August 20, 2018 - 21.14
Crack Isolation Basics
by MAPEI Product Support
We've all seen them - unsightly cracks running through tile floors. While ceramic and stone flooring is durable, it can't overcome the laws of physics. When cracks open up in the substrate below, they often will telegraph up through the tile (and grout). Anyone who has chipped out several tiles to replace them can tell you - it is not fun project. The answer for most installations is the use of a crack isolation membrane.
What is a Crack Isolation Membrane?
As the name implies, crack isolation membranes are designed to isolate the stuff above them (the tile and grout) from the stuff below them (the substrate). They do this by providing a stretchy layer between the two. Typically, crack isolation membranes will state that they comply with ANSI standard A118.12
. This standard requires the membrane to isolate the tile from cracks of 1/16" for standard performance and 1/8" for high performance. Crack isolation membranes can protect tile, stone, and grout from either new cracks that form in the substrate or existing cracks that get larger as long as crack does not exceed the width of the stated performance of the product. What isn't a Crack Isolation Membrane?
Crack Isolation membranes don't protect tiles from cracking because of force from above like something falling on the tile. They also won't keep a tile from cracking if it has been poorly installed and has voids in the mortar beneath it. They are not 'anti-fracture' membranes, tile can always fracture in the presence of stress. Crack isolation membranes are designed to keep the stress away from the bottom of the tile. While some companies tout crack isolation mortars, no cement-based mortars are flexible enough to meet the ANSI requirements for crack isolation. Crack isolation membranes also don't protect against out-of-plane cracks. In general, there are three categories of crack isolation products on the market today:
Sheet Applied -
Sheet membranes typically come in rolls and are applied with a 'peel and stick' application. The positives of sheet applied membranes are that they can be immediately tiled after they are placed and often will give superior protection from wider cracks. Mapeguard 2
, for instance, states that it can protect from in-plane cracks up to 3/8" in width. Most of these membranes do require a primer
to develop proper bond with the substrate.
- Liquid applied crack isolation membranes like our Mapelastic CI
have become very popular in recent years. These membranes are typically rolled on with a roller to a certain thickness (a wet film gauge should be used
) and allowed to dry. Once dried, these membranes will adhere to the substrate and stretch if cracks develop. In some cases they are used to treat existing cracks but can offer extra insurance when concrete has been recently poured and cracking is only a matter of time.
Uncoupling and multi-pourpose Membranes -
Unlike sheet- and liquid-applied crack isolation membranes, uncoupling membranes work differently. Instead of relying on the product stretching, these membranes (such as our Mapeguard UM
) typically have a fabric layer that allows some movement before shearing from the upper plastic mat. There are also a variety of membranes that combine crack isolation with waterproofing
(ANSI A118.10) or sound countrol
With a wide variety of crack isolation membranes on the market, there is an option for every job schedule and budget. These products are great added insurance that today's beautiful tile floor won't end up tomorrow's cracked floor in need of replacement. For more information about MAPEI products or for help in choosing the correct one, contact us
. We're here to help!