cast stone
Posted by Aggenbach from Cape town, OT, ZA on July 6, 2007
Hello BruceMy company is called Cemstone,we produce mainly wet cast cladding and paving products,cast into polyurethane moulds,vibrated and stacked to dry.We spray our releasing oil with a compressor onto the moulds,turning them face down to get rid of excess releasing oil,we oil every 3 days.We found that we get a lot of surface bubbles after oiling the moulds,these bubbles get less on the second and third cast.Are there problem directly linked to my releasing oil,,we have tried a couple ,all show the same results.My mix consists of Birla whitecement,a 6 mm stone ,coarse sand,calsium,oxide and water.Haveyou got any ideas how we con better this problem,even tried vibrating for longer periods
Regards Hennie Aggenbach
Hennie,
Since the bubbles get less on the 2nd and 3rd cast means either the mold reslease or its amount or application is one of the problems.
I had read in an article which said that mold release agents based on reactive agents generally perform better than barrier type mold release agents.
Try adjusting the mix design, especially the fines content and adjust the vibration time. Try spraying of the mold release using a finer size nozzle. It might be a trial and error process initially till you it right.
Goodluck.
