Cement Fiber Board

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
Also known as Hardie Board.
I may possibly need to mount a box and small disconnect on this.
What is the best way to mount to this?

Can't find anything on the Hardie Board instructions other than how to install it.
 

tkb

Senior Member
Location
MA
Use a carbide bit, but don't set the drill to hammer. You might crack the boards if near the edge.
 

Fulthrotl

~~Please excuse the mess. Sig under construction~~
Also known as Hardie Board.
I may possibly need to mount a box and small disconnect on this.
What is the best way to mount to this?

Can't find anything on the Hardie Board instructions other than how to install it.
3M 550 urethane adhesive and sealant.
put duct tape outside the area of the disconnect, to make splooge
removal possible. not easier, possible.

put a bunch of the adhesive on the back of the disconnect.
stick it on a clean surface, and prop it in place so it doesn't fall off.
wait a couple hours, run a razor knife around the edge, and peel off
the duct tape.

don't get any on you. you won't clean it off, you'll wear it off.
 

JFletcher

Senior Member
Location
Williamsburg, VA
It's very brittle and will wear out any bit you use on it that's not carbide. You want to get screws long enough to get through it into the plywood behind.
I've done at least two houses (in the same neighborhood) that had no wood behind the hardyplank, just that presswood sheet insulation stuff that looks like compressed sawdust (and has about the same strength: none). Hardyplank was attached directly to the studs.

I was doubting that being a "standard" install, but beware it's out there.
 

tkb

Senior Member
Location
MA
I've done at least two houses (in the same neighborhood) that had no wood behind the hardyplank, just that presswood sheet insulation stuff that looks like compressed sawdust (and has about the same strength: none). Hardyplank was attached directly to the studs.

I was doubting that being a "standard" install, but beware it's out there.
I doubt that installation meets the building code without sheathing being behind the siding.
 

Strathead

Senior Member
Curious, I haven't dealt with it a lot and I agree it is brittle, but no more so than say, lathe and plaster. I can't imagine that using a carbide bit, and toggle anchors wouldn't be sufficient to hold a small disconnect.
 

JDB3

Senior Member
I would suggest that you use shallow unistrut. Pieces long enough to fasten it to the studs that the hardiboard is attached to. Then mount your panel and/or disconnect to the strut.
 

junkhound

Senior Member
Location
Renton, WA
Can't find anything on the Hardie Board instructions other than how to install it.

That is because hardi is not made to be a support for anything.
Adhesive (as already suggested) is a possibility, but if you cannot locate your box over a stud and there is not at least OSB behind the hardi, It WILL break, sometime in the future if not right off.

Even over a stud, do not tighten your screws anywhere beyond just slightly snug.

If mounting right over a stud impossible, add an EXTERNAL strut bridging to the studs on either side.
 

Chamuit

Senior Member
Location
Texas
Can you mount the disconnect near a stud? If you can, get one screw into the stud. If not, use toggle bolts with flat washers on the disconnect side, for rigidity. Use a new flapper/spade bit for your holes, should work for a few holes without a problem.
 

GoldDigger

Moderator
Staff member
The only residential use I know of for cement board is behind tile (potentially supporting significant weight, but primarily in shear). Is it commonly used "bare" in commercial environments?
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
The only residential use I know of for cement board is behind tile (potentially supporting significant weight, but primarily in shear). Is it commonly used "bare" in commercial environments?
Commonly called "Hardie Board", it's used for siding a house. It is also called "cement fiber board".

I'm going to try and talk the customer into mounting the equipment somewhere else.


Thanks for all the useful replies!
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
As mentioned I would go with the fastener that's been around for almost 90 years, a simple toggle bolt.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
.... Use a new flapper/spade bit for your holes, should work for a few holes without a problem.
As mentioned I would go with the fastener that's been around for almost 90 years, a simple toggle bolt.
Toggle bolts are a great idea, but you need a bit that will get through the stuff. A paddle bit will make one good hole and one half of a hole after that, so you would need at least three bits to make two holes.
 
Hardie Plank / Hardie Board siding is outdoor finish product for siding buildings, including houses. This is not the cement backer board to replace drywall in wet locations.

I have used the 4 x 10 sheets and it works great. Looks good for long time, even got a better insurance rating for the house since it is fireproof. Tough to work with, though! Rgeular saw blades, Roto zips and drill bits go dull fast. Use carbide.

SturdyBrace is one brand name of that fiberboard used as sheathing.

http://www.blueridgefiberboard.com/sturdybrace-insulating-exterior-wall-sheathing/

It may be able to pass structural inspections, but I like OSB or plywood better. Of course, price is why you see it on construction sites.

Mount things to Hardie Plank / Hardie Board? I would also go with toggle bolts. Unistrut would make the home owner cringe.
 

JFletcher

Senior Member
Location
Williamsburg, VA
I doubt that installation meets the building code without sheathing being behind the siding.
I found its exact name: fiberboard sheathing. It was behind the hardyplank, attached to the studs. The hardyplank was attached to the studs as regular fiberboard has no strength at all.

Another vote for toggle bolts if you cant locate a stud. Adhesives may work but setting time may be a major downer. like ActionDave wrote, Hardyplank is too thin for screws.

What about mounting the disco and outlet on a 4x4 post? or lower, into the block/brickwork (if it isnt planked to ground level)
 
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