support material for mother molds

[Snakescales]

I'm pretty annoyed at the prices of hemp fiber in the US for making mother molds and I don't quite like to use burlap as much, fiberglass is great but I have a small workspace and I don't like to keep it around due to health hazards. Does anybody know of any inexpensive fabrics or fibers that work well as a support for making mother molds. Of course the thinner and stronger the better, thanks.

-A

[Arrow]

Good question. I was wondering what else I could use too.

Nylon Netting, used cotton clotheing, fishing line, chopped baleing twine...

Packaging Netting:
http://www.sheerlund.com/products/xmas/net.html

Knitted Pallet Netting
http://www.cwestern.com/products/packaging/knitted-pallet-netting.html

Not sure what the netting cost....my computer hates pdf files......

[realsculpt]

hemp is your best bet, though a loose weave burlap is just as good, the trick is to wet the burlap before dunking it in the gypsum. also try using Ultracal instead of other plasters, it is the same price but more effective and strong.

but the cost of the hemp is nothing compared to a good mold that will last. dont try to save 10$ and end up with a inferior mold.

[Snakescales]

You make a good point Realsculpt, but I feel it's worth investigating, it's just a bit ridiculous to me because the same hemp in Mexico costs only a couple of bucks as compared to 100 for a bale here in L.A. I would prefer hemp over most other materials but as long as the mother mold holds, it shouldn't affect the face mold so I'm willing to see what i can get away with.

-A

[Snakescales]

Thanks, Arrow. Those are sone interesting suggestions. I tried fiberglass drywall tape today, it seems to work fine for the edges but then I have to use burlap or cloth for the body since it doesn't want to bend or fold into the spaces too well.

-A.

[clifton]

I use the mesh drywall tape in making silicone molds. Cut it to help in shaping. Works well for that.

[Merlion]

I do have problem with plaster molds breaking, especially when I try to bend to open them after casting.

When I can remember it, I reinforce the larger molds with fiberglass chopped strand mats beforehand, and they become much stronger against bending.

These chopped strand mats cut into rectanglar strips are the same ones we normally use for reinforcing to make thin walled fiberglass resin sculptures.

But as so many books mention the use of woven burlap, I got hold of some and tried it. Unfortunatly I found this does not help to make the mold stronger. It seems to be just as weak. I think it is because, unlike fiberglass mats, burlap can stretch easily so it does not strengthen the plaster molds against tension when bent.

But burlap does help to keep the broken mold pieces together instead of falling apart. This makes it easier to repair by adding plaster outside.

Do others have the same experience ?

[Landseer]

I never use reinforcements in my plaster molds, when I did and a piece cracked it seemed to make it more difficult to repair than two separate pieces because you couldn't get glue in the crack easy without bending the pieces apart and stretching the reinforcement.

You shouldnt need to do much pressure to open the mold, if all undercuts are allowed for the mother should all but fall off. I use plenty of Murphy's oil soap if needed on the outside of the rubber and the inside of the plaster shell, and all mating edges, and the outside of the plaster shell too.

[Andrew Werby]

[QUOTE=Snakescales]You make a good point Realsculpt, but I feel it's worth investigating, it's just a bit ridiculous to me because the same hemp in Mexico costs only a couple of bucks as compared to 100 for a bale here in L.A. I would prefer hemp over most other materials but as long as the mother mold holds, it shouldn't affect the face mold so I'm willing to see what i can get away with.

I've tried just about everything to reinforce my plaster molds, and sisal (also known as Manila hemp) is the best. Yes, a bale (~40 lbs) is over $100, but that's enough for a whole lot of molds. Just the convenience factor - not having to cut pieces of cloth to fit - makes it worth getting. I don't think any cloth or fiber is going to be much cheaper. A bale seems to last me a long time, but if you really use a lot of it, go to Mexico and fill your truck.

Burlap will cause voids and separations, fiberglass makes you itch (the best is either scrim or that yellow open-weave cloth sold at roofing supply outlets), onion bags are good, but you need to find the old-fashioned type made with string (the new type is plastic, which doesn't work) and they're hard to prepare for use. The other thing I use for reinforcement is copper tubing, which is easy to bend and provides stiffness the fiber doesn't, but that has really become expensive lately - sisal's still cheap...

[Merlion]

While doing a search, I notice these advisory comments relevant to this thread.

Plaster mold casings ( the "mother mold" that holds the rubber) can be made stronger by reinforcing the plaster with "Sisal". Sisal or "Manila hemp" is the raw fiber from which manila rope is made. Look for it at construction materials supply houses. They may call it hemp, or casting fiber or by some other term. A bale of Sisal will set you back about $150 but will make100 or so average sized molds. Others like to use fiberglass-either loose chopped strands or loosely woven scrim cloth- or 7 oz. burlap (the more common 10 oz. burlap is too tightly woven to be useful). In general, the woven materials are best for larger or simpler molds, the non-woven ones conform better to the concavities of a small or complex one.

Larger molds may benefit from more rigid reinforcement as well as the use of harder plaster, like Ultracal 30 to allow thinner molds. (This is more difficult to work with, as the setting curve is more abrupt.) You can use steel for reinforcement if it is galvanized. Uncoated steel will rust and crack the plaster as it expands, wood absorbs water and acts similarly. Copper tubing, though relatively expensive, is easy to conform to a desired shape.


These comments are part of a detailed write-up by Christopher Pardell on "Working with Plaster" which form a part of his alt.sculpture FAQ. The link is here (http://users.lmi.net/~drewid/plaster_faq.html).

Actually the write-up is very good, and I learned quite a lot more about plaster from reading it.

[David Spence]

I am wondering why you are useing plaster? Why note new plastics.. I have not used plaster in 20 years or more. Of course I have no idea what your needs for the mold may be. Mine is for wax, for the lost wax process in casting bronzes. I use products from smooth-on... may want to look into them, may cost more, but they are very clean and I have worked out ways to make them go faster and better and they are very light to work with once done. Just a thought. I am a foundry owner and wanted only to give some input.

[Landseer]

I am wondering why you are useing plaster? Why note new plastics..
Several reasons in my case- I work in my HOUSE, I don't want the toxic fumes, proven carcinogenic chemicals etc in here!

You can't mould or shape it like you can plaster, it costs a lot compared to cheaper plaster of Paris. Plaster is real easy to use, you can't mis mix or misweigh, you dump it in a pail of water till it's the consistency you want (liquid for pour, thicker for troweling) and it works perfectly every time.


Mine is for wax, for the lost wax process in casting bronzes. I use products from smooth-on..In fact I have made complex plaster/sand piece molds to cast my waxes in.
I don't care about the weight, I design my molds so the largest piece becomes a "base" to support the rest and stays on thw casting bench, only the smaller pieces need be removed. There's times when you WANT the weight for the stability.
I've never made shells out of plastic and never will, in a studio I worked years ago they had one shell mold made of some kind of plastic, it was very brittle as I remember.

[Dup-Csapo Reka]

It shouldn't break if it is well shaped.Anyhow you might use plastic based textile material for curtains by example.But I guess the problem is with the shape of the mould.If you do it properly it shouldn' t broke when you take it off.

[Landseer]

It shouldn't break if it is well shaped.Anyhow you might use plastic based textile material for curtains by example.But I guess the problem is with the shape of the mould.If you do it properly it shouldn' t broke when you take it off.The stuff was brittle like glass, I don't know who made the molds, it was a yellowish fiberglass and most of the positives were just flat plaques/ wall hangings in hydrocal. The shape wasn't the problem, the brittle fiberglass WAS.

[Daniel]

I remember watching a video by Mark Prent in which he showed how to use sheets of "friendly plastic" -type material to make very quick mother molds. I never bothered to try it out, but it looked very fast and the molds were surely very lightweight. The sheets were submerged momentarily in hot water until softened, then just draped over the part. The sheets harden into plastic as they cool. He probably sells this stuff. Pinkhouse Studios.
I think I'll just stick with my good ol' hydrocal and hemp, though.

[RWJR]

how about pine straw? real cheap

[Merlion]

I remember watching a video by Mark Prent in which he showed how to use sheets of "friendly plastic" -type material to make very quick mother molds. I never bothered to try it out, but it looked very fast and the molds were surely very lightweight. The sheets were submerged momentarily in hot water until softened, then just draped over the part. The sheets harden into plastic as they cool. He probably sells this stuff.

This is an interesting way to make mother molds, and fast and convenient if it works well.

Some plastics do get soft in boiling water, and they may be available in sheet form. Not sure if the plastics material used is PE (polyethylene) or even PVC. But this can be tried out easily.

[Scout]

I've only just started thinking about making molds. I don't know anything about it yet (anyone know of a good basic book?) But I have seem a material that is used to make a removable cast for broken bones. They just heated a sheet of blue material and shaped it around a broken bone. Have you heard of this or is it already a common thing to use? Scout

[AKRyeGuy]

I use drywall (gypsum) setting mix and fibertape myself. I used 45 minute or 90 minute Ez-sand, depending on how long I wanted to go before taking a break. No problems with brittleness, and I had some long, thin pieces I really had to torque on to get air underneath the brush on rubber mold so it would come off. The piece I was casting from was an ornate plaster cornice.

I used plaster for casting, FRG-95, adaptive to fire code for architectural use. I used loose fiberglass after a face mix and never had any problems with it getting airborne. Never itched. I wore a nuisance mask. A high-speed fan in a window could give some re-assurance there. I did have problems with tracking plaster dust everywhere though!

The old plaster (c. 1890) itself had horsehair and excelsior inside it.
I guess it's all what one gets acclimated with using. A lot of ideas here.

Fiberglass and gypsum I remember reading about as being something one could engineer when properly laminated (load bearing for buildings). Can't remember an actual PSI rating, but it was up there with high performance concrete. It's also easy to patch.

[SPRINGFIELD]

I'm pretty annoyed at the prices of hemp fiber in the US for making mother molds and I don't quite like to use burlap as much, fiberglass is great but I have a small workspace and I don't like to keep it around due to health hazards. Does anybody know of any inexpensive fabrics or fibers that work well as a support for making mother molds. Of course the thinner and stronger the better, thanks.

-A
I wanted to ship some molds with backup mother molds so weight was a big factor. Fiberglass molds are pritty light but I don't like working with the stuff. So It occured to me that I could use paper mache. I made some real stong paper mache but the problem was it all shrunk. Next I tried using WEP {water extended polyester instead of glue. I thought it would work because it's already made to work with water. The place I bought it from saids that it was used that way all the time. Anyway it never set up right and the parts that did wern't strong at all. Anyway here is how I make my mother molds now.
Depending on how big the mold I fill up about three containers with water enought so that alltogather they will make enough plaster to make the mother mold or part of the mother mold if it's going to have more that one part. Than I mix into each bucket of water some sodate retarder. Than I add the appropriate amount of plaster powder to each bucket. Let them all soak for a few minutes. I than mix up the first bucket only {the plaster in the other buckets won't start to set until you mix them] After i mix the first bucket I than start adding dried paper mache pieces to the mixed plaster. [i must admit to being lazy at this point. I don't make my own paper mache pieces I go to my pet store and buy "TOTAL COMFORT critter frendly bedding it's a real bargin and it's basically dried paper mache. Last time I went they had a sale and I got 2400 cu in for $10. That's a lot more paper mach than I'd ever want to make.} When I add the paper mache to the plaster I don't realy measure it. I just keep addding it till it makes the plaster nice and thick enough to apply vertically. Than I start putting it on my mold if it isn't thick enough I just add some more paper mache to the mix to make it thicker[This is why it's important to use dried paper mache it draws in the moisture without affecting the setting of the plaster because the plaster is already mixed. I try to cover the whole area {rather than just a section] after that I mix the plaster in the next bucket add the paper mache etc. I realy like doing my moter molds this way it beats the heck out of waighting for the plaster to start setting and hurring or not waighting and having everything slipping and sliding arround. After the first piece of the mother mold sets in about an hour I can start on the other mother mold pieces. I like these mother molds because they feel tough unlike plain plaster which feel brittle. I posted some photo's hope they work.

[syrus]

Yes Springfield, I'm interested in trying this paper mache mother mold over latex. Do I need to apply some type of release to the Latex before applying the paper mache/plaster mix?

[SPRINGFIELD]

Yes Springfield, I'm interested in trying this paper mache mother mold over latex. Do I need to apply some type of release to the Latex before applying the paper mache/plaster mix?

Yes it's necessary to use a release and it is very easy to do because your not worried about losing detail. Just be sure that the release does not contain any petrolium oil which will ruin the latex. Some people use vasolene but I don't like to use it because it's a petrolium derived product. I make my own vegitable based vasoliene using Bee's Wax and Canola oil {the same oil that is sold for cooking in the food store] I melt the Bee's wax in a double boiler and than stir in the oil. The nice thing is that you can make a real thick batch or a real thin batch depending on the weather. I usually make it thick and than pour it in a container. After that when using if I want it thinner I pour in a little alcohol in the container and mix up a small puddle with a acid brush which I than use to apply it to the latex. It also workes to seperate the plaster pices from each other when making multible piece molds. I made a huge batch last time so I can't give you the exact amounts but you can start out with 3 parts wax and 1 part oil by weight. Ps don't use patching plaster.

[syrus]

Thanks for your reply.... O.K. so use plaster of paris? Any kind of vegitable oil will work?.........

[SPRINGFIELD]

Thanks for your reply.... O.K. so use plaster of paris? Any kind of vegitable oil will work?.........

I've tried different vegitable oil's and canola oil works the best for me. Arround here canola oil is easy to buy in any grocery store and it's pritty cheap. So I haven't tried any other kind of oil in a long time. I kind of remember olive oil working good.
I've only used plaster of paris in this system except I once used patching plaster once. I was attracted to patching plaster because of it's hour long working time but it took a long time to dry and it stuck to the latex.I had to tear the mother mold apart just to get it off.

[spinkways]

Hi Springfield

I have read this post, after you kindly referred my from my more recent question about making mould supports. I like your idea of using papier mache mixed in plaster then packed around the latex. (I think I got that correct).

But being a total novice, this might sound stupid or I didnt read your post correct, what do you place in the latex to stop it crushing in? If you know what I mean. But I suppose if the mould is thick enough, it wont push in any sides etc? Have I got that right.

Well against popular belief, I think thats a great idea!!

Thanks

J Spinkway :cool:

[SPRINGFIELD]

Hi spinkways you are right about the latex caving in. The latex that I was talking about was still on the original model so I didn't have to worry about crushing it. I once bought a latex mold on E-Bay that came without a mother mold. It was thick enough to be self suporting but still needed a mother mold. So what I did was mix up some plaster and than I carefully painted on a thin layer on the latex mold. One layer was enough to do the job but more layers could have been painted on if it was a big mold. I guess after the thin layers of plaster set than you could go and use the paper mache and plaster for the final mold. It might be a little tricky making a multiple piece mold this way. I only wanted to make a plaster model from my latex mold. So after I painted on the thin layer of plaster I just poured my plaster into the mold. After the plaster dried I just peeled the latex rubber of the casting and outside plaster schell just crumbled off. I guess you could do the same thing but instead of peeling the latex off you could find a way to remove the plaster schell without disturbing the latex. Lanspeer said at one time that a solution of Lye and water will disolve plaster don't know what the solution would do to the latex. Perhaps you could gently sand blast the plaster schell off. Blasting sand pritty much just bounces off rubber. Anyway thanks for answering my post and please let me know how things work out.

[Sand Man]

I use fiberglass chop, 1 to 2" strands - it's totally harmless in its loose form (unless you eat it) - Just dont sand it after it sets up! The larger health problem in my opinion is polyester resin :( Now that makes my liver itch! Smooth On has a urethane resin that is not so stinky :) .

[Sand Man]

You've got the stinky or the shrinky -

I would worry about shrink with any organic fiber substrate, thereby deforming your shape. And a lot of plastic resins have the harsh chemical thing. Fiberglass chop with a urethane or plaster is low stinky and almost no shrinky.

[SPRINGFIELD]

You've got the stinky or the shrinky -

I would worry about shrink with any organic fiber substrate, thereby deforming your shape. And a lot of plastic resins have the harsh chemical thing. Fiberglass chop with a urethane or plaster is low stinky and almost no shrinky.

I think you make a good point about shrinkage and I kind of expected my plaster with paper mache to shrink. Since I put one layer over another layer of set plaster I thought it could possibly warp. I've been using this method for almost a year now with no problems. I think the key is mixing the plaster first and than adding the dry paper mache. Also it might work with dry hemp strands instead of paper.{ I haven't tried that} Another thing is that so far my largest mother mold has been only two feet long. Maby size would make a difference.
I tried some polyester resin without any fiberglass, only cabosil for a thickener
and I managed to get both stinky and shrinky. What is the shelf life of urethane resin and is it as sensitive as polyurethane rubber. I've had trouble with using polyurethane rubber before.

[Sand Man]

I tried some polyester resin without any fiberglass, only cabosil for a thickener
and I managed to get both stinky and shrinky. What is the shelf life of urethane resin and is it as sensitive as polyurethane rubber. I've had trouble with using polyurethane rubber before.

Glad to hear your plaster & fiber works well ! Im always looking for ways to avoid chemicals and if I find something clean that works I recomend it as well - so thanks for that input :) - I have had trouble with that Urethane rubber also. I made a bunch of molds back in the early/mid 90's when there were a few companies really pushing that rubber. I shelved some of them and had not looked at them for some time (2 or 3 years) - and someone was visiting my shop and we were talking about a certain part that I had molded, so I went to get it off a pallet rack shelf and I almost had a heart attack when I seen it - the rubber was literally leaking out of the mold cavity thru the spru and vent holes! as well as the 30 or so other molds I had used it to make :( - I started using silicone rubber after that.

Ive been trying to get away from polyester for a few years now (styrene is not my friend) - so I went to urethane insted, the stuff is great! but a little expensive. It seems to have a good shelf life if you keep it tight (very moisture sensitive) - Its much more stabil than the rubbers in terms of longevity because the chemistry is a bit different and because its so dense after setting up that it does not seem to absorb moisture at all.

I was sceptical when I first started with it so I poured out a small puddle of it and let it set up on the blacktop outside my shop door three years ago, it gets baked by the sun all day in the summer, rained on, snowed and iced on in the winter, and I recently hit it a few times with the 3lb sledge and its still hard as a rock, Im starting to feel better about using it now, I just wish it was cheaper. But in my case I have to use an alternative to polyFester, because of a styrene sensitivity, which sucks because I can chop a backing with my venus chop rig fast and cheap with the polyfester, but the external mix chop gun wont do urethane - it probably would not work cost wise using the urethane with the chop gun even if it did mix because theres a lot of blow by waste, so I just do it by hand and roll it out and use the gun to shoot dry chop into a bucket and apply it by hand with the roller.

[Aaron Schroeder]

Consider " Sculptamold ", It's not cheap, a little over a buck a pound but it would enable you to do more with less. What I love about this product is that it sets up like plaster in about 30 minutes and when dry is light weight and for lack of better words " wood " like. You can lay it down in layers with a resist between the layers and when dry you can screw your overlapping mold pieces together. It's a friendly material that allows for complex molds. It might be a little pricey for big molds but it's a great all around material that suggest allot of possibilities. " Sculptamold " is fun stuff, try it, you'll like it.

[SPRINGFIELD]

[QUOTE=Aaron Schroeder]Consider " Sculptamold ", It's not cheap, a little over a buck a pound but it would enable you to do more with less. What I love about this product is that it sets up like plaster in about 30 minutes and when dry is light weight and for lack of better words " wood " like.

I've used "Sculptamold" and was very happy with it.It set up good but it took a long time to dry. Still I would think it's a great solution if you don't mind the price. I liked it so much that I even thought of making the stuff myself. If you look up the patent [which is on the package]on the internet you will get detailed instructions on all the ingredents and how their mixed togather. It seems that blending all the ingredents can be quite a trick and you will need a hammer mill to prepare the paper. That's why I came up with my idea of just adding dry papermache to already mixed plaster. You end up with pritty much the same thing and after it sets it dries a lot faster. The "sculptamold' is still a lot lighter. I think it takes the "sculptamold" a lot longer to dry out because it has starch in it.

[jeff dubin]

Hello, We do professional production molds at our studio for many sculptors, FGR 95 plaster with fiberglass is the strongest combo and the best results for us.

It is easy and long fiber glass can be ordered from Douglas and Sturgess at 2.50 a yard which is 54" wide, we pull the 5 or 6 layers apart and build the matrix up with the FGR... the final cases are light, less that 1/4 inch thick...try it you will like it.. hemp and burlap are of no value to us, the finished molds are weak,to thick heavy etc etc....

[dilida]

ditto to what Jeff said about fgr 95. It can't be beat, and it isn't too expensive, although sometimes hard to obtain. One 100lb bag is around 25$ and goes a long way, the same with a roll of fiberglass. We have molds made with other materials that come through our foundry and so far nothing really seems to compare. Hemp or burlap seem like a waste of time and effort because they deteriorate so much. Longevity is important to an artist who intends to cast multiples over a span of years, plaster just doesn't seem to hold up as well as FGR95. And rats don't seem to gnaw on the stored molds. I would think anything with papermache in it would attrack chewing varmints.

[Landseer]

We have molds made with other materials that come through our foundry and so far nothing really seems to compare. Hemp or burlap seem like a waste of time and effort because they deteriorate so much.

plaster just doesn't seem to hold up as well as FGR95. And rats don't seem to gnaw on the stored molds. I would think anything with papermache in it would attrack chewing varmints.Plaster and burlap is an ages old standard, I have a number of antique plaster architectural sculptures, one from a church, including 3 from Cairo Egypt that were made of thin walled plaster with embeded burlap for reinforcement. The trick was to use an open weave burlap and get it embeded right, then in theory it was like the reinforcement rods in concrete slabs.
FGR95 and their Garden Cast stuff as I understand it is little more than hydrocal, it's a USG plaster product and it's one that their directions say MUST be used with the chopped fiberglass, so that tells me this is probably just another marketing scheme to sell more re-packaged hydrocal under a new name and that the FIBERGLASS is what is doing all the work- you could probably mix that with ordinary hydrocal and find it's the same end results.

I have a major issue with using chopped ground up strands of GLASS or the woven stuff which also releases some particles and getting this material in the air and on everything in the room, Owens-Corning and the other companies that make fiberglass have had many injury lawsuits from people whose lungs were basically destroyed by inhailing fiberglass particles- many employees who worked in the production plants as well. One may as well consider this stuff in the same light as asbestos, it's the asbestos of the 21st century.
Owens-Corning, Johns-Manville and the others have big law firms on the payroll to nix lawsuits over their products, do a Google search for fiberglass health and lawsuits keyword variations and you get hundreds of cases and pages.
They claim the glass breaks down and goes away in the lungs LOL, does building insulation just vanish like evaporating water? how about broken window glass? glass is glass, and it's practically indestructable.

I don't use ordinary weak plaster of paris for mother molds, I use white hydrocal as it IS considerably harder.
According to the official MSDS sheets on this, FGR-95 consists of;

MATERIAL

Plaster of Paris WT%= +95
Crystilline Silica WT%= -5


It is aproximately 95% Plaster of Paris, the rest is silica.

PRODUCT(S): Hydrocal FGR-95 Gypsum Cement
CHEMICAL FAMILY: Calcium Sulfate Hemihydrate (Plaster of Paris, CaSO_HO)
============

HydroSTONE is composed of;

MATERIAL
Plaster of Paris WT%= +90
Portland Cement WT%= -5
Crystalline Silica Wt%= -5

HydroCAL A-11 is composed slightly differently;

MATERIAL
Plaster of Paris WT%= +85
Portland Cement WT%= -10
Crystalline Silica Wt%= -5

HydroCAL WHITE has no Portland Cement at all which may explain why it has a nice set curve where you can shape, hollow and mould it;

MATERIAL
Plaster of Paris WT%= +95
Crystalline Silica Wt%= -5
PRODUCTS: USG Hydrocal White Gypsum Cement
CHEMICAL FAMILY: Calcium Sulfate Hemihydrate Plaster of Paris, CaSO4 H2O

So as anyone can see, the major differences between these products is just the inclusion or not of Portland Cement percentages by weight.
The hardness differences may be a result of different processing, maybe with higher heat, and the Crystilline Silica which would probably be a surface hardening additive and/or a set time adjuster.

In any case, USG's products are Gypsum -Plaster of Paris based formulas, they are after all- a plaster production company so it stands to reason all their products are made from that material and despite the claims on their Garden Cast stuff- if it's plaster it won't last out in the garden, but maybe what they and most people consider lasting or permanent today for a $75 sculpture placed in the garden is a 5-6 year time span anyway, and even hydrocal white alone should last pretty close to that- I've done the tests.

One concern worth mention, yes, while the MSDS sheets do not have to reveal specific proprietary or trade secrets they DO have to list something for those, and the "something" is simply a line that says;

Proprietary/trade secret ingredient -3%

or wording to that effect.

As the USG sheets lack this line, we can assume pretty well that hydrocal, hydrostone, FGR-95 and all the rest are at least 90% Plaster of Paris, with the remainder being Portland Cement, Silica etc.

As far as vermin damage, I would worry a lot more about the general damage rats and mice will do BEYOND just gnawing plaster- one needs to keep them under total control because they LOVE to gnaw on electrical wiring in the walls, they will RUIN insulation in the walls, their droppings are a health hazzard, their urine is extremely corrosive to metals like copper and brass used in light fixtures , contacts, motors, switches, relays and others.
Mice can get into a building thru a hole as small as 1/4" diameter or slip under a door that has a gap the size at the threshold.
Rats can squeeze in through a dime sized hole, they can also swim under water as well as come thru sewer pipe vents and up through a toilet- I've seen the demonstration on video using clear plastic pipes.


I think I ran into another one of those KURL bugs here in posting this, some may remember that posting problem, seems to be the use of greater and less than brackets prevents the text from appearing in a post past those brackets- munging the post,so I removed them and replaced with + and - for the originals.

[dilida]

As always, everyone has different experiences based on thier needs and methods. I've used moulding plaster, ultra-cal 30, hydracal white. All with fiberglass and without. I've seen few molds with burlap in them and that were in good shape, but I know it can be done. For my circumstance only, and with my 10 year experience with one single foundry, hydracal FGR95 can't be beat. Time is a concern of mine, as well as weight, and storage in a humid, rural backwoods setting. I offer, as always, my unique experiences so maybe someone else can glean a bit of knowlegde, or at least a "Hey that gives me an idea!" In that vein I offer an "Oops it didn't work". If there is any gypsum in whatever you are using, it will eat the fiberglass. There is concrete-resistant fiberglass, but I've been told it is expensive and hard to find. I know I couldn't find it.

Happy Molding!
lisa

[Landseer]

I guess if someone says the FGR-95 is superior then it must be, but according to the MSDS sheets it's no different than Hydrocal white note too it says HYDROCAL FGR-95, the full name says it all.

HYDROCAL FGR-95
Plaster of Paris WT%= +95
Crystilline Silica WT%= -5

PRODUCT(S): Hydrocal FGR-95 Gypsum Cement
CHEMICAL FAMILY: Calcium Sulfate Hemihydrate (Plaster of Paris, CaSO_HO)
--------------------

HYDROCAL WHITE
Plaster of Paris WT%= +95
Crystalline Silica Wt%= -5
PRODUCTS: USG Hydrocal White Gypsum Cement
CHEMICAL FAMILY: Calcium Sulfate Hemihydrate Plaster of Paris, CaSO4 H2O
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The two products are according to the sheets the SAME in the bag, it's just your additive of the fiberglass that is the change and the FGR-95 bags state you MUST add the fiberglass to it to get the stated specs from it, it's pretty clear to me it is the addition of the fiberglass by the end user that is the entire difference between using regular probably cheaper Hydrocal white and the hydrocal FGR-95 which I believe is more expensive.

'So I guess the BIG question besides their obvious marketing ploy here of selling the same stuff packaged with two names, one priced higher than the other is, does anyone know WHAT exactly this 5% addiion of Crystalline Silica DOES?

[dilida]

I don't have to know why, I just care that it works. FGR95 doesn't set up as fast, but "cures" faster. I can pull a mold off in 45min-1hr. Hydracal White sets up faster, more like moulding plaster, but takes longer to cure. I learned to let them set overnight, NOT good for deadlines. The Hydracal white is supposed to be tougher for casting figurines with small extrusions. Tried that too, not tough enough for what I wanted, but my main interest is the "mother"molds.

[Landseer]

I don't have to know why, I just care that it works. FGR95 doesn't set up as fast, but "cures" faster. I can pull a mold off in 45min-1hr. Hydracal White sets up faster, more like moulding plaster, but takes longer to cure. I learned to let them set overnight, Hmmm, well I have used hydrocal white for mother molds since 1980, always in multiple sections. I typically form each section just as soon as the previous section is steaming hot and has liquid soap applied on it.

I also typically remove the molds off the originals 15 minutes after I form the last section- while the stuff is steaming and hot. Unless I FORCED something using a tool because I misestimated an undercut or opposing angle- I never had a problem removing mother molds right away so I don't know what you mean by "takes longer to cure" necessitating leaving it overnight!
I've never had to wait more than a few minutes after the last section is formed to remove mother molds.You might be mixing the stuff too thin or not mechanically mixing it long enough, I usually make my slurry for mother molds with very warm water, very thick and mix it well with a drill for a couple of minutes, that way it is almost like thin whipped cream to start with and I can start applying it to the model right away with a spatula, knife or whatever since it will more or less STAY put and not run.

USG says mixing this stuff mechanically with a drill is all but required to get the full strength and qualities, hand mixing won't cut it. Water that is 100ºF USG says has the max soluability for Hydrocal, so my slurry water is at least that, it's also more pleasant to work with when the stuff is warm than ice cold.

I don't use burlap or any reinforcement, I DO make the sections thick enough they don't break from normal handling, they are also designed in sections with a base that stays on the casting table and keeps all the sections in place on top of it, that way generally the largest section- the base always stays on the table I don't have to move it.
As far as mold weight goes, I'm 116# and hardly a body builder, but I have little trouble working with molds weighing 100+ pounds, they are designed in such a way I never have to move more than individual sections of them to remove casts.
Heaviest mold I made was over 1,000# of hydrocal, with 15 gallons of latex back in 1984, but it was made in about 20 sections that all fit on top of a bathtub sized base about 2-1/2" thick that stayed on the floor, it holds all the sections together.


I learned to let them set overnight, NOT good for deadlines. Not to be critical or condescending, but if this few hours of difference is causing that kind of deadline concern, is there not something that should be examined at the beginning of all of this and looked into as to why a deadline is allowed to be cut THAT slim? If this is that slim then one tiny mistake or problem willtotalyl screw up everything, I don't know about anyone else but I don't think I would put up with that kind of scenario wfor long without examining every step of the process and find out why the time is being used up along the way to the point where the mold has to be RUSHED through with haste within a few hours or else. The mold making process is probably the LAST one that you want to rush or take shortcuts with.

[dilida]

I'm sorry this has gotten way off thread, but mother molds consume a lot my energy and I don't get to talk to a whole lot of people who understand them. I work in a business, I have a boss, things don't always run the way I would do it if I were working for myself. The system I've got going serves me pretty well, it's those unexpected gliches that send me scrambling for alternate methods. Usually that means I can't get the right supplies, and I am forced to get creative. I live with deadlines. Period. As long as artists have shows to go too, I will have a deadline. It sounds like you have all the control over your working situation, while my boss gives me plenty of leeway to do my job, certain things I don't have control over.

Back to mother molds. With my system, if the mold has more than 2 sections that can't be banded easily with a rubber bands of some kind, then I drill through the separation ridges. The MM has to be set enough to withstand pressure from the drill. I don't make thick molds, 3/16'' is ideal, thus when I remove them, they need to be set. I rarely make molds that are thick enough to remove while hot and steamy. I rarely make just one mold at a time, if things are going the way I like, I have a whole tablefull to do, and spend a couple of days making them, OR, a few hours each day. No set schedule, it changes with every piece an artist brings in the door. The unannounced 8' figures really change my so called schedule.

I also have to please the wax room that uses the molds I make. They have to be light, strong, as easily put together as possible, and as flawless as possible, or I hear about it. God forbid that I should make thier lives harder that they already are! Oops, sorry, foundry nastiness. Most of the wax pouring is done by women, they have to be able to handle the weight. In some cases a guy will help if the heaviness couldn't be helped.

Any way thank you for you comments, I do appreciate them and they will be in the back of my mind, as I work today. I think it's cool to have this forum and exchange of information and different experiences.

Have a wonderful day!
lisa

[Landseer]

Back to mother molds. With my system, if the mold has more than 2 sections that can't be banded easily with a rubber bands of some kind, then I drill through the separation ridges. The MM has to be set enough to withstand pressure from the drill. I don't make thick molds, 3/16'' is ideal,
Ok, well I only have a little more to add I guess, to the above, and that is has no one heard of those great NYLON mold bands available from ceramics suppliers like Georgies to use instead of rubber bands which "give" no matter how many you put on if the mold is large and being filled with something heavy?
They have been around since the 80's that I know of and they are only around $4 each and they don't "give", you can crank the things as tight as you want.
Instead of using 47 rubber bands you use 2 or 3 of these.
Rubber bands suck, I stopped using those things 25 years ago

3/16" for mother molds in my mind is asking for warpage and distortion, that is another reason I make mine at least 1-2" thick- so I can crank down on the mold straps and ensure it's all tight, unmoving and any seems are not going to leak. Nothing worse than a floppy mold that starts leaking, moving, shifting or bowing- producing defective casts.

Here's a mold I just finished the other day, it's 4 sections, the mold straps I use can also be seen- only takes one instead of a dozen rubber bands.
Hard to see the "base" I do for the rest of the sections to set on top of, the base stays on the table

http://i23.photobucket.com/albums/b375/Randall2/mold-1.jpg

[ahirschman]

OK Dilida/lisa, how about some pics of your mold work? We can all probably learn something from a few pics, if available. Landseeir is quite generous with pictures (Thanks LS)

Thanks everyone.

Ari.

[dilida]

Ok, I will try to post some pictures, not real computor savey, but I'll try to get some pics at work today.

The rubber bands are innertube sections. Anywhere from bike size to car tire size, we cut them into about 1" wide pieces. They will break after a couple of years use, but they are cheap. Motorcycle size is what we use most. If the mold is bigger, we use ratchet bands.

The fiberglass is what makes the 3/16'' work. no warping, no collapsing, no give at all.

If it's a complicated mold, more than 3 piece MM, then I drill through the dividing ridges, and the empty molds are "banded" using bolts and wingnuts, spaced about 5-8'' apart.

I'll post pics later, if my boss says ok.

lisa

[Landseer]

The rubber bands are innertube sections. Anywhere from bike size to car tire size, we cut them into about 1" wide pieces. I know what they are, but when you figure the time spent acquiring the tubes and cutting them all up...
I don't even want to think about what can happen when you are stretching those and it breaks- hitting you in the eye.

[dilida]

I'm trying to post some pictures. not to much luck yet, but I went back and read Julianna's how-to.

The bands do break after considerable use, but you can tell when one is starting to weaken, and then throw it away. I don't believe we have ever paid money for them, some one always has an innertube that is no good, and we do use rachet bands for larger piece.

I stated a 3/16" thickness earlier, I was thinking 5/16", Sorry! But that is only an "ideal" thickness, it dosen't have to be exact. I go by the feel of the fiberglass layers, when it has a "spongy" feel to it, I have enough layers on, and I cover it with a layer of just hydrocal to seal the fiberglass fibers so handling the mold won't be so prickly.

When I click on the manage attachements button, nothing happens.