carcentric
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| posted on 29/12/04 at 06:50 PM |
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Concrete molds for fiberglass parts
I remember reading somewhere that concrete makes a good mold material for fiberglass parts - it's supposed to be extra durable and won't
flex. Now that I want to try it, I can't find the article/post/whatever . . .
Can anybody point me in the right direction? Issues would seem to be:
- what type of concrete mix?
- how thick should it be?
- standard release agents, or something different?
- part pulling technique differences, if any?
- put rebar or wire mesh in the concrete?
The fenders I want to dupe are from a Gazelle kit car - long "flying wings." In case the process isn't clear, you make a concrete
(female) mold from the original fiberglass fender, pull apart, make new giberglass fender in the concrete mold, pull apart - the goal is NOT to make
fenders from concrete.
[Edited on 29/12/04 by carcentric]
M D "Doc" Nugent
http://www.carcentric.com
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stephen_gusterson
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| posted on 29/12/04 at 08:03 PM |
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i would have thought it would be easier to shape a softer material such as filler - im assuming that you are suggesting concrete as a buck?
also, it would need to have a smooth, sealed surface.
my amateur attempts are on my web site, but alanB and syd bridge seem to have the best experience on here....
atb
steve
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Cita
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| posted on 29/12/04 at 08:35 PM |
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I have done some concrete molds a few years ago.
First of all you need to be absolutely sure that the original can be pulled from the mold (no parts curved inside)
Next thing to do is stabilize the original by filling the inside with foam,plaster or whatever.
The most tricky part is,and this is very difficult to explain without a drawing or picture,to form an edge around the bottom side.
Reinforcements bars of 5/6 mm are easy to bend in shape and can be hold together with wire.
I used fine grid for the concrete and since it's not a structural thing,dont move the concrete to much once you are sure everything is
covered,otherwise the grid will sink on to the original and the cement can crack around where the grid is visable.
Be sure to leave at least two handles to lift the concrete mold cause it's allways heavier than you think.
The concrete takes about 3 weeks before the chemical process is ended.
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Hugh Paterson
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| posted on 29/12/04 at 09:54 PM |
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Waste of time nowadys, much easier methods to achieve the same result
Shug.
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Cita
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| posted on 29/12/04 at 10:22 PM |
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quote:
Originally posted by Hugh Paterson
Waste of time nowadys, much easier methods to achieve the same result
Shug.
I agree that it's labour intensive but it's about the cheapest way to make durable molds.
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Volvorsport
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| posted on 29/12/04 at 11:43 PM |
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a GRP mold will be more durable than concrete .
www.dbsmotorsport.co.uk
getting dirty under a bus
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Cita
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| posted on 30/12/04 at 02:10 AM |
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quote:
Originally posted by Volvorsport
a GRP mold will be more durable than concrete .
A titanium mold will be more durable than GRP...but concrete will still be the cheapest
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Geoff011
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| posted on 30/12/04 at 02:17 AM |
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Try googling "plaster splash mold" - plenty of info available to use plaster reinforced with heshian.
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Cita
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| posted on 30/12/04 at 02:22 AM |
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what's heshian?
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David Jenkins
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| posted on 30/12/04 at 08:10 AM |
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Hessian, I think he means.
A coarse, open-weave cloth material used for making sacks, usually made of natural fibres such as jute.
rgds,
David
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Cita
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| posted on 30/12/04 at 09:07 AM |
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thanks David
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David Jenkins
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| posted on 30/12/04 at 09:24 AM |
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Also known as "burlap" in the US of A (isn't Google a wonderful thing...  )
David
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Simon
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| posted on 31/12/04 at 12:29 AM |
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Could also try using Herculite plaster instead of concrete.
Will be lighter, smoother and is very very hard when set (allow a couple of days if thin)
If using hessian, cut to size and lay into whatever you finally use, then holding one end, with other over bucket, ring out by sliding clamped hand
down wet hessian (helps ensure you get it completely wet!!)
ATB
Simon
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Volvorsport
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| posted on 31/12/04 at 12:34 AM |
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well , for the £50 in materials using concrete wouldnt be my foirst idea - anyway there is a system out there that is not 100% grp , but a mix of
fibres and plaster .
Its used by the guys who do one off stuff and prototyping , its pretty easy to use , you put it one once and thats it , and can be used for
autoclaving stuff .
Still , youll get more pulls from a grp mold than concrete .
www.dbsmotorsport.co.uk
getting dirty under a bus
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Cita
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| posted on 31/12/04 at 07:16 AM |
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quote:
Originally posted by Volvorsport
well , for the £50 in materials using concrete wouldnt be my foirst idea
If the concrete for a mold will cost you 50 quid than i'm very interested in the price of your house Volvosport
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Volvorsport
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| posted on 31/12/04 at 03:43 PM |
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well , alright , concrete is a £10 say , you still need the correct release agents to work with , and i dont think the surface would be as good ,
anyway , if it serves it purpose then do it - people use latex for concrete molds . I dont know how youd trim a concrete mold for instance !
www.dbsmotorsport.co.uk
getting dirty under a bus
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Cita
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| posted on 31/12/04 at 04:44 PM |
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Poor some concrete in a plastic bottle,let it cure remove the bottle and take a look at the finish,you will be surprised.
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undecided
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| posted on 31/12/04 at 05:01 PM |
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yeah but that plaster and fibre stuff is a bitch to use or rather make any repairs to as nowt will stick to it...........only really any good as a one
hit wonder as mould tends to break and is also affectied by damp.......best thing to use for moulds is grp.
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stephen_gusterson
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| posted on 31/12/04 at 08:05 PM |
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do you actually mean cement or mortar?
concrete had large particles (stones) in it and can set with quite large surface voids......
atb
steve
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Cita
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| posted on 31/12/04 at 09:01 PM |
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Cement and/or mortar are brittle.The pebbles and reinforcement bars gives the strong structure.
Fine grid pebbles must be used for a mold and a not too wet concrete otherwise the pebbles will sink onto the buck.
There will be some cracks but these can be filled with plaster and sanded smooth.
Concrete on itself is not waterproof so the surface must be painted to seal it off.
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