marble backsplash question

[dogboy]

i am helping a neighbor prepare her kitchen wall for an upcoming contractor installation of marble.

 

the existing drywall to the left of the sink is intact to about 4 inches above the counter height, and i installed some 1/2 inch sheetrock that i had around the house from that seam up to the bottom of the kitchen cabinets

 

behind the sink, however, the whole six inches or so between the counter and the windowsill is pretty well shot, and the sheetrock i have is just plain old sheetrock

 

even though there is little chance that the seam between the granite counter and granite backsplash will ever fail, i want to use something more water resistant

 

i was wondering if 1/2 inch exterior grade plywood would be okay to use in terms of the mastic sticking to it the piece in question is about 6 inches wide and 3 feet long...i have just enough sheetrock to do it, also plywood kicking around....i was hoping to avoid buying wonderboard for such a small bit of work....the existing wallboard at counterlevel appears to be blueboard

 

the only reason any of ot needed replaceing is because the ceramic tiles glued to it were stronger than the wallboard, and it was destroyed while removing the tile

 

also, i thought it would be a good idea to leave a small gap at the bottom so if it a leak ever does develop and not discovered for a long time that the water won't wick up into the substrate and cause problems

 

any thoughts?

[speedracer]

Use a piece of 1/2 tile backer board and never worry about it again. It's brand name is Hardibacker and its very easy to cut unlike Wonderboard. Anything else you use will eventually get wet and rot, especially plywood.

 

Hardibacker is $10 a sheet.

[Bristol Lou]

Yep Hardi board 1/2". It comes in 3' x 5'

[fishn808]

As speedracer said, don't use plywood.

 

Hardiboard or Wonderboard will work. Make sure your wall studs are in good shape before installing the water-proof wallboard. If they are rotten, best to replace them or scab them if you must. If the studs are in bad shape, your wallboard may fail over time.

[dogboy]

hardiboard it is...thanks!

 

 

what about the small gap on the bottom?...is it a good idea?...i saw/read it/ heard about it somewhere when the topic was what to put behind a tub surround

 

it is an outside wall on an older home, but it is insulated already

[DarkSkies]

DB - you will not have problems with water wicking up behind the backsplash/countertop transition if the grout is mixed and applied correctly. One mistake people sometimes make when mixing grout is to use too much water. When the water evaporates, and the grout sets up, this sometimes promotes cracking, which will allow water to enter when it is splashed there. If you are grouting and you have to push the grout in, and it's a little difficult, it's the right consistency. A little creamy is not good. Try to follow the mixing directions precisely. Also, once the grout begins to harden, try to make it as professional as possible by going over and smoothing the lines with a damp grout sponge.

 

People sometimes leave a gap in transition areas when there may be "unaccounted for" flex or movement in the future. Thats one of the reasons why you will see vinyl adhesive caulk (I like Phenoseal) at the transition between bathtub edge and wall tile, & bathtub and floor edge. It's also more durable in a specific spot that repeatedly gets wet . There are colored caulks available to match the grout you are using. Again, you will be using one or the other depending on the specific spot - not both.

 

In your first sentence, you mention a marble installation, then go on to represent that the contractor will be installing granite. I'm assuming granite it is, one long slab, maybe some seams, and one backsplash. If you are subbing that part of the job out, those guys usually come in and handle the whole install from start to finish. No need to worry about any gaps. Hope this helps - Dark

[DarkSkies]

DB - also, if a sub is doing the installation, generally the kitchen counter backsplash will be butted up tight to the countertop, and the seam sealed with some type of silicone - no probs with leaks after that.

[dogboy]

it is granite, not marble, and the missus and i are getting a free dinner at a nice italian restaurant out of the deal

 

(plus maybe a big stainless steel sink i could use at work)