Accurately diagnosing the source of water penetration in a masonry structure should be the first step toward correcting the problem. If the structure is a chimney, the flashing needs to be intact and the crown must be in good condition. But the composition of a chimney is an important factor in its susceptibility to water penetration. Although masonry is relatively durable, it is a porous material composed of a network of interconnected pores, like capillaries, that circulate water by means of suction. Exterior masonry structures, especially chimneys, require a good weathering grade of brick that has been fired at high temperatures, and a compatible water resistant mortar.
Rain and other moisture sources erode masonry by a process of expansion and contraction cycles. Masonry building materials, such as brick and stone, are composed of different minerals that expand and contract under various temperature extremes. These cycles can lead to stress cracking which reduce strength and increase susceptibility to water penetration. Mortar joints are particularly water absorbent and hold water in areas adjacent to the wet joints. As a result, these damp areas surrounding the joints take longer to dry out.
In addition, salts which are inherently present in some building materials often leach out after initial construction, a type of efflorescence sometimes referred to as "new building bloom". But efflorescence also results when rainwater penetrates the masonry and dissolves these natural salts. When the masonry begins to dry, the water moves toward the surface and evaporates leaving the dissolved salts at the surface where they remain as white efflorescence. When these salts are present just beneath the surface they can exert pressure which in turn causes spalling or surface crumbling. The best way to avoid this type of damage is to prevent the movement of water through masonry.
To add to the deterioration problem, chemical corrosion is becoming more common throughout the country. Sulfuric acid mixed with dust, soot and moisture corrodes masonry surfaces by reacting with the binders in mortars and concrete forming a destructive gypsum that can be seen on buildings and statues. In addition, when surfaces are continually exposed to dampness they are prone to attack by moss and microorganisms.
An increased awareness of these factors has prompted considerable research into the causes and prevention of water damage in masonry structures. Recent studies indicate that most leaks in brick masonry occur at the intersection of the brick and mortar, particularly at head joints and bed joints. Head joints are the vertical joints, sometimes called "T" joints, between bricks. Bed joints are the horizontal joints that are formed between layers of brick. These joints need to be completely filled in order to maintain good resistance to water penetration.
Although excellent construction and workmanship are the ideal, in the field you often encounter chimneys that are poorly constructed, bricks in various stages of deterioration, and partially filled mortar joints. Because most leaks occur at the interface of brick and mortar it is essential to repoint these joints with a compatible mortar mix using a recommended tooling technique.
Joints with missing mortar should be filled before applying any water repellent. Sections where more than an inch of mortar in depth is missing should be filled first. An effective method of filling these deep joints is to compact new layers of mortar, allowing some drying time between layers. Setting time can be somewhat controlled by wetting the brick and old mortar before filling the joint. It is important to avoid too much water in the joints which can cause excess shrinkage and delay the final tooling. On the other hand, if the joint is too dry, water from the mortar can be absorbed into surrounding masonry which may prevent the joint from setting properly. This not only reduces bond strength, it increases the likelihood that the joint will leak.
Permeability is influenced by numerous factors including the composition and surface texture of the masonry, as well as the composition of the mortar. For instance, type N mortar is recommended by the Brick Institute of America (BIA) for above grade exterior structures, such as chimneys and parapet walls, that are subjected to severe weathering conditions. Yet even though type N mortar mixtures containing equal parts of cement and lime are still recommended, it is now recognized that mortar with a slightly higher concentration of lime is preferable for these severely exposed structures. The higher lime content appears to provide better resistance to water permeability. Properly tooling the finished joint affects the appearance and the effectiveness of the repair. A uniform color match with the existing mortar is affected by the composition and moisture content of the newly placed mortar which should be allowed to set to thumbprint firmness before final tooling. If the mortar is too soft the joint will appear lighter than surrounding mortar and be subject to hairline shrinkage cracks.
Finish tooling mortar that is too firm may result in dark streaks and poor bond interface between the brick and mortar. The BIA recommends that only concave, v-shaped or compacted grapevine mortar joints be used for exterior masonry work because these methods compress the mortar to achieve a better bond with the brick. In addition, weathered joints are also commonly recognized as acceptable for exterior use. None of these joints tend to collect water and therefore provide better rain resistance than flush, struck, raked or extruded joints which are acceptable for interior applications.
VARIOUS TEST METHODS
There are a variety of tests used to analyze masonry wall systems in reference to levels of water penetration. Testing agencies can be hired to perform certain tests but they can cost up to $1,000 a day. The following group of tests differ in terms of cost, ease of performance, and reliability, but they are some of the more common testing methods in use today.
Plastic Test
This simple test is used to determine if a moisture problem is being caused, or contributed to, by interior moisture or condensation. Begin by duct taping a clear plastic sheet to an exterior wall section. Check the sheet in a day or two; any moisture that collects on the inside of the sheet or wall is most likely condensation, caused by interior sources.
ASTM E 514 Test
The ASTM E 514 was originally developed by the American Society for Testing and Materials as a laboratory test method to determine the resistance to water penetration and leakage through masonry subjected to wind-driven rain. This test is also used to evaluate the design and workmanship of a given wall system, as well as the degree of weathering to which it has been exposed. An alternative to the laboratory method, the modified ASTM E514 was developed for field use on existing walls. It involves constructing a three by four foot test chamber that is mounted and sealed to an existing masonry wall to measure the amount of water that leaks into the wall. Water is pumped from a tank to a spray bar mounted in the chamber, sprayed at a controlled rate, and pressurized to simulate driving rain. Water readings are taken every half hour up to a period of up to eight hours until two consecutive readings are obtained. Leakage rates up to a half gallon per 12 square feet per hour are generally considered acceptable. The problem is that this test requires considerable setup time, is expensive to execute, and takes nearly a day to perform.
Spray Test
This simple test is performed by spraying a masonry surface with a garden hose equipped with a calibrated nozzle. The test often covers an area five to ten feet wide and simulates exposure to wind driven rains of various intensity. Interior walls are periodically checked for water leaks during the test which can be completed in about an hour.
GWT Test
Germann's Water Permeability testing device (GWT) is designed to measure permeability, surface porosity and initial rate of absorption (IRA). The device is attached to a masonry wall by metal anchors that are drilled into the joints. Water is pumped into the device and then forced into the wall at a specific pressure for a period of about 55 minutes at which time the chamber pressure must be released and refilled. The quality of mortar joints can easily be determined with this method as the weaker, poor quality joints will take on water much faster. Although a number of tests can be performed within a day, it does require considerable time and effort to drill into the masonry to anchor the device. In addition, the drilling process tends to destroy bonding and increase permeability.
Tube Test (Masonry Absorption Test)
Calibrated test tubes originally developed by the European organization, RILEM, measure the amount of water absorbed into a surface over a specific period of time. The amount of absorption depends on wind speed and the composition, as well as the condition, of the masonry. Concrete, limestone, and brick for example have different pore sizes and will absorb water at different rates simply due to their varying structures. Constants for these various types of masonry have been established which indicate that certain types of masonry are more inclined to absorb and distribute water throughout a structure. Two types of reusable test tubes were designed so that both horizontal and vertical surfaces could be tested for water permeability.
The purpose of the tubes is to detect leaks, predict vulnerability to water damage, diagnose water penetration problems, and determine the effectiveness of a water repellent treatment. The tube used to test vertical surfaces is pipe shaped with a circular brim at its base. Putty is wrapped around the brim and the tube is then p reused to the masonry unit and filled with five milliliters of water, which when full roughly corresponds to a wind pressure of 89 miles per hour. The amount of water absorbed is checked at five minute intervals up to 30 minutes or longer and may be recorded in simple graph form. Note that absorption rates for brick, concrete, and other masonry units will vary considerably depending on how porous they are. Most untreated mortar joints will absorb five milliliters of water in 15-25 minutes, but serious problems are indicated if all five milliliters of water are absorbed in less than five minutes. However, the same surface properly treated with a water repellent will absorb significantly less water over much longer periods of time.
One of the chief advantages of the absorption tubes is that they serve as inexpensive diagnostic tools for field testing. They are useful for detecting potential vulnerability to water penetration, which often results in spalling and deteriorated mortar joints. Readings obtained during testing on questionable areas can then be graphed and compared to values obtained fromareas that have been protected from weathering, such as under the eaves. In this way, for a customer's benefit, a standard of comparison can be created on an individual job basis by comparing problem areas with weathertight areas on the same job.
For example, the comparison chart on the left, is a graph of the average time in which five milliliters of water were absorbed into four by six laboratory test panels at each location type including leaking joints, bed joints, and top, bottom, and middle head joints. The test panels were built by journeyman masons according to BIA's "Construction of Brick Masonry" recommendations. Conditions were controlled in an attempt to build the most watertight single width wall panels possible. On each supposedly "perfect" wall panel there were several leak points where water actually flowed through to the back side during testing.
For this reason it is important to perform tests at each location type since different locations in the same wall system will have different leakage rates. Another factor to consider is that the test tube has a fluctuating pressure as the water is absorbed into the masonry unit with the greatest pressure being exerted when the tube is filled. In fact, the variability of pressure as the tube is emptied was an initial objection to the test tube method. But recent research indicates that this may actually be an advantage in that is more closely resembles the variability of gusting, wind driven rains. The values obtained in the comparison chart are simply averages that relate to the test panels used in that series of experiments. However, research is being conducted to establish standards, or average values, that will make the data obtained from absorption tube testing even more useful. It is possible that standards can be determined that will correlate absorption tube testing with ASTM E514 testing.
In the meantime, the tube is simple, inexpensive, and well suited for laboratory and field use. The advantages of this type of testing device are numerous. A masonry unit, such as a chimney or a parapet wall, can be analyzed to determine where, and how much water is being absorbed. For example, the photo at the right illustrates the wetting pattern on the front face of a laboratory test panel to which a vertical tube had been attached at the bottom of a head joint. Notice how the area at the base of the tube darkened as water was absorbed into the brick and mortar. A photo of the back side fot the same panel was taken later on in the test. Water was actually running down the backside at the bottom of the head joint where the tube was attached on the other side.
But even though most leak points occur at the head joint, they can occur wherever there is a poor bond between the brick and mortar. In most cases it is best to test several joint locations, as well as the masonry surface itself. Once necessary tuckpointing, waterproofing, and other repairs are completed, retesting can establish their effectiveness. In order to accurately compare the readings obtained from masonry surface before and after treatment with a water repellent, it is important to record the exact location of the tube and use the same location for further testing after the surface has been treated.
Preventing leaks in masonry wall systems depends on proper design, quality of materials, workmanship, and maintenance. Part of that maintenance includes treatment with an appropriate water repellent because moisture is a prerequisite for most of the deterioration that occurs in masonry. To prolong the life of masonry it is important to use a water repellent that penetrates, rather than seals, the surface. In fact, it is better to leave a masonry surface untreated than to treat it with a product that will seal in moisture. By itself a water repellent cannot prevent water penetration that results from poor construction for careless maintenance. This is why diagnostic tools like the masonry absorption tubes are being developed to help determine how absorbent a masonry surface is, and whether the problem is with the masonry, the mortar joints, or both. Only proper and timely maintenance of masonry structures will prevent the costly damage that results from water penetration.
Efflorescence is a crystalline deposit of water-soluble salts (usually white) on the surface of masonry. All masonry materials are susceptible to efflorescence. Water-soluble salts that appear in chemical analysis in only a few tenths of one percent are sufficient to cause efflorescence on a masonry surface. The amount of salts and character of the deposits can vary widely, according to the nature of the soluble materials present and atmospheric conditions. Temperature, humidity, and wind affect efflorescence. In the summer, even after long rainy periods, moisture evaporates quickly and small amounts of salt or efflorescence are brought to the surface. Usually efflorescence is more common in the winter, when the slow rate of evaporation allows the migration of salts to the surface.
Efflorescence that occurs on new construction after the masonry dries is referred to as "new building bloom". New building bloom is generally an unsightly nuisance and no cause for concern, as it will normally weather off within a few months to a year. Efflorescence that persists in masonry walls and chimneys generally means that excess moisture is entering the system and (if not remedied) is a precursor to more serious damage.
Efflorescence producing salts are usually sulfates of sodium, potassium, magnesium, calcium, and occasionally iron and/or carbonates of sodium, potassium, and calcium. There have been over twenty different compounds identified as crystalline deposits on masonry walls. In mortar and concrete, the hydrated cement contains some calcium hydroxide (soluble) as an inevitable product of the reaction between cement and water. When this calcium hydroxide is brought to the surface by water and combined with carbon dioxide in the atmosphere it forms calcium carbonate, which appears as a whitish deposit. Some minerals such as vanadium, molybdenum and magnesium compounds, present in some ceramic units, may produce a greenish deposit, commonly referred to as "green stain". Occasionally, " brown stain" may occur, resulting from the deposits of manganese compounds.
Cause and Conditions
Three conditions must exist before efflorescence will occur. First, there must be water-soluble salts present somewhere in the wall. Secondly, there must be sufficient moisture in the masonry to render the salts into a soluble solution. Thirdly, there must be a path for the soluble salts to migrate through the surface where the moisture can evaporate, deposit the salts and then crystallize. If any of these conditions is not present, efflorescence cannot occur.
Prevention
Little can be done about the mineral make up or the path soluble salts may travel through an existing masonry wall. Solutions to solving efflorescence problems should focus on eliminating the source of moisture into the structure. In chimneys there are three major sources of moisture. Rainwater is the primary source of moisture that causes efflorescence in masonry chimneys; the problem is often compounded by cracks in the crown, mortar joints or masonry units. Poorly bonded or improperly filled mortar joints and faulty flashing are common sources of rainwater penetration as well. Another source of moisture that commonly occurs in masonry chimneys is condensation.
Water vapor, a natural byproduct of the combustion process, can often migrate through a system and condense within the wall. This is especially true in improperly vented high-efficiency gas furnaces in masonry chimneys and masonry chimneys with large chase areas. A third and often-overlooked source of moisture that can occur in masonry chimneys is groundwater. During heavy rains the water table may coincide with the ground surface. If the fireplace or chimney foundation does not have an adequate moisture barrier, moisture can be wicked up through the masonry by way of capillary suction. The cause of the moisture must be determined and corrective measures taken to keep water out of the chimney.
Removal Techniques
Because moisture causes efflorescence it is generally best to remove efflorescence by dry methods such as brushing, vacuuming or light sand blasting. If dry removal methods are unsatisfactory, it may be necessary to wash the surface with a diluted muriatic acid solution: generally 12 parts water to 1 part commercially available muriatic acid. (Caution: acid resistant gloves, splash goggles and other protective clothing should be worn when using any chemical solution. Precautions on label should be observed because many chemicals can affect the eyes, skin and breathing). For integrally colored concrete masonry units or mortar, a more dilute solution (15:1) may be necessary to prevent surface etching that may reveal the aggregate and change colors and textures.
Before using any chemical to clean masonry, it should be tested in a small, inconspicuous area to be certain that there will be no adverse effect. When using any chemical cleaning compounds flood the surface with clean water to prevent the chemical from being absorbed deeply in the masonry work causing damage. Application should be to a small area, not more than three or four square feet at a time. Wait about five minutes before scouring off the salt with a stiff non-metallic brush.
Immediately and thoroughly flush with clean water to remove all acid. Since an acid treatment may slightly change the appearance of treated areas, it is generally best to wash the entire chimney to avoid discoloration or mottling. Green stains, which more commonly occur on buff or gray brick from vanadium or molybdenum compounds or brown salts from magnesium, should never be treated with an acid. Acids will react with these compounds and produce an insoluble brown stain or salt that is extremely difficult to remove.
To remove "green stain" dampen masonry with clean water, then wash in same manner as above with a solution of 1 part, by volume, sodium hydroxide crystals (lye) and 10 parts water and thoroughly rinse with water. If chemical and water washing must be used it is best to do this in the summer when the water will evaporate quickly and not cause additional efflorescence formations.
Efflorescence that is not the result of "new building bloom" is often a visible sign of excessive moisture in a chimney system. Chimney professionals should examine the chimney system closely and offer the appropriate corrective measures. Early detection and prevention of moisture sources that cause efflorescence can save homeowners hundreds or even thousands of dollars in future repairs.
