WATERPROOFING BRIDGE FLOORS. 181 



I to the summit and exposing one-third of each width of burlap to the weather. Press each 

 ip firmly into the asphalt, then mop well with pure melted asphalt taking care to thoroughly 

 unite the burlap and to fill all cracks and blow holes. Lap the joints in the strips 6 in. On 

 this three-ply layer of burlap spread a continuous layer of hot asphalt mopping well until a layer 

 of I in. is obtained. See (f) Fig. 26. 



(4) Summit Joints. After the work has been brought up to the desired point from both 

 sides interl.ip in order the strips which reach across the joint, mopping asphalt between burlap 

 surfaces. Place a strip of burlap along the joint for a closing strip; and complete by laying the 

 UPJKT i in. of asphalt as before described. See (g) Fig. 26. 



(5) Longitudinal Joints. If possible the waterproofing should be laid in one run the full 

 idth transverse to the drain slope of the surface to be waterproofed. The ends of the burlap 

 rips should be (lashed into recesses in the walls, curbs or parapets as shown in (e) Fig. 26. Where 

 ngitudinal joints are necessary cut the burlap long enough to extend 12 in. beyond the primed 

 id asphalted surface of the concrete and use care as the strips are laid that the 12 in. strip is 

 pt free from asphalt. When the succeeding section is to be waterproofed fold back the projecting 

 rips of burlap over the completed waterproofing and bring the new up against the completed 



portion of the waterproofing, interlapping the projecting ends of the burlap with the new burlap 

 as the work progresses, (f) Fig. 26. On concrete trestle or subway slabs longitudinal joints in 

 the waterproofing should preferably be on the center line of the slabs. If it is necessary to place 

 joints in the waterproofing over joints in the slabs special care should be taken. 



(6) Expansion Joints. Lay two continuous strips of tar paper 36 in. wide over the expansion 

 joint, being careful to see that no asphalt gets between or under the two strips of tar paper. Then 

 mop the top strip with hot asphalt and carry the waterproofing over the top of the paper the 

 same as if no joint existed. See (b) and (h) Fig. 26. 



(7) Concrete Protection. After the i in. layer of asphalt on top of the burlap has become 

 cold, spread a f in. layer of concrete evenly over the surface. Then press a layer of expanded 

 metal into the concrete, and cover the metal with a layer of concrete i in. thick making the total 

 thickness of the concrete I J in., and trowel the concrete smooth. Protect the concrete from the 

 sun for 24 hours after laying. The joints in the expanded metal should be lapped 6 in. See (d) 



. 26. 



(8) Materials. Burlap. The burlap is to be treated 8 oz. open mesh furnished in widths 

 36 in. to 42 in. 



Concrete. The concrete is to be I part Portland cement, 2 parts torpedo sand, and 3 parts 

 >ne or gravel that will pass a i in. ring. 



Mortar. The mortar is to be I part Portland cement and 2 parts washed torpedo sand. 



Primer. The primer is made by pouring hot asphalt in 80 per cent gasolene until mixture 

 will spread readily with a brush. 



Asphalt. Pure asphalt conforming to accepted specifications is to be used. Before using 

 the asphalt heat it in a suitable kettle to a temperature not exceeding 450 F. The temperature 

 is to be taken with a thermometer. Asphalt heated above 450 degrees F. or giving off yellow 

 fumes is to be discarded as overheated. 



Expanded Metal. The expanded metal is to be equivalent to Northwestern Expanded 

 Metal Go's. "2j in. No. 16 Regular" expanded metal. 



Tar Paper. The tar paper will be furnished in rolls 36 in. wide. 



CHICAGO, BURLINGTON & QUINCY R. R. SPECIFICATIONS FOR WATERPROOF- 

 ING. The specifications of the Chicago, Burlington&Quincy R. R. for waterproofing are as follows: 



(1) Description. The waterproofing shall consist of a mat of 4-ply of burlap and i-ply of 

 felt thoroughly saturated and bonded together with waterproofing asphalt and covered with one 

 inch of sand and asphalt mastic. 



(2) Preparing the Surface. The surface of the concrete shall be smooth, clean and dry. 

 Upon this surface apply a coat of primer, which shall be thin enough to penetrate the concrete 

 and form an anchorage for the waterproofing. No waterproofing shall be done when the temperature 

 is less than 60 degrees F. 



(3) Applying the Burlap. After the priming coat has dried, a heavy coat of waterproofing 

 asphalt heated to a temperature of 400 degrees F. shall be applied with mops the width of the 

 burlap, and while the asphalt is still hot a layer of burlap shall be bedded in it. The burlap 

 shall be laid just behind the mopping and shall be swept free from folds and pockets with a broom. 

 The surface of the burlap shall be heavily mopped with waterproofing asphalt. Three more ply 

 of burlap shall be laid in the same manner, making a 4-ply burlap mat all thoroughly saturated 

 and bonded together. 



The top of the burlap mat shall be heavily mopped with asphalt and one layer of felt saturated 

 with asphalt shall be laid on the burlap and the edges of the felt lapped at least 3 inches and sealed 



f'i asphalt. The top of this felt shall also be mopped with waterproofing asphalt. 

 (4) Mastic Protection. The burlap and felt mat shall be covered with one inch of asphalt 

 tic laid in one layer, the mastic to be composed of one part waterproofing asphalt and four 



