392 



PRINCIPLES AND PRACTICE OF PRUNING 



When a block of cement has partially hardened, it will be nec- 

 essary to smooth carefully the outer surface or cut it down with 

 the rlat trowel to the level of the cambium, taking great care 

 that the latter is not injured in the operation. If the 

 cement is allowed to become too hard to trim with the trowel, it 

 can still, with more or less difficulty, be cut back to the cambium 

 line with a cold chisel and a hammer. It is a rule with most tree 

 surgeons to trim back the outer surface of the cement to l /s inch or 

 more below the cambium and then use a layer of stronger cement 

 (one part of cement to one to two of sand) to raise it to the level 

 of the cambium, after the rilling has partially hardened. 



The thinner mixtures of cement will set more firmly. If any 

 mixtures thinner than the one already mentioned are used to fill 

 a cavity, some sort of cloth or wire dam will have to be used to 

 hold the cement in place until it is hard. For this purpose strips 



of burlap wrapped tightly around the 

 tree so as to cover the lower part of 

 the opening may be sufficient if the 

 mixture is not rery thin ; otherwise, 

 a more closely woven fabric, such as 

 canvas or carpet, may be used. This 

 dam at first should cover about a 

 foot of the lower part of the open- 

 ing. The cavity may then be filled 

 with cement to the top of the dam. 



The top is smoothed and covered 

 with tarred paper, as already de- 

 scribed, the height of the clam is in- 

 creased and the operation repeated. 

 Before the cement has become too 

 hard, the dam is removed and the 

 surface of the cement finished in the 

 usual manner, either to the level of 

 the cambium at once, or it may be 

 cut a little farther back and a finish- 

 ing layer of stronger cement applied 

 to bring the surface to the proper 

 level. The surface of the cement 

 must be wet before the stronger finishing layer is applied. 



A very large proportion of the cemented cavities seen in trees at 

 present are made in one piece, without the use of tarred-paper 

 partitions. Long cavities of this sort are particularly subject to de- 

 fects, so one-piece fillings are not recommended except for short 

 cavities, where these particular objections do not apply. The method 

 employed is only a slight modification of that already described, 

 and will readily be understood by a study of Fig. 308 B, C, D, and 

 the legends which accompany them. These figures show successive 

 stages of work in the same cavity. 



FIG. 307 HOW NOT TO COVER 



A CAVITY WITH CEMENT 



OR CONCRETE 



