Masonry, Waterproofing Masonry
Sealers are basically clear water repellents, though color-stain types are available. They can be used on stucco, plaster, tilt-ups and block walls.
by Jeff Woodard
pre-cast concrete panel, veneers, tilt-ups and block walls have in common?
They all pose challenges for specifiers and contractors who are deciding which coatings and sealers will be most effective in preventing water penetration and UV damage.
Sealers are basically clear water repellents, though color-stain types are available, says Dick Olson, Sales Representative for Merlex Stucco, Inc. in Portland, Oregon. “They can be used on stucco, plaster, tilt-ups and block walls. Most substrates are treated similarly, except some take more material to seal the wall.” Jim Glessner, President and General Manager of White Mountain Products in San Leandro, California., says sealers are used to prevent water transmission and degradation resulting from continual movement of water. “This varies from region to region and various climates,” says Glessner.
Aesthetics are also a factor. “If the building owner wants to change appearance, he’ll need a film former,” advises Paul Fisher, construction chemical/technical services consultant for Dow Corning in Midland, Michigan. “But trends in the industry are such now that buildings already have pigments, and they don’t want to change the aesthetics. So then they use a penetrating type material.” Another decision is whether to use silicone or organic material. “The preferential treatment is silicone,” says Fisher, “because silicones are breathable. Most organic systems are film formers.”
Silicone, however, has competition. “You have the old stand-by, silicone, which will get 1-3 years’ life,” says Olson. “And now there is the siloxane, which has a very long life due to good penetration and a history of long, successful uses on stucco, brick, block and concrete.” Silane is another effective penetrant, says Olson, especially on such uses as concrete bridge horizon surfaces.
Glessner says the three sealers have a lot in common. “Silicone, silane and siloxane are all invisible. All impart water. All have similar longevity. Ten to 15 years ago, silicones were a big deal. The other two are now more paramount, although we find silicones still hold their own.” In general, says Fisher, it boils down to aesthetics. “Silicones are better for not changing the appearance of the substrate. They’re breathable, penetrating, alkaline resistant and very water repellent.”
At least one painting contractor no longer uses silicones. “They do not have a long life,” says Don Hansen, president of Dependable Painting in Cleveland, Ohio. “Many of the clear sealers are made with siloxane. We also have used elastomeric coatings and cementitious-based coatings. They are not transparent, so they are not used typically on face brick, split-face block or other finished substrates.” Hansen recommends solid pigmented coatings over clear coatings for better waterproofing performance.
The breathability of a silicone sealer helps surfaces dry more quickly. Still, says Olson, a few conditions must be met. “Temperatures need to be above 40 degrees and rising, and surfaces should be dry. Do not apply when it is windy or hot, and don’t apply in foggy conditions.” In climates with diverse weather conditions, a sealer’s durability is even more crucial, notes Glessner. “In places such as the Hawaiian islands, which have lots of rain and lots of moisture, surfaces will degrade that much faster.”
Water content trapped in the substrate makes it difficult to determine the most effective sealer application—especially when the sealer prevents moisture from escaping. Most resin-type sealers are film-forming products, says Olson, and do not allow walls to breathe well. When moisture is trapped, whitening of the wall—a condition known as efflorescence — can become more than just an aesthetic problem. Applying the sealer is no problem, says Glessner. “But if the substrate is not cured completely, you’ll dilute the solids of the product.” Hansen adds that some sealers are designed to be breathable to allow small amounts of moisture to pass through while still affording protection against rain.
Silicone sealers are not recommended for below-grade application. “That type of product is not made to impart water in that way,” says Glessner. “A non-breathable coating would be recommended for sub-surface applications.” Cementitious waterproof or membrane coatings work well for below-grade situations, “all the way down to the footer if you can,” says Olson.
Most high-quality sealers on today’s market will hold up from 5 to 10 years. Hy Dubin, president of Dumond Chemicals, Inc., in New York City, says the life span of any sealer or coating depends on the preparation of the surface before application, proper application, weather conditions and maintenance.” Preparation should include fixing cracks and replacing missing mortar joints. The surface must be free from dirt, efflorescence, grease, oil, graffiti and any other element that can affect the integrity of the product being applied. Regarding some claims of a sealer’s lifetime durability, Glessner has a word of caution: “There’s no such clear product that will last more than 10 years as long as it’s exposed to the elements. It will all degrade.”
Preparing previously sealed substrates poses unique challenges for contractors. Notes Olson, “If a wall has been previously sealed with a resin type of product and is failing, it would probably have to be sandblasted. You need to test the surface to see if it will penetrate the material on the wall.” One tricky situation is applying water-based products to water-repellent surfaces, says Fisher. “You may have to re-coat with a solvent-based system, or sandblast so it will accept water-based technology.”
On new construction, all manufacturers request a 28-day period of curing before coating, says Olson. “We ask for that much time, but in the real world, you are lucky if you can get 14 days for the walls to cure.”
Sealing may be one of the last steps in a long, involved construction process. But it’s hardly the least important, points out Fisher, who warns builders of the dangers involved in cutting corners at the end of a project. “One of the last things to be put on a building is water repellent, but if budgets are tight near the end, sometimes the most important thing to put on the building is the first thing that gets cut.”
One of the first things to consider in applying a sealer is surface preparation. Glessner recommends a pH-positive or alkaline cleaner, strongly discouraging the use of solvents such as muriatic acid:
“It’s dangerous. The residue can cause discoloration, etching and degrading. It’s effective as an etching agent in preparation for certain types of coatings, but as far as a cleaner, it’s not something that should ever be used. Muriatic acid will pull color out of anything. It can break down the substrate. It’ll eat concrete.”
Until recently, records on sealer maintenance have not been a high priority for building owners. “Most sealers are not inspected to see how repellent they are until a water leak develops,” says Olson. Many contractors don’t recognize the benefits of maintenance—and they pay dearly. “It’s a problem in both horizontal and vertical surfaces,” says Glessner.
“There’s a lack of education on maintenance.” Fisher says building owners are gradually becoming aware of the importance of maintenance. “They’re now starting to realize that it’s a significant savings to do water repelling work early. It’s a building owners insurance policy. The biggest unmet need out there is educating building owners who don’t know they need a water repellent.”
Contractors can help customers understand the economics of proper care by encouraging them to periodically check a sealer’s durability and performance. An inspection every few years is a good idea, too. “For aesthetics, like split face block, the economics is cost of maintenance,” says Glessner. “Pressure washing and sealing get costly. In doing cost analysis, an initial sealing is far cheaper than repair and subsequent sealing. Most people are shortsighted and don’t want to spend a little now to save a lot later.”
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