to comment Share on other sites More sharing options...
Andy48 Posted December 7, 2021 Share Posted December 7, 2021 Use brown Gorilla glue, it works well with both epoxy and polyester provided you lightly sand the bits to be glued to provide a good key and get rid of any moulding release agents. It does foam so the pieces need clamping together. Quote Link to comment Share on other sites More sharing options...
David P Williams Posted December 7, 2021 Author Share Posted December 7, 2021 Thanks everyone for your helpful replies. This is the problem I have (serves me right for wanting a totally different engine than the kit was made for) I'm trying to leave the cylinders exposed and either just cover the exhaust collector ring or butt up to it with a small gap and this is the inside of the moulding. I've tried sanding it and it maybe smells a bit marzipan-y but my sense of smell isn't great The more I look at it and try to measure in three dimensions, the more I think I need to start from scratch and make a mould somehow. It's supposed to look something like this. I obviously won't get true scale representation but a reasonable looky-likey will do. Quote Link to comment Share on other sites More sharing options...
Piers Bowlan Posted December 7, 2021 Share Posted December 7, 2021 Epoxy/glass by the look of it. Quote Link to comment Share on other sites More sharing options...
Paul De Tourtoulon Posted December 7, 2021 Share Posted December 7, 2021 No, it's chopped strand mat = polyester,,,, Woven mat = epoxy,,, Quote Link to comment Share on other sites More sharing options...
flight1 Posted December 7, 2021 Share Posted December 7, 2021 (edited) 2 hours ago, Piers Bowlan said: Epoxy/glass by the look of it. ? your observation is good oops bit sarcastic me? Well it's made from chopped strand glass and a resin of some sort which you can not determine by a picture so with alterations use epoxy and woven cloth it will work good. the fact that it is chopped matting doesn't matter as it has cured . also with matting you can get Emulsion bound for Polyester and Vinylester resins and powder bound for epoxy so its all a guess unless you can ask the one that made it I would use the back end of your existing cowl cut off where the yellow stops on the picture of the real one and then with the front bit you have cut off to simulate the manifold/exhaust cover on the real one . then laminate the bits together together. Edited December 7, 2021 by flight1 more info Quote Link to comment Share on other sites More sharing options...
Allan Bennett Posted December 7, 2021 Share Posted December 7, 2021 I would be sorely tempted to use that cowl as a master to make a mould from. Add all the little bumps and other raised details using P38 or equivalent, cut or file the panel lines and other recessed details, then make a mould of it. Quote Link to comment Share on other sites More sharing options...
David P Williams Posted December 7, 2021 Author Share Posted December 7, 2021 Yes I think hacking the cowl around and patching it up is the first go, and then possibly using it to make a mould. I need to make it a two piece affair anyway or I won’t be able to fit it. Morris at Morris Mini Motors has confirmed I can cut down the exhaust headers by 15mm to move the collector ring closer to the cylinders for a more scale look and to give me more wriggle room. Quote Link to comment Share on other sites More sharing options...
flight1 Posted December 7, 2021 Share Posted December 7, 2021 that's probably the best way to go- hack the cowl until you got what you want the use it as a plug to make a mould for a new one. lighter stronger and a better finish. made a custom petrol fuel tank that way recently, took the same time as trolling through the internet trying to find one that fitted my application. Quote Link to comment Share on other sites More sharing options...
Paul De Tourtoulon Posted December 8, 2021 Share Posted December 8, 2021 (edited) If you have the know how, go with making a mould and moulding a new epoxy / roving one, it's lighter and stronger than Polyester. you can always make a plaster of paris mould as it's for a one off,,, Edited December 8, 2021 by Paul De Tourtoulon plaster Quote Link to comment Share on other sites More sharing options...
David P Williams Posted December 8, 2021 Author Share Posted December 8, 2021 Now I’ve done more measuring and faffing with cardboard templates I think a cut’n’shut might do the trick. Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted December 8, 2021 Share Posted December 8, 2021 I would pop a mould (plaster ok) from the cowling before butchering it as then you have a starting place. Also a plug with holes in it can present few release issues. chris Quote Link to comment Share on other sites More sharing options...
David P Williams Posted December 8, 2021 Author Share Posted December 8, 2021 Thanks Chris, good tip Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.