Have you ever experienced an earthquake? Think of the start of a slab crack as an earthquake in your floor — a sudden release of energy causing cracks across your substrate. The effect of this energy being released horizontally and vertically in your substrate can and will most likely transfer through your tile or stone flooring creating a one-of-a-kind look. These slab cracks are described as in-plane cracks or out-of-plane cracks. In-plane cracks move horizontally and out-of-plane cracks move up and down. In this article, we will primarily refer to in-plane cracks.
With ceramic, porcelain and natural stone tiles becoming more and more popular, contractors and end-users need to find effective and affordable methods that will ensure their installations will last for years. One of the main issues that occurs when tiling over concrete slabs is cracks. There is an old adage in the industry that says, “There are two types of concrete: cracked and going to crack.” When poured correctly and in the right application, concrete will last a long time. However, nothing lasts forever and concrete is no exception. It will crack; it is just a matter of when.
Three main types of products are available to prevent or isolate these types of cracks from telegraphing through the finished tile installation. They are commonly referred to as liquid applied membranes, sheet membranes and uncoupling membranes.
- Liquid-applied membranes — typically a single component load bearing liquid primarily comprised of latex that provides a monolithic surface with excellent elongation. These types of membranes absorb the energy and stress from in-plane crack movements. They are the easiest to use. These apply directly to a clean sound substrate free of contaminates. The liquid-applied membrane is also monolithic meaning no seams. These types of membranes also do not raise the overall height of the floor.
- Sheet membranes — a composite sheet designed to relieve the stress caused by in-plane movement in the substrate. Sheet membranes have been around the longest. These types of membranes typically are applied with a mortar and rolled flat or are self-adhered. Unlike the liquid-applied membrane, these do have seams and will slightly raise the height of the overall floor.
- Uncoupling membranes — a plastic or fleece membrane system geometrically configured to provide air space between the tile and the substrate to allow independent movement between the two and limit the transfer of stresses. They are the newest type of crack prevention technology. These function with the science of relieving the stress of a crack with an air space/gap between the substrate and tile. Uncoupling membranes have seams and will raise the height of the floor.
Products made specifically for crack isolation are sold for everything from isolating the tile from shrinkage cracks to tiling over control joints to protecting the entire floor from potential cracking in the concrete.
So which membrane should you choose? Personal preference is typically the most common answer. Each of these membranes will do the job needed to prevent typical in-plane movement cracks from transferring through your beautiful tile installation. When used to cover the entire floor, many manufacturers will warrant the entire floor installation, including the cost of replacing and installing new tile.
It is a frequent misconception that anti-fracture membranes allow you to eliminate expansion joints. They do not. Always include soft joints in the install to allow for expansion and contraction. Guidelines for expansion joint placement are given in the Tile Council of North America (TCNA) Handbook for Ceramic, Glass, and Stone Tile Installation.
In the TCNA Handbook you will find that almost all installation methods over concrete provide an optional membrane choice for that method. There are two specific methods that deal with pre-existing slab cracks. These are F-125 Partial and F-125 Full. Refer to the TCNA Handbook for additional information pertaining to crack isolation.