Hi, I am doing a belly cast for a friend, and I used the plaster bandage to make a fairly thin copy of her belly.
I would like to lay fiberglass or something tough into the plaster bandage negative in order to get out a positive.
I tried this once before, and the fiberglass stuck so well that when I tried to pop the positive out, the mold was destroyed and it took forever to clean the positive up.
I don't even mind losing the mold, but I do mind the amount of work required to get off all the bits of plaster bandage that sticks to the positive.
What can I use as a mold release on the plaster bandage?
Thanks for the help,
I am not sure how the fiber glass will react to vasaline (or something along the lines - some oily substance) that might work. Because the plaster is porous it absorbs liquids from fiber glass (or what ever else you decide to cast in) and kind of fuses with the cast... so you need to do a trial and error to see how you can avoid this. maybe even a thin layer of lacker on the inside of the mold would work.... make a small mold and experiment. If you understand the principal you can work something out.
Let us know what happened
Okay, could I cast plaster into the mold? What would I use as a release then?
Just to clarify, I am proposing casting plaster such as Hydrocal into a plaster bandage mold.
I have used vaseline before for various things, but often the vaseline is thick enough that it changes the object to be cast.
You can buy special release agents.
here is one idea for a release agent. I did a search for release agents for plaster molds and this is only one of the answers. I would try the crystal clear acrylic paint - it seem that it would be a cheap and easy solution if it worked!
Let me know what happened...
This is just what I'm trying to do today but I thought I would try to put clay into the bandage plaster mold of the torso, which I did last night.
My plan has been to then put fibreglass onto that. I'm worried about the porousness of the clay in the same way as the plaster but I didn't want to wreck the plaster original that's why I'm doing it this way.
Might spray it with acrylic car primer and lay a couple of layers of wax release agent and then a layer of blue rubber onto it, as this is a tried and tested method when I've made a plug out of fibre board and car bog (also porous). only problem will be that I haven't fired the clay and so it's REALLY unstable and might crack.
I wonder if I can spray the plaster mold with the acrylic primer ????? any thoughts??
Well, I have two new answers to the question I posted, sort of anyway.
Ways to belly cast:
1. Plaster bandage male
-lay on a thin layer, then soak in epoxy or polyester resin for strength
-I tried this one, worked well.
Plus: fast, easy, hard to **** up
Minus: detail is limited to basic shape, often plaster bandage sags/wrinkles.
2. Fiberglass Male from bandage
-lay on a thick layer of plaster bandage, then pour/paint in gelcoat,
-back up with multiple layers of laminating resin and fiberglass cloth/roving
-I tried this one, worked, but lots of work.
Plus: guaranteed to work, gives a tough-as-nails fiberglass male, with very good detail of shape (no skin detail, but will capture wrinkly bits)
Minus: gelcoat penetrates weave of cloth, makes cleanup a pain, removing bandage, then sanding off bits left, time consuming doing layup, trimming cast etc. more expensive due to extra materials
3. Fiberglass Male from Alginate
-pour/spread/whatever alginate on model,
-back up with layer of plaster bandage
-integrate ribs and strengthening measures
-pour/paint/whatever gelcoat into alginate and back up with multiple layers of laminating resin and fiberglass cloth/roving
-haven't tried this one, sounds good though, need alginate and willing pregnant woman.
Plus: captures very, very good detail, skin texture too. Gives very tough positive, very little cleanup
Minus: longer time in the chair, higher cost again, alginate only stays good for short time (hours) so there may only be time for one attempt at gelcoat/fiberglass male
So, the question was about a release agent and I have answered it by avoiding the need for a release. Here's why: I don't want a plaster male! It is far too heavy for people to put on the wall. So, fiberglass is the best choice and the question changes. I hope that this is useful for someone out there.
What is this blue rubber business?
Thank you so much for the options.
I agree, I too am looking for a lighter alternative to plaster.
I have gelcoat so that's good for a start but I don't know what alginate is so will have to investigate that one. Problem being there is - the baby has been born so can't use the model again!
Blue rubber is the PVA Rubber release agent which is sprayed, poured or painted on before the gelcoat and keeps good detail from the mould. I got it from a place that is making fibreglass boats and shapes. Also asked at a car paint supplier and they said they could get it in so it's not such a common thing to use but it is an extra guarantee that your mould will release.
OK, so this is exactly what I was planning on doing with my belly cast soon. Only problem is I've never done anything with fiberglass before, so I'm a little hesitant and thinking I need to do a few test runs first.
But, about removing the plaster bandage mold... Why do you need to at all? I mean, I understand trying to keep the weight of it down, but the plaster bandages aren't that heavy. Why not fiberglass the outside and then when it's dry, fiberglass the inside? Cover the edges really well and just seal the plaster bandages inside...?
I would especially love to see photos of this if anyone has success!
Best of Luck,
Just wanted to say Hi and Welcome to the forum, Jana I hope photos will show up soon
Why use a layer of fiberglass inside?
Well, as you've noticed, the detail that you get from plaster bandage is less than a perfect replica of the skin.
If you lay fiberglass into the bandage mold, the resulting positive is an exact replica of the contours of the skin of the model.
Think of the bandage mold as the eggshell, and the fiberglass laid into it as the inside of the egg. Which one will look better?
The inside is perfectly smooth, the outside is bumpy, lumpy and hides all contours. The bandage has inconsistent thickness which messes with the contours and overall shape.
I am now thinking of using alginate with a fast-set epoxy to form the gelcoat layer and to take all the detail from the alginate. Polyester resin is no good, is water inhibited, won't cure. Epoxy should do the trick. Now I need time and more pregnant ladies!
Ok so far I still haven't had success but haven't totally destroyed my mold.
So far I've put a layer of fibreglass resin (without glass fibres) on outside of plaster to strengthen mold then turned it over and put a layer of fibreglass resin(without glass fibres)to seal the plaster as it is so porous. Then I put a layer of gelcoat on. Now I've lost any wrinkle detail and just going for the shape of torso. Then I put 7 coats of wax on, buffing in between layers,and then PVA (a water soluble rubber type release agent) then a layer of fibreglass WITH the glass fibres.
It STILL wouldn't release!! I have tried to prise some fibreglass off and pour water down it which helped a bit but now I am cutting it up into sections with a grinder and going to piece it together again and fibreglass it together and then mosaic the outside of it so it won't matter that I loose detail.
I'll let you know how it goes. Still curious what alginate is....
ps Fibreglass is really easy to use. You just need to get a proper measuring bottle for the catalyst. 1.5% or a bit less if it's as hot as it is here in Australia
The problem that you have is apparently (from books I have on hand, and a fiberglass expert I speak to regularly) caused by styrene migration.
I had the same problem, I patched the inside of the mold with bondo and then laid in wax and pva for release. The plaster actually let go fairly easily, but the spots where the bondo was nearly didn't come off at all.
So, as I understand it from my expert, the styrene which makes up the bondo and the polyester resin was not blocked by the PVA. So, it happily migrated across the thin membrane and bonded with the new layer of polyester.
You have a similar version of the same problem, exacerbated by the fact that you used a full layer of the gelcoat, which subsequently bonded with the reinforcement layer.
Basically, your problem was caused by the barrier layer of wax/pva not being thick enough.
In industry, they will do a bunch of layups on a plug as throwaways in order to "condition" the plug surface. What they're actually doing is reducing the reactivity of the styrene monomers on the surface of the plug, so that later layups will part cleanly and easily.
We, doing mostly one-offs need a different solution. What that solution is, I don't know. If I did, I'd post it.
Alginate is like hardened yogurt. It takes a mold of a thing, but refuses to stick to it. It is also very floppy and easy to accidentally tear. It will take detail down to fingerprints no problem. It is used by lifecasters and makers of prosthetics for film/tv/medical. It sets very rapidly, like 2-3 minutes.
Dentists use it. Ever have them give you a mouthguard-like thing and they ask you to bite down for like a minute? That was alginate that you were biting into. It is used to take a perfect impression of your teeth for later copying or fitting of dental castings or fillings/crowns, whatever.
Take it easy, your solution sounds good, if troublesome and kind of disappointing. Next time you will do it differently I'm sure.
Next time, just reinforce the outside to prevent the mold bending, then lay the fiberglass into the bandage. You'll still have to destroy the bandage mold to get the piece out, but at least the removal will go easier and the cleanup will be less.
Oh, if you still want to take stuff apart, I've read that sometimes you can use compressed air and a thin wand to separate laminates. I've never tried it.
Thanks for the welcome! Learning lots already!
I was looking for some articles on the web to help me deciding which materials to use to cast my belly and then I found this thread.
I'm 34 weeks pregnant and I really wanna cast my belly. However, I'm living in the USA temporarilly and I'll be going back to the UK on June.
So, I need to use a material that is light as well as resistent (all due to the transportation from here to there).
When I first decided to cast my belly, I thought of using bandage plaster as mold.. but, after reading a bit, I decided that alginate (mother molded with plaster) would be best
As a casting material I thought of resin but I read it shrinks and smells pretty bad.. so I'm reconsidering..
So.. here is my drama: I wanna do it nicely (I wanted a pearl finishing) but need to keep the cost low, the level of difficulty up to medium and long durability of the final cast (I don't really care about the durability of the mold)
So, could you guys help me brainstorming???
Thanks a lot
Cheap and durable hey? Hmm. Well, there is no way to do it CHEAP but there are less expensive ways, that's for sure. The cheapest is bandage, but as you pointed out, not very durable.
Polyester or Vinylester Resin is indeed stinky. A coat of paint and some time usually fixes it. I don't know about this shrinking thing that you are referring to. I did a whole belly with it, and I can not tell any shrinkage. The stink factor is a far more compelling reason to look further (but it's cheap!)
So, if I had your set of restrictions, I'd make a bandage mold, keep it thin, and then dry it out and coat it with epoxy resin. You can get enough to do a belly cast for probably 50$ or less. Don't get the pumps, just measure it out in cups, save the cash.
Epoxy resin does not stink nearly as much, pretty non-stinky I think. It will soak the bandage, and make it much, much stronger. It will be strong, but brittle, so as long as you are somewhat gentle, it should fare fine.
For shipping, put it in a box with packing material all around, packed tight, tight, tight.
Then put that box into another box with packing material all around, and seal it up. The box in a box method is wicked awesome for shipping. I sent a 18" glass platter from Greece to Toronto, Ontario, no problem.
Bandage, approx 30$
(don't go cheap here, if you blow the first one making it too thin, you can always make another)
Epoxy, approx 50$ Fast hardening
(no need to buy West System. Go to a boat supply or look up "composites" in the yellow pages)
-if you get fast hardener, you don't have to wait around for 24 hrs for the stuff to stiffen up.
-just keep brushing it on until it starts to gel and then leave it for at least 24 hours.
-Keep it thin on the front side, thicker (if you want) on the back where it won't show
-brush on the epoxy, catch all the drips in a big pan (line a cardboard box with a garbage bag) and get ready to re-brush on the epoxy, after it drips off.
Alginate cost (depending on size of model) is at least 75$ (includes extra for screw-ups)
bandage for mother mold 10-20$
gypsum casting material for pouring into mold min. 20$
So, Alginate method is not fast, cheap, easy, etc. But boy are the results fan-friggin-tastic.
green soap works good. they have it in most pharmacys etc.paint it in let it dry... make sure you dont have bubbles, and repeat a few times.
I made a mold of my wife when she was 8 1/2 months pregnant recently using Body Double silicone rubber from Smooth-On; worked great.
I chose the Body Double because I wanted the mold to last for awhile since I was not sure when I would be able to make the casting; and now with the baby here, who knows!
But at least I have the mold, which is sitting out in the open air, and there is no degradation or shrinkage. Plus is does not give off any heat when curing, so it is completely harmless to the skin.
I failed to get the plaster away from anything I put onto it so after putting fibre glass resin onto it to strengthen it. I actually really like the effect the glass resin has on the plaster and may revisit that effect with another project in the future.
I decided to mosaic the outside. I have got half way through it now. The lady that I took the image of is part Inca so I have used this theme in the glass tiles I am using. I have found patterns that use in their weaving.
Cost for silicone?
Yes, that works for plaster, but does it work with polyester and vinylester resins? I've never tried it, so I don't know.
Looks good! If you like the look of seeing the reinforcement, try carbon fibre on the next one! That will catch some eyes.
I like using her background as inspiration, cool.
What is the mottled white/grey colouration on the cast from? Is that intentional?
carbon fiber with epoxy resin looks really cool..
Could you get a textured look though? Or is it always flat. I think I've only seen the carbon fibre used in the boating industry and they do sand it to get the smooth shape they want such as carbon fibre boat masts. Do you paint it on or pour it into a mold?
This will have to be explored more! Hmm, Sounds great!
carbon fiber can be laminated with wet epoxy then lay-ed up; it also comea pre-impregnated with epoxy resin - called Pre-pregs; these are typically heat-cured, so you would need an oven to cure the material as they are kept cold prior to use; room temps are not hot enough to fully catalyze the materials.
Depending on the weave of the fabric (glass, carbon fiber, kevlar, etc) you can get some texture, but you somewhat limited by the weave already present; you can pull the weave apart, but then you reduce the strength of the carbon fiber, which is why it is used primarilly. Carbon fiber drawback is that it is expensive.... so it depends on what the finished objective is.
It's used just like regular fiberglass cloth. Get it wet, lay it into the mold, get rid of any wrinkles (easier said than done) and wait.
Can't sand it really. Best to use a thick layer of resin over top and sand that. There may be easier ways to get that "look" though. You'd really have to be dedicated to get into the whole carbon thing. It's not cheap to buy, and for a belly, you need a yard at least.
on a plaster bandage negative mold you have the problem of the plaster being dry so you will need to seal it first with shellac(50% orange shellac and 50% denatured alcolhol) Put a few coats on then use vaseline as a separator or a paste wax, making sure that you apply two coats of separator to be sure that you got in everywhere and didn't miss any spots.
Sorry it took me so long to reply to the question:
'What is the mottled white/grey of the background?'
Well It is a plaster base (from the original cast) and fibreglass (resin only) over the top of that and then I sanded that back slightly to make a smoother surface to glue the tiles onto. So the white coming through is the original plaster and the grey is the resin. The resin did not lay on flat so had occasional sharp raised surfaces in places.
Still a work in progress and I have put more glass tiles on it. don't know if that was the correct decision but that is art. It doesn't always work out and it is really hard to know when to stop and when to leave something that half finished raw look either.
hi, i read your answer about the layups that been done by indudtrial profesionals on mold,which is exactly what i need to know,because i am trying to use my plaster mold is the default molds for manufacturing clear polyester lighting objects.
i didn't understant was is it that you mean by 'layups' to 'condition' the mold,maybe it's some phrase i'm not familiar with,not being a english speaker by native. can you explain for me again what is this process?