Masonry Magazine September 1977 Page. 15
system, followed by 1/2 to 1-in. of sand in the joints formed by the grid members.
The required reinforcing steel is positioned according to the drawings and anchored in place. The grout core is then placed along with the second wythe of brick which is usually laid in mortar. After sufficient time has been allowed for setting and curing, the forms are stripped, the sand falls out, and all joints are tuckpointed from below (see Technical Notes 7, "Dampproofing and Waterproofing Masonry Walls").
Built-in-Place Brick Bonded to Concrete Slab.
Forms are constructed and a grid system is devised similar to the one described for built-in-place RBM soffits. Brick are then laid in place followed by 1/2-in. to 1-in. sand in all joints. There are two methods for bonding brick to concrete. One way is with metal ties, while another involves spreading a cement slurry over the brick just prior to pobring the slab. Where die skin or heavily sanded brick are used, a mechanical bond with corrosion-resistant metal ties is desirable.
Ties may be those used in cavity wall construction, such as 3/16-in. Z or rectangular shape, of required length spaced as required to carry the soffit units.
When metal ties are used, the joints are grouted and the ties are shoved into the joint as the wet grout is placed. The required reinforcing steel is anchored in place after the brickwork has received initial set. The slab of concrete is then placed and cured. The form should remain in place as required for strength development of the concrete (see ACI 318-63). After the forms are stripped, the sand falls out and all joints are tuckpointed from below.
Where there is difficulty in developing good tensile bond, the use of metal ties is necessitated. However, soffit brick can be bonded to concrete without metal ties as long as the brick have a surface which will bond well (see discussion under "Masonry Units"). A method of bonding brick and concrete is to utilize a cement slurry which is placed over the brick to a depth of 1/2-in. to 3/4 in. just prior to placing the concrete slab. The portland cement slurry should be mixed with sufficient water so it will easily flow and remain fluid during placement of concrete. Units with suctions above 20 g should be wetted to reduce the suction to less than 20 g prior to placement of the slurry. It is recommended that the joints be partially filled with sand prior to slurry placement and then tuckpointed from below after the forms are removed.
Precast and Prebuilt Reinforced Brick Masonry.
Precast RBM brick soffits may be produced either at the job site or a plant. The prime advantage for either method is ground level fabrication in reuseable forms or beds. Ideal curing conditions can be maintained as well as better control over workmanship.
Some RBM soffits can be advantageously built by masons, as they would build a wall, and then tilted or lifted into place. Where required, joint reinforcement and, in some cases, reinforcement threaded through brick cores can be placed by the masons as they prebuild the soffits.
Precast Brick Bonded to Concrete Slab.
This type of soffit can also be built either at the job site or at a plant. The construction as discussed for "Built-in-Place Brick Bonded to Concrete Slab" soffits, pertains to this type of precast soffit as may the discussion on prebuilt RBM soffits. The main difference is the location and position of the forms which are generally placed horizontally on the ground for easy access or, in the case of prebuilt RBM soffits, the prebuilt section would be tilted to a horizontal position and a concrete slab cast on the back of the prebuilt brick section.
Brick Adhered to Support with Adhesives.
Epoxy adhesives have also been used to adhere brick to steel and concrete structural members. If adhesives are used, the manufacturer's instructions should be followed for best results. A publication by the American Concrete Institute, ACI publication SP - 21, "Epoxies with Concrete", may be useful in designing and specifying this particular application. After the brick units have properly set for sufficient time, the joints may be tuckpointed with mortar to match the surrounding walls.
CONCLUSION
Several methods of constructing brick soffits are discussed in this issue of Technical Notes. Each type discussed has its own merits and drawbacks. The method selected for a particular project or application should be one that is suited to the design and construction scheduling for the project. As brick soffits are more widely used, other methods of construction will be developed. These new methods may be evaluated by the procedures outlined in this Technical Notes.