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View Full Version : Durock board - how to finish to match drywall?



Stephen Tashiro
08-25-2017, 10:36 PM
How is Durock cement board finished to match drywall when the cement board isn't covered with tile?

I have a wall mount sink to install that specifies that it should have cement board on the wall behind it. I don't plan to tile that area of the wall - certainly not the the part of the wall that is under the sink. What should go over the cement board so it roughly matches the finish on the drywall in the rest of the room? - joint compound?

Roger Nair
08-25-2017, 11:15 PM
You can use joint compound but ordinary joint compound dries by evaporation, so if you need a thick application it will take a long time to dry and will develop cracks while it sets. What you need is a hardening joint compound, look for something with a 90 minute pot life. Mix a small amount or else it may harden before application is complete. Any builder's supply or home center should have a suitable product such as Durabond 90.

Wayne Lomman
08-26-2017, 7:46 AM
Stephen, the manufacturer will have an installation guide. That will tell you the recommended products to use. In general though, any half decent jointing compound and tape for the joints will work. Use a powder type and mix it up. They are self curing, not evaporative drying. Premix ones are only ok for top coat. Cheers

roger wiegand
08-26-2017, 8:10 PM
Skim coat with plaster should work fine (though, as stated above, consult the manufacturer for compatibility), use fiberglass tape on the joints just like with blueboard. Plaster will give you a much nicer, harder surface than joint compound.

Stephen Tashiro
08-27-2017, 3:32 AM
Stephen, the manufacturer will have an installation guide.

True, of course, but deciphering it is an interesting exercise.

The installation guide (https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/usg-durock-brand-cement-board-installation-guide-en-CB237.pdf ) page 5 says:


See SA932 for finishing nontiled cement board.


Document SA932 ("System Catalog" https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/durock-cement-board-system-guide-en-SA932.pdf ) says, on page 11:



For Dry Untiled Areas—For small areas where the USG Durock® cement board will not be tiled, such as a board
extending beyond the tiled area and abutting another surface, treat joints as follows. Seal USG Durock® cement
board with Type 1 ceramic tile adhesive. (Mix four parts adhesive with one part water.) Embed USG Sheetrock® Brand
joint tape over joints and treat fasteners with USG Sheetrock® Brand Durabond® setting-type joint compound (45 or
90) applied in conventional manner. Flat trowel USG Sheetrock® Brand setting-type joint compound over board to
cover fasteners and fill voids to a smooth surface. Finish joints with at least two coats USG Sheetrock® Brand ready-
mixed joint compound. Do not apply ready-mixed or setting-type joint compound over unsealed board


It's discouraging to read that the directions apply only to "small areas". They refer both to "setting-type" joint compound and "ready-mixed" joint compound. I don't know how that squares with the advice not to use pre-mixed joint compound, but Roger Nair's advice makes sense for large areas. The directions imply that one would "seal" the cement board with ceramic tile adhesive before using the joint compound. How would that look on a large area of the wall? I'm unfamiliar with ceramic tile adhesive. Would it be a thick coat?

Some interesting information on page 3 is:


8. Do not use drywall screws or drywall nails. Do not use drywall joint tape

Rich Engelhardt
08-27-2017, 7:00 AM
Use Hardi instead of Durock.
Hardi has a smooth side - for painted finishes & a grid side for tile.


Plus Hardi is 1000 times easier to handle. (IMHO - I despise Durock...but, that's just me)

Skim coat the Hardi with topping compound. I use the 25 min stuff, but, I'm impatient & fairly quick. 45 min will work for most.

The Hardibacker instructions say just prime it with regular old interior drywall primer then finish it with whatever. We usually use Kilz 2 to prime it - but - we use Kilz 2 for just about everything interior.

Stephen Tashiro
08-27-2017, 11:14 AM
Use Hardi instead of Durock.
Hardi has a smooth side - for painted finishes & a grid side for tile.


Plus Hardi is 1000 times easier to handle. (IMHO - I despise Durock...but, that's just me)

Skim coat the Hardi with topping compound. I use the 25 min stuff, but, I'm impatient & fairly quick. 45 min will work for most.

The Hardibacker instructions say just prime it with regular old interior drywall primer then finish it with whatever. We usually use Kilz 2 to prime it - but - we use Kilz 2 for just about everything interior.

Thank you for that information!

The manufacturer's directions for Hardibacker ( https://www.jameshardie.com/JamesHardieMainSite/media/Site-Documents/HardieBacker/HardieBacker-Installation-Guide-English_Spanish-HB1710.pdf )are indeed simpler.



FINISHING WITH PAINT, WALLPAPER OR TEXTURE

(Interior Application Only)

1 | Painting or Wallpapering

Apply a drywall primer suitable for high-moisture areas, as recommended

by the
paint manufacturer. Paint HardieBacker board as you would drywall. If
wallpapering, prime surface of HardieBacker board with a primer suitable for
high-moisture areas as recommended by the wallpaper manufacturer.
2 | Texturing
Texture can be applied to HardieBacker board in the same way as drywall


The directions say the screws that are used should be "corrosion resistant". Many types of modern screws look "corrosion resistant" to me - at least they aren't bare metal.
The possible objection to using drywall screws is that the directions say to use ribbed "waferhead" screws when installing on walls. (What feature makes a screw "ribbed"?) Typical drywall screws have a "bugle head"

(Is there a difference between "waferhead" and "truss head"? Home Depot seems to prefer the terminology "truss head" and only shows 2 types of "waferhead" screws. Lowes has many types of screws that it calls "waferhead".)




3 | Fasteners
For floors and walls:

Minimum 1-1/4 in (for interior)
&
1-3/4 in (exterior walls) long
corrosion-resistant roofing nails.

Minimum 1-1/4 in (for Interior) &
1-3/4 in (exterior walls) long No. 8 x
0.375 in HD self-drilling corrosion-
resistant ribbed waferhead screws.





If compliance with ANSI A108.11
is not required, minimum 1 in long
No. 8 x 0.323 in HD self-drilling
corrosion-resistant ribbed buglehead
screws may be used for floors

Rich Engelhardt
08-27-2017, 1:34 PM
What feature makes a screw "ribbed"?Under the head, it has little ribs so it can "drill" into the cement board.
Drywall screws won't work because they stand proud of the surface.
You could always go to Harbor Freight and pick up a countersink & toss it later on since the cement really tears up even carbide.

Truss head are like an "anorexic" sheet metal screw. They have a very thin flat head.

Wafer head screws are all purpose - like Spax - screws for fastening most stuff.

I think.....


Really though, for what sounds like a real small area that you're doing & it's not supporting the weight of ceramic tile, some Lock -Tite construction adhesive would probably work just fine.
Once you fiberglass the seams, it should stay in place - - unless an earthquake hits.

Larry Edgerton
09-01-2017, 7:24 PM
GRK screws have "Nibs", the term for the cutters on the back of the screw head that will make it sink in to durarock. As suggested tape, and here I disagree with the use of mesh tape, with durabond of whatever set time you are comfortable with, do a base coat at the same time, sand, as there will be some grit to knock off, and do finish coats feathered out on to the drywall with reg mud. Be very smooth on your durabond coat as it is very hard sanding.

Rich Engelhardt
09-02-2017, 3:12 AM
GRK is a brand name. They make all sorts of different fasteners.
Usually HD & Lowes carry Backer-on brand - made for cement board. They call their cutters "Ribs".

Mesh is the preferred material where water or moisture is present - - but - - once it's embedded in the topping it probably doesn't matter. My contractor buddy refuses to use fiberglass tape anywhere & I refuse to use paper tape. :D
When we do a job together, whoever tapes is responsible for the first coat of mud.
'course - that doesn't matter much since he's never happy with the way I put the first coat on ;).