Mixing large amounts of dry plaster and silica

[Peter Angel]

Hello. Does anyone know how to mix large amounts of dry plaster and silica together without making lots of dust?

Pete

[MarkNotMarc]

depends on what you mean by large amounts?

You could use a 5 gallon plastic bucket with a lid and roll it around on the floor.

For larger quantities get a cement mixer and fabricate a plywood lid with toggle clamps to hold it on.

I have heard it works best if you remove the interior blades from the barrel and throw in a few short pieces of 4" x 4" lumber to stir things up. Makes it easier to scoop out when done mixing.

I have also seen some plastic composting barrels that are on a rotating stand that could be modified to work, I think they are made by rubbermaid or someone similar.

good luck, Mark

[Kevin Midgley]

This is exactly what you need but where you will find one in Australia is another question.
http://www.amazon.com/Scepter-04239-7-G ... B000BPK766

[rosanna gusler]

why would you mix that dry? you will never get an even mix so your castings would be un predictable. you slake the proper proportions into water when making molds. the mix happens in the water. r.

[Kevin Midgley]

well, you'd probably get an even mix, mixing the dry powders in an Oddjob mixer but the assumption is that you would be doing it wet with the tumbling action of the oddjob mixer is like a cement mixing truck.

[Peter Angel]

why would you mix that dry? you will never get an even mix so your castings would be un predictable. you slake the proper proportions into water when making molds. the mix happens in the water. r.

I thought that you mixed it dry, then added the mixed dry powder to water, then mixed it wet. That way it gets mixed twice ???

[Peter Angel]

This is exactly what you need but where you will find one in Australia is another question.
http://www.amazon.com/Scepter-04239-7-G ... B000BPK766

I tried to order this from Amazon, but the total was too expensive as postage to Australia was almost the same price as the Odjob mixer!

Oh the tyranny of distance!

[Buttercup]

Hi Pete,
Will this work:
http://www.gumtree.com.au/s-ad/point-co ... 1083889219

Jen

[Bert Weiss]

I think Rosanna is right. Use this http://www.proplaster.com.au/catalogsea ... ster+mixer

I once considered manufacturing a plaster refractory mix using an industrial waste ingredient. I would have had to figure out how to make a good consistent dry mix. The thought of handling all those nasty powders stopped me from bothering.

[MarkNotMarc]

why would you mix that dry? you will never get an even mix so your castings would be un predictable. you slake the proper proportions into water when making molds. the mix happens in the water. r.

I disagree, dry mixing will give a better plaster/silica distribution than just scooping both into water and mixing. How could it not? Then you get the added benefit of remixing when you add to water. I learned this from Dan Clayman who dry mixes his plaster/silica for 20 minutes in a cement mixer before adding to water. I originally learned to just scoop both into water straight from the bag and it does work, but I can't see why dry mixing wouldn't improve the distribution.

[rosanna gusler]

overkill. mixed is mixed. when it is mixed wet properly it is even . you want to do extra work just because then fine.

[Soozin]

On large scale investments I need to use, I learned from Richard Whiteley to mix dry ingredients first and then sprinkle into the water. However, I use both methods, depending on the amount of investment required for the cast. For small investments I just sprinkie directly into the water and then mix by hand gently.

[Morganica]

I wouldn't disagree with Whitely or Clayman (I would sweep their floors just to take moldmaking classes from either), but I think it depends on how you engineer the mold, and the moldbuilding techniques you employ.

I have a base mix that I order from the place where I get my raw materials (Seattle Pottery Supply), and one day they mentioned that as long as I ordered a minimum quantity they'd be happy to premix for me. So that stuff I have them mix up and package in conveniently sized, sealed tubs, I know it's extremely uniform and it saves time, wear and tear (on me and my studio).

So if the mold I'm making doesn't require anything special (say, it's just a box mold for a bas-relief pate de verre panel), I'll just use base mix.

Anything more, and I have those materials shipped to me raw, unmixed, and mix them myself, directly in the mixing bucket. I tend to hand-build my casting molds in layers because it gives me a lot more control, and hand-mixing small quantities separately lets me alter the proportions of ingredients as I go along. The face coat needs to be very hard, very smooth and take detail well, so the particles must be extremely fine. The strength coats usually need to support pieces in different directions, and sometimes I need to build in areas that will break down on purpose as the glass starts to contract.

I weigh out water into the bucket, weigh out the dry ingredients and sift them into the water, let them slake. Then I power-mix the contents with a paddle mixer for 2-5 minutes. That gives me a very smooth, uniform mix, ensures I've got saturation, and is the right consistency for hand-building. I can run 6-7 one-gallon buckets in sequence that way, letting me build up layers of mold mix, and I've not had problems.

Think about it--if you're mixing up bread dough, or cake batter, you do dry ingredients in one bowl, wet in another, and sift together. The sift+mix is what creates uniformity. I'm not sure why it'd be any different for mold plasters.

[Jordan Kube]

I premix in a Harbor Freight cement mixer I got on sale. I made the lid out of a piece of plexi glass with a floor mat glued to one side. A couple of wraps of duct tape around the side and it's sealed. You can use plywood or whatever, that's just what I had lying around. Fits a 50# bag of each perfectly. Dumping it out into bins is dusty though. I do it outside and then transport it to my studio. Mix it once and then you only have to measure one thing. Very convenient.

[Ed Cantarella]

I premix . . . . Mix it once and then you only have to measure one thing. Very convenient.