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Resin casting.

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  • Resin casting.

    Hi. I’m hoping to make a Lego man lamp, using resin, for one of my grandsons. I am fairly new to resin but not new to craft and having a go. I plan to buy a silicone Lego man mould. Just a question, do I pour a layer then leave it to set. Then another layer and then another. Is it best to build it up in layers
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  • #2
    It's been years since I did any resin casting, so you may find a better answer elsewhere. However, as I understand it, the normal reason to do pours in layers is when the hardening process involves air (nitrogen or oxygen) cures.
    With resin, the mix contains hardener (which does need to be mixed thoroughly) - and doesn't require air curing.

    Other points coming to mind
    During the pour / hardening, the resin lets of lots of fumes (or certainly used to) - so I would definitely go for somewhere that is very well ventilated.

    The weight of the resin will cause your mould to bulge - so you may well want to reinforce the mould with a casing before starting - if you have done lots of moulding before, you will have far more experience than me with this, but a plaster mould casing is not unusual.

    If your mould is a full front and back, poured from the base, it will probably be in two parts. If it is a front mould only (such as from the cake moulds I can see on google) you will be pouring the resin into the back of the model. (if you are doing a multi-part mould, you need more instruction - I have a text somewhere, so should be able to assist - but it's a little more complex).

    In both cases you will probably want to make a mould casing - this is often made with plaster. If you do that, then soap the outside of the silicone (just diluted washing up liquid) just before applying the plaster to prevent beading and bubbles adjacent to the silicone. Depending on the thickness of the silicone, you may need to fill your mould with damp sand (or something else that will keep the form and is easily removed) so that you keep the shape of the mould while applying the plaster around it.

    If you are doing a waste mould (one big lump of plaster which will be chipped off to release it - important with overhangs, etc) then using an inner, food-coloured (eg RED), layer of plaster around the silicone mould will allow you to know when you are getting too close to the silicone mould. You then make the waste mould in two parts - a coloured, applied layer about 1 cm thick around silicone - and then once it is dry, put it into a lined box and pour in white plaster for the outer mould. The box just needs to be big enough to keep the mould flat and stable - and you can fill up the gaps with bits of stone or gravel which cuts down on the plaster cost, and helps with the chipping away. So then you will have a white brick with a bit of red inside, and with the silicon inside that - which now needs to be cleaned / washed.

    Then you apply your release ready for the resin, then you can pour the resin, adding any lights or bits; de-bubble it (I seem to remember that a vibrating plate worked quite well, as I never had a vacuum pump or anything like that - anyway, resin de-bubbles far easier than plaster does), let it set fully (and add a few hours), and then de-mould by chipping off the white - then carefully removing the coloured plaster, and then lastly removing the silicone mould itself.

    You may need to sand & polish the open side(s) of the resin cast - but you should end up with a really good moulded resin lego man.
    If you are going for precise measurements, you will need to check the shrinkage of the resin you are using. Some resin shrinks quite a bit - but for this sort of thing, you probably don't need to worry about it.

    Also, a fresh resin model does tend to give off fumes for some time afterwards, so it may be worth thinking about leaving it to age a bit before gifting it?
    Last edited by Konchog; 18-10-2021, 12:56 PM.


    • #3
      Wow! Fantastic reply. Lots to think about. Thank you so much