From the Technical Expert

Expansion Joint


Construction Joint
The need for a crack isolation standard originated at the MMSA, Material and Methods Standards Association in the early '90s. It has now progressed into a new proposed ANSI standard. The committee is proposing a standard that identifies crack isolation membranes for thin-set ceramic tile and stone installations that shall act as a shock absorber to isolate the installed products from minor in-plane cracking.

Contraction Joint
This standard will apply to all membranes, namely liquid, sheet and trowel applied, including multi-layer systems. As with most standards, you are requested to contact the individual manufacturers and/or suppliers of these products for specific application instructions and especially limitations. This is important as every crack isolation system has limitations.

The proposed standard will point out that:

1. Cracking is limited to horizontal plane movement of the substrate.

2. It is stressed that it is important when working with a cracked substrate that the expansion joints are properly located and properly treated.

3. All movement joints in the sub-strate shall be continued thought the installation.

4. Requirements for expansion construction and control joints can be found by contacting the Tile Council of America (TCA). These details are available in the 2003-2004 Handbook For Ceramic Tile Installation 41st edition.

5. Various trowel applied, not all, crack isolation membranes can also be used as the setting material for the ceramic tile and stone. Other liquid membrane products are allowed to dry and thus become the substrate for the installation of the ceramic tile and stone. The proposed standard addresses all types of movement joints associated with concrete slabs. Of particular importance to the tile industry is the control/contraction joint, which is mechanically constructed to provide a weakened plane that will “regulate” the location of cracks that are the expected results from dimensional change in the concrete. Usually this means shrinkage.

Note 1:

All slabs crack. That is why control joints ensure that no random cracks develop that affect the flooring. Construction joints or cold joints are a result of different pours on different days which are adjacent to each other.

Note 2:

Expansion in a floor slab is generally less than shrinkage so expansion joints are unnecessary in the slab but absolutely necessary in your ceramic tile and stone flooring.

Note 3:

Substrate movement, departing from the norm. Substrates that are cracked, dimensionally unstable, or demonstrate a tendency to “move” require a membrane that allows free movement between the mortar bed and the substrate. Under a mortar bed this is known as a cleavage membrane, and is intended to be a material unaffected by moisture to separate the mortar material and the tile.

When a waterproofing membrane is desired, it can also serve as a crack isolation membrane. For deflection purposes, ANSI A 108 limits for deflection are expressed in AN 2.3 as “floor areas over which tile is directly bonded to subfloor shall not have a deflection greater than 1/360 of the span when tested per ASTM C627”.

In the proposed specification material, property tests will include fungus and microorganism resistance. For system performance, there will be shear tests to show shear strength to ceramic tile and cement mortar. These tests will include 7-day shear strength. Values to be greater than 50 PSI (pounds per square inch).

7-day water immersion shear strength with shear strength again greater than 50 PSI. There are also 4-week shear strengths and accelerated aging shear strength tests. In all cases, the values for shear strength must be 50 PSI or greater.

Additional performance tests include a point loading test with a minimum of 1,000 PSI and a Robinson Floor Test when and if performance data is required for a particular substrate and tile. There is no single Robinson Floor Test in this proposed standard due to the variety of components. There is also the System Crack Resistance Test. There are two proposed standards, one being a high performance standard where the tile is not cracked at a 1/8-inch opening. Then there is a Standard Grade where the tile performance is not cracked at 1/16-inch but fails before a 1.8-inch opening.

So, keep in mind that all men are created equal but not so for membranes.