Lately I have been having loads of trouble making my sculptures stable as they are getting bigger and bigger. I have tried thelma's cd base and just can't get the hang if it. I know IRS probably a matter of preference so I thought I'd ask you all what sort of bases you all use the most and why?

Geos can be filled with salt or water for weight, and tied together to make larger bases.   Doughnuts make good bases too.

5" rounds with a 5" double stuffed water weight are good, here is a thread about weights and there are a couple of more threads from this one;
how-fix-bouquet-into-geo-centerpiece-weight-t3093.html?hilit=water%20weight
Hope it helps?

Brilliant guys thanks do much that's exactly what I needed.

why does it have to be salt water that the geo is filled with? why not just water from the tap?

No either Or, you can put water in the balloon, salt in the balloon or even sand in the balloon.

Hi Sarah,

I have found it can be a bit tricky using water in Geo's, it gets a bit slippery tying the knot. It can also be a bit disasterous ...but very funny... if it bursts  

Where I live we are lucky to have a beach with very fine (no gritty or sharp bits) sand just 5 mins walk from my house.......and all the sand is free !!!!!

This is how to fill a Geo with enough sand to weigh it down. I used a clear one so you could see what's happening.

1.  Blow up the geo, and streach the neck over a bottle filled with sand (or salt)

2.  making sure the balloon doesn't come off the bottle, invert the bottle allowing the sansd to run into
     the balloon

3.  take the balloon off and tie it when you have enough sand in it. If any air escapes and you need to
     inflate the balloon a little more BE VERY CAREFUL OF "BLOWBACK" or you will get a mouthfull of sand

Darren has come up with an idea which makes his bases look excelent  

Here is the link     geo-balloon-base-t5637.html