The mortar coat should be mixed rather dry; and should be troweled firmly to give a dense surface, but not so persistently as to disturb the initial set.
Finishing the Surface. There is a difference of opinion as to whether the surface should be considered finished when it has been troweled, or whether it should be afterwards brushed with a slightly wet brush. An ordinary flat paint brush, with extra heavy bristles, cut off about one inch below the wood portion, may be used for this purpose. The objections to the trowel-finished surface are that the trowel marks show more or less, and that the surface has a glaze or shine clearly indicating that the stone is artificial; while the brush finish has a uniform dull surface similar to a smoothly dressed natural stone. The objections to the brush finished surface are that the brush leaves a porous surface that is not so durable as a trowel-finished one, which objection has con siderable force if the surface is not first thoroughly troweled and if the brush is not used lightly. The less the troweling and the more the brushing, the mor3 rapidly the surface can be finished; and hence it is difficult when brushing is permitted to prevent the slighting of the work. Both methods of finishing are employed by competent engineers.
Recently a method of finishing by drawing a template over the curb and gutter has been introduced. The few trials made seem to show that this method is a little less expensive than fin ishing with a trowel, and that it gives a better general appear ance and a better alignment, particularly at the joints.
Cost. The cost will depend somewhat upon the price and the quantity of the labor and materials, but chiefly upon the pro portions of the mortar and the concrete. The amount of cement required will vary a little with the per cent of voids in the sand and gravel or broken stone, but will depend chiefly upon the pro portions of the mortar and the concrete. On three contracts for a total length of about 21 miles of the form of combined curb and gutter shown in Fig. 110, page 353, using gravel in the concrete, laid by two separate contractors, the length laid for each barrel of Portland cement was 13.4, 13.44, and 14 feet respectively. A
barrel of cement made enough 1 to 11 mortar for the surface coat on 33 linear feet.
A yard of gravel was required for each 33 lineal feet.
The amount of labor will vary a little with the amount of exca vation required and with the kind of forms employed. On two of the contracts referred to above, one contractor averaged 2.25 feet of completed curb and gutter per man per hour, while the other contractor averaged 2.56 feet per man per hour. The latter exca vated the trench by hand before the roadway was excavated, while the former excavated the roadway and the gutter with scrapers before commencing the construction of the curb and gutter. The curb was straight and practically continuous. The working force was usually divided about as follows: 1 foreman, 11 men wheeling and tamping cinders, 5 men setting formA, 24 men mixing and laying concrete, 2 men finishing, 3 assistant finishers.
The contract price for the curb and gutter referred to above was 48 cents per lineal foot, including the excavation and the back filling.
A concrete curb is suitable only for residence streets, but is more durable for a business street, than soft sandstone or lime stone.