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Yes, correct, I found that out few days ago, or to put it better, remembered it again, as I knew this long ago because of so much production
and yes, did a test just mixing plaster with water and noticed how long it took to harden
almost a day
way too much water, on a side note, it will harden anyway, as long as the plaster is fresh, fresh bag. It will work regardless, but one has to wait a long time.
the official ratio = 25 kilo of Gypsum with 16 Liters of water
ends up with 30 kilo thick plaster
That´s what´s on da bag.
This is the ratio the builders use for plastering walls etc, hardens way too fast for most folk.
But for those in a hurry hahaha yes , two parts plaster one water and the rest , sand, salt, crystal(water) etc
I add a lot of river sand, mixed sand, or beach sand, whatever, as long as it is mixed with quartz , minerals, it will do.
so the mixture will harden out even faster in that case, concrete in the bucket, etc etc
Again , depends on the brand too, one has to play with it what suits the needs.
Also, for those who want to make the big broadcasters, I often use the fast hardening plaster of Paris, same stuff just with an additive that speeds up the hardening.
Oh I forgot, silly me, usually , nine out of ten time I use HOTTTTTTTTTTTTTTTTTTTTTTTTTTTTT water
How did I forget that ?
Hmmm…alzheimers ?
Anyway, yes, normally , but this time I forgot as had not cast anything in half a year, I use HOT water
Not boiling, but hot
it speeds it up dramatically
This time I used cold water and it took a longggggggggggggg time to harden
Nevertheless, boys and girls, it will still do the job, no question about it but might take some extra cups of coffee…
Hot water instead of cold water makes it set up much faster. The addition of ordinary table salt, say a dessertspoon full in 10 liters of plaster, or a combination of hot water and salt will do the trick.
Another trick is to take old dry plaster, turn it into powder and add this to freshly mixed plaster. Ratio: about 1 to 2 cups per 10 liters mixed plaster. Adding old plaster will cause the plaster mix to become thixotropic, (not runny) and this makes it very easy to model rapidly using fairly large amount of plaster. Take care when you model with plaster that the first surface is properly wet with water before adding the next layer, otherwise you will have adhesion problems between layers.
I usually use hot water, salt and old plaster all in one mix. If you are able to sculpt/model rapidly this technique will open new vistas for you. Good luck, and keep us up to date!!!!
Be aware that adding salt to the mix weakens the final product, depending on how much salt is added the loss of strength can be significant, that’s the trade-off.
Use HOT water, (at least 100 degrees) F, mix it rich so it’s thick almost but not quite like ketchup instead of watery, and mix it “violently” with an electric drill mixer without getting air in it, and it’ll set about as fast as it can.
Densite comes in 50# bags.
Additives such as tints and colors tend to retard the setting, depending on how much you add it can be significantly longer setting.
Dentist plaster comes in at least two formulas, a normal set and a FAST set I discovered by accident when my supplier shipped me the fast set by mistake, it sets so fast I almost didn’t have time to mix it well and get it out of the buckets before it was already starting to set.
Plaster of paris does not dry to become hard, it crystallizes similarly to concrete. It may still be wet but will have attained it maximum strength long before it has dried. To speed up the crystallization process use hot water and add ordinary table salt. You can make it hard within 10 minutes if you wish to. The more you agitate the mix the quicker it will set. The larger the mix the shorter the setting time.