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Technical Information | Water Repellent Treatments

(Excerpted from Clear Water Repellent Treatments for Concrete Masonry, published by CMACN and MIA)

Desert Block Co., Inc. supplies this information as an educational aid in understanding the benefits of concrete masonry construction and our products. It is the responsibility of the user to obtain engineering or other advisory services from licensed professionals as the basis for incorporating into any project any information, detail, or product offered herein.

Recommendations and Guidelines

In 1992 the Concrete Masonry Association of California and Nevada (CMACN) and the Masonry Institute of America (MIA) held several meetings with masonry contractors, concrete block producers, water repellent treatment manufacturers, applicators, architects, and developers to discuss the proper design and construction methods to make concrete masonry buildings water resistant. Numerous recommendations and guidelines were developed including the following:

1. Pay particular attention to the design phase of the project. Limit horizontal projections, sills, and tops of walls and waterproof those required by the project design with elastomeric coatings. Give special attention to the design of parapets.

2. Cross reference the appropriate specifications sections in Division 4 on masonry construction (typically Section 04220 Concrete Unit Masonry) with those in Division 7 on water repellent treatments (typically Section 07180 Water Repellents).

3. Specify pre-installation meetings to familiarize all parties with the intended methods for prevention of water penetration. The masonry materials, construction, water repellent treatments, and treatment at joints should be discussed along with the expected results and testing procedures.

4. Encourage the use of samples and mockups of masonry construction with the proposed water repellent treatments. Test the mock-ups for water repellency. Mock-up panels should be a minimum 5 ft. by 5 ft. panel and testing should be for at least two hours. Control joints and joint sealants should be included in the mock-up. Tests should be based on the Navy Hose Stream test or a similar field hose stream test.

5. Ensure the use of full shoved head and bed joints (mortar for at least the thickness of the face shell of the masonry unit), if necessary through the use of third party inspections.

6. Specify double struck joints for exterior masonry construction. Require beeholes visible from 5 to 10 feet to be filled by a qualified mason prior to application of the water repellent treatment.

7. Fill cracks that exceed 0.02" in width or 5% of the joint length with mortar by a qualified mason or with joint sealer by a qualified applicator.

8. Apply water repellent treatments in strict accordance with the manufacturer's installation instructions and recommendations, by a trained experienced applicator.

9. Field test the concrete masonry walls after the water repellent treatment has cured to assure water repellency.

10. Require a ten year material and labor warranty from the manufacturer and the applicator through the general contractor.


Selecting concrete masonry as an integral part of the building's appearance provides numerous benefits for the designer and the owner. Where the gray color of standard cementitious products might provide a cold appearance, use of integral colors gives concrete masonry a warm appearance. The multitude of concrete masonry textures available provides an almost infinite variety of possibilities for building design. And, cost is typically competitive with other types of construction for many buildings.

Applying a clear water repellent treatment to concrete masonry can maintain the appearance of the concrete masonry while providing protection from water intrusion. Additionally, most clear water repellent treatments will keep the concrete masonry looking cleaner longer since a lower permeability prevents dirt from being drawn into the concrete masonry with the water.


Projections and Sills. The cells in concrete masonry construction, and the need to maintain alignment of the cells for reinforcing, limit the tendency of designers to create additional patterns by extending some units beyond the face of the wall. Although this process is possible with concrete masonry, the problems of increased water absorption and penetration through the exposed horizontal surfaces should be considered.

Most clear water repellent treatments are not designed to resist water penetration on horizontal masonry surfaces. Accordingly, ledges formed by projecting units out beyond the face of the wall should be either flashed with sheet metal or patched with an elastomeric coating (see Figure 1).

Figure 1: Ledge Detail

Sills provide a special challenge and proper design of sills at windows, louvers, and other openings is critical. Where possible, integral sills of window and louver units should extend beyond the face of the masonry unit. Where windows and louvers are recessed and sill extensions are not desired, special care needs to be taken to minimize potential water intrusion at the sill.

Dense, precast concrete sills, properly sloped and with drip edges, can provide an acceptable sill condition (see Figure 2). Masonry unit sills should also be coated with an elastomeric coating. Avoid mortar sills since they are porous and crack. If used, they should be covered with flashing or coated with an elastomeric coating to prevent water.

Figure 2: Sill Details

Copings, Parapets, and Tops of Walls. Masonry parapets require special attention during design and construction since they will be exposed to weather on both faces as well as on their tops.

Sheet metal caps can effectively resist water penetration through the tops of the parapets if the metal covers the entire top and extends at least two inches down over both faces of the masonry (see Figure 3).

Three inch extensions are preferred to allow for tolerances, and should be considered the minimum extension for split face and scored units. Four inch sheet metal cap extensions are preferred for fluted units to avoid winddriven rain being blown under the cap. Refer to the Sheet Metal and Air Conditioning Contractors' National Association (SMACNA) literature for proper design of sheet metal, including laps and weathertight installation.

Figure 3: Parapet Wall Details

Note that the recommendation is to extend the sheet metal cap two to four inches over the face of the unit, not to have only two inch to four inch legs on the metal cap. Where wood nailers are used and where the cap flashing is sloped to drain the water from the metal cap, the extension needs to be increased by the dimension of the nailer.

Extensions of the roofing cap sheets over the top of masonry parapets are not recommended. Roofing contractors tend to end the cap sheet several inches from the face of the masonry unit to prevent staining from the bituminous materials. This leaves several inches of the top of the masonry wall exposed. In addition, cap sheets tend to fishmouth due to expansion and contraction, allowing water to enter beneath the cap sheet. Sheet metal caps are therefore preferred.

If mortar caps are placed on top of parapets, they should be amply sloped so water will drain freely. They should also be painted with an elastomeric coating since mortar caps are prone to cracking. Similarly concrete masonry, precast concrete and stone copings should also be painted with an elastomeric coating due to the joints between the units.

Roof Flashing Connections to Concrete Masonry Walls. Counter flashing and base flashing are vital in resisting water penetration between roof structures and concrete masonry walls (see Figure 4). Consideration should be given so the wall strength is not adversely affected by extending the flashing too deeply into the mortar joints.

Figure 4: Base and Counter Flashing Systems

Control Joints. Proper design of all structures requires recognition of expansion, contraction, and building movement. In concrete masonry structures control joints are used to reduce cracking from these movements. Reinforcing required in seismic areas permit wider spacing of expansion and control joints in concrete masonry.

A control joint is recommended where an interior masonry wall intersects an exterior masonry wall unless the walls are designed to support each other. Control joints are also recommended: at large openings in concrete masonry walls; where there are major changes in concrete masonry wall heights; at changes in wall thickness; where there are control joints in foundations, floors, and roof construction; and in long runs of walls.

Where continuous horizontal steel reinforcing is required to extend through a control joint, sleeves can be placed over the reinforcing to allow the joints to move as designed. Nonstructural reinforcing may be cut at the control joints to allow less restricted movement at the joint (see Figure 5).

Recommendations vary regarding the appropriate location of joints in long, continuous masonry walls (see Table 1).

TABLE 1: Spacing of Control Joints for Concrete Masonry Units with Horizontal Reinforcing.

Recommended Spacing of Control Joints Recommended Spacing of Control Joints
Expressed as Ratio of Panel Length to Height. L/H
2 1/2
With Panel Length (L) not to Exceed
40 ft
45 ft
50 ft
60 ft

Figure 5: Control Joint Details

Wall Elevation 2

Section A-A: Typical Control Joint

Section A-A: Doweled Control Joint

1. Additional vertical bars on each side of all control joints.
2. Terminate all non-structural reinforcing 2" from control joints.
3. Provide 4'-0" long smooth dowels across the joint. Prevent bond between bar and grout with grease or a plastic sleeve. Cap all dowels to allow 1" of movement.

Section A-A: Control Joint Detail to Achieve a
4-hour Fire Rating
(Based on UBC Figure No. 43-9-M-2)

Wall Elevation 2

Section B-B: Wall Abutment Joint

Joint Sealer Detail

Penetrations. Openings throughout concrete masonry walls for scuppers, drains, plumbing, and electrical conduits must be properly flashed and sealed so that the wall can effectively resist moisture penetration. Proper installation of joint sealers around pipes and conduits is especially important since the sealer often serves as not only a moisture barrier but also a flame barrier.

Figure 6: Pipe Penetration Detail

Figure 7: Scupper Through Fascia with Conductor Head

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