Tech Notes

Tech Note:

Installation on slabs that move

The vast majority of quarry tile installations are on concrete substrates with a high percentage of these construction slab-on-grade. This means the concrete slab is at ground level, subject to all the stresses and/or movements that specific geographic areas are impacted by Mother Nature. Stresses range from heat and moisture induced contraction and expansion through live and dead loading. Movement of the earthen substrate comes in many forms, including earthquakes, unstable soil and expansive soil. Great strides have been made in the last several decades in designing concrete slabs to withstand these pressures, such as soil compaction, thicker slabs, higher psi concrete, steel mesh reinforcing, expansion and control joints. However, for a variety of reasons there are still concrete slabs that can cause problems.

INDUSTRY RECOMMENDATIONS
Because concrete substrates move, the tile industry (TCA*) has recomended maximum spans between expansion joints -- interior: 24' to 36' in both directions, and exterior: 12' to 16' in both directions.

THE ABCs OF PRE-INSPECTING CONCRETE SLABS BEFORE INSTALLING TILE
A. Look for expansion, control and cold joints, as none of these can be ignored by just tiling over them. Look also for irregular cracks in the slabs that were not planned, indicating excessive slab movement. When there is movement along any of these broken planes, tile obviously will not hold these points together and will be seen on the floor's surface as cracked tile. Everyone is quick to blame the tile, but fault begins with the cracked slab.
B. Check the concrete slab's surface condition, as bond failure is the number two consumer complaint, cracked tiles being number one.
C. Verify how true the slab is to the required plane (level or sloped). According to ANSI** and the TCA Handbook, "Maximum permissible variation in the plane or slope, 1/41' in 10 feet (6mm in 3m) from the required plane when measured with a straight edge."

NOTE: If the concrete slab that is about to receive tile does not meet all of the above requirements, DO NOT INSTALL TILE without notifying the general contractor or owner in writing of your concerns. If ordered to proceed anyway, obtain a written release prior to installation. If you proceed without a written release, you have in effect, accepted the slab and all future liability.

DEALING WITH JOINTS IN CONCRETE SLABS
All full-depth expansion joints, cold joints, and surface saw-cut control joints in the concrete slab should continue through the tile work.

TYPES OF CONCRETE SLAB JOINTS
There are the three basic types of planned movement joints that are placed in the concrete slab because it is a moving floor. All of these joints must either be brought through the tile application or allowed for.

Expansion (isolation) joints permit free movement both vertically and horizontally with complete separation for the full depth of the slab. Depending on their span, joint width varies from 3/8" to 1/2" or four times the expected movement. The recommended flexible filler is a urethane sealant for both exterior and interior horizontal tile surfaces.

Control joints are typically saw-cut joints that are cut to a depth of one fourth of the thickness of the slab. They are designed to control and accommodate random cracking attributable to initial drying shrinkage, thermal and moisture changes and load stresses inherent in a concrete slab. This creates a deliberately weak plane that controls cracking into a straight-line isolation joint. The most common example is the use of control joints in freeway construction that permits continuous rather than sectional pouring.

Cold (construction) joints are just the opposite of expansion and control joints; they restrict rather than allow for movement. Cold joints occur where two sections of a concrete slab poured at different times meet. The time difference of the pours may be less than one hour or years apart, the reinforcing steel mayor may not carry through, where they meet is considered a 'cold' or 'construction' joint.

An alternative to cutting tile to align joints with substrate control joints is to use a Sheet Membrane System cut into a continuous wide strip, which can also be used to isolate smaller concrete slab cracks from tile.

Waterproof membranes (sheet or liquid applied) See the TCA* Handbook,
F-121 & F-122-99.
Specialty Membrane Sheets See TCA Handbook, F-147-99.

Another option is to completely isolate tile from the concrete slab.

IMPORTANT CONCLUSIONS
1. Although concrete slabs move (shrink and expand), they are not a flexible material and can crack.
2. Do not install tile over an obvious problem floor. If you do, you have potentially accepted liability for the floor.

*TCA = Handbook for Ceramic Tile Installation, Tile Council of America, Inc.

**ANSI = American National Standards Institute for the installation of ceramic tile

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		Tech Note: Installation on slabs that move The vast majority of quarry tile installations are on concrete substrates with a high percentage of these construction slab-on-grade. This means the concrete slab is at ground level, subject to all the stresses and/or movements that specific geographic areas are impacted by Mother Nature. Stresses range from heat and moisture induced contraction and expansion through live and dead loading. Movement of the earthen substrate comes in many forms, including earthquakes, unstable soil and expansive soil. Great strides have been made in the last several decades in designing concrete slabs to withstand these pressures, such as soil compaction, thicker slabs, higher psi concrete, steel mesh reinforcing, expansion and control joints. However, for a variety of reasons there are still concrete slabs that can cause problems. INDUSTRY RECOMMENDATIONS Because concrete substrates move, the tile industry (TCA) has recomended maximum spans between expansion joints -- interior: 24' to 36' in both directions, and exterior: 12' to 16' in both directions. THE ABCs OF PRE-INSPECTING CONCRETE SLABS BEFORE INSTALLING TILE* A. Look for expansion, control and cold joints, as none of these can be ignored by just tiling over them. Look also for irregular cracks in the slabs that were not planned, indicating excessive slab movement. When there is movement along any of these broken planes, tile obviously will not hold these points together and will be seen on the floor's surface as cracked tile. Everyone is quick to blame the tile, but fault begins with the cracked slab. B. Check the concrete slab's surface condition, as bond failure is the number two consumer complaint, cracked tiles being number one. C. Verify how true the slab is to the required plane (level or sloped). According to ANSI and the TCA Handbook, "Maximum permissible variation in the plane or slope, 1/41' in 10 feet (6mm in 3m) from the required plane when measured with a straight edge." NOTE: If the concrete slab that is about to receive tile does not meet all of the above requirements, DO NOT INSTALL TILE without notifying the general contractor or owner in writing of your concerns. If ordered to proceed anyway, obtain a written release prior to installation. If you proceed without a written release, you have in effect, accepted the slab and all future liability. DEALING WITH JOINTS IN CONCRETE SLABS All full-depth expansion joints, cold joints, and surface saw-cut control joints in the concrete slab should continue through the tile work. TYPES OF CONCRETE SLAB JOINTS There are the three basic types of planned movement joints that are placed in the concrete slab because it is a moving floor. All of these joints must either be brought through the tile application or allowed for. Expansion (isolation) joints permit free movement both vertically and horizontally with complete separation for the full depth of the slab. Depending on their span, joint width varies from 3/8" to 1/2" or four times the expected movement. The recommended flexible filler is a urethane sealant for both exterior and interior horizontal tile surfaces. Control joints are typically saw-cut joints that are cut to a depth of one fourth of the thickness of the slab. They are designed to control and accommodate random cracking attributable to initial drying shrinkage, thermal and moisture changes and load stresses inherent in a concrete slab. This creates a deliberately weak plane that controls cracking into a straight-line isolation joint. The most common example is the use of control joints in freeway construction that permits continuous rather than sectional pouring. Cold (construction) joints are just the opposite of expansion and control joints; they restrict rather than allow for movement. Cold joints occur where two sections of a concrete slab poured at different times meet. The time difference of the pours may be less than one hour or years apart, the reinforcing steel mayor may not carry through, where they meet is considered a 'cold' or 'construction' joint. An alternative to cutting tile to align joints with substrate control joints is to use a Sheet Membrane System cut into a continuous wide strip, which can also be used to isolate smaller concrete slab cracks from tile. Waterproof membranes (sheet or liquid applied)** See the TCA* Handbook, F-121 & F-122-99. Specialty Membrane Sheets See TCA Handbook, F-147-99. Another option is to completely isolate tile from the concrete slab. IMPORTANT CONCLUSIONS 1. Although concrete slabs move (shrink and expand), they are not a flexible material and can crack. 2. Do not install tile over an obvious problem floor. If you do, you have potentially accepted liability for the floor. TCA = Handbook for Ceramic Tile Installation, Tile Council of America, Inc. *ANSI = American National Standards Institute for the installation of ceramic tile

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