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christo 08-05-2008 08:14 AM

Casting seating wall in Concrete
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I was working through options on a seating wall for the outdoor kitchen.

I wanted something that would look similar to the oven and rest of the landscaping. With the built up level of the patio, it was a bit too late to dig down and make solid concrete footers. I did not like the modular block look - but that is my fall back position if the mold fails.

So I decided to try my hand at making a form and use it to create 5 seating wall modules. After the seating modules are poured, I'll make another form for the columns between the seats that will have a planter on top and wired for lighting.

Wall thickness is 2.5 to 3 inches - wire reinforced and a bit of rebar as well. I used plain door casing applied to the front to see if it will look like a raised panel after the pour.

I'll use cooking spray as a release agent.

First pour is tonight!


Wiley 08-05-2008 09:52 AM

Re: Casting seating wall in Concrete
I'd suggest vibrating the concrete to help minimise the problem of rock pockets and trapped air. If you don't have one, pounding the outside surface of the mold with a rubber mallet helps. Trapped air is such a pain to get out.

Also, when I have tried these sort of things I also found that adding a 1-2 qts of straight cement to the Quikrete or Sakrete stuff helps alot (if that's what you're using for concrete). The bag for Sakrete says not for slabs less than 4" but by adding cement you can get around that limitation. If you're going wetter, upping the ratio of cement to aggregate still results in good strength. I have a graph someplace that shows the curve. That's how concrete pumpers get away with pumping a very wet mix (they run a 6 or 7 bag mix or more for thin sections, elevated slabs, engineered stuff etc. ).

Alot of these products have air entraining additives and that work against getting a smooth finish right next to a mold. But you probably know all that.

Good luck, and be sure to show us pictures of the final product!

christo 08-05-2008 01:18 PM

Re: Casting seating wall in Concrete
I bought a few bags of cement while I was out today, I'll definately try it.

I'll be hammering on the form as well as trying my electric drill with an unbalnced weight chucked in it for vibration.

Thanks for the advice!!!


brokencookie 08-05-2008 01:34 PM

Re: Casting seating wall in Concrete
You can also use an orbital or finish sander on the outside for vibration


christo 08-06-2008 06:13 AM

Re: Casting seating wall in Concrete
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I went out and bought a couple 74 lb bags of cement to assist in the pour.

I split one bag equally between 5 ea 80lb bags of concrete and loosened up the mix accordingly.

Having the extra cement in there makes me feel better about a more soupy mix. I don't think I would have had much luck with just concrete in a stiff mix.

Overall it went well. I did not have much mix leftover when done.

Hit it a bunch with rubber hammers - my sander and drill contraption did not have enough umph to make a big impact on the form - I think it's too much mass. So I spent a lot of hammer time.

I did not fix the center cores and they tried to move on me - so that's a lesson for next time.

I went out an hour later and beat it with the hammers again - and did it again an hour after that... I hope it releases.

Looking at the picture - it looks like a huge cinder block!

In two days, we attempt to disassemble the form!!!


egalecki 08-06-2008 07:29 AM

Re: Casting seating wall in Concrete
Is that melamine shelving you used for the form? I'm anxious to see if your seating works! I don't need seating, but I have a countertop to figure out, and a leg or post for it to make. I'm still trying to figure that part out...

The way you've set them up is ingenious. Did the bar clamps go on after the cores moved? Did you have any trouble with the long sides wanting to bow?

Sure hope they'e a success for you. Your whole project looks great and has so many good ideas for the rest of us to make use of! :D

christo 08-06-2008 02:49 PM

Re: Casting seating wall in Concrete
Hi Elizabeth!

I bought several 4x8 sheets of white melamine to make concrete countertop forms. I've done a bunch of reading about it and it looks pretty straight forward.

Those sheets are super heavy - I cut them on the driveway using a straight edge vs trying to run them through the table saw.

Based on the weight of the forms I'm rethinking making 30x96" concrete counterops for my kitchen and will make smaller units and piece them together.

Also - as far as the inner cores on my seat - I wrapped them with some 1/4 inch pink foam - firm closed cell stuff vs fluffy. - My hope is that it will actually allow me to remove the cores without breaking them out.....

We'll see!


christo 08-14-2008 10:13 AM

Re: Casting seating wall in Concrete
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I'm back.

Poured the second bench over the weekend.

Lessons learned:

1st pour:

Wiley said it would be a good idea to remove the form on the first day as concrete shrinks - I wrapped the inner core forms with foam so I was not worried. Besides I was away on a business trip and couldn't take them out if I wanted to.

Inner core forms removed fairly well - foam helps.
Rest of form removed easy enough but all of the moulding was stuck in the face of the bench. I drove screws into the moulding to jack them out of their prisons - worked well and did not lose a single piece of moulding.

Melamine form still looks good - no appreciable water absoprtion. BTW I coated all exposed edges with silicone caulk as well.

Had lots of small voids in the bench (no big ones!!!) and grouted them with 100% cement. After hitting them with the sander it looks nice.

2nd pour:

took a while to clean up the dried glue from where the moulding had separated from the form - no glue this time - just a few brads and silicone caulk around the edges.

Put the form back together - used lots of spray PAM - a whole can. Also wired the center cores to the form at the top and bottom they did not move this time!!!

Used same mix as last time but poured half of the bench and used my home made vibrator around all the edges - later found that this made a big difference - almost no voids in the 2nd pour (bottom half).

Pushed the metal reinforcement into the concrete - was not bad as there was enough of the form exposed to make sure I was centered.

Filled up the rest and could not fit my home made thing between the walls and reinforcement wire. Used plan B - Vibrator on the outside and whack it all over the place with my rubber hammers.

This time I took Wiley's advice and removed the forms the next morning. Probably in the form 20 hours.

The form was loose from the bench in half the time and all of the moulding stayed attached to the form!!! - no rework for the next pour.

The forms are starting to show a little orange peel look - I hope I can get 3 more pours out of them. Only 2 sides will show when I'm done - so even If I have to make some new ones it won't be the end of the world.

Was going to pour concrete tops for the benches but am now looking at using IPE decking for the tops - it should warm up all the concrete out there.

Still not sure what do make the planters out of that will go between the benches - Wood or poured concrete? Not sure now. Original plan was concrete with a light embedded in the front.

Going for 2 sections this weekend!! - one on early sat morning and one late on Sunday!!! Wish me luck!! Maybe I will swing by the orange tool store and see if I can score a vibrator.


egalecki 08-14-2008 11:36 AM

Re: Casting seating wall in Concrete
Those look great! I like the idea of the decking for the tops. You know, if you make it removable, you could store stuff in there...

I've been looking at hypertufa sites- I think they look neat. Maybe you could fit some of that in there for planters? Or will that mix your metaphors too much, design-wise?

Ken524 08-14-2008 11:48 AM

Re: Casting seating wall in Concrete
Very Cool, Christo!!! Again, I'm amazed by the skills, creativity and ingenuity of the people on here!

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