By Tom Plaskota
|Tile installation at a YMCA indoor swimming pool. All images courtesy of TEC.|
Moisture is a simple word that can strike fear into the hearts of installers, general contractors and building owners. When those in the construction and masonry industry think about moisture, they envision efflorescence, cracking, bond failures, and mold – all leading to costly callbacks. But moisture does not have to be a cause of distress. Careful selection and application of moisture solutions can prevent the aggravation associated with moisture damage.
Moisture can affect an installation in a variety of ways. Before beginning an installation, consider the possible sources of moisture that could reach it. The source of the moisture your installation faces will determine the best products and methods for addressing it.
|Surface preparation with TEC LiquiDAM.|
Excessive Moisture Vapor Emission
One potential – and often unseen – source of moisture is “excessive moisture vapor emission.” Historically, this problem has been more frequently associated with soft-flooring failures than with the failures of stone or tile installations. However, the increasing popularity of impermeable tiles, changes in installation methods, the composition of membranes and underlayments, and increasingly demanding construction schedules have made today’s tile installations more susceptible to excessive moisture vapor emission than ever before. But don’t let that intimidate you. With a clear understanding of the causes of moisture vapor emission, you can select the right products to keep it from negatively affecting your installations.
In cases of excessive moisture vapor emission, moisture enters the flooring installations through vapor transmission. This process sometimes starts long before the installation of masonry begins. In fact, moisture enters the subfloor when concrete is first poured. A pressure differential then causes the water to migrate from an area of high vapor pressure – such as damp concrete or wet soil – to an area of low vapor pressure, like a dry building interior. This can damage the installation system. Moisture also may migrate from within the mortar used to set the stone or tile toward the installation’s surface.
When migrating moisture begins to collect and condense under a tile or membrane, it can affect the installation, both aesthetically and in terms of performance. This process can discolor tile and reduce the functionality of adhesives, grouts and membranes. It also can lead to unsightly efflorescence.
It is a contractor’s job to identify potential moisture problems – even if they begin long before crews arrive at the job site. After all, if left unaddressed, vapor transmission can cause costly and frustrating failures. And selecting the very best moisture vapor emission solution means taking several factors into consideration – especially the relative humidity and condition of the slab and the job’s specific requirements and timeline. The most reliable test is the ASTM F-2170 test for determining relative humidity of concrete. This test relies on “in-situ probes” – or probes that test the moisture levels beneath the substrate’s surface. Because moisture migrates upward from within the slab, measuring moisture at its surface will not accurately portray the subfloor’s relative humidity. Probes placed at specified depths inside the slab more accurately measure its relative humidity levels, and as a result, more reliably measure the risk moisture poses to a particular installation. Be sure to follow the instructions of your relative humidity equipment, and refer to the tile manufacturer’s guidelines for the recommended relative humidity levels.
Note that the moisture test results indicate the moisture condition of the slab only at the time of the test. Although concrete often absorbs water from the ground, it also can absorb water vapor from the air in humid conditions. Moreover, concrete releases more vapor when the air humidity is low. These fluctuations in environmental conditions can affect relative humidity levels, and tests should be repeated over time.
Once the concrete slab is in place, topical application of a moisture vapor barrier is the only option for moisture mitigation. The most common moisture mitigation systems, particularly for commercial applications, are two-part, 100-percent solids epoxies. These liquid coatings are applied to the slab, where they will prevent moisture from migrating up and into the flooring system. Some of the best products reduce the moisture vapor emission rate to less than 3 lbs. per 1,000 ft² per 24 hours and deliver permeability of less than 0.10 perms through the membrane.
Keep your job’s timeline in mind when selecting a moisture mitigation system. Some products can be applied to damp or new concrete as soon as 48 hours after concrete placement, and cure within four to five hours, allowing for same-day tile installation. When time is an issue, look for these products.
|A completed tile installation.|
|Installers should properly prepare the substrate before applying a moisture vapor barrier.|
|Prepping for a LiquiDAM application.|
Installers also should properly prepare the substrate before applying a moisture vapor barrier. This includes addressing dynamic and static cracks in the concrete, as per the product’s instructions. The substrate also should be cleaned of any contaminants before applying the moisture mitigation system.
When you’ve determined that mitigation is necessary and selected the right product for the job, ensure that your surface is strong enough for a proper bond with the moisture vapor barrier. Some moisture vapor barriers require no shot blasting for clean, sound concrete. To determine if your concrete surface is sound, test the substrate with a knife. If it produces a fine powder, mechanically prepare the surface by grinding or shot blasting. Then clean the surface until it is free of debris. Consult with the moisture mitigation system’s instructions for more specific surface preparation requirements, as well as mixing and application instructions to use your moisture mitigation system most efficiently.
Expansion and Contraction
Even if moisture does not migrate upward, it may still affect your tile and stonework – particularly in seasonal climates. As moisture levels change, subfloors, adhesives and tile can expand, contract and even crack. The right installation materials, working as one system from subfloor to sealant, will help indoor and outdoor tile installations withstand this moisture-driven movement for longer lasting spaces.
Supplementary products can mitigate or prevent the cracking associated with changing moisture levels. Waterproofing and crack isolation membranes isolate existing substrate cracks – keeping them from spreading – and also prevent in-plane cracks in the subfloor from telegraphing to tile. That way, in plane movement of the substrate will not affect the appearance of the tile or stone installation. These products’ waterproofing characteristics prevent topical moisture from affecting the substrate.
Moisture also may affect the mortar and grout of your tile installation. Mortars in wet conditions have to perform, and you need to make sure the mortar you use is up to the challenge. Many polymer-modified mortars are better equipped for moisture resistance than other adhesives. Look for mortars that combine bond strength with flexibility to allow for shifts in the substrate caused by changing moisture levels. Polymer modification may increase mortar performance and flexibility in cold weather, helping it withstand the expansion and contraction associated with changes in temperature.
Similarly, choose a polymer-modified grout that has lower water absorption. Grout additives often are mixed with standard grouts, in place of water, to provide a grout that is stronger, denser, and more resistant to freeze/thaw damage and water penetration. They also can increase grout flexibility, providing crack resistance. Many of the newer, high-performance grouts are formulated with these qualities already built in.
Moisture from Above
If a stone or tile installation will be repeatedly exposed to moisture from an exterior source, you will need to make sure it is equipped to handle it. Wet installations – such as fountains, showers, pools and spas – must be prepared adequately to withstand the repeated exposure to moisture. Otherwise, they will be susceptible to bond failures, mold, and efflorescence.
Fortunately, today’s waterproofing materials are much easier to use than these products have been historically. Waterproofing membranes can form a smooth, monolithic, watertight surface over walls, floors and ceilings – just below the surface of the tile. Tile then can be bonded directly to the membrane. These products prevent water from penetrating into the substrate – avoiding the development of moisture issues below the tile installation.
Like moisture mitigation systems, waterproofing membranes can be used efficiently. Some products can be applied over new concrete, as little as three days old, with a trowel, roller or spray, and are ready for tile installation in just two to three hours. And, mesh is only required at changes in-plane and substrate joints.
Tile installers in wet environments should not ignore testing – a final and critical step of the waterproofing process. After the system is in place, but before tile is installed, you must make sure waterproofing products have been completely effective. This confirms that you have a functioning system, which is essential to a long-lasting installation. If a leak is detected, it can be repaired before it causes any damage. Everyone makes mistakes, but correcting them turns mishaps into success stories.
Once a waterproofing system is in place, you can return to the basic aspects of installing tile: using proper setting materials. When choosing setting products, confirm that they will work with both the type of tile being used and the waterproofing system. For example, mastics are not acceptable for bonding tile to membranes. Look for high-performance tile-setting products with lower absorption rates. Normally, in an installation that will be exposed to water, you will need to use a modified mortar; however some uncoupling membrane manufacturers require unmodified mortar. When possible, try to use the same manufacturer’s materials for all steps of the installation. Having one point of contact for all installation materials simplifies matters, should any issues arise.
You also must remember that tile installations in wet areas, such as showers, require 95 percent mortar coverage. With natural stone, this requirement increases to 100 percent. To check that you are achieving proper coverage, pull a tile up right after placing it, and look at its backside. You will immediately be able to tell if you are using the right techniques to achieve a proper bond.
Improvements in grout and sealant technologies have expanded the products available to installers and their customers. For wet areas, many owners request grouts that are low in absorption, stain resistant and do not require any sealing. These types of grout are now available and recommended for such applications. One hundred percent silicone caulk has become the product of choice for the flexible sealant required in wet areas. These caulks prevent mildew and cracking in the grout joints.
|YMCA tile installation. Wet areas, such as showers, require 95 percent mortar coverage.|
Both efficiency and frugality are valued during stonework and tile installations. Although addressing moisture – from a variety of sources – requires an initial expenditure of time and money, doing so can ultimately save you and your client from frustrating and costly callbacks.
Tom Plaskota is a technical support manager for TEC®/H.B. Fuller Construction Products. For more information about addressing moisture, visit www.tecspecialty.com.