bathroom drywall damaged - to tile or no...

[nereo]

The drywall around our bathroom sink is starting to get really icky - no doubt the result of 3 years of moisture in the seam between sink and wall.

Next weekend I think I"ll tackle this project.  As I understand it, it'll involve
1) removing the sink (simple enough),
2) cutting out the damaged drywall and replacing that (a PITA, but doable, I think...)
3) mudding, sanding, priming and painting (stuff I've all done before... but see below)
4)putting the sink back in.

It occurs to me that I ought to tile a back-splash behind the sink to prevent this from re-occurring.  Here's where I get a bit lost.  Can I just cut out the drywall section I need to replace (making sure to be on-studs) and put hardiebacker there, then tile over?  BY doing this how do I keep the thicknesses the same between drywall and backer-board?

The space I'm trying to fix is maybe 32" x 12".
EDIT: at work now but will update with a photo this evening.

[NoStacheOhio]

You might want to look into waterproofing that section behind the tile.

[Spork]

I would almost always put backer board in there behind tile.  I know LOTS of builders do not do this.  I disagree with their methods. 

I've always been able to find 1/2" backer board to match up with drywall.  I don't think that's a problem.  Tape and mud the backer board with thinset and fiberglass tape.  If you super paranoid, put redguard on it (but I doubt that is a real issue for a backsplash.)

[nereo]

I would almost always put backer board in there behind tile.  I know LOTS of builders do not do this.  I disagree with their methods. 

I've always been able to find 1/2" backer board to match up with drywall.  I don't think that's a problem.  Tape and mud the backer board with thinset and fiberglass tape.  If you super paranoid, put redguard on it (but I doubt that is a real issue for a backsplash.)

Thanks. I'm definitely not super paranoid here... I'm likely moving in 1-3 years but I want my fix to be better & last longer than what the builders did before I moved in.  The area isn't constantly wet, but there is/was a seam between the sink and the drywall.  Moisture would get in there and just sit.  If I had noticed I might have caulked that right away as a cheap fix.  Too late now.

Follow up question - can I tape and mud the backer-board directly to the surrounding painted drywall, or do I need to sand down the surrounding painted drywall to get good adhesion?

You might want to look into waterproofing that section behind the tile.

Serious question here - isn't using backerboard + thinset + tile + grout make that area moisture-proof?  I realize there's a difference between waterproof and moistureproof... but this isn't an area that gets continuously sprayed with water.  It's more drips from hands turning the faucet on and off...

[Spork]

I would almost always put backer board in there behind tile.  I know LOTS of builders do not do this.  I disagree with their methods. 

I've always been able to find 1/2" backer board to match up with drywall.  I don't think that's a problem.  Tape and mud the backer board with thinset and fiberglass tape.  If you super paranoid, put redguard on it (but I doubt that is a real issue for a backsplash.)

Thanks. I'm definitely not super paranoid here... I'm likely moving in 1-3 years but I want my fix to be better & last longer than what the builders did before I moved in.  The area isn't constantly wet, but there is/was a seam between the sink and the drywall.  Moisture would get in there and just sit.  If I had noticed I might have caulked that right away as a cheap fix.  Too late now.

Follow up question - can I tape and mud the backer-board directly to the surrounding painted drywall, or do I need to sand down the surrounding painted drywall to get good adhesion?

I can't say I absolutely know the answer, but if it were me, I'd sand the adjoining drywall.... at least a few inches. 

Alternative if you don't want to:  Let the drywall extend an inch or so underneath the first tile.  In other words, have your drywall meet the backerboard behind your first tile.  I'd minimally sand the paint/texture off this bit.  Don't sand so much as to remove the drywall paper, but enough to rough the paint and knock off texture.

[RichMoose]

I am actually currently doing a bathroom reno. I believe that Hardibacker is overkill for this application. Just get some moisture resistant gyproc (blue board). If your tile extends over the seam where the new gyproc meets the old, don't bother mudding and taping. Just cut the boards straight so you get a tight fit. Then install your tile. After grouting use a bath rated silicone to seal where the tile meets the countertop. Be careful not to grout between the countertop and the tile and install the tile 1/8" above the countertop. I just use tile spacers for this.