$9.95
CLICK THE "LEARN MORE ABOUT THIS ITEM" LINK JUST BELOW TO READ THE FULL DESCRIPTION FOR THIS ITEM.
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Please note the "instructions" are in this description.
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Brief instructions (see below for more details at "More on how to use"):
Please note that this material has a recommended proportioning of 26 parts of water to 100 parts of duracal. It is a thick but pourable mix. As with all gypsum cements and plaster, it's much more accurate if you proportion it by weighing. It eliminates any guesstimating and results in the optimal end product.
Gypsum cement shares the basic principles as plaster mixing: Always add the cement to the water, never the other way around.
Slowly sift the powder into the correct amount of water, let the water wick up the mound of powder and wet it, then start stirring. Use cold water at first, it will extend the working time. Use disposable plastic cups to mix it in (if you reuse a container it will accelerate the set so you won't have time to mix).
This is a gypsum cement. It looks like 'regular' portland cement because it's about the same (dry) color. But it's quite a different material. USG is the largest manufacturer of plasters and gypsum cements in the world and this is one of their products. There are maybe a dozen different gypsum cements. Think of them as "super" plaster. You mix them with water using the same tools and methods as plaster (if you're not familiar, the basics are: sift the plaster/gypsum cement gradually into the correct amount of clean water, then mix. Those last two are crucial. You must use the correct water/plaster ratio or your end product won't be as strong, and the better you mix it the better the physical properties will be. A jiffy mixer on a drill is preferable). There are charts from the manufacturer that give the water/plaster ratio for each type of plaster/gypsum cement.
I mentioned this particular gypsum cement looks like portland cement. It also has one other similarity, USG markets it as a concrete patch material. The advantages of it over a concrete patch is that it's easier to mix (no aggregates needed although you can add some aggregate), and it sets up much quicker than concrete.
I'm not sure how the final physical properties compare to other gypsum cements like hydrostone, hydrostone may be stronger. I should mention that if you've used plaster but never the higher grades of gypsum cements, you're going to be surprised with how "thick" they are. One of the things that make them so strong is the relative-to-plaster low water ratio you need to use. They've added deflocculants so they will flow with a very little added water (if you know something about clay and slip, you'll know what deflocculants do). As a result of the low water usage it is very much a thixotropic material: stirring it (making it move) will allow pouring it, but if it sits motionless it will become paste-like. You just need to get it moving by stirring it so you can cast it.
Here's a nice brief chart giving essential mixing info (from Laguna Clay):
http://www.lagunaclay.com/support/plaster-mixing.php
NOTE: I recently checked these last two links and they no longer take you to where the description says (they end up at a general sales brochure from USG with a brief and pretty useless description of the product).
Here's a specific pdf on duracal from USG:
https://www.google.com/#q=duracal+usg
Here's a very technical pdf on plasters and gypsum cements from USG:
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0ahUKEwj_iqqoxN3OAhVB2WMKHU_uDB0QFgg3MAQ&url=http%3A%2F%2Fwww.usg.com%2Fcontent%2Fdam%2FUSG_Marketing_Communications%2Funited_states%2Fproduct_promotional_materials%2Ffinished_assets%2Fplaster-mixing-procedures-application-en-IG503.pdf&usg=AFQjCNF7ckKZCt9Ad99M16sXqZZjjZN5aA
HERE IS A NEW LINK TO A DATA SHEET ON DURACAL:
https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/duracal-cement-data-en-IG1478.pdf
More on how to use ("instructions"):
Weighing is always the best way. If you have a digital lab scale that will measure grams (they are very inexpensive nowadays, check Amazon), weigh out the water and the gypsum cement powder. These types of gypsum cements want to be correctly proportioned. They are deflocculated like clay slips are (thus the thixotropy) to minimize the amount of water needed.
If you don't have a scale?
Forget about all of the above and do this instead (it's a bunch of guesstimating):
Start with just a 4 or 6 oz container with a small amount of water (couple tablespoons or so) in it and start sifting duracal into it. Keep adding until you've got a mound of powder a half inch or so out of the water. Wait some seconds to see how high the water wicks up the mound for future reference (it should be just high enough to suck about all the water up into the mound), then start stirring. It should be paste-like but still stir-able, and still be able to wet all the powder into a smooth consistency. If it stirs too easily you don't have enough powder in it. Sprinkle a little more in, since this is just a test. It should take some noticeable effort to stir. When you think you're there, pour it out of the cup onto some flat surface. Tap the cup as you pour. If it was a larger amount (like a quart), gravity would provide some force to keep it moving and pouring. It should form a thickish puddle on a flat surface and then stop flowing as its momentum slows. If it all flows off the surface you used too much water. If it won't pour out of the cup with tapping, just spoon it out onto your surface, then tap the surface. If it stays as an unmoving blob of cookie dough and doesn't spread out then you used too little water.
It would help if you repeat that a few times with just very small amounts until you get a feel for how far you can push the water/hydrostone proportion towards very viscous, but still being able to flow with tapping. The setting time is dependent on temperature, thickness of the casting, and the proportion of water/cement you ended up using. Poke at the puddle over the next hour or so to get a feel for how fast it sets. Using warm water speeds the set.
All of the above guess work is eliminated if you have a scale.
On the subject of coloring and adding aggregates or fillers, it's experimentation. Normally you don't add aggregates to gypsum cements, they don't require them like concretes do. I do remember USG saying you can successfully add aggregates (sand, stones, etc) to duracal. They've never said similar about hydrostone but the creative at heart don't follow recommendations. Duracal was actually designed to be a 'quick setting' concrete patching material (another subject: plaster and gypsum cements expand upon setting (and they also exotherm)).
There is a wealth of sources about these materials on the internet . (Please note that I have other materials in my shop which could fit into this 'cementitious mixes' category. To locate them do a shop search on "Colloidal", "Thixo", "Cab-o-sil", "Cement", "Kaolin", and "Calcium": Calcium Chloride is a cement accelerator and Calcium Sulfate Dihydrate (raw gypsum) is a pozzolan).-
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Nov 19, 2023
Paula
Mar 22, 2022
Perfect ! Exactly what I wanted
Cindy Davenport
Mar 10, 2022
I thought it was pricey for the amount
Christina Makar
May 18, 2021
Shipping was cheap and fast, got a rebate back on it too, and the powder is high quality - seller was very polite and answered my questions promptly and descriptively. Absolute legend of a shop, highly recommend!
Laura
Jan 29, 2021
Barbara
