elbow to the riser pipe, by the beginning of the metal lining plates in the 7-foot 7-inch diameter tunnel to the farthest downstream valve in this upper tier, and further limited in the vicinity of the other three 7-foot 7-inch diameter diverting outlet tunnels by the theoretical excavation surfaces in the main penstock tunnel, as determined by the specified average thicknesses of the concrete. It also includes the corresponding concrete lining for the upper tier of valves in the horizontal section above the 15-foot 9-inch riser shaft from the 50-foot inner diversion tunnel, and the corresponding concrete in the horizontal section for the lower tier of valves, except that the limiting vertical plane passes in this case through the point of tangency with the elbow to the 24-foot 3-inch diameter riser pipe. 128. Concrete in linings of shafts for outlet works and connecting galleries.—The item of the schedule, “Concrete in linings of shafts for outlet works and connecting galleries,” includes all concrete in the 24-foot 3-inch diameter riser shafts from the inner diversion tunnels and in the 15-foot 9-inch diameter riser shafts, as limited by the descriptions of other items of concrete in paragraphs 118 and 127. It also includes all concrete in the elevator shafts for the canyon wall outlet works and the adits leading to these elevators from the lower canyon wall outlet works and from the power house, as limited by the concrete in the walls of the upper canyon wall valve houses and in the walls of the power house. It also includes all concrete in the adits from the downstream inner diversion tunnel plugs to the elevators for the canyon wall outlet works. 129. Concrete in canyon-wall outlet works,—The item of the schedule, “Concrete in canyon-wall outlet works,” includes all concrete in both the upper and lower canyon-wall valve houses, including concrete around slide gates and needle valves, and all concrete in the 7-foot 7-inch diameter tunnels leading directly to the slide gates and valves, as limited by the description of the concrete in outlet and penstock tunnels as given in paragraph 127. In constructing the valve houses, special care shall be used to insure a high quality of workmanship, accurate dimensions, and strict adherence to alignment and grade, and no irregularities in alignment due to inaccurate finishing of surfaces, bulging of forms, or other defects will be permitted. 130. Concrete in intake towers, foundations, and superstructure.-The item of the schedule, “Concrete in intake towers, foundations, and superstructure,” includes all concrete in the towers and the foundations thereof above the inlets to the 30-foot diameter outlet and penstock tunnels, all concrete in the gate houses, parapets, and other features on top of the towers, and in the seats to serve as supports for the movable ends of the intake tower bridges. Extreme care shall be taken by the contractor to construct all parts of the intake towers, including the gate houses on top, accurately to the lines and dimensions as shown on the drawings or directed by the contracting officer. No irregularities in alignment due to inaccurate finishing of surfaces, bulging of forms, or other defects will be permitted. All anchor bolts, gate guides and seats, and other metal parts to be embedded in concrete shall be carefully cleaned and firmly and accurately anchored in place before the placing of concrete. Uniting of the outside surface of the towers below the elevation of the gate-house floors shall be done by the contractor under the provisions of paragraph 136. 131. Concrete in bridges to intake towers.-After the structural steel through plate girder bridges from the top of the dam to the downstream intake towers and from the latter to the upstream intake towers have been completed and all supports removed, they shall be partly encased in concrete, as shown on the drawings or as directed by the contracting officer. Prior to placing concrete, all parts of the structural steel to be in contact with the concrete covering shall be thoroughly cleaned of all paint, rust, scale, and other loose particles which might interfere in any way with an effective bond between the steel and the concrete. Should any reinforcement fabric or metal lath be used in addition to bar reinforcement, as determined by the contracting officer, in the concrete covering these bridges, these materials will be furnished by the Government under the provisions of paragraph 27. Payment for placing reinforcement fabric or metal lath, if required, in the concrete of these bridges will be made at the unit price bid in the schedule for placing reinforcement bars and rails. The item of the schedule, “Concrete in bridges to intake towers,” includes all concrete in each bridge between the fixed and movable end. 132. Concrete in power house and penstocks,—For the purposes of payment the concrete in the power house and penstocks is separated into two items in the schedule; viz., “Concrete in power house above generator floor,” and “Concrete in power house below generator floor and in penstocks.” The first item is self-explanatory but includes, in addition to the concrete in columns, walls, and other members of the building, concrete in pedestals, anchors, and foundations for machinery. The second item includes, in addition to all the concrete in the power house and concrete anchors and foundations for machinery below the elevation of the generator floor, all concrete in the power penstocks from their diversions from the inner diversion tunnels and the penstock tunnels, as limited by the description of other concrete items in paragraphs 118 and 127, respectively. The concrete in both of the above items is limited or bounded upstream by the theoretical downstream face of the dam. In constructing the power house, exceptional care shall be used to insure high quality of workmanship, accurate dimensions, and strict adherence to alignment and grade, and no irregularities in alignment due to inaccurate finishing of surfaces, bulging of forms, or other defects will be permitted. It is contemplated that the parapets and other parts may be required to be specially finished, as provided in paragraph 123. - . 133. Concrete for switching station and steel tower footings.-The item of the schedule, “Concrete in switching station and steel tower footings,” includes all concrete for the footings of structural steel switch structures, bases for mounting oil circuit breakers, and other apparatus as may be required for the switching station, and also includes all concrete in footings for steel towers which will support the transmission lines from the power house to the switching station. The switching station shall be located as shown on the drawings or as directed by the contracting officer. The footings for the transmission line steel towers are not shown on the drawings, but shall be constructed at the locations, and to the lines, grades, and dimensions as directed by the contracting officer. The steel towers will be erected by the Government. 134. Concrete in inclined freight elevator structures.-The item of the schedule, “Concrete in inclined freight elevator structures,” includes all concrete in the guide structure for the elevator, loading and unloading platforms, the foundation for the spur track from the bottom of the elevator to the power house and the concrete in the hoist house, and any other concrete that may be required to be placed, as determined by the contracting officer, for permanent construction of the inclined freight elevator. The sections of the guide structure and spur track foundation shall be as shown on the drawings or directed by the contracting officer. 135. Concrete in highway structures,—The concrete in all highway structures, including parapets, retaining walls, collars, and headwalls for corrugated metal culverts, and in a reinforced concrete arch culvert, if required, shall conform to the requirements of paragraphs 96 to 112, inclusive, and of paragraph 114, where applicable, as determined by the contracting officer. Measurement for payment and the costs to be included in the price bid for concrete in highway structures shall conform to the provisions of paragraphs 111, 112, and 114. 136. Gunite surfacing on concrete.—The entire upstream face of the dam up to the bottom of the coping, the outside surface of the intake towers up to the elevation of the gate house floor and the upstream face of all plugs in the inner diversion tunnels, shall be surfaced with gunite placed as shown on the drawings or as directed by the contracting officer. Unless otherwise directed by the contracting officer, the total thickness of the completed surfacing shall be 1 inch, measured normal to the exposed surface. The gunite surfacing shall be continuous without construction joints, except as otherwise provided in this paragraph. Gunite shall usually be a mixture of 1 part cement by volume, measured loose with 3 parts of sand, but the relative proportions of sand and cement used will be subject to change by the contracting officer as the materials used or results obtained indicate desirable at any time during the progress of the work, and the contractor will not be entitled to any additional compensation by reason of such changes. The sand and cement shall be thoroughly mixed in a relatively dry state before being placed in the gunite machine or its hopper. Machine mixing will be required unless specific authority to use hand mixing is given by the contracting officer. The machine and its operation shall be subject to the approval of the contracting officer. The mixing operation shall continue for a period of not less than one minute after all sand and cement are placed in the mixer. If there is an excessive amount of moisture in the sand, the sand shall be dried before mixing or it shall be mixed with the cement immediately before placing in the hopper, to insure that partial setting of the cement has not taken place. Cement for gunite will be furnished to the contractor by the Government, as provided in paragraph 27 . The requirements for cement for use in gunite shall be the same as those for cement for concrete, as given in paragraph 97. Sand for gunite shall be furnished by the contractor and shall meet the requirements of paragraph 98. In placing gunite the contractor shall employ as foremen and nozzlemen only men who can show to the satisfaction of the contracting officer that they have been employed in a similar capacity on at least two other similar jobs, and that they are fully qualified to do the work properly and carry out the terms of these specifications. Gunite shall be placed with the machines operating at an air pressure of not less than 35 pounds per square inch and a water pressure of not less than 50 pounds per square inch. In case of increase of air pressure, the water pressure shall be increased proportionately. Care shall be taken by the nozzlemen to direct the line of flowing material as nearly normal to the surface being covered as possible, and the nozzle shall generally be held about 3 feet and not more than 5 feet from the surface. The nozzlemen shall also take precaution to use only sufficient water necessary to properly hydrate the cement. Care shall be taken to prevent the occurrence of sand pockets, and if any should develop they shall be immediately cut out and replaced with perfect gunite at the expense of the contractor. No hand patching will be allowed. The gunite shall be applied in a continuous sheet for the full length of section in lifts approximately equal in height to the lifts of concrete. The joints of the gunite surfacing for the dam at the radial contraction joints and at the top and bottom edges of each lift shall be as shown on the drawings or as directed by the contracting officer. The contractor shall apply the surfacing in such a manner that no sloughing of the gunite occurs at any time during or following its application. If the required total thickness of surfacing is built up by layers, the intervening time between the application of each layer shall not be such as to permit the gunite to take a permanent set. When, for any reason, it is necessary to interrupt the placing of gunite for a sufficient length of time to permit the gunite taking a permanent set, thereby forming a definite construction joint, the contractor shall cut back the irregular edges of the gunite last placed with a trowel or other suitable tool to a clean unbroken surface perpendicular to the face of the dam or intake tower, such as will provide a suitable connection or construction joint between such gunite and the gunite to be subsequently placed. Care shall be taken in performing this work not to shatter the remaining gunite or to disturb or destroy the bond between the gunite and the concrete. Before gunite is placed against the surfaces of such joints, these surfaces shall be carefully cleaned and wetted by the contractor to insure a good bond between the fresh gunite and the gunite previously placed. Feather-edged construction joints will not be permitted. The contractor shall take such steps as the contracting officer may deem necessary to prevent injury to the completed gunite surfacing by particles of rebound from the guniting operations at higher elevations falling on such completed surfacing. The finished surfacing shall be free from cavities or angular projections and shall have a uniformity and Smoothness, as directed by the contracting officer. At the option of the contractor the gunite surfacing on the upstream face of the dam and on the intake towers may be placed from barges after storage of water in the reservoir is begun, but the Government assumes no responsibility for the rate of rise in the water level or for any interference with the guniting operations on this account, and permission to use this method will not relieve the contractor from the obligation to complete the gunite surfacing in full compliance with the specifications. Before placing the gunite the surface of the concrete shall be throughly cleaned and roughened by sand blasting or other methods, as directed by the contracting officer. The concrete surface shall then be thoroughly wetted immediately before the placing of the gunite. During the period immediately following the placing of the gunite, it shall be protected against injury by freezing, by waste water flowing down over the gunite, or from other causes which, in the opinion of the contracting officer, may result in a weakening of the bond between the gunite and the concrete. As soon as the gunite has hardened sufficiently, in the opinion of the contracting officer, it shall receive the same treatment and protection as specified for concrete, as provided in paragraph 108. No gunite surfacing shall be placed in freezing weather except with the approval of the contracting officer and then only under such restrictions and regulations as the contracting officer may prescribe. Any gunite damaged by freezing or otherwise before final acceptance shall be removed and replaced at the expense of the contractor. Measurement of gunite surfacing for payment will be made of the entire surface area of the completed surfacing. The unit of measure shown in the schedule is a square yard of surface area for gunite one (1) inch in thickness. No additional compensation will be paid for the slightly thicker gunite necessary at re-entrant angles. The contractor will be charged for any cement wasted due to improper mixing or other fault of the contractor. Payment for gunite will be made at the unit price per square yard bid in the schedule for 1-inch gunite surfacing on concrete, which unit price shall include the cost of furnishing all labor, machinery, tools, and materials, except cement, required in the preparation of the concrete to receive the gunite, and in mixing, placing, curing, and protecting the gunite until acceptance. The Government reserves the right to increase or decrease the thickness of all gunite surfacing, and no increase or reduction in payment shall be made on account of such changes, except that where thicknesses other than 1 inch are required the payment to be made therefor will be in direct proportion to the required * based on the unit price bid in the schedule for gunite surfacing on concrete, 1 inch thick. 137. Rough finish for tile floors.-The top of the concrete in all floors in the power house and such other structures as may be designated by the contracting officer shall be left approximately two and one-half (2%) inches below the finished floor elevation, unless otherwise directed by the contracting officer. When anchor bolts and pipes are placed, proper allowance shall be made for floor finish to be placed later. The type of floor finish has not yet been determined and Where a special finished floor is required, as determined by the contracting officer, such special finished floor will either be placed later by the Government or if required to be placed by the °ontractor will be ordered in writing by the contracting officer and paid for as extra work under the provisions of article 5 of the contract and paragraph 10 of these specifications.

138. Cement mortar finish for concrete floors.-Floor finish, consisting of mortar in the proportions of one part of cement to two parts of clean, well-graded sand which will pass a No. 8 sieve, shall be applied to all concrete floors in the outlet valve houses and such other structures as may be designated by the contracting officer, after the installation of machinery is completed. The top of the concrete shall be left approximately 3% inch below the finished floor elevation shown on the drawings, and allowance shall be made for this finish when anchor bolts, pipes, and other metal parts are placed. Before applying the floor finish the surface of the concrete shall be thoroughly washed and roughened. The finished surfaces shall be given a slope for drainage, as directed by the contracting officer. The floor finish shall be at least 3inch thick, and shall be brought to a true and even surface by means of a straight-edge and then carefully floated to close all voids and hollows. The surface shall be finished by sprinkling dry cement evenly over it by means of a fine sieve, after which it shall be carefully floated and troweled. A second steel troweling shall be given after the cement has set sufficiently to finish hard and smooth. The floors shall be marked into 30-inch squares by means of a small expansion joint tool or other means satisfactory to the contracting officer. Cement floor finish will be measured for payment to the required neat lines and all openings will be deducted. Payment for placing the 34-inch finish for concrete floors, as described in this paragraph, will be made at the unit price per square yard bid therefor in the schedule.

139. Thin walls of metal lath and plaster-Thin walls of metal lath and plaster having a finished thickness of approximately 3 inches shall be constructed in the power plant and other buildings where and as directed by the contracting officer. The framing shall consist of vertical steel channels spaced on about 24-inch centers, bent on each end and fastened to inserts in the floor and ceiling. Expanded metal lath sheets, similar or equal to Hy-rib, with the ribs in a horizontal position, shall be fastened to the vertical channels with soft iron wire ties at six-inch centers, and the ends of the sheets placed in grooves in the walls. All metal lath sheets shall start at the ceiling, be staggered with one another, and lap around corners. The laps at sides shall be formed by nesting outside ribs and the sheets shall lap not less than one inch at ends, The sheets shall be braced temporarily on the channel side at intervals not exceeding five feet vertically before the application of plaster. Grounds and bucks shall be set as directed by the contracting officer. The plastering shall first be applied on the side on which the expanded metal is fastened, with about 4 inch over the ribs, and pushed through to form a good key; and this operation shall be carried on continuously from the bottom up without allowing the plaster to dry at the edge. When this coat has set dry, a similar coat shall be applied on the other side of the partition with 4-inch covering over the vertical channels. To the materials for these first coats shall be added sufficient hair or fiber to bond the mortar. As soon as the first coat has become firm, but not fully dry or hard, the entire surface shall be cross scratched diagonally, Scratching shall be deep enough to provide good bond for the following plaster coat but not deep enough to injure the keys. Before applying the finish coat the plaster shall be wetted to saturation to prevent absorption of water from the fresh mortar. The finish coat shall then ho applied, using for this purpose one part of cement to two parts of fine sand with hydrated limo but without hair or fiber. The finish coat shall be troweled smooth with as little rubbing necessary to produce a workmanlike finish reasonably free from irregularities, and matching in color and texture the adjoining concrete walls to the satisfaction of the contracting officer The material composing the plaster shall be as follows: Portland cement, 1 part; sand, which is practically free from organic matter and uniformly graded in size from coarse to fine, all to po through a sieve having eight (8) meshes per inch for the ground coats and 12 meshes per inch for the finish coats, 3 parts; hydrated lime, which is uniform in quality and perfectly hydrated