Not sure what your form is but try a piece of PVC or sonotube with a smaller diameter tube(to cover the pump) inside and fill with your mixture turning the center tube often so it won't stick, remove all and carve or file the design you want on the outside. No worry's about slumping the tufa.
Paws

To make it more manageable weight-wise, use a PVC tube or Sonatube cut to the size you want (PVC: harder to find, but 6"-8" might be appropriate), then wrap it with an overlapped layer of hardware cloth/wire mesh or several layers of chicken wire. You don't want the wire tight to the tube.

Set the tube upright on an oiled board or piece of plywood, & start smearing your mix on. I generally start from the bottom and work my way up. For the first coat, concentrate on getting the mix pressed well into & around the wire. It doesn't matter if the wire shows at this point. I also only mix about half of what I think I'll need, so it doesn't set up too fast. Then I mix a second batch (no frantic hurry, just let the first layer set a bit), and apply it on top of the first layer, being sure to cover ALL the wire with (IMHO) at least a 1/4" of the mix. Any exposed wire will rust, staining your piece, and open channels for water and frost damage.

If you are intending to embed some kind of anchor into the mix, don't forget to do it.

You can leave the forms inside.

Sue

I bought a mold for a pedestal and it works really well.
shown here but you have to as k them to buy the pillar mold seperatly.http://cgi.ebay.com/ws/eBay
ISAPI.dll?ViewItem&item=8201187027&category=83897&tc=photo

I don't know what the matrial is but it is a sheet of white plastic of some kind that is 16" x 40".

This is for making a 16 " tall pedestal that is 6" across. You get the 6" by rolling like a poster to get the size you want and tape it securely with duct tape or ? ?

The over lapping gives the form strength so It doesnt bow out , And withstands the rubber mallet tapping every few inches to get rid of air bubbles.

You can stack and cement 2 together for a taller pillar . but who's gonna move it ? LOL

Dufuss me couldn't wait to get to HD , thinking maybe a formica overlay would work . HAH !
NOT !

The tube is filled standing upright on a piece of cardboard which leaves a clean end and does not stick. I did see the imprint from the pop cans that were in the cardboard tray .

Sooooo folks , gotta find out what and where this plastic sheet material is. Yer supposed to get at least 50 castings from it. Beats buying sonatubes , unless you will only be casting one piece.
Shirley (((*-*)))

I bought a mold for a pillar and it works really well.
shown here but you have to as k them to buy the pillar mold seperatly.http://cgi.ebay.com/ws/eBay
ISAPI.dll?ViewItem&item=8201187027&category=83897&tc=photo

I don't know what the matrial is but it is a sheet of white plastic of some kind that is 16" x 40".

This is for making a 16 " tall pillar that is 6" across. You get the 6" by rolling like a poster to get the size you want and tape it securely with duct tape or ? ?

The over lapping gives the form strength so It doesnt bow out , And withstands the rubber mallet tapping every few inches to get rid of air bubbles.

You can stack and cement 2 together for a taller pillar . but who's gonna move it ? LOL

Dufuss me couldn't wait to get to HD , thinking maybe a formica overlay would work . HAH !
NOT !

The tube is filled standing upright on a piece of cardboard which leaves a clean end and does not stick. I did see the imprint from the pop cans that were in the cardboard tray .

Sooooo folks , gotta find out what and where this plastic sheet material is. Yer supposed to get at least 50 castings from it. Beats buying sonatubes , unless you will only be casting one piece.
Shirley (((*-*)))

See if this works

Here is a link that might be useful: {{gwi:70857}}