# Using Hardi siding as form for concrete patio



## TCS-Austin (Apr 21, 2011)

We have started to build the form to a 600 SQ FT Patio using 8" wide pieces of Hardi siding. ( much of the patio is curved) I'm starting to wonder now if they will hold up to the weight of the concrete. Any suggestions or advise please.


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## DangerMouse (Jul 17, 2008)

I think they will, as long as you have a sufficient amount of stakes going all around the edges.
I wonder how much moisture that stuff will suck up though. (swelling = bumpy surface)
If it were me, I'd lay sheet plastic over the inside edge to keep the 'wet' inside till it's set.
I could be totally wrong too. The guys here that do this sort of thing for a living will interject if needed though.

DM


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## STL B. (Oct 29, 2010)

I think it would suck to have the hardi crack or break when you hit it with a shovel, and your going to hit it. I say masonite or flexable plywood ($20-$40) to prevent an O sh*t moment while the trucks there and the timers running.


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## DexterII (Jul 14, 2010)

STL B. said:


> I think it would suck to have the hardi crack or break when you hit it with a shovel, and your going to hit it. I say masonite or flexable plywood ($20-$40) to prevent an O sh*t moment while the trucks there and the timers running.


+1

I don't know for sure, but this is exactly what I thought when I first saw the post. I'd give you an A+ for thinking outside of the box, but as far as going any farther with it, I'd stick to something more traditional, as STL B mentioned. Concrete is enough work when everything goes as planned, but a busted form can really mess up your day.


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## 95025 (Nov 14, 2010)

STL B. said:


> I think it would suck to have the hardi crack or break when you hit it with a shovel, and your going to hit it. I say masonite or flexable plywood ($20-$40) to prevent an O sh*t moment while the trucks there and time is running.


Yep. Hardi siding is good stuff, but I'm not sure this is the right application. It's too brittle.


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## TCS-Austin (Apr 21, 2011)

STL B. said:


> I think it would suck to have the hardi crack or break when you hit it with a shovel, and your going to hit it. I say masonite or flexable plywood ($20-$40) to prevent an O sh*t moment while the trucks there and the timers running.


I found this article on Wiki which says to use Hardi as the form

http://www.wikihow.com/Build-Forms-for-a-Curving-Concrete-Sidewalk

I did not use the 12" wide pieces, ripped down, I used the 8.25" pieces with 2" buried in the ground. I'm thinking if there is enough stakes and support behind the mold I should be fine ... (prayer under my breath) lol

I had gone to HomeDepot and did not find anything else to use.

Are there not any concrete pro's on this site to give me any advice? Does anyone have any experience in this matter or is it all theory and guessing?

Thanks for your help.


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## DangerMouse (Jul 17, 2008)

I'll move this to C+B section, you'll get many more members there seeing it.
You'll get an answer in no time.

DM


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## DexterII (Jul 14, 2010)

I have poured a lot of concrete, but not an "expert", so sorry to have shared in STL B's thoughts, but for what it's worth, I did not see any reference to Hardiboard in your link; it refers to "hardboard siding (sometimes called Masonite)", just as STL B mentioned. Hardiboard and hardboard are not the same thing. Good luck!


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## TCS-Austin (Apr 21, 2011)

My bad! guess I was in a hurry. Where can I get the Hardboard at? And how flexible is it?


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## STL B. (Oct 29, 2010)

I think Hardi is a little bit brittle for use asa form......but......chances are that you could form your pad with Hardi plank and every thing would go off without a hitch. My main concern would be that it would crack with a good wack from a shovel or your wheelbarrow'er isnt perfect and gives the Hardi a good bump. The pre-mix delivery company's usually only give you 15-25min. to off-load (closer to 10-15) the truck, so if you had to stop the pour to fix your forms it's going to cost you royaly. I just think that hardboard/masonite would be money well spent. (just in case) 

P.S. I looked at the link you provided and think you should have a shovel handy and be prepaired to use it. Also if your going to use hardboard for the entire slab( I recomend you use 2x4's or 2x6's for your straight runs) back it up with dirt all the way around (for support, if you dont back-up your forms you will have "wavy" edge on your new slab..not-cool). Check every thing two..three..four times to make it as trouble free as possible. 

How much help are you going to have ?


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## TCS-Austin (Apr 21, 2011)

How many people should I have helping me? 

There is only 2 sections, less than 16 ft total that has a straight run and I am using 2x6 for that.

I went back with masonite over the Hardi just to be safe.

Thanks for all your help


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## 95025 (Nov 14, 2010)

TCS-Austin said:


> How many people should I have helping me?
> 
> There is only 2 sections, less than 16 ft total that has a straight run and I am using 2x6 for that.
> 
> ...


Quite a few years ago, my artistic/creative wife decided that we HAD to have a curved sidewalk up to the house. So guess who obeyed? 

Anyway, the hardboard siding worked just fine (sorry, I was thrown off by the "hardiboard"). 

Just be sure to use lots of stakes (we used the smaller ones). They're cheap insurance.


If it was me pouring this, I'd want 3-4 people helping - with a strong preference for people who have worked concrete before.


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## jagrrr (Feb 11, 2011)

*Don't use Hardi - Not meant for this type of application*



TCS-Austin said:


> We have started to build the form to a 600 SQ FT Patio using 8" wide pieces of Hardi siding. ( much of the patio is curved) I'm starting to wonder now if they will hold up to the weight of the concrete. Any suggestions or advise please.


Using Hardi-board for forms is NOT a good idea. Hardi is porous and brittle if not handled correctly. You are much better off buying form material as it's not very expensive and is made specifically for making concrete forms. Trying to shortcut the preparation always results in one conclusion. It will result in nothing but problems.

Have a wonderful day. btw, I love Hardi boards and planks for the proper application.


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## TCS-Austin (Apr 21, 2011)

Finished back in May. Been so crazy busy I hadn't had a chance to follow up on this thread. Thanks for all your help. I went back and added Masonite to the form and the finished project looks great!!! Doing the outdoor kitchen now.


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