Pictured is a just-installed urethane waterproofing product in a residential bathroom. Photo courtesy of Bostik-Findley.

Waterproofing membranes are available in a variety of forms. Among these are liquid-applied products, sheet membranes and composite membranes (which are made on site by combining two or more components).

Governing the use of such products is an American National Standards Institute guideline - specifically, ANSI A-118.10-93. This standard applies to thinset ceramic tile and dimensional stone installations. It covers trowel- and liquid-applied products and sheet membranes. The standard's main purpose is to develop materials that prevent moisture in wet areas from migrating to surrounding areas (or areas on a lower level) and thereby damaging them.

As I mentioned, currently available are liquid-applied membranes, sheet membranes, liquid mortar membranes, as well as membranes that utilize a mesh that is covered and embedded by one or more coats of a liquid-applied product.

Liquid-applied waterproofing membranes are usually installed with a roller or brush. These are one-part formulations that require no mixing, which makes them easy to use. Because some of these products are also elastomeric, they can serve double duty as crack-isolation membranes as well.

Guidelines for the use of liquid membranes specify that any cracks in concrete greater than 1/8-inch wide be considered expansion joints and treated accordingly. Gaps in plywood sheets should be treated in a similar manner.

Liquid-applied membranes require a second coat. An approximate coverage figure is 35 to 40 square feet per gallon. The product requires a minimum of 24 hours' drying time.

An alternative trowel-applied waterproofing and anti-fracture membrane uses a liquid latex with a cementitious powder mixed into it. This particular type of trowel-on membrane can be applied especially fast, allowing ceramic tile or stone to be placed as soon as four to six hours after the membrane has been installed. A key advantage that trowel-applied membranes have is their ability to go up a wall without sagging.

Also available are liquid-applied membranes reinforced with a synthetic fabric. These types of products require overnight curing. In addition, waterproofing anti-fracture membranes that utilize asphalt-modified latex are also available.

Urethanes are considered part of the "liquid class" of waterproof membranes. These urethane products require moisture to act as a curing agent. They should be allowed to cure for 24 hours.

A variety of sheet membranes are used today for waterproofing and anti-fracture purposes. Some are manufactured as vinyl. Some are manufactured as chlorinated polyethylene. Some are produced using a bitumen-modified sheet form, and at least one other is made of butyl rubber.

All of the sheet-format products I've mentioned require seaming to provide a waterproof substrate for a ceramic or stone installation. They allow the advantage of proceeding with the tile or stone installation as soon as the membrane installation is complete.

In addition, two of the sheet membrane varieties mentioned above have pressure-sensitive bonding abilities. However, the surface to which they are bonded must be primed prior to the installation of the membrane.

A word of caution: whichever or whatever you consider using, make sure that the product meets the standard of ANSI A-118.10 and is accepted by the Uniform Plumbing Code.

The following companies contributed to this article:

Bostik-Findley:(888) 592-8558
Custom Building Products:(502) 598-8808
Mer-Krete Systems:(800) 851-6303
National Applied Construction Products:(800) 633-4622
Mapei:(800) 426-2734