Control joint installed through a tile installationThat title right there is absolutely ripe for me to go off on a sophomoric, mildly humorous rant about the viability of inferior illegal plant use. But I’m not gonna do that. (Okay, maybe later…)

A soft joint, or control joint,  is simply one grout line, all the way down the length of your installation, that is filled with colored silicone or caulk rather than grout. The purpose of a soft joint is to allow movement in your installation without cracking tiles or grout. When placed properly it will absorb any ‘normal’ seasonal and structural movements inherent in structures.

There are guidelines that need to be followed for a soft joint to be effective. The TCNA guidelines call for a control joint every 20′ – 25′ in each direction for interior installations and every 8′ – 12′ in each direction for exterior installations. Interior installations which are exposed to direct sunlight also need control joints every 8′ – 12′.

This simply means that if you install tile in your living room and it is larger than 25′ or 30′ you need a control joint – period. It is non-negotiable. If you do not have it chances are likely that your tile installation will fail. The number one reason for tile installation failure (on a floor) is lack of proper control joints. You need them! *It’s either lack of proper control joints or improper coverage, there are conflicting views. Both will lead to a failure and both are installer error – both need to be correct!

You need them on wood, you need them on concrete, you need them inside, you need them outside. And no, that is not the beginning of a Theodore Geisel book. I’m simply trying to illustrate the importance of a soft joint in a large tile installation. Because it is. Very important.

Along with these control joints you also need to ensure proper perimeter spacing. This simply means that your tile around the perimeter of your room is not butted against the wall or framing. You need room for stuff to expand.

You don’t realize it but there are a lot of things in a structure which move – constantly. With temperature changes, normal construction shifts (settling), even sunlight causes enough significant heat to expand and contract structural elements several times a day. You absolutely need to allow for this movement.

If you do not allow for this movement your tile installation will not last long-term. Your grout will crack. Your tile will crack. Your dog will burst into flames. Your tile may ‘tent’ which means that there is so much pressure pushing two adjacent tiles together that the bond from the mortar will eventually fail and the two tiles will pop – literally – off the floor and tent. They will sit there right in the middle of your room looking like a little teepee.  I tapped a tile once in an installation which did not have control nor perimeter joints and they literally popped – loudly – and tented.

Control joints also need to be installed above expansion joints in concrete – whether you use a membrane or not. A membrane will allow you to ‘shift’ the control joint in the tile over up to six inches (depending on which membrane you use) but it still needs to be there. If your concrete has a control joint it needs to follow all the way up and through your tile installation.

Most grout manufacturers make a matching caulk or silicone which can be used for these joints. When cured they match the color of the grout exactly or nearly so. You can tell it’s there – if you look for it. Don’t look for it. I understand that a control joint may change the look of your installation – you may not like it. I know. I get it. I don’t like them either. But you need them.

The photo at the top of this post shows a control joint through the middle of a tile installation. This is right after I finished installing it so the caulk has not yet cured – that’s why you can see it. Once cured it matched the grout color exactly. In my next post I will show you exactly how to prepare this grout line as a soft joint and install the caulk or silicone.

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  • Katrina S

    I’m going to use these terms for clarity:
    Expansion Joint: in concrete slabs to control cracking
    Soft Joint: Allows tile movement, should be placed above control joints.

    I am planning on eventually tiling my entire home (I have asthma, hard flooring is a blessing). I have orthogonal expansion joints (15 ft spacing), and I plan to use elongated (large format) wood tile in most of the home. Regardless of how I orient the tile, it’s eventually going to come perpendicular to one of the expansion joints. How would I add a soft joint to the tile in these perpendicular situations? Can I zigzag above the control joint and be okay?

    Finally, I’m tiling on concrete slab, but I am debating on using an uncoupling membrane. My house was built in 1976, and seems to be pretty quiet today. I have a few tensile cracks with 2mm or less of separation, but nothing else. Someone suggested I consider using RedGuard instead of an uncoupling membrane mat, since it still has crack isolation protection but is cheaper. What is your thought on the roll on “paint like” RedGuard membrane? Does it give me the same flexibility as an uncoupling mat when placing soft joints above a control joint?

    • Roger

      Hi Katrina,

      Yes, you can zig-zag the soft joint above the control joints, it’ll be fine. Redgard is a great crack isolation membrane, that’s actually what it was developed for. The properties for crack isolation are comparable to an uncoupling membrane. The membranes have other properties, such as moisture mitigation, that you will not get with the redgard. But if you don’t need those the redgard will work just as well for you.

  • Autumn

    Are expansion joints only the thickness of the tile or do they run all the way through to the subfloor? Thanks!

    • Roger

      Hi Autumn,

      If they are being placed over an expansion joint in concrete it needs to run all the way to the concrete. If it’s only in the tile installation as a soft joint it’s only the thickness of the tile.

  • Dave B

    Hey Roger,

    When it comes wood-look tile that is laid in a randomized pattern I know you’ve said its OK for the soft joint to be done in a zig-zag pattern when a straight line is not possible.

    Question: Would using epoxy grout on the whole floor take the place of having to install soft joints? I’m guessing the soft joints are still needed but just wondered if any of these newer flexible grouts could replace the need for control joints altogehter?

    BTW – This is porcelain 6×36 wood-look like over a TEC SLU pour with Nuheat radiant wire.


    • Roger

      Hi Dave,

      Despite what you’ve heard, there is no ‘flexible grout’ which will replace the movement requirements of a soft joint. In my honest opinion the ‘flexible’ aspect of any of those grouts marketed as such is only marketing. In the installation application it makes zero difference except in very limited, specific installations. You ALWAYS need a soft joint.

  • Paul Pieterse

    Hi, Is a pencil joint appropriate for a 18 inch x 18 inch travertine floor tile surface?

    • Roger

      Hi Paul,

      Not sure if a ‘pencil joint’ is 3/16″ or not. Regardless, it depends on the uniformity of your tile sizes. Read through this.

  • renate

    “If your concrete has a control joint it needs to follow all the way up and through your tile installation.” Are you referring to contraction joints in the concrete slab? I want to make sure I understand. Big thanks in advance!

    • Roger

      Hi Renate,


  • James

    Hi we are laying opus pattern floor in a granite room nothing square and we have skribe the natural stone floornto the walls
    Room is about 6m x5 m and flows through to hall way and kitchen we will put exspation joints in door ways would you run an expansion joint around the permitter edges onto granite ?

    • Roger

      Hi James,

      Yes, you need perimeter joints.