"Remember, in block work, when you cast brackets, dentils, coping, etc., with overhangs, that you can bed these blocks better if they arc made of such length that the center of gravity is a good distance from the edge of the masonry below. This costs very little more, and will enable you to bed these overhanging stones without weighting down the back, and will prevent excessive strain on the facing below the bed, which, as a rule, will not stand a concentrated pressure.
"Long, thin concrete blocks to be cast on the ground and set in place should be reinforced with steel so that they may be safely handled.
"On large work permitting the use of air tools, the concrete surfaces may be bush-hammered or crandalled at an actual cost of from 1 ct. to 3 cts. per sq. ft. Tooling a structure gives it a better appearance, removes form marks, lipping, and efflorescence. Efflorescence may be permanently removed in this way, provided, before its execution, the drainage of water which has been carrying the efflorescence to the face of the wall has been cut off.
"Large masses of concrete having cross-sections of over say 200 sq. ft. will frequently hair-crack when the concrete sets up. In using the word 'hair-crack' in this connection, I mean long, thin hair lines running ver tically up the face of the mass work, somtimes at inter vals of 10 and 20 ft. These hair lines are apparently independent of temperature, and are due to the concrete in the face of the mass work setting up before the inte rior. These hair lines are not seriously detrimental to the structure nor are they noticed by laymen. However, on a 'show job,' you may overcome this trouble by using a light reinforcing of expanded metal, wire mesh, or light rods, about 4 ins. from the face.
back of retaining walls which will hold water, you can't expect the waterproofing man to prevent seepage.
"Don't apply paper to vertical walls, as it frequently bulges, making pockets which hold water so that prac tically the water is forced through the wall. All that the back of a retaining wall properly built needs is a couple of coats of coal tar, which must be applied when the surface of the concrete adjacent to it is dry—not super ficially dry, but when the concrete is thoroughly set and the wall is dry for several inches in from the surface. Then place a light stone drain at the back of the wall as the back-filling is made. Then back up your weep holes with half a yard or more of broken stone; a handful of stone soon gets stopped up by silt.
"It is a common error in subway construction to take great care in waterproofing the roof, with often satis factory results, but to take no precautions to carry this water over the expansion joint at the abutments. This results in the water running off the roof and down the face of the abutments.
"In applying waterproofing on approximately hori zontal surfaces, apply the waterproofing in consecutive layers, after the method of shingling (the shingling should be done in the direction of the flow), and iron smooth upon the completion of these applications.
"Provide for expansion in retaining walls by using construction joints about every 50 ft. Provide for uncer tain foundations in a similar manner. Provide expan sion and construction joints over arches. Use expansion joints at the abutments over piers in such work, and construction joints on the haunches.
"If it is economical to use an arcade of spandrel arches resting on your main arches, run the axes of these spandrel arches longitudinally rather than transversely. Of course, this cannot be done if a vista is desired through the spandrel, or if, on account of freshet or other local causes, open spandrels are required. Longi tudinal spandrel arches are easier to construct, and simplify the expansion.
"If concrete piers are subjected to the impact of heavy floes of ice, they should be protected by a nosing of stone or iron.