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Greetings

I'm planning on building an outdoor firepit table and am having a lot of trouble settling on the appropriate way to do it. I've attached a picture of more or less what my goal is - I want the appearance of a solid block of concrete. My preference is to build a frame, attach Hardiboard on all sides, and then use RapidSet Cement All, or similar product, to layer a few coats on all sides and seal up the corners. Finally, sand and polish.

My concern is humidity expansion if the frame is wood, or temperature expansion if I go with stainless or aluminum framing. The outside edges/seams are what I'm thinking will end up giving me problems.

Does anyone have experience with something like this and advice about the best way to approach it?


Thanks in advance!
Charlie
 

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The most stable product would be form ply or sign ply They are the plywood with a water proof paper face used for concrete forms and real estate signs.
Thanks Neil. I don't think I did a good job wording my question. At the moment I'm thinking rather than form and pour concrete, I would essentially build a box with 2x4s or metal square tube - then attached hardiboard to it on all sides and put a few layers of concrete on that. It would give the appearance of a concrete block without the weight.

However I'm struggling with whether or not this is even possible - perhaps the only reliable approach would be to form the entire block (hollow inside) and set it over a frame.
 

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Thanks Neil. I don't think I did a good job wording my question. At the moment I'm thinking rather than form and pour concrete, I would essentially build a box with 2x4s or metal square tube - then attached hardiboard to it on all sides and put a few layers of concrete on that. It would give the appearance of a concrete block without the weight.

However I'm struggling with whether or not this is even possible - perhaps the only reliable approach would be to form the entire block (hollow inside) and set it over a frame.
I was thinking building the box out of plywood and cover it.

Steel and concrete expand much like each other, that would make it stable.
 

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I was thinking building the box out of plywood and cover it.

Steel and concrete expand much like each other, that would make it stable.
Ah, ok great! You're right, I did some googling and steel and concrete have almost identical expansion rates. So it looks like the best approach is to make the frame for the table out of steel (trying to determine whether to use standard or go with stainless and spend twice as much). I was originally going to screw Hardiboard to the outside because it won't absorb moisture, are you saying that form ply or plywood would be better?

Cheers
Charlie
 

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Ah, ok great! You're right, I did some googling and steel and concrete have almost identical expansion rates. So it looks like the best approach is to make the frame for the table out of steel (trying to determine whether to use standard or go with stainless and spend twice as much). I was originally going to screw Hardiboard to the outside because it won't absorb moisture, are you saying that form ply or plywood would be better?

Cheers
Charlie
If I was using any plywood then I wood do all plywood and never mind the steel. Not sure the deference in expansion there.
Attaching cement board to steel?????????????
 

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Build a metal frame apply lath and stucco no wood required if you need to keep the in side neat than use paper backed lath. If corners need reinforcement use one of the Synthetic stucco fiber glass reinforcement.
For the stucco apply as you would any stucco for the stucco finish use a green sponge float for a very fine sand float finish.
For the final polished look use a Venetian plaster finish, these finishes will give you a polished marble look or a modeled look.
Look for some of these Venetian plaster.
I will list the ones I have used first in order of preference.
Master of Plaster
TexStone
Variance Venetian
American Clay
There is also Vasarl Venetian I have not used this one.
If you would like to make it with out the frame use block EPS board apply a bond breaker to foam apply lath and Stucco, stucco would be about 1&1/2 inch if this method is used you will need struts at the bottom
For a lighter weight system do the wood frame box cement board Synthetic stucco applied direct to board apply Synthetic finish.
 
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