Cement Backer Board

[Brian]

Hi All,

I'm finishing a bathroom project with a fiberglass shower.  I have a 18" opening around the top of the shower.  I bought cement backer board to cover the opening.  I'm not planning to tile the opening - probably just a couple coats of latex/waterproof paint.  Is Durock backer board correct or should I use another type of cement drywall?

Thanks,

-Brian

[Rick]

Durock is good.  Prime and paint with mildewcide like Zinsser bath paint, and then use exterior caulk the top of the shower.  Don't use drywall screws.  HardiBacker is also good.

Don't try to use pocket screws on it.  ;-)

[Ken Darga]

Rick,

Do you have, or know of, a suitable screw for affixing the boards you described?

Thanks.

[Brian]

I found some at Lowes called Backer-On.  They come in a couple counts depending on your needs.

[Rick]

Here's a pic of the screws Brian referred to.  They are square drive. 

The screws are supposed to c'sink themselves using the ribs on the underside, but even with my Makita impact driver, they would strip or break before burying themselves flush in the Hardiboard.

IIRC, with most of the screws I had to remove them, c'sink the hole with a c'sink bit, and then re-screw them flush. 

Don't try these in pocket holes.  ;-)

Ken Darga said:

Rick,

Do you have, or know of, a suitable screw for affixing the boards you described?

Thanks.

[Ken Darga]

Thanks Rick,

The "square drive" is the feature in the head---

which dictates the type and size of driver bit to install/remove the screws.

The "type of screw", which is the style and thread-pitch, is the main factor for use in such material.

The threads in your photo, appear to be akin to fine-theard drywall screws.

I've found that some products are identical in nature, except repackaged a "specific" purpose.

The next trip to Lowes, I'll peruse the screws.

Perhaps a "trim" screw would suffice nicely.

Trim head screws have a smaller diameter/size head---

permits recessing without countersinking---

with little to no distortion in the workpiece surface---

prevent splitting.  

(the screws will split the workpiece, if installed near an edge/end, without drilling a pilot hole and countersinking.  (The OEM's claim they won't split---yah right.  When i've brought it to their attention, they don't respond).

Dry wall screws feature a "bugle" head, which can split delicate wood or when installed close to the edge/end of a workpiece.  These heads will require a "countersinking" operation before installing, so as to avoid distortion/splitting, or the like.

Rick said:

Here's a pic of the screws Brian referred to.  They are square drive.  .../p>

[Rick]

I used Hardibacker panels under Swanstone solid surface panels which make one of the nicest showers around -- you can scrub it with brillo pads and no grout lines.  The screws are course thread 0.195 in diam., but definitely not brittle like drywall screws, which are case hardened.  Neither will these screws rust, since they have to survive in a shower.

Since the backer board is so hard, deriving its hardness from silica sand, even the scoring ribs under the screw head could not c'sink the screw.  The screw is countersunk so that tile, solid surface panels, or fiberglass panels can lie flat.  

Trim head screws are also very brittle, and tend to break in anything harder than pine.

Ken Darga said:

Dry wall screws feature a "bugle" head, which can split delicate wood or when installed close to the edge/end of a workpiece.  These heads will require a "countersinking" operation before installing, so as to avoid distortion/splitting, or the like.

[Ken Darga]

Thanks Rick.

I'll keep that in mind when I do a new shower/tub install.