Concrete Plasticizer

[coisinger]

Has anyone attempted to use a plasticizer in their castings?

I'm new to this concept, seeing if it actually would be worthwhile.  It seems that Plasticizers reduce the amount of water required to get the materials to flow and also reduces and or eliminates the need for vibration to get a consistent cast.

[peterberg]

Most suppliers of proper castable refractories advice strongly against the use of plasticizers or Air Entraining Agents. Because castables are designed materials, requiring less water than normal concrete. When the water content is reduced even further and air is entrained, the chance that the thermal specifications aren't met in the end product. Everything which is add to the castable will inevitable change the properties one way or the other.

Just once, I did cast a small item using a well-known castable refractory with the addition of 10% fine vermiculite. Slightly more water was needed to get the mix to working consistency and the end product after proper vibrating, drying and curing was like biscuit. I could dig a small hole in it with my nails, while the source product casted on its own was hard as a brick.

[coisinger]

Agreed Peter, any additive will change the complexion and structure of a casting.  Potential uses for this would not so much be for refractory areas, but more so secondary bells and non-fired areas.

I know from seeing your posts you are a proponent of using professional grade materials for your castings, likely based on previous experimentation with 'DIY' cast materials.  

[peterberg]

Actually, I started with professional grade and started to look for DIY materials some years later. What I found out about concrete is the least heat resistant component, so to speak, is the silicon that is present in the aggregates and the cement binder itself. So I tried, among others, a type of concrete that contains crushed limestone as aggregates. That wasn't entirely refractory either, but could replace a surprisingly number of parts inside a Finnish contraflow heater. I used that for a couple of years in a design which resembles our present red bell heater.

All that is long ago, since then I learned that the long lifespan of a mass heater is much more worthy to have than one made of cheap materials which is over and done in 5 years. Overhauling or completely rebuilding the thing every 5 years costs a lot more in the long run.

So I built one entirely out of the same refractory material and it lasted 31 years. Never saw the inside of the thing again, which still happened to be in working condition when we sold the house.

[pigbuttons]

I tried putting some plasticizer in a test batch of calcium aluminate (CA, one of the common cements used in castable refractories) and vermiculite. Looked good until I tried to fire it, at which point it was soft enough to crush with my fingers. Since then I've been using CA without additives and it is harder than most Portland Cement concrete I've made.