MORTAR FOR BRICK MASONRY

Mortar is the bonding agent that integrates brick into a masonry wall. Mortar must be strong, durable, and capable of keeping the wall intact. In addition, it must help in creating a water resistant barrier and it must accommodate dimensional variations and physical properties of the brick when laid. Because concrete and mortar contain the same principal ingredients, it is often erroneously assumed that good concrete practice is also good mortar practice. In reality, mortar differs from concrete in working consistencies, methods of placement and structural performance. Mortar is used to bind masonry units into a single element, developing a complete, strong and durable bond. Concrete, however, is usually a structural element in itself. Mortar is usually placed between absorbent masonry units and loses water upon contact with the units. Concrete is usually placed in non-absorbent metal or wooden forms, which absorb little if any water. The importance of the water cement ratio for concrete is significant, whereas for mortar it is less important. Mortars have a high water cement ratio when mixed, but this ratio changes to a lower valve when the mortar comes in contact with the absorbent unit.

Historically, mortars have been made from a variety of materials. Burned gypsum and sand were used to make mortar in ancient Egypt, while lime and sand were used extensively in this country before the 1900’s. Currently, the basic dry ingredients for mortar include Portland cement, masonry cement, hydrated lime and sand. Each of these materials makes a definite contribution to mortar performance.

There are four general mortar types:

Type M. A high compressive strength mortar specifically recommended for masonry below grade and in contact with earth.

Type S. A mortar recommended for use in masonry where maximum flexural strength is required.

Type N. A medium strength mortar suitable for general use in exposed masonry above grade and specifically recommended for parapets, chimneys and exterior walls subjected to severe weathering conditions.

Type 0. A relatively low compressive strength mortar suitable for limited exterior use and general interior use in load bearing and non-load bearing masonry. Type 0 mortar should not be used where it will be subject to freezing in the presence of moisture.

No single type of mortar is best for all purposes. The basic rule for the selection of a mortar for a particular project is: Never use a mortar that is stronger (in compression) than is required by the structural requirements of the project.

Type N Portland cement-lime mortar is recommended for brick veneer, except that Type M Portland cement-lime mortar should be used for brick veneer below grade where the brickwork is in contact with earth. The Portland cement-lime mortar is recommended because they have a long history of proven performance in brick veneer construction.

MORTAR MIXING

Mortar is perhaps the last building material in history that is still manufactured at the project site. The following on site practices should be followed to insure the quality of mortar meets the required specifications:

1. Cementitious materials and aggregates shall be stored in such a manner as to prevent deterioration or contamination by foreign materials.

2. The method of measuring materials for the mortar used in construction shall be by either volume or weight, and such that the specified proportions of the mortar materials can be controlled and accurately maintained. Measurement of sand by shovel shall not be permitted. Table 1 list proportion requirements of the various mortar types. Note that a Type N masonry cement may be combined with Portland cement to produce Type S or Type M mortar.

3. All cementitious materials and aggregate shall be mixed for at least 3 minutes and not more than 5 minutes in a mechanical batch mixer, with the maximum amount of water to produce a workable consistency.

4. Mortars that have stiffened because of evaporation of water from the mortar may be retempered by adding water as frequently as needed to restore the required consistency. Mortars should be used and placed in final position within 2-1/2 hours after initial mixing.

5. When coloring mortar, use the minimum quantity of pigments that will produce the desired results; excess may seriously impair strength and durability. The maximum permissible quantity of most metallic oxide pigments is 10 percent of the cement content by weight. Although carbon black is a very effective coloring agent, it will greatly reduce mortar strength when used in greater proportions. Therefore, limit carbon black to 2 percent of the cement by weight.

BRICK CLEANING

The bucket and brush cleaning is the most widely used method of cleaning newly constructed brick walls in both small and large jobs. A minimum amount of equipment is needed and workmen do not need to he highly skilled. This method may be used for cleaning all colors and textures of brick. However, care must be used in selecting the proper cleaning solution for the job.
The safest way to determine the proper cleaning solution for a given type of brick is to ask the brick manufacturer for his recommendation. Listed below are some of the recommended commercial cleaning compounds:

Formulation of most commercial cleaners is so complicated that the users should rely on the chemical manufacturers’ recommendations as found on the containers and on the recommendations of the brick manufacturers.

The Detering Company DOES NOT recommend the uses of muriatic acid for the cleaning of any bricks lines they represent.

THE FOLLOWING PROCEDURES ARE RECOMMENDED FOR CLEANING BY THE BUCKET AND BRUSH METHOD:

1. Schedule cleaning at least seven days after the brick masonry is completed. Mortar must be thoroughly set and cured. Prolonged time periods between the completion of the masonry work and the actual cleaning should be avoided when possible.
2. Remove large mortar particles by hand with wooden paddles, non-metallic scrape hoes or chisels.
3. Protect metal, glass, wood, limestone and cast stone surfaces. Mask or otherwise protect windows, doors and ornamental trim from cleaning solutions.
4. Presoak or saturate the area to be cleaned. Flush with water from the top down. Saturated brick masonry will not absorb the cleaning solution or dissolved mortar particles. Areas below should also be saturated in order to prevent absorption of the run-off from above.
5. Starting at the top, apply the cleaning solution. Use a long handled stiff fiber brush or other type as recommended by the cleaning solution manufacturer. Allow the solution to remain on the brickwork 5 to 10 minutes. For proprietary compounds follow the manufacturer’s instructions for application and scrubbing. Wooden paddles or other non-metallic tools may be used to remove stubborn particles. Do not use metal scrapers or chisels. Metal marks will oxidize and cause staining.
6. Heat, direct sunlight, warm masonry and drying winds will affect the drying time and reaction rate of cleaning solutions. Ideally, the cleaning crew should be working on shaded areas to avoid rapid evaporation.
7. Rinse thoroughly!! Flush walls with large amounts of clean water from top to bottom before they can dry. Failure to completely flush the wall of cleaning solution and dissolve materials from top to bottom may result in the formation of “white scum”.
8. Work on a small area. The size of the ‘“wash down” area should be determined after a trial run. This will permit the cleaning crew to examine the work for initial results.