Masonry Magazine January 1984 Page. 35
Mud Screeds
Mud screeds are formed of mortar. They will be either spots or ribbons which are generally no further apart than the length of the straight edge being used. Spots or ribbons should be no further apart than the length of the straight edge being used. A spot screed is formed by placing a small amount of mortar at desired locations. The mortar is tamped down firmly with a float or heavy trowel to the proper height, and leveled off. A smooth, flat, hard material, such as a small piece of tile or brick, can be embedded in the screed for the straight edge to ride upon. The slope and elevation of the finished surface will determine setting bed thickness. Typically the bed is between 4" and 14" thick. Ribbon screeds are three to six inch wide strips of mortar between the dots which have been straight-edged off to the proper height of the setting bed. They act as guide rails for straight-edging the setting bed between them. Float strips, wood laths of 1" x 2" wood strips, may be embedded into the top of the screed to ensure that the straight edge rides true on the screed. Float strips are moistened before being embedded into the screed.
After the mud screeds have been established, the deck mud is shoveled into place between them, approximately three quarters to one inch higher than the screeds. It is then tamped down firmly with a float or trowel. After a section is tamped down, rod off the excess mud between the screeds with the straight-edge. The straight-edge is worked in a zig-zag, or "lazy-Z" fashion, first dragging one side forward, then reversing the procedure. Float in an area of setting bed that can be covered within about two to four hours. This time will vary greatly due to weather conditions, such as temperature, humidity and wind. After the setting bed is rodded off, remove the float strip and hard material in the dots. Fill the voids and float off even with the adjacent surface. Before setting any paving units, any control lines or expansion joint layout can be easily marked by using a chalk line and reel.
Setting Pavers
Pavers are not set directly on the mortar just laid down. Instead, another bond coat is used to bond them securely to the setting bed. One method of forming a bond coat is to sprinkle at least one-eighth inch of pure portland cement evenly on the surface. Use a water brush or fine mist to wet any cement that has not absorbed moisture from the setting bed. Another method of bonding the pavers to the setting bed is to trowel a water and cement slurry directly onto the bed using a " notched trowel. There are several methods which can be used to lay out and control proper alignment of pavers-the rack, a story pole and a layout with "legs."
Rack Method
When a rack is used, the pattern and layout is determined by the shape of the rack framework. A rack should be handled carefully so it does not get sprung out of square or shape. The rack's position on the deck mud is lined up by setting the edge of it to the chalk line drawn earlier. This corner serves as the starting point for the rack. The pavers are set into the rack slots. It is important that they are set to the same side and end of each space and all butted toward the same corner of the rack. When the rack is full the units are "beat in." Use a "two by four" or "two by six" block of wood, long enough to span 12" to 16". Place the block on the units and hit it sharply with a hammer. This is an important step, since it not only levels the units, but also forms a tight bond between them and the setting bed. It is a good practice to occasionally pick up a unit which has been set and "beat it" to check for proper coverage and bond. If the coverage and bond are adequate, the unit will pull up deck mud on its entire surface.
Pavers are then set into the rack slots. It is important that they are set to the same side and end of each space and all butted toward the same corner of the rack. After all paver units have been set into the rack and they have been "beat in," the rack is picked up and re-positioned for the next section. Each time the rack is re-positioned check for proper joint spacing between the rack edges and the installed pavers. Once its position is in proper alignment, the procedure is repeated. After the rack is re-moved, a straight edge can be used to make any final adjustments.
Story Pole
When using a story pole for layout and alignment control, lay out several rows of pavers dry to determine proper joint spacing. You will need to mark rows on the story pole and the units within a row on a straight edge. Using a pair of dividers (callipers) will eliminate the necessity for using the mason's rule to calculate inches and fractions when making both. Set the divers to the dimension of a unit plus one joint thickness. Beginning at one end of the straight edge or story pole, make a mark with the dividers and rotate them 180°. Continue to rotate the dividers the entire length making marks.
Units being laid on horizontal surfaces are commonly referred to as rows, unlike vertical brick and tile which are referred to as courses.