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Community and Q&A

Best backsplash backer? Are Hardie / alkali tape / thinset airtight?

jamesboris | Posted in General Questions on
Hello, I’m building a kitchen addition. The wall with the stove (not the sink) will have a big tile backsplash, extending up the wall. I’ve installed a backsplash before, but it was in a place that already had drywall and paint (so we had to work with that). But here, the stud frame is still open. 

One GBA-type question… if I use Hardie and finish th seams w/alkali tape + thinset, will that be airtight? I can’t find anything about the airtightness of those materials.

And one general building question… I’d rather use drywall, for practical/silicosis/timing purposes — and because I know how to air-seal it perfectly with gaskets/sealant. If I do that, should I just install drywall and an appropriate primer on the wall, then mortar? Anyone know a good primer for this? Thanks!

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  1. Expert Member


    Yes. Once tiled it will be entirely airtight. It would be easier to use a water-resistant drywall than Hardi-backer though.

    1. jamesboris | | #2

      This area won't see water. There's nothing on the wall but a range/hood/shelves. So if drywall is fine... does it matter what primer I use?

  2. scottperezfox | | #3

    If it's new construction (or a remodel with new walls), the mastic will adhere to unpainted drywall no problem. You shouldn't need a primer in that case. If it's over existing paint, you should clean it thoroughly to remove grease, and consider using a universal bonding primer — Killz or Rustoleum make them, not hard to find. You don't need anything out of reach for homeowners.

    But as you say, this isn't a "wet area" so you have a lot of wiggle room. A tiled backsplash is not a high-performance piece of your home — it can be pulled off and redone in the worst case. That's why you can use Mastic and not Thin Set — it's more of a glue than a cement, and much more user-friendly. You don't have to mix it yourself, for a start.

    In terms of air tightness, look at the outlets and lightswitches that may be cut in. Those are actual holes! As long as your joints are taped, you have little to worry about through the backsplash itself.

    1. jamesboris | | #4

      Thanks! I've done some tiling, but always in bathrooms, so no mastic... any type you'd recommend?

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