What are the signs that indicate that you got the right plaster to water ratio? Furthermore, how can you tell if you got too much or too little water?
How can you tell if you got the right plaster to water ratio?
- Thread starter mikebalcos
- Start date
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For me, it depends on where and how I want to use it. A thick mixture will set up pretty fast, whereas a wetter mixture takes longer. I use both kinds, pouring it tu run down sides of mountains, or applying with a putty knife. A very small amount of venegar will slow setting time considerably. It sets up pretty good, but stays workable longer and takes many hours to dry and cure. No hard and fast rule for mixing. Just add water until you get what you want.
Lynn
For me, it depends on where and how I want to use it. A thick mixture will set up pretty fast, whereas a wetter mixture takes longer. I use both kinds, pouring it tu run down sides of mountains, or applying with a putty knife. A very small amount of venegar will slow setting time considerably. It sets up pretty good, but stays workable longer and takes many hours to dry and cure. No hard and fast rule for mixing. Just add water until you get what you want.
Lynn
I'll usually make a mix so that the plaster/water has the consistency of pancake batter. Thick enough to work with but not so thin that it will runn all over. It's best to make small batches so you will have time to work with it before it sets up and hardens, then all you'll have it a solid mess in your mixing bowl you have to clean up.
Jeff's formula is about right...You should add the plaster to the water & not the other way around and mix for about 3 minutes +/-. Make sure you wet any existing plaster before applying new plaster over it, otherwise the older plaster will soak the water right out of the new, and you'll end up with a flaky, not very strong layer of plaster.
A lot also depends on the type of plaster you use. Drywall compound can be mixed to almost any consistency, but it's fairly soft when dry, and tends to crack if applied too thickly. Hydrocal and dental plaster both have a catalyst in them, so will set-up within a specified time. Both dry hard and their fine texture is good for casting from patterns. For scenery, I use a product called Durabond 90. It's made by Canada Gypsum, but I believe U.S. Gypsum makes a similar product. This is a patching plaster, and the "90" refers to the setting time, in minutes. Other setting times are available. This is not as fine as Hydrocal, but is a lot cheaper: around here, about $20.00 for a 35 lb. bag. This also contains a catalyst, and will set no matter how thin or thick you mix it: very watery mixtures set in the indicated time, but may take several days to fully harden. Once hardened, this stuff is very strong, and hard to sand or carve. I used if for all of my scenery shell (over aluminum or fibreglass window screen), and also for my riverbeds, (over plywood). As with applying over dried plaster, mist some water over the wood so that it doesn't remove the moisture from the wet plaster. And Gus is right: add the plaster to the water. If you mix it in a flexible container (I use a plastic litterbox), you can flex it to remove the dried residue, making clean-up a bit easier. Save those dried bits, they make great rip-rap when broken down to a scale size.
Wayne
Wayne
One thing I have not seen mentioned. If you are dipping paper towels or such in the plaster, wet the towels first otherwise they will absorb the water out of the plaster and it will harden to soon.
Loren
Loren
It's been recommended in many articles that a good plaster to water ratio is 2 parts plaster to 1 part water. Let the plaster absorb the water then mix.
You can use this ratio for pouring rock castings.
You can use this ratio for pouring rock castings.