# Best screws for attaching conduit to fiber cement siding?



## clawlan (Nov 29, 2015)

I may be running some conduit up the side of the house and want to know if there is a particular screw that should be used when fastening it to the fiber cement siding. There is not going to be much weight on the screws.


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## Windows on Wash (Aug 30, 2011)

Pre-drill. 

Stainless or a coated screw for outdoor use.


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## Yodaman (Mar 9, 2015)

Can't go wrong with Stainless. That said I do find myself using these ceramic coated sheeters for outside general purpose quite often. This is typical screw used with metal roofing applications. Can't see it due to the coating, but it has a rubber washer backed by a metal washer under the head.


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## clawlan (Nov 29, 2015)

Thanks for the tips. Would not have thought to pre-drill.


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## jlhaslip (Dec 31, 2009)

Will those actually thread into the siding? 
Or do you need to bite into the sheathing/studs?


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## Yodaman (Mar 9, 2015)

jlhaslip said:


> Will those actually thread into the siding?
> Or do you need to bite into the sheathing/studs?



As long as the pilot hole is about the same as the root diameter of the screw I would trust it for light duty. Practically any other siding mat'l would not require a pilot at all.

Anything heavy like service cable straps I would want to hit some lumber.


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## ront02769 (Nov 28, 2008)

No need to pre drill. The correct screws do that on their own!


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## ChuckF. (Aug 25, 2013)

I would get the heavier brackets that mount with only one screw, and go into a stud. A screw into hardie alone might hold, but if it breaks away it will make a mess.


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## Windows on Wash (Aug 30, 2011)

ront02769 said:


> No need to pre drill. The correct screws do that on their own!


What screw would you recommend here then? I would be very cautious for a home DIY'er zipping in some screws in FC given how brittle it is. 

Seem more than a few contractors blow out corners and edges of FC. Its overly fragile fiber board if we are going to be honest.


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## Yodaman (Mar 9, 2015)

I assume Ron is referring to a self drilling screw similar to this.

But I would have two concerns. One, these are only really good on metal to metal or possibly two other thin wall mat'ls. If you hit sheathing or any lumber just under the surface, the drill point slows down the penetration rate of the screw and blows out the surface portion that would normally hold the screw.
Two, I am not sure if HSS will cut into fiber cement or if you need a carbide drill.
But a self drilling screw will be carbon steel and about 1/3 the hardness of HSS.

Around here we see more asbestos siding that looks like fiber cement. And a carbide drill is required. 



http://www.fastenersplus.com/12-X-1...ized-Pkg-250?gclid=CJSB1JCQ-dICFZmIswod5zYMag


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## clawlan (Nov 29, 2015)

Since I am planning to run the conduit next to/behind a gutter downspout, I could just use some sheet metal self drillers to fasten right to the downspout...


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## Yodaman (Mar 9, 2015)

clawlan said:


> Since I am planning to run the conduit next to/behind a gutter downspout, I could just use some sheet metal self drillers to fasten right to the downspout...



Probably not a great idea. Gutters are not always permanent. I see many in these parts ripped off the house from various reasons. Mostly snow and ice.

What are you running in the conduit? If 120V electric, then definitely do not use the gutter as a anchor.


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## clawlan (Nov 29, 2015)

Yodaman said:


> Probably not a great idea. Gutters are not always permanent. I see many in these parts ripped off the house from various reasons. Mostly snow and ice.
> 
> What are you running in the conduit? If 120V electric, then definitely do not use the gutter as a anchor.


I'm running ethernet cable. Regardless, you make a good point about them getting ripped off. We don't get a lot of ice here in Atlanta, but wind is another story. Maybe I'll just use gaffer tape...:biggrin2:


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## Garygrayhandyman (Jun 12, 2021)

ront02769 said:


> No need to pre drill. The correct screws do that on their own!


Wrong! Always pre drill in hardie siding or trim. If you don't you will blow it out more often than not. Even with rock-on and backer-on screws.


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## chandler48 (Jun 5, 2017)

@Garygrayhandyman welcome to the forums. You are responding to a 4 year old thread. Hopefully they got it handled.


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## wolfdogg (Dec 10, 2021)

@chandler48, maybe hes replying to a 4 year old thread, but im using this thread 4.5 years later, and his is the only post that corroborates, and reassures, that we want to pre drill!! Its usually as much about the forum building a knowledge base, as it is to the individual in the OP. I was on the fence on the pre drilling, thanks Gary!

Those self drillers looks really tempting, i used a t-25 stapler, for Cat5 cable, but ill admit i had to use alot of staples to get the job done! (most would pop out, its been holding for years now. you can see the top ones popped out there during install, i just left it that way) Now i know what to use. What's the common term for them? "Coated sheeters"? as in coated sheet metal screws with washers?


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## HotRodx10 (Aug 24, 2017)

ront02769 said:


> No need to pre drill. The correct screws do that on their own!


Depends on how close to the edge of siding plank/panel the screw will be going in. Anything less than 1 1/2" from an edge, I'd predrill.

I just noticed the thread and most of the responses are old, but I'll leave my comment up for any future readers.


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