7 years ago#1
Irmi
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Greetings!

I am a newcomer to this group, and in dire need of advice.

I have made a 24 x 18 ' clay relief, taken a high density plaster mould and sealed it with PVA. To take a concrete positive from this mould (the end result is to be an outdoor plaque) raises two questions:

a) what would be a suitable barrier between plaster and concrete to ensure clean separation of positive from negative? (I have tried spraying the plaster with WD40 on a sample - doesn't seem to work)

b) would you consider commercially available Mortar Mix (suitably reinforced with galvanised wire mesh) a useful casting medium?

I would be grateful for advice from anyone with experience in this field.

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7 years ago#2
kdavis004
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[The traditional release is potter's soap, also known as tincture (for the alcohol-based) or solution (water-based) of green soap. Ask your local chemist. In a pinch, you can also use liquid dish- washing detergent (Lux, Dove, <email> liquid- but not the sort used in automatic dishwashers. Let the release dry before applying concrete. Test this on a sample to see if it works. If there is a problem with releasing you might try motor oil in one of the heavier grades, but this is difficult to remove from the finished casting. Be careful of undercuts- no release will work if the plaster locks itself into the mold. ]

[Not really. Better would be to brush in a first coat consisting of white portland cement (1 part) and fine (60 mesh or finer) white silica sand (2 parts) and limeproof pigment to taste. Mix the dry ingredients first, then add water until it is about the consistency of yoghurt. You can use the wire and mortar mix as a backup to fill the mold after the first coat has set. Remember to attach your hanging hardware to the wire before embedding it.]

[Let us know how this works for you, or if you have any problems.]

Andrew Werby

UNITED ARTWORKS- Sculpture, Jewelry, and other art stuff http://unitedartworks.com http://www.computersculpture.com for 3d design tools

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7 years ago#3
David Simmons
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Thank you, Andrew, for your helpful advice, especially on the type of separator and the cement mix.

The need to think of a hanging/fixing device right from the beginning had crossed my mind, but I am still wondering what best to use.

I gather from your and other's e-mail comments that there are various options for achieving a concrete cast from a plaster mould. It is now up to me to test them in a nice, orderly fashion on a row of samples.

I shall report back - victoriously, I hope - when the concrete plaque is finally in place.

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7 years ago#4
swarnavel_mp
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polytek company, for flexible rubber, urathane, or silicone mold making materials, www. polytek.com

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7 years ago#5
richard2
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Hello!

I'm interested in recipes for mixing lightweight concrete (colored) for casting shapes for table bases, and garden scultures, etc.

I'm thinking of products like Syndecrete (http://www.metrokc.gov/market/ 99prod1.htm) Which uses Fly Ash and carpet fiber to give twice the strength and half the weight of regular concrete.

Syndesis makes Custom Architectural Elements such as counter tops, floor and wall tiles, table tops, fireplace surrounds, fountains, Accessories including bowls, vases, soap dishes, candle holders, picture frames.

I'd like to experiment with casting such a mix. Any advice on what to use and mixtures?

Thanks

Mac

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7 years ago#6
camellia
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(http://www.metrokc.gov/market/

Dear Mac

You can also use paper pulp to add strength and lightness to concrete, much the same way that potters add pulp to clay. The pulps colour depends on the paper's colour of course, so be careful not to use newspaper if casting light cements.

Watch for matching the size of the pulp fibres to the detail required from the caste.

The technique can also be used for direct work over assorted armatures, as long as there isn't too much pulp in the mix as it will eventually rot away leaving the structure unstable.

The other thing you can try is to use vermiculite, again another potters idea...and really cheap. I've heard that kitty litter works too.

One of my friends suggested that you can buy the chemicals which when added to your mix will aerate the concrete, but I haven't experimented with this idea yet....should though cos it might be useful.

Good luck

Bernice

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7 years ago#7
richard2
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99prod1.htm() Which uses Fly Ash and carpet fiber to give twice the

[Twice the strength perhaps- making concrete with half the weight would either take some other sort of aggregate or whipping a lot of air into the mix. From the detail photos, it looks like the latter technique was employed.]

[Fly ash isn't too hard to come by, but where would you get loose carpet fiber? Perhaps there is a machine one can feed old carpets into that will produce it, but I've never seen one- it would have to be very large and powerful. There are fibers made for concrete reinforcement which can be purchased- or you could volunteer to sweep out a barber shop...

Using fiber in concrete does increase its strength, but it makes it less pourable too. I mostly use it when I'm applying concrete to a screen, and don't want it to fall through.]

Andrew Werby

UNITED ARTWORKS- Sculpture, Jewelry, and other art stuff http://unitedartworks.com http://www.computersculpture.com for 3d design tools

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7 years ago#8
Man In Black
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This is hardly a recipe ,but vermiculite added to the mix makes a very light weight concrete with fanatsic colouring, particualrly if you polish it back. It contains a glistening gold in places. Using a ciment fondu with the vermiculite gives a great contrast with the black of the cement. The mixture is also very light; vermiculite weighs very little. The resulting concrete can easily be drilled or even nailed if you are careful.

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5 years ago#9
RTV Steve
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