Managing the risks of efflorescence

Installation materials

Figure 3: Proper flashing using a drip edge.
Figure 3: Proper flashing using a drip edge.

Portland cement products naturally contain lime, which is a source of the salts that migrate to the tile surface. Practically every installation material manufacturer disclaims liability for efflorescence formation with Portland cement products for this reason. Concrete, plasters, mortar beds, dry-set mortars (thin-sets), grouts, and some tiles are manufactured with Portland cements. So, efflorescence is difficult to avoid, but it can be controlled. There are alternative products available that greatly lower the possibility and eliminate some of the sources of these salts. When such products are used as a system, the risk of efflorescence is very low.

Efflorescence from concrete substrate.
Efflorescence from concrete substrate.

The first step is to include a flat membrane (such as a liquid- or sheet-applied type) able to restrict water from entering the substrate. Concrete and other cement substrates are the most likely culprits to provide a source for efflorescence in an assembly, so use of flat drainage membranes can significantly reduce the risk of this problem. Due to their geometric cavities, uncoupling mats may also trap or slow water from draining and result in efflorescence. Drainage mats are perforated to allow water to pass through them, but typical uncoupling mats are not. A drainage mat creates space under a mortar bed with its egg carton configuration. However, a cleavage membrane is in 100 per cent contact with the mortar bed and substrate so water slowly drains from the assembly. In this time, freeze/thaw effects are more likely to occur and cause heaving and efflorescence. Adding a drainage mat under a mortar bed in exterior applications instead of using a cleavage membrane will be a great help to move water to a membrane and out of the assembly (Figure 1).

Second, mortars and grouts made with calcium aluminate (CA) cements or blends of primarily CA are much less likely to contribute to efflorescence, as these cements contain little or no lime. These product formulations are exothermic and cure quickly, using up water at a faster rate. Many manufacturers advertise CA cements will not contribute to efflorescence or effloresce at all. This is especially important in cold and damp conditions. Premixed or single-component grouts and epoxy grouts are another option, as they are noncementitious, typically free of efflorescence-contributing materials, and warranted to be so.

To help prevent minerals from migrating out from cement-based tiles or natural stone, penetrating sealers might be a solution. To adequately accomplish this, a ‘six-sided’ sealing process is employed, in which the cement-based tile or stone is immersed in penetrating sealers, and, after removal, are allowed to dry until the next day. Some penetrating sealers will allow adhesion with cement mortar. It is important to note, not all sealers, even penetrating types, are acceptable.

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