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Posted: Thu Mar 20, 2008 6:56 pm
by PeterP
I'm looking for help for something a bit different which I hope someone can help with.
I want to cast a simple square pedestal for a garden statue.
Pedestal to be approx 14 inches square and 18 inches high and I was going to make a box mould from some thick chipboard. However to reduce the weight I was going to put another piece of formwork in the centre so that the pedestal is actually hollow. The top of the pedestal would be a paving slab.
My questions are.......
What mix of concrete should I use and how wet?
and
If having a hollow centre, how thick should I make the walls and will they need any reinforcement?
To be honest the statue is not that heavy as its only 4 ft tall and just about liftable by one person.
Any advice gratefully received.
Posted: Thu Mar 20, 2008 8:27 pm
by MRA
If you want a plinth, why not just use some reclaimed facing bricks, natural walling stone or concrete substitute for the job? It would give a much nicer finish than cast concrete and can be paved over, (although I would recommend a concrete fill to support the weight from above).
If you do use concrete however, assuming the concrete plinth is visible, a vibrating poker will need to be used to eliminate unsightly air bubbles and also stick some reinforcing bar in it too.
Posted: Thu Mar 20, 2008 8:49 pm
by James.Q
MRA wrote:*If you do use concrete however, assuming the concrete plinth is visible, a vibrating poker will need to be used to eliminate unsightly air bubbles and also stick some reinforcing bar in it too.*
me thinks a poker on 18 inch x 14 inch hollow concrete is a bit of over kill just tap the mold with a hammer plenty of times, but to be honest I would just keep lintel solid at 18 inch high not that heavy and less hassle to make.
Posted: Thu Mar 20, 2008 8:57 pm
by PeterP
Thanks for your replies....I was thinking of using a white cement to match the white of the statue.
An absolutely smooth finish is not essential as the statue does not have a perfect surface
Just wondering what mix to use 6:1 ballast:cement?
Presumably the wetter the mix the smoother the surface might be but don't want to weaken it too much.
Posted: Thu Mar 20, 2008 9:01 pm
by MRA
PeterP wrote:Thanks for your replies....I was thinking of using a white cement to match the white of the statue.
An absolutely smooth finish is not essential as the statue does not have a perfect surface
Just wondering what mix to use 6:1 ballast:cement?
Presumably the wetter the mix the smoother the surface might be but don't want to weaken it too much.
I know a poker is overkill, but if your gonna do it, do it properly! 
If it's 450mm (18") high, then why not just build 2 courses of 100mm blockwork and render it?...especially if you think a smooth finish is not vital.
Posted: Fri Mar 21, 2008 9:40 am
by seanandruby
"Rodding and tapping" the outer shutter should expel most air bubbles. 6 + 1 should be fine. i would be tempted to put angle fillet on the corner edges to stop them breaking off.
Posted: Fri Mar 21, 2008 4:37 pm
by matt h
made loads of these varying sizes, and the only thing you have to worry about is the topple factor. I,d drill the base of the statue and insert rebar and anchor it to the deck and then concrete my base to it... stops the thievin toerags from removing your statue, base and all...
Posted: Sat Mar 22, 2008 1:11 am
by PeterP
Thanks everyone for your suggestions....take your point about the 'topple factor' - was just going to set it in mortar but drilling and reinforcing the joint is probably the best bet.
Thanks.
Posted: Sat Apr 05, 2008 5:12 pm
by Ted
I would use melamine for the form to give the pedestal a nice finish. I don't think a vibrator is necessary you can just tap with a hammer and lift the mould up half a centimeter or so and drop it to vibrate it. I reckon you could make the hollow 8" square but I would add a ring of rebar as reinforcement. If you are going to use a white cement I would use a white sand too.