Ask Experts Questions for FREE Help !
Ask
    435Studio's Avatar
    435Studio Posts: 93, Reputation: 4
    Junior Member
     
    #1

    Mar 1, 2010, 09:32 AM
    Tile over expansion joint in slab
    I'm looking at laying tile (12"x12") directly on a basement slab for my bathroom floor. The expansion joint that is cut diagonally across part of the basement floor is in the corner of this room (probably 3 or 4 tiles will actually be over the joint). Will this cause any problems? Also, is there any other prep that should be done to the slab prior to laying the tile?
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
    Uber Member
     
    #2

    Mar 1, 2010, 10:44 AM

    You really can't guarantee anything. Design with Flexibility -- Ceramic Tile Installation | Extreme How To, DIY - Do it Yourself, Home Improvement, Home Decorating

    What I ight suggest is to keep the joint in place. Cut the tile and fill with polyurethane caulk through the joint. e.g. a small 1/8" intensional seam. That, in my opinion would be better than an unintentiional crack.

    If you could disguse the diagonal to make it part of something else like a zig zag, it might be better. I also believe there may be metal expansion joints that can be used. Building Homes or Extensions: concrete, metal expansion joints, stone balustrade

    TCNA - Technical Services: FAQ

    Why not tile diagonally and make the grout joint over the expansion joint. You don't use grout there. Use caulk.

    Another alternative might be to place a thin subfloor.
    Bljack's Avatar
    Bljack Posts: 245, Reputation: 28
    Full Member
     
    #3

    Mar 1, 2010, 10:55 AM
    The expansion joint that is cut diagonally across...
    If it were a true expansion joint, where you have two separate slabs with a filler between them, you would have to honor the joint up through the tile at the exact location of the joint. By describing it as "cut" I will assume this is not an expansion, or "cold joint" but a "control joint" which is a saw cut designed to encourage any future cracking of the curing slab to occur at predetermined places. They still need to be honored through the tile installation, but they can be relocated. You have two options...

    To relocate a control joint, the control joint is covered on both sides by an antifracture membrane that extends at least 1.5 tile widths past the joint on all sides. If the tile is on a diagonal to the control joint, make sure to take the diagonal measurement for your 1.5 tile widths. When your tile is done being installed, the grout joint on either side of the tiles that are bridging the control joint are filled with a color and texture matched caulk instead of grout.

    In your case, since it's a bathroom, you're probably better off just covering the entire area with an antifracture membrane and letting the clear perimeter gap (or caulk filled perimeter gap) be where any movement is released from the tile assembly, just for the sake of not having caulk joints within the tile field which just like any caulk joints, will need periodic maintenance.

    To answer the rest of your post, as long as the slab is free of dirt, paint, sealers, water soluble adhesive residues, and will absorb water, you are good to go.
    435Studio's Avatar
    435Studio Posts: 93, Reputation: 4
    Junior Member
     
    #4

    Mar 1, 2010, 01:19 PM

    Thanks for the quick answers; I like the diagonal design idea, since the space is so small I think either that or a thin subfloor may be the answer. One question regarding the subfloor; how is that best attached to the slab?
    JazMan's Avatar
    JazMan Posts: 219, Reputation: 14
    Full Member
     
    #5

    Mar 1, 2010, 02:19 PM

    I use Ditra whenever possible and appropriate. But in this case also consider Noble's CIS. With CIS you can maintain the pattern without make new unwanted joints. Sheet Membranes for Waterproofing, Crack Isolation and Sound Isolation

    Jaz
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
    Uber Member
     
    #6

    Mar 1, 2010, 04:22 PM

    No reason why it can't float especially if the subfloor can be one piece or you can attach at a couple of points (cement anchors) with some play. Just make sure it doesn't attach to both sides of the joint.
    Bljack's Avatar
    Bljack Posts: 245, Reputation: 28
    Full Member
     
    #7

    Mar 2, 2010, 11:12 AM
    Quote Originally Posted by 435Studio View Post
    Thanks for the quick answers; I like the diagonal design idea, since the space is so small I think either that or a thin subfloor may be the answer. One question regarding the subfloor; how is that best attached to the slab?
    There is no thin "subfloor" such as you might think by adding such a product as a plywood or cement board layer over the slab. An unbonded mud job which would be tar paper and lath with a minimum thickness of 3/4" of mud (4-5 parts sand to 1 part portland cement) packed tight is one version of an acceptable "floating" floor system for tile. Antifracture membranes are also a floating floor of sorts, the Noble CIS allows up to 1/8" of horizontal movement below. Schluter refers to it as "uncoupling" as their fleece backing on the Ditra allows the plastic to float above the movement. (Jaz, how it is Ditra "uncouples" while CIS "crack isolates" when they are both fleece backed? :confused: ). Liquid membranes like "Redgard" or "Floor and wall watertight" available from HD or Lowe's, respectively, are liquid membranes that allow elongation of the membrane below where it bonds to the substrate while maintaining the integrity of the tile above. All of these are what you should be thinking of when you think about floating a tile floor. In your case, skip any idea that involves mechanical fasteners, wood products or cement boards.

Not your question? Ask your question View similar questions

 

Question Tools Search this Question
Search this Question:

Advanced Search

Add your answer here.


Check out some similar questions!

Failed Concrete Slab Expansion Joint [ 2 Answers ]

I have a concrete expansion joing that failed. Looks to me like it was not the fiber type expansion joint, but some type of wood. Is there material I can fill the void, 3/4", with and it will expand and not rot.

Tile won't stick to concrete slab [ 5 Answers ]

We are re-modeling our bathroom in a 27 year old home. Have tore up the cement bed in the shower, replacing our shower liner and then pouring our mortar mix. When starting to lay the tile down, we find that our pre-mixed adhesive is not holding the tile down very good. It seems as though the mortar...

Under the slab sanitary pipe expansion joint ? [ 2 Answers ]

Do I need an expansion joint for the 3" pipe that's going under the slab of my storage garage which is 72 feet long (pipe). This is the sanitary drain pipe under the slab in a non heated storage space!

Concrete expansion joint came out [ 1 Answers ]

My house is 6 years old. In my driveway and backyard patio, the expansion joint in the concrete has come out in several places. This has left a gap of about 1/2 inch wide. How do I fill these gaps. I checked with home improvement stores and they don't have any good solutions. I have three...


View more questions Search