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-   -   Backsplash Guidance Needed (https://www.johnbridge.com/vbulletin/showthread.php?t=109160)

cascade 09-08-2013 07:22 PM

Backsplash Guidance Needed
I'll be as brief as I can:

I am a DIY guy, fairly proficient. I have some experience setting tile and more with thin brick. I need to install a tile kitchen backsplash 6 1/2" high, 20' long (runs of 12' and 8'). The existing countertop is new 3cm. granite butted up to old, moderately damaged-in-the-course-of-demo wallboard. The studs are roughly (the original construction is not precise) 14" o.c. I have the tiles on hand. They are 5/16" thick. They are fired and glazed (of course) but they are Mexican and the body material is, as you may expect, quite porous.

I plan to remove a horizontal strip of the wallboard approximately 6 1/2" high and to replace it with 1/2" cement board (without advice to the contrary, I would do that regardless of the condition of the wall board), probably using a Hardie product, furring as needed to correct a major wow in the wall, and to set the tile with thinset. I can mud the remaining wallboard above the furred portion to achieve a plane parallel to that of the tiles' surface. Assuming my basic idea is OK--and I am certainly willing to listen to alternatives--I have the following questions.

1. Is horizontal blocking necessary (toed in) to back up either the upper or lower edge of the cement board or the wallboard? I guess there will enough strength and rigidity at both edges without blocking, but I am not sure (and please see Question 3).

2. What fasteners should I use? They will be set in awkward places and I am more reliable with a drill-driver than with a hammer, so my bias is toward screws rather than HD roofing nails. Also, pounding tends to shake up old work nearby in unexpected ways.

3. How do I handle the joint between the granite and the tiles to keep water away from both the cement board and the drywall? Ideally, the granite would run back to the studs but that is no longer possible. Blocking would provide a backstop for backer rod, which would in turn enable me to caulk the joint the way I would like to. I could as an alternative leave a small gap above the wallboard and below the cement board. That might be adequate to contain and control the back of the backer rod without blocking. Is there a better way? I have in mind to make a 3/16" joint at the bottom of the tile and to caulk that joint with a Sika product. Are there caulks of equal quality that have a better choice of colors? Assuming that blockless approach is correct, what diameter ought the backer rod or maybe parallel backer rods be?

4. What sort of waterproofing membrane should I use and how can I avoid buying too much of it? I am totally inexperienced with this product. I assume it goes on the face of the cement board with thinset, and that the same the same thinset is used to set the tile on it. The detailing of the membrane at the bottom seems also to relate to Question 3.

New here, I hope that my post is not too long and that I am not asking too much. Thank you.

Davy 09-08-2013 07:46 PM

Hi Pres, welcome. A kitchen backsplash is considered a dry area and really doesn't call for any waterproofing but you can add a waterproofing if you want to.

I try to avoid cutting the sheetrock horizontally along the countertop, it makes the backsplash real weak. Blocking helps of course in case the sheetrock has to be replaced. Usually I would apply a thin coat of thinset to the back splash to fill in any holes and divots. A small amount of floating can be done with thinset if there is a crooked stud. You can tile right to the sheetrock if you can get it smoothed out.

cx 09-08-2013 07:52 PM

Welcome, Pres. :)

Kitchen backsplashes are among the most forgiving of tile installations. There is generally no need to replace the existing (usually) drywall with a CBU, but you certainly can if you like. If you do, I'd certainly recommend replacing the entire section between upper and lower cabinets, but, again, that's not a requirement.

1. If you elect to replace only a narrow strip with CBU, I'd strongly recommend blocking at the seams both top and bottom. Needn't be attached to the studs at all, just to both wallboards. My choice for such blocking would be 1/2" or 3/8ths" plywood rips.

2. In that dry application, drywall screws would be fine, but you may need to use manufacturer's recommended screws for the CBU to get them to set flush.

3. You appear to be anticipating quite a bit of water there and that's something we don't usually anticipate. If you do expect that much water, I'd strongly recommend you replace all the drywall with CBU.

But normally, any drywall joint in that wall, including drywall/CBU, would be finished with drywall compound like any other wall in the kitchen.

4. I would use none, but if you want one, and if you have installed a CBU, you can use any of a dozen or more available as direct bonded waterproofing membranes that can be tiled over. Look for ANSI A118.10 on the product.

We generally recommend 100 percent silicon caulk in the joint between the tile and the countertop, which would customarily be about 1/8th" wide.

My opinion; worth price charged.


cascade 09-09-2013 09:39 AM

Many thanks, gentlemen. This website is magical.

Tiger Mountain Tile Inc 09-09-2013 09:32 PM

Hi Pres,

Don't forget to tape the seams with 2" alkaline resistant mesh tape and mud them with thinset. If you only replace a narrow strip with cbu I think you could get away without blocking the top as long as the mesh tape is used. The bottom is a different story as it's harder to remove the flex in the board.

If you do as cx suggests and replace the entire section of wall board I might leave a 1" strip of sheetrock at the top, under the cabinet, so you can mesh tape to it. That way it eliminates a cold joint there.

cx 09-09-2013 09:48 PM


Originally Posted by Jim
I might leave a 1" strip of sheetrock at the top, under the cabinet, so you can mesh tape to it. That way it eliminates a cold joint there.

I'll second that 'cept I'd prolly leave more like two inches.

cascade 09-10-2013 10:36 AM

Thanks for the further replies guys. The OCD path is a steep and rocky one--but you all already knew that.

On the 8' run of wall, which is reasonably straight and nowhere near the sink, I now think I'll just set the tile on the wallboard. However, the wallboard has an original texture coat that much of the mastic which was used to hold the old tile did not adhere to well. Any ideas on prep? Plaster Weld? Bubble gum?

The 12' run presents different problems. There, more of the paper pulled away. It delaminated leaving about half the thickness of the paper on the gypsum. There is a noticeable concave bow, 3/4"+ in 5' of wall that would require a lot of mud to level. I think I'll replace all of that board and might as well use CBU while I'm about it. I'll fur out the studs where needed, use plywood backing rips in the usual way only where the old board and the new are on the same plane and I have access to put screws through the old board, and block elsewhere.

Moral of the story: Check everything including the walls with a straightedge before having anyone install a counter top. I'll be glad to hear your advice.

Marge 09-10-2013 10:40 AM

Hi Pres,

You mentioned the tiles are porous. Have you considered what you plan to do when grouting?

cascade 09-10-2013 12:17 PM


No, not a bit. What do you have in mind?

cascade 09-10-2013 04:45 PM


I didn't mean to be abrupt. Is there something I should know about grouting these tiles?

Marge 09-10-2013 04:50 PM

Not abrupt at all. :)

Since they are porous, you may want to consider how grouting will affect their surface appearance. I haven't worked with those tiles much but I know others around here have. There are products and techniques that help prevent grout adhering to the surface.

cascade 09-11-2013 10:16 AM

Thank you.

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