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Construction & Repair
I have a white powder on my exterior brick and mortar. It’s up above the glass window of my storefront. It seems to wash off with a garden hose, but comes right back after the surrface dries. What is it and how can I get rid of it?
That’s a good description of efflorescence. The white powder is actually a kind of salt from inside the brick, block or mortar. When water from rain or other sources penetrates the masonry, it dissolves these salts. Sometimes rain will carry more salts into the masonry. As the force of evaporation pulls the moisture back out to the surface, the moisture carries the dissolved salts with it. Once on the surface, the moisture evaporates, leaving the dissolved salts behind. They build up into those deposits. Washing with a garden hose won’t help, because it puts more water into the masonry. To control efflorescence, first check that water isn’t getting in through failed joints, cracks or other defects. Fix it, if that’s the case. Once you’re sure the masonry is sound, let it dry thoroughly. Then give it a good cleaning. Start by testing Sure Klean® Light Duty Concrete Cleaner. This is usually effective for red brick and gray mortar. For colored mortars and light- or unusually colored brick, test with Sure Klean® Vana Trol®. Once the brick is cleaned, let it dry thoroughly. Then apply Sure Klean® Weather Seal Siloxane PD. This breathable, penetrating water repellent will protect your brick storefront from efflorescence, mold and mildew, freeze/thaw cycles and a host of other water-related problems.
I am building a structure with Single Wythe CMU walls. Do I need flashing and a water repellent coating?
Concrete block, particularly lightweight concrete block, is not weather tight if you do not apply a water repellent coating to it. Water repellent coatings usually last between 2 and 10 years, depending upon the exposure of the building and the competence of the applicator. As a rule of thumb, penetrating water repellents last longer because they are not as prone to ultraviolet degradation as surface coatings are. I recommend Silane and Siloxane-based coatings because of this longevity. If you want to read more about water repellent coatings for concrete block, go to the web site for the National Concrete Masonry Association. Look for an icon labeled “E-Tek”. Click on this heading and it will take you to another web site where you can download technical articles. I suggest you download: Tek Note 8-1A - Maintenance of Concrete Masonry Walls Tek Note 19-1 - Water Repellents for Concrete Masonry Walls My favorite flashing/weep system for single wythe walls is called Cavity Vent. It is a strip of corrugated plastic that you install at the base of the wall, where the block meets the foundation. I like the product because it is fast and easy to install and it does not deteriorate over time. Structural engineers like it because it does not interfere with rebar placement and it does not cause shear plane weakness at the base of the wall. For more information, visit www.masonrytechnology.com and click on the drawing of “Cavity Vent” to see more information about this system.
Which flashing is best?
We like to give generic advice whenever possible but I do have some preferences. Do NOT use any flashing with vinyl in it. The high pH of wet mortar eats holes in vinyl. This eliminates any PVC flashing products from my recommended list. According to Architectural Graphics Standards, mortar is also corrosive to pure aluminum and pure zinc. Alloys with these materials do not seem to have trouble with corrosion. I recommend metal flashings only for the longest lasting buildings (like cathedrals and university buildings). Although the metal flashing is slightly more expensive than flexible flashings, the time required to cut it, fold it and weld it accounts for the real price jump between flexible flashings and metal ones. Flexible bitumen flashings are my personal favorite for Colorado’s climate. The material is cost effective, easy to work with, long lasting and tolerant of the high pH of mortar. The tar coating will even self-heal small holes and cracks once the sun comes out and heats the wall.
The manufacturers tell you to peel off the backing and install the flashing sticky-side down on a clean, dry substrate. You must also hold the flashing back 1/2” from the face of the wall so that the sun doesn’t melt the tar and have it drip down the face of the building. If you want the flashing to continue to the face of the wall, you can either pair the bitumen flashing with a 1” wide galvanized metal drip edge or you can use Hyload flexible flashing, a bitumen-based flexible flashing system that comes with an integral drip edge.
Do retaining walls over 3’0 tall need to be engineered?
Yes. Any walls over that are taller than 3’0 in height or will support a heavy load (i.e. driveway, street, or additional surcharge) should be engineered by a qualified civil engineer. Check with local authorities having jurisdiction for all requirements.