Guidelines To Effectively Waterproof Masonry Construction
General Thoughtful design and careful detailing of a masonry building can significantly reduce potential leaks. Special attention should be given to leak-prone areas.
Mortar Joints Certain types of mortar joints (concave and V type joints) are more weather resistant. Well-tooled joints compact the mortar, filling voids and cracks which could lead to water migration.
Movement Joints Generally too few movement joints are provided in masonry structures to properly accommodate moisture and temperature fluctuations. Shrinkage and temperature cracks, which can develop without these joints, allow passage through the masonry. Additionally, leakage can occur at the movement joints themselves, through cracked, unbonded or misapplied caulks and sealants.
1. Construction Procedures and Application Methods
Workmanship is critical to provide good water resistance. Quality workmanship with quality materials helps insure weather tight walls. Choose qualified, well-established contractors for all aspects of construction.
• Masonry industry standards and procedures should be followed throughout the construction process to help eliminate potential for water penetration.
• Special care should be taken to provide adequate bond between masonry units and mortar (leaks often occur at bed joints).
• Masonry materials should be properly stored, generally off the ground and away from detrimental materials.
• If exposed to rain or snow, masonry units should be covered because excessively wet units may not adequately bond to mortar and grout.
• Drying shrinkage cracks and efflorescence can develop if masonry materials become saturated.
• Mortar and grout must be mixed thoroughly.
• Properly tooled mortar joints compact the mortar, reducing cracks and improving bond. Additionally full head and bed joints are often prudent.
• Grout should contain sufficient water for a slump of 8 to 10 inches to flow readily into small voids and cavities.
• Grout should be thoroughly consolidated to eliminate voids and provide better bond to masonry units and reinforcing steel.
• Masonry surfaces must be clean and properly prepared, prior to applying waterproofing products.
• Oil, dust efflorescence and other detrimental substances must be removed from the surface of masonry so applied coatings will adhere properly.
• Since few waterproofing products effectively span over cracks, all cracks should be repaired.
• Some coatings require masonry surface to be dry prior to application of coating while others require damp substrates. Product manufacturer should confirm that the surface is properly prepared prior to application of their products. Always follow the manufacturer’s recommendations fully and endure that the products are applied at appropriate coverage rates.
2. Waterproofing Products
Numerous waterproofing products are available, each with their own special characteristics and attributes. The following briefly describes the major types of waterproofing products, which are readily available. Note that no product works equally well on all substrates and the manufacturer should always be consulted to determine the best product for the job.
• Bituminous Waterproofing Products Used primarily below grade to resist moisture penetration through basement and retaining walls. To perform effectively, a system to remove seepage and/or groundwater must be provided. Bituminous products can be combined with felts or fabrics to form a built-up membrane.
• Clear Water Repellents Clear water repellent products may be used on brick and block walls to shield masonry from rainwater. They are clear so that the color and texture of the masonry can be seen. Some repellents can also include colored stains to enhance masonry.
Most of these coatings repel water by producing high capillary pore angles so the masonry will no longer readily absorb water. They span over only the smallest cracks and every effort should be made to fill cracks and bee holes.
Breathable water repellents should be used so that internal moisture can escape. If moisture becomes trapped in the wall it can freeze causing severe cracking and spalling. Unfortunately, salts cannot as readily escape through some waterproofing materials. As these salts build up within the wall they may cause cracking and spalling of the brick.
Water repellents should not yellow with age nor should they abnormally darken masonry surface. Repellents, which do not give sheens, are generally considered more acceptable. Select a repellent effective in resisting wind driven rain. Note that no known water repellents withstand water under pressure and therefore they should not be used below grade.
Four generic types of clear water repellents are prevalent: acrylics, silicones, silanes, and siloxanes.
• Acrylics and Silicones are deposited on the surface of the masonry, forming a thin film as the solvent evaporates. Generally they are applied with a low-pressure, airless sprayer on an air-dry surface. Some acrylics may slightly darken the color of the masonry.
• Silanes and Siloxanes are characterized as penetrating repellents which, by undergoing a chemical reaction, form a water repellent barrier in the pores of the masonry. Some of these products, especially many silanes, react more completely in the presence of moisture and alkalies. Since concrete is by nature an alkaline material these products often form an effective barrier on moist concrete block.
• Paints Paints can provide a relatively low cost method to achieve water resistance. They can add a variety of color to a masonry structure although their opaque nature can also be a disadvantage since it hides the beauty and texture of the masonry.
Paints should normally be breathable, so internal moisture will not be trapped within the wall. Since moisture vapor enters through the interior surface of walls in cold climates and tries to exit through the exterior face of the wall, exterior paints should generally be more permeable than internal paints. If an impermeable paint is applied on the outside face of such a wall, the trapped water may cause blistering and peeling of the paint or even worse, cracking and spalling of the masonry. Because of this, impermeable paints are generally recommended only for surfaces, which are constantly subjected to moisture (such as swimming pools).
The two most common types of paint for masonry work are cement-based and latex-based paints. Oil-based paints are sometimes used but generally reserved for interior applications.
• Cement-based paints are very durable and form a hard, flat, breathable coating. They are not normally harmed by alkalies, allowing them to be placed on a new concrete masonry as soon as the mortar dries. Unfortunately, these paints often chalk and fade with time and will crack and chip if applied too thickly.
• Latex paints are also breathable and quite durable under normal conditions. They have excellent color retention, and are easy to use. Although latex paints are permeable to water, some trap salts within the wall as the water vapor escapes. Since salt build-up within the wall generates extreme pressures, which can cause spalling and cracking of the masonry, it is important to use materials relatively free of salts when using these paints.
• Elastomeric Coatings Elastomeric Coatings are extremely water resistant although they can have a high initial cost. They have excellent flexibility, allowing them to bridge over hairline cracks when properly applied. They can be blended into a variety of colors but, unfortunately, like paint, they cannot yet be clear and transparent.
• Integral Water Repellents Used primarily in concrete masonry construction, integral water repellents provide an effective alternative to clear water repellents. These products are added directly into the concrete mix used to make the block units and must be added in the mortar. They coat the pores of the concrete masonry units and mortar, making them more water resistant. Because they are added directly into the concrete and mortar, they should not wear off like other repellents. Concrete masonry walls, which have integral water repellents, also have the advantage over normal concrete masonry of being easier to clean or paint.
The largest drawback of integral water repellents is their durability to span over cracks or gaps in the masonry. If the mortar does not bond well to the units, water will pass through the cracks just as in any other concrete masonry wall. Therefore, whenever using these products, special care should be taken to assure mortar joints are well tooled and ample movement joints are provided.
Integral water repellents cannot withstand water under pressure and should not be relied on in most below grade situations. Integral water repellents must be added to the concrete mix and mortar in precise dosages, as stated by the manufacturer. Adding excessive amounts of these products may increase the water repellency of the wall, but over dosage can also decrease bond between units and mortar. Similarly, excessive amounts of integral water repellents have been reported to retard mortar set.
• Membrane Waterproofing Continuous waterproofing membranes can effectively resist water penetration. Designed and installed correctly, membrane waterproofing can withstand water under pressure, and are often applied against basement walls. By using asphalt for water resistance, and plastic polymers for added ultra violet radiation durability, waterproofing membranes can also effectively resist moisture penetration through the roof side of parapets.
3. Maintenance of Waterproofing Systems
Throughout the service life of a structure, maintenance must be performed to keep any waterproofing system working as intended. Periodic inspections of the structure should be performed to define areas requiring maintenance. Any work required should be performed promptly as waiting often allows significant damage to occur.
Roof drains, gutters, and weep holes must be kept cleaned and free from clogs. Cracks in masonry should be filled as they form. Paint and other applied waterproofing products require periodic applications in order to remain effective. Likewise, caulking and sealants should be removed and replaced as they crack or separate from the substrates. In severely deteriorated structures, broken or cracked masonry units should be replaced and deteriorated mortar joints should be re-pointed.