what is the reason for crack development in cultured marble block?

what should be the mix of cobalt and resin and catalyst in the marble aggregates ?

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Gorfram7 years ago
Most cracking that occurs as a material is solidifying is due to the shrinkage that takes place as the material frezes or "sets up." Shinkage in resins is often caused by too much or too little of an ingredient. Each formulation is different, so if you don't know what the correct proportions of your resin, catalyst & other ingredients are; you'll need to find out from the resin manufacturer. Cracks can also form in composites when the resin doesn't form a good chemical bond with aggregates like the marble dust. Success or failure of this bond can be very sensitive to the proportions of the resin mix; as well as to temperature, time, mixing conditions, and any moisture or other contaminants that may have affected the marble dust or other ingredients. Again, you'll need the mixing specs from the resin manufacturer, along with good quailty ingredients and clean shop technique.
ashok -1955 (author)  Gorfram7 years ago
Dear Gorfram, Thankyou for the reply. As you say I have experimented in various combinations of aggregates and resins+cobalt+catalyst additions and found encouraging results. I only want to confirm from experts as to my findings is ok. I also hope it could be due to the excess exothermic heat given out of the block. or due to high addition of cobalt in the mix. How should the aggegate mixture look like, or feel like when mixed with the resins ?
Dear Ashok, I'm sorry, but you're not likely to find any experts on the casting of epoxy-stone composites on this site. I suspect that I'm about as close as it gets around here, and while I am a Materials Engineer, I have no specific expertise or experience in Surface Science or the Kinetics of State Transformations. Very few people do, and most of them work for big chemical companies who demand that they keep their techniques strictly proprietary. I do know enough to make an educated guess or two. If your solifiication reaction is proceeding too rapidly, the liquid/solid interface may become unstable and undergo what's called "dendritic solidification" (I think you can Google this), which can result in cracking and internal cavities in the casting. I also wonder if the exothermic heat or reaction could be very locally increasing the reaction rate just at the liquid-solid interface, although I'm not sure what sort of effect that might tend to have. May I ask how high a proportion of cobalt you are using in your mix, and in what form you are adding it? (And I'm sure I don't have to mention this, but you are taking proper precautions against using radioactive cobalt, or exposing yourself to cobalt posioning, of course?) Sorry I can't be of greater help.

Man-made marble

Which ingredients, marble powder resin, type of catalyst or which process could be at cause for delayed setting?

kelseymh7 years ago
This is a fairly technical question; I don't know if we have an stonemasons as active members. You might be better off trying Google Scholar if you need research results, or checking with the cultured stone industry groups.