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 
