concrete casting

Recently, I came across a concrete casting that was done in an unusual manner. The piece was a simple birdbath type pedestal which was cast in a latex mold. The pedestal had fallen over and broken and what was unusual was that upon closer examination of the break, it seemed that the piece was created with a 1/16' thick shell against the surface and then filled with a concrete mix. Has anyone ever tried this? The concrete mix used to fill the pedestal was made using 1/2' crushed rock and the surface were you would expect there to be a lot of bugholes was smooth. Could the surface have been sprayed in with a mortar type mix (gunite) , allowed to set and then filled? Could this be done even with the very narrow opening in the mold? Thanks beforehand for any help.

I doubt it. Could the mold have been spun on its vertical axis, putting a layer of fines on the surface?

[It seems more likely that a fine mortar facecoat was poured in and poured out, then the coarse mix was added.]

Andrew Werby

What is a fine mortar facecoat? and would it be possible to use this technique in a high production environment with larger items?

'> [It seems more likely that a fine mortar facecoat was poured in and poured Or hand laid up with a real sticky mix, and then tamped/vibrated with the coarse mix. Another technique I have always wanted to try - hand layup (GFRC a good candidate) then fill the cavity with moist sand, tamp the heck out it, when the piece cures, the dry sand pours out and you have a good, lightweight cast. You could fill the cavity with a lightweight concrete (the ultimate oxymoron), like perlite fill, as well. Here's an interesting link for you cementheads, http://www.geocities.com/flyingconcrete/ - look up the lightweight concrete link. Perlite also adds considerable insulating and fireproofing properties.

I have bought a tirolessa sprayer now, for spraying concrete over expanded mesh forms like on this site, but I haven't had a chance to try it out yet. - Maybe I should take the RV out to memphis and blast out some trees with Dan. My only concern with this method is that it does not last over 50 years, my reference is the Watts district of LA, they are having to do major repairs all the time there, but I haven't had the time to find out why. I know the galvanized diamond mesh is superior to cheap, galvanized, chicken wire. On the other hand, there are many in the construction industry who think that a twenty five year life is more than adequate for our economy, and certainly past their working lifetime - sad but very tru> [It seems more likely that a fine mortar facecoat was poured in and poured Or hand laid up with a real sticky mix, and then tamped/vibrated with the coarse mix. Another technique I have always wanted to try - hand layup (GFRC a good candidate) then fill the cavity with moist sand, tamp the heck out it, when the piece cures, the dry sand pours out and you have a good, lightweight cast. You could fill the cavity with a lightweight concrete (the ultimate oxymoron), like perlite fill, as well. Here's an interesting link for you cementheads, http://www.geocities.com/flyingconcrete/ - look up the lightweight concrete link. Perlite also adds considerable insulating and fireproofing properties.

I have bought a tirolessa sprayer now, for spraying concrete over expanded mesh forms like on this site, but I haven't had a chance to try it out yet. - Maybe I should take the RV out to memphis and blast out some trees with Dan. My only concern with this method is that it does not last over 50 years, my reference is the Watts district of LA, they are having to do major repairs all the time there, but I haven't had the time to find out why. I know the galvanized diamond mesh is superior to cheap, galvanized, chicken wire. On the other hand, there are many in the construction industry who think that a twenty five year life is more than adequate for our economy, and certainly past their working lifetime - sad but very true.

[Basically a mixture of cement powder and fine sand, about 1 part cement to 2 parts sand, with up to a half-part of clay powder thrown in to add plasticity, some admix to help keep it together, and water added to produce the correct consistency. This is usually used as a splash-coat in open molds, but I suppose it could also be poured.]

and would it be possible to use this

[I don't see why not (anything's possible)- why don't you give it a try and tell us how well it worked? The tricky part would be mixing up something that would evenly coat the inside of the mold while being strong enough in a semi-set state to withstand the addition of another layer without disruption. This might take some experimentation to get right.]

Andrew Werby http://unitedartworks.com