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Making Molding Bucks
scootz - 13/9/08 at 10:15 PM

I've started making a buck for the interior of my car and started using polystyrene to work out angles, etc.

Turned out that I made a pretty good 'shape' using it!

Only problem is - I had to use tape to piece it together as I found that glue dissolves the polystyrene.

Sooooooo.... if my polystyrene buck is structurally the biz, can I still lay glass / resin on it, or will it dissolve as it did when the glue was applied?

stevebubs - 13/9/08 at 10:37 PM

likely that the resin will dissolve it.

Thin layer of body filler will put a decent barrier in the way.

Not tried it but multiple layers of brown parcel tape are reputed to work, too....

Peteff - 13/9/08 at 10:44 PM

Wrap it in parcel tape and cling film and it will also be self releasing when the glass goes off plus it gives a half decent finish.

scootz - 13/9/08 at 11:22 PM

I had thought about the cling film bit, but didn't want to mention it in case you all laughed at me!

Cheers guys!

zilspeed - 14/9/08 at 07:20 AM

Whippy reckons that a layer of PVA over the polystyrene works well.

Never tried it myself.

cs3tcr - 14/9/08 at 10:08 AM

Typically polyester resin will eat it, epoxy wont. But if you're really wanting to see the effects, then test a sample (if you've got a few hours to spare). Take a couple pieces of your scrap foam and lay them up in all of your ideas.

From my experience, i try tests of most things. I'm a believer in text books, but i do have to try things for myself.

scootz - 14/9/08 at 08:08 PM

I've basically completed the buck... made of polystyrene ceiling tiles and coving lengths - all held together by parcel tape!

Sounds awful, but I'm really happy with the shape!

So my options appear to be... give it a brushed coating of PVA to give it a bit of protection before slapping the epoxy resin on.

One more Q... obviously there are lots of vertical bits. How do I apply the epoxy resin in a manner that won't have it running down the sides and pooling at the bottom? Do I mix it up and then allow it to thicken before applying... does that assist in the process?

Oh, and one very last Q (promise... well in this subject!). The rest of my Ultima bodywork doesn't appear to have any glass fibre in it - just looks like pure moulded epoxy resin - does this sound right, or should I mix some glass matting in with my epoxy resin? I need strength as I'll be stepping onto this piece (and I'm 17 stone!).

All opinion welcome!

Thanks (as always) in advance!

Peteff - 14/9/08 at 08:28 PM

I'd put some 3x2 under it as well as matting Your Ultima body is probably made from the sprayed stuff for easier construction.

mr henderson - 14/9/08 at 08:33 PM

quote:
Originally posted by scootz
The rest of my Ultima bodywork doesn't appear to have any glass fibre in it - just looks like pure moulded epoxy resin - does this sound right, or should I mix some glass matting in with my epoxy resin? I need strength as I'll be stepping onto this piece (and I'm 17 stone!).



It won't be pure resin, what it probably will be is very well laid up glass fibre, if they get all the air out it can be quite translucent.

To get epoxy to stick to vertical surfaces you need to add special filler to make it thixotropic. Available from all good resin suppliers.

John

scootz - 14/9/08 at 08:45 PM

Cheers John. I'm off to see what thixotropic means and how it interacts with the epoxy resin I have!

The 'base' of the seats will rest on a metal sheet floor, so it won't be taking all my weight... I just want it to be robust enough to last!

scootz - 14/9/08 at 08:48 PM

Seen THIS

Would I be just as well using this as a stand alone with glass matting... would it be as strong as an epoxy resin coating?

scootz - 14/9/08 at 08:50 PM

The Ultima site says the the bodywork is Unstressed GRP with Isophalthalic high heat distortion resin.

Whatever that means!

mr henderson - 15/9/08 at 08:31 AM

quote:
Originally posted by scootz
Seen THIS

Would I be just as well using this as a stand alone with glass matting... would it be as strong as an epoxy resin coating?


That's a contact adhesive!

If you are going to buy epoxy resin then almost certainly the people you buy it from (unless you are buying Araldite from the local ironmongers) are going to be able to sell you the thixotropic filler. That is the right stuff to use.

Thixotropic just means that it's like a gel coat, and will stick to vertical surfaces but is still liquid(ish)

John

scootz - 15/9/08 at 10:22 AM

Cheers (again) John.... !

THIS is the epoxy resin I'm using.

I'l perhaps just try doing repeated thin glass mat applications.. may take )a lot) more time than just dolloping it on, but I want good results, so will just have to suck it and see!

mr henderson - 15/9/08 at 10:28 AM

This is the filler you need (from the same web site)

http://marinestore.co.uk/Merchant2/merchant.mvc?Screen=PROD&Product_code=HA1486&Category_code=blakes-and-sp-epoxy

Avoid sucking the FRP, it tends to be poisonous.

John

Syd Bridge - 15/9/08 at 11:37 AM

quote:
Originally posted by scootz
The Ultima site says the the bodywork is Unstressed GRP with Isophalthalic high heat distortion resin.

Whatever that means!


That's Scott-Bader 272 resin, or so it says on the drum out the back. SB reps like to say that Ultima and TVR(when they were alive) used all their resins. Been using it for 21 years. Excellent stuff, and wets out real quick and easy. Only downside is that it costs not far short of lower end epoxies.

Cheers,
Syd.

scootz - 16/9/08 at 08:43 PM

So... so I should mix this thixotropic / Microballon stuff with my Epoxy Resin / Hardener for a thicker working product... should I also use some glass matting with it if applying it onto a plywood surface for flat sections?