258 HARBOUR CONSTRUCTION. 



work, either Medina or Roman cement, or a mixture composed 

 of one part of Medina to one or two parts of Portland cement, 

 should be used in preference to plain Portland cement mortar, 

 all joints being pointed as quickly as possible with neat Medina 

 cement. 



The face-stones may be made of various thicknesses if 

 desired, so as to minimize the amount of rock cutting. Wlien 

 the setting of these has been satisfactorily accomplished, the 

 space between them may be filled with rich concrete of either 

 Portland or Roman cement, as the necessities of the case may 

 require, rough rubble stone being incorporated. 



The surface should then be carefully finished off, so as to 

 resist the fretting action of the waves when the tide reaches it. 1 

 I have found no system answer so well as that of roughly 

 pitching the whole surface with flat-topped stones of a size that 

 can be easily handled. These should be well worked down into 

 soft concrete, until the latter rises to within about half an inch 

 of their surface. The spaces between them should then be filled 

 with freshly mixed Medina cement mortar, trowelled over so as 



FIG. 79. System A. 



to render its surface as smooth and regular as possible. Abrupt 

 irregularities should be avoided, as they cause small eddies 

 and overfalls, which are very trying to the newly formed 

 skin. 



Work finished off in this manner, with due care, if allowed 

 from 10 to 15 minutes to harden before the tide reaches it, will 

 generally be found to stand well ; but in all such work there is 

 an element of sea-risk, proportionate to the exposure of the site, 

 which no amount of care can entirely eliminate. 



System B is similar to System A, excepting that the squared 

 stones are omitted, and the levelling of the rock surface is thus 

 rendered unnecessary. 



1 If good Roman cement concrete be used, it should be able to take care of itself. 



