Masonry Magazine June 1988 Page. 19
Projections
When a circular masonry wall is to be laid up in running bond the projections of the corners of units beyond the face of the units in the courses above and below may need to be limited for reasons of aesthetics. Generally projections of approximately 1/8 in. for nominal 8 in. long units and 1/4 in. for nominal 16 in. long units are acceptable.
If the surface of the wall is to be stuccoed or otherwise covered, projections of 1/2 in. to 3/4 in. may not be objectionable. However, if it is desirable to obtain a smooth appearance for the curve or limit the shadows created by the projected corners, the projections should not exceed those indicated above. Minimizing projections to less than 1/8 in. is usually not practical because of construction tolerances.
The projection of the corner of a unit beyond the faces of the units in the courses above and below in the previous example is found by the use of Equation 4.
p = (S1/4) Sin a
= (16/4) Sin (0.9375)
4(.01636)
0.065 inches
= 1/16 inch
The minimum radii, number of units and length of projection for circular concrete masonry walls using 3/8 in. and 1/2 in. wide exterior mortar joints are provided in Table 1 for units having a nominal length of 8 inches. Similar data for units having a nominal length of 16 inches are listed in Table 2.
TABLE 1. MINIMUM RADII NOMINAL
8 IN. LONG UNITS (UNCUT)
| Nominal Width (in.) | 3/8 in. Ext. Mortar Joint r (ft.-in.) | n | P (in.) | 1/2 in. Ext. Mortar Joint r (ft.-in.) | n | P (in.) |
|---|---|---|---|---|---|---|
| 4 | 9′-9″ | 92 | 1/16 | 6′-6" | 61 | 3/32 |
| 6 | 15′-1" | 142 | 1/16 | 10′-1" | 95 | 1/16 |
| 8 | 20'-4" | 192 | 1/32 | 13′-7″ | 128 | 1/16 |
| 10 | 25′-8 | 242 | 1/32 | 17′-2" | 162 | 1/32 |
| 12 | 31-1 | 293 | 1/32 | 20′-8" | 195 | 1/32 |
Interior Mortar Joints Maintained at Approximately 1/8 inch
TABLE 2. MINIMUM RADII NOMINAL
16 IN. LONG UNITS (UNCUT)
| Nominal Width (in.) | 3/8 in. Ext. Mortar Joint r (ft.-in.) | n | P (in.) | 1/2 in. Ext. Mortar Joint r (ft.-in.) | n | P (in.) |
|---|---|---|---|---|---|---|
| 4 | 19′-6" | 92 | 1/8 | 13′-1" | 61 | 7/32 |
| 6 | 30′-2" | 142 | 3.32 | 20'-4" | 95 | 1/8 |
| 8 | 40′-9″ | 192 | 1/16 | 27-5 | 128 | 3/32 |
| 10 | 51′-4" | 242 | 1/16 | 34′-8" | 162 | 3/32 |
| 12 | 62′-2" | 293 | 1/16 | 41'-9" | 195 | 1/16 |
Interior Mortar Joints Maintained at Approximately 1/8 inch
Likewise, data for units having 3/4 in. cuts on the interior face at one end only and at both ends are listed in Tables 3-4 and 5-6 respectively.
TABLE 3. MINIMUM RADII NOMINAL
8 IN. LONG UNITS
(3/4 in. Cuts Interior Face, One end only)
| Nominal Width (in.) | r (ft.-in.) | n | P (in.) | r (ft.-in.) | n | P (in.) |
|---|---|---|---|---|---|---|
| 4 | 2-5 | 23 | 9/32 | 2-3 | 21 | 5/16 |
| 6 | 3-10" | 36 | 3/16 | 3-5" | 32 | 3/16 |
| 8 | 51 | 48 | 1/8 | 47 | 43 | 5/32 |
| 10 | 6'6" | 61 | 3/32 | 5.9 | 54 | 1/8 |
| 12 | 7'-10" | 74 | 3/32 | 6-11 | 65 | 3/32 |
Interior Mortar Joints Maintained at Approximately 1/8 inch
TABLE 4. MINIMUM RADII NOMINAL
16 IN. LONG UNITS
(3/4 in. Cuts Interior Face, One End Only)
| Nominal Width (in.) | r (ft.-in.) | n | P (in.) | r (ft.-in.) | n | P (in.) |
|---|---|---|---|---|---|---|
| 4 | 4′-10" | 23 | 9/16 | 46" | 21 | 19/32 |
| 6 | 7-8 | 36 | 11/32 | 6-10 | 32 | 13/32 |
| 8 | 10' 2" | 48 | 1/4 | 92 | 43 | 5/16 |
| 10 | 12-11 | 61 | 3/16 | 17 | 54 | 1/4 |
| 12 | 5-8 | 74 | 3/16 | 13′-11 | 65 | 3/16 |
Interior Mortar Joints Maintained at Approximately 1/8 inch
TABLE 5. MINIMUM RADII NOMINAL
8 IN. LONG UNITS
(3/4 in. Cuts Interior Face, Both Ends)
| Nominal Width (in.) | r (ft.-in.) | n | P (in.) | r (ft.-in.) | n | P (in.) |
|---|---|---|---|---|---|---|
| 4 | 1′-6" | 14 | 7/16 | 1′-4" | 13 | 16/32 |
| 6 | 1-3 | 21 | 5/16 | 2′-1" | 20 | 5/16 |
| 8 | 3'-0" | 28 | 7/32 | 2'-9" | 26 | 1/4 |
| 10 | 3'-9 | 35 | 3/16 | 3'-6" | 33 | 3/16 |
| 12 | 4"-6" | 42 | 5/32 | 4′-3" | 40 | 5/32 |
Interior Mortar Joints Maintained at Approximately 1/18 inch
TABLE 6. MINIMUM RADII NOMINAL
16 IN. LONG UNITS
(3/4 in. Cuts Interior Face, Both Ends)
| Nominal Width (in.) | r (ft.-in.) | n | P (in.) | r (ft.-in.) | n | P (in.) |
|---|---|---|---|---|---|---|
| 4 | 2′-11" | 14 | 7/8 | 2'-9" | 13 | 15/16 |
| 6 | 4-5 | 21 | 19/32 | 4′-3" | 20 | 5/8 |
| 8 | 5′-11" | 28 | 7/16 | 5'-7" | 26 | 1/2 |
| 10 | 7-5 | 35 | 3/8 | 7′-0" | 33 | 3/8 |
| 12 | 8-11" | 42 | 5/16 | 8'-6" | 40 | 5/16 |
Interior Mortar Joints Maintained at Approximately 1/8 inch
Where projection length is a consideration, the minimum radii, number of units and cutting required to limit projections to 1/8 in. and 1/4 in. for nominal 8 inch and 16 inch long units, respectively, is listed in Table 7 and 8.