REPAIR OF SHADE TREES 163 



two coats of coal tar over the shellac and creosote. If the 

 cavity is shallow and so shaped that it will drain water, 

 this treatment is all that will be necessary. It must be 

 borne in mind that water is the great enemy of wood, and 

 if the cavity is such as to permit the accumulation of 

 moisture, an opening should be made at the bottom to 

 allow any water to run out freely. 



A small cavity may be filled with cement mixed with 

 sand, in the proportion of two parts of sand to one part of 

 cement, and with enough water to make it plastic, or with 

 tar and sawdust. To hold this filling, the inner walls of the 

 cavity should be shaped in a way that will serve to anchor 

 the cement by giving it a foothold, just as a dentist cuts 

 grooves and angles into the walls of a tooth to hold a fill- 

 ing. If the opening is smaller than the interior of the 

 cavity, no particular anchorage is necessary, as the shape 

 of the cavity will hold the filling in place, but with a 

 cavity in which the opening is the largest part, a means of 

 holding the filling must be provided. One useful form of 

 anchor is made by cutting a deep groove in the wood 

 immediately inside the opening and encircling the edges. 

 This groove grips the cement and serves to hold it firmly 

 after the hardening process has taken place. If more 

 anchorage is necessary, it may be provided by means of 

 flat-headed wire nails or staples, half-way driven into the 

 walls, the projecting heads furnishing a grip for the 

 cement. 



In placing the cement use a trowel and a tamping 

 stick. The stick should be an inch or two in thickness and 

 two or three feet in length, or of such length as may be 

 best used in the cavity. After a two or three inch layer of 

 cement has been placed at the bottom of the cavity, the 

 material should be spread with the trowel and then com- 

 pacted by use of the tamping stick. This process should 



