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Old 02-03-2010, 08:27 AM
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Default How to attach hardibacker to a rebar skeleton

I know most people use steel studs, but let's assume for the moment that I build my enclosure out of rebar instead. Just bear with me. How might I attach hardibacker to it?

I was thinking that I could use those brackets which hold small pipes in place. I don't know what they're called: a small flat strip of metal bent so as to wrap 180 degrees around a pipe, then bent 90 degrees out to the sides to make a flap with screw holes in each flap (lower-left in the linked image below):

http://www.siathaiyew.com/images/oth...e-brackets.jpg

If I could find those in the right size for the rebar (I assume HD has them), I could use it to attach to the hardibacker...but how? I assume I can't just drive a screw in. The hardibacker isn't thick enough. I'm afraid that a screw would rip out. Do people agree with this concern or would very short screws (1/2") work?

Alternatively, I could drill holes through the hardibacker (what kind of drill bit do I need?) and attach the same brackets with nuts, washers, and bolts instead. I would have to figure out how to deal with the protruding bolt head when I surface the hardibacker, either with stucco or stone. Does it sound feasible that bolt heads could be dealt with when surfacing or would they represent a a serious problem with this design?

Thanks.
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  #2  
Old 02-03-2010, 09:23 AM
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Default Re: How to attach hardibacker to a rebar skeleton

Personally, I would drill a hole in the board on each side of the rebar and loop a fairly heav gauge wire through it the tighten the wire like a twist tie. Easy cheap and effective
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Old 02-03-2010, 09:26 AM
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Default Re: How to attach hardibacker to a rebar skeleton

Quote:
Originally Posted by shuboyje View Post
Personally, I would drill a hole in the board on each side of the rebar and loop a fairly heav gauge wire through it the tighten the wire like a twist tie. Easy cheap and effective
+1 That was my very first thought as well.
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Old 02-03-2010, 09:58 AM
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Default Re: How to attach hardibacker to a rebar skeleton

I can't think of any reason in the world you would want to do that, nor can I think of any way to do so such that your structure would not be loose and wriggly.

People have been building for thousands of years, a hundred of which involved cement board and rebar. If there were any reason or advantage to using the 2 together, it would be done.

Sometimes it is better to state your idea or issue rather than try to attempt to re-invent the wheel. Do you have an excess of rebar and hardi board?

Last edited by Tscarborough; 02-03-2010 at 10:00 AM.
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Old 02-03-2010, 10:24 AM
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Default Re: How to attach hardibacker to a rebar skeleton

Well, there seem to be a zillion ways my "vision" might be realized. I guess I haven't posted a recent CAD model, but the terraces, as described in another thread (Terraced enclosure), are still more or less my goal. The CAD model in that thread is a little out of date but still approximately resembles my goal. The design is now octagonal instead of circular. I should post another CAD model.

My local HD and Lowes don't carry steel studs. They can order them, but I can't look at feel and think about them in advance. So to go the steel stud route I have to basically dive in blind. Not only do I no have experience with steel studs, but I can't even get a feel for them in the store before I buy them. In addition, I believe a stud approach would require significant tapconing to the hearth. I have driven a few tapcons into my hearth already (for the screen that will enclose the loose InsWool HP), and it was a real bear. Half the holes didn't even end up deep enough to fully drive the tapcons in. That isn't a problem for the screen b/c all it really needs to do is loosely hold the InsWool in place while I build the enclosure, but for a stud-frame, the tapcons need to go all the way down or the frame will be loose. I don't own a hammer drill and I'm not dropping $200 on a drill for this project. I would like to do this with as little tapconing as possible.

That leaves many remaining design plans. One I have leaned toward heavily is framing and pouring the terraces in solid vermicrete, perhaps shored up with a "shrink-wrap" of chicken-wire after it cures. I was about to go this route when I became overly concerned about cooking the plants growing on top of my oven, which motivated maximum insulation, which pushes me toward loose vermiculite instead of vermicrete, so I'm back-paddling on my design, trying to figure out an enclosure once again, but still without steel studs.

Another possibility is fermocement. Rebar and chicken-wire the entire terrace framework, then cement the whole thing together. Problem with that is I have no good way to apply the cement to the inside of the mesh (I won't be able to reach inside once the chicken-wire is in place), nor do I have a good surface on the inside to push against when applying to the outside of the mesh. I could apply the chicken-wire "as I go" so I can reach down from the top to work on the inside, but it seems like a difficult approach.

Which leads me to this idea. Rebar as a framework, hardibacker as a surface.

There are yet other ideas floating around. Build stringers out of angle iron, rest them on an outer wall of either angle iron or concrete. I don't know. I don't have any welding equipment (or experience) and I'm not sure the structure can be built solely by cutting, bending, drilling, and bolting. I suspect some welding would be required, especially at the apex where the stringers and "rafters" would all meet in a big mess in the center. Plus, angle iron is SUPER expensive. I just don't want to spend hundreds of dollars on the enclosure.

So, that's more or less where my thought process has been meandering on the whole issue. I just cannot figure out how to make a few simple self-supporting terraces. I guess the solid vermicrete idea seems very feasible. I was literally about to charge forward on that, measuring wood for the form, when I became suddenly concerned that the insulation might be insufficient.

You asked, probably way more than you wanted to know.

Any recommendations or feedback are appreciated...I suppose at this point this thread has fully overlapped with my original terrace thread (Terraced enclosure). I wonder how to tie them back together.
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Old 02-03-2010, 10:34 AM
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Default Re: How to attach hardibacker to a rebar skeleton

I've posted an updated CAD model of my (final?) design in the terrace thread (Terraced enclosure).
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Old 02-03-2010, 10:36 AM
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Default Re: How to attach hardibacker to a rebar skeleton

An idea: Wire tie expanded metal lath to your rebar structure, finish with whatever concrete product you want. The wire ties may not last forever, but the concrete shell should be self supporting.
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Old 02-03-2010, 10:43 AM
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Default Re: How to attach hardibacker to a rebar skeleton

How is this different from the ferrocement approach? Don't I need to push the cement against the lathe from both sides to get it solidly encased in concrete? Even if I don't need to apply concrete to the inside, don't I still need a hard surface behind the lathe to push against when applying from the outside?...or is lathe tough enough (unlike chicken-wire) to support that kind of application?
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Last edited by kebwi; 02-03-2010 at 12:20 PM.
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Old 02-03-2010, 12:16 PM
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Default Re: How to attach hardibacker to a rebar skeleton

FWIW, you don't need to use tapcons to attach to your slab. Those are always my last resort for the reasons you mention.
The conventional method to attach anything to a concrete slab is to use a power nailer. A handheld, hand loaded variety can be had for about $30. Amazon.com: Desa International 78708 Powerhammer 476 Fastening Tool: Home Improvement

I prefer the trigger-actuated style for a bit more $. Either way, fast and easy, just wear your earplugs.
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Old 02-03-2010, 12:45 PM
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Default Re: How to attach hardibacker to a rebar skeleton

Quote:
Don't I need to push the cement against the lathe from both sides to get it solidly encased in concrete?
Nope. It may actually be counterproductive to do so. Lath works by creating a key with the material forced through it:

That's an image of the old wood lath, but the expanded metal stuff works the same way. When that bulge on the back hardens it holds the surface material solidly to the lath.
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