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Thread: Best density foam for mold making

  1. #21
    Senior Member Don's Avatar
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    Re: Best density foam for mold making

    Nick;

    Your process sounds pretty good for mould making. Only addition I would also put in before doing the gel coat is to use mould release of some sort. I use PVA and spread on my bucks with a soft cloth for my simple moulds but a lot of people also spray the PVA on to get an even coat all across. I figure I end up sanding the resulting piece enough to not worry about the slight imperfections that come from using a soft cloth. The mould halves should pop right off with mould wax and mould release.

    I also use unwaxed gel coat that you don't need to worry about having to sand before you apply the layers of glass. The fiberglass and the mould buck will pull the wax out to the surface so unwaxed works well. If you use waxed gel coat, let it cure all the way and then sand the surface before applying the fiberglass otherwise you end up getting mixing between the gel coat and the fiberglass when only waiting to get the gel coat tacky....

    I look forward to your pics and updates on the roof.

    Cheers
    Don
    308 Ferrari replica
    Prova Countach 5000QV

  2. #22
    Senior Member nicktruman's Avatar
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    Re: Best density foam for mold making

    Quote Originally Posted by Don
    Nick;

    Your process sounds pretty good for mould making. Only addition I would also put in before doing the gel coat is to use mould release of some sort. I use PVA and spread on my bucks with a soft cloth for my simple moulds but a lot of people also spray the PVA on to get an even coat all across. I figure I end up sanding the resulting piece enough to not worry about the slight imperfections that come from using a soft cloth. The mould halves should pop right off with mould wax and mould release.

    I also use unwaxed gel coat that you don't need to worry about having to sand before you apply the layers of glass. The fiberglass and the mould buck will pull the wax out to the surface so unwaxed works well. If you use waxed gel coat, let it cure all the way and then sand the surface before applying the fiberglass otherwise you end up getting mixing between the gel coat and the fiberglass when only waiting to get the gel coat tacky....

    I look forward to your pics and updates on the roof.

    Cheers
    Don
    Hi Don
    Thank you!
    So do you use PVA instead of mould release wax?
    As for Gel coat, I have just bought some coloured gel coat, I dont know if it has wax in it.

    So
    1. Spray with PVA spray
    2. Cover in mould release wax and let harden
    3. paint with (unwaxed) gel coat and leave until just tacky
    4. lay a layer of CSM and wet down using just enough resin to soak through
    5. let harden completely
    5. lay up as many layers as i need in stages to build mould

    Sorry to sound simple, but I am a bit confused with the waxed/unwaxed gel coat part.
    Regards
    Nick

    Twin turbo V8 Zonda inspired thingy

  3. #23
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    Re: Best density foam for mold making

    I think Don means a flowcoat when he talks about waxed gelcoat. It's not something I've ever heard of before. Flowcoat is a gelcoat with added styrene built in which raises to the surface when curing to form an air tight barrier to help it cure and create a non-tacky finish. It is designed for the last stage of a part and shouldn't ever be used as the first. You should always use regular gelcoat, or ideally tooling gelcoat, but if you're only planning one or two pulls you'll be fine with the regular gel.

    When you're talking about releases you should always give it at least 5 thick waxes, each time leaving it 5mins before polishing it off and applying another layer. When you've done them all you can use pva if you are really worried about it not releasing, although personally I hate the stuff and never use it. If you do though, spray a couple of thin coats with 15mins drying time between them, give it half hour or so to dry fully then apply your gel directly onto that. Whatever you do don't rub the pva off first, I know some people have got confused when using pva and wax..

    After the gels gone tacky you cam start laying up the glass. Best to keep the first layer thin and resin rich, but not soaked. Once that has cured keep adding more layers with as lillte resin as possible. Unless you use decent tooling resin you are right not to lay up too many layers at once. Let every two layers start to go off and cool down before laying up the next one. As a general rule your mould should be 3 times as thick as the parts you want to pull. However if you use a good tooling resin it will only need 2/3 layers of 600gsm matt after the first thin layer.

    I hope that helps

  4. #24
    Senior Member nicktruman's Avatar
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    Re: Best density foam for mold making

    Thank you, that is awesome!
    There probably is one, but if there isnt, someone should write an idiots guide to.. for this.
    I have learnt so much, and it would be great to see all this vital info in one place.
    from the gap between windshield and buck to sealing polystyrene with latex (emulsion) paint.

    Fantastic guys I owe you big time

    PS Here is a bizare twist..
    I was shaping the polystyrene at the weekend with a sharp knife and got bored. So i tried my angle grinder with an oxide disk. very delicately i glanced the disk across the surface, and I am not joking but I got an almost mirror finish! I wish i had tried it before..
    Regards
    Nick

    Twin turbo V8 Zonda inspired thingy

  5. #25
    Senior Member Don's Avatar
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    Re: Best density foam for mold making

    Actually I mean waxed and un-waxed gel coat.

    I am not sure what a flowcoat is but it sounds like what I get as waxed. Here in Canada, I can buy waxed or unwaxed gel coat. I actually says that on the can. As for your steps, do the waxing. Again, this is another area that might be a difference between countries as I have bee's wax mould wax that I put at least 4 coats on to the part to be moulded shining between coats. I then spread on the PVA over the wax. Then I do the gel coat. Then the glass layers until I am happy. I haven't had a part stick to the mould yet except for some old painted parts on the 308 nose clip but the paint came off the car and all I had to do was lightly scrape the offending paint off the mould piece and it came right off.

    The steps and products you have sound like they will be just fine and 8c explains it very well above as well.

    Good luck and have fun.
    Don
    308 Ferrari replica
    Prova Countach 5000QV

  6. #26
    Senior Member nicktruman's Avatar
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    Re: Best density foam for mold making

    So last night i did some more filling and decided not to use too much catalyst with the Bondo. Its 40 degs C today and after 20 hours it still hasnt gone hard and is still rubbery! GRRR. more of the red stuff needed?
    On the plus side I found a great way to add bits of polystyrene. I used gorilla glue and to hold bits in place the steel pins from used rivots!
    Tonight I want to make a hot wire cutter that can cut the length of the roof air intake in the shape of 3/4 of an elipse, that should be a challenge!
    Regards
    Nick

    Twin turbo V8 Zonda inspired thingy

  7. #27
    Senior Member nicktruman's Avatar
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    Re: Best density foam for mold making


    Can anyone help with this issue?

    I need to extend the arches/fenders. My idea was to carve polystyrene and epoxy glue it to the existing fender then seal it, and glass over that. leaving the polystyrene inside the fender. I thought it will not add much weight and add to the strength.

    I do not seem to be able to get epoxy resin here (not in small quantities) so how can i make the polystyrene polyester resin proof. I have not been able to find shelac either. If i give it a load of coats of emulsion paint will that do?

    I will still try and get epoxy resin, but it will not be easy. The best price here is about 7.50 GBP or $12 a litre but only in 20 litre containers

    Regards
    Nick

    Twin turbo V8 Zonda inspired thingy

  8. #28
    Senior Member nicktruman's Avatar
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    Re: Best density foam for mold making

    Quote Originally Posted by AutoCNC
    Nick, have you tried with Polyurethane coat? It does pretty good job in such applications.

    Bobi
    Hi Bobi
    No, I havent can you give me more information? What is Polyurethane coat? do you have a brand name/type I can look for?

    Regards

    Nick
    Regards
    Nick

    Twin turbo V8 Zonda inspired thingy

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