98 



it will extend from two or three feet l)elow the mud line to n point above high water. 

 The proportion of a pile which must be coated will therefore depend on the length 

 of piling required to get a good bearing, and the depth of the water. In soft bottom 

 in shallow water it may be necessary to protect but a short portion of the pile. The 

 cost per pile may then be quite low, although the cost per lineal foot treated is in 

 practically all cases higher than that of creosote treatment. 



The chief disadvantages of protections of this kind is the ease with which the 

 surface coat of paint may be destroj'ed and the battens exposed. Rubbing together 

 in the raft, careless handling and other mishaps during driving, or battering by drift- 

 wood during storms after the piles are in place may very easily scale off patches of 

 paint or even portions of the battens themselves and the materials beneath them. 

 Barnacles and mussels, developing in crevices and raising the covering are a contribut- 

 ing factor. When the battens are thus uncovered, borers attack in the bared spots, 

 enlarging the area, destroying the battens and exposing the material beneath. Ex- 

 perience seems to show that without the protection of battens the burlap and paint 

 coating underneath is soon destroyed . Wire mesh quickly fails from corrosion when 

 its bituminous covering is damaged. It is highly important therefore that piles pro- 

 tected by such coatings be handled and driven in such a manner as to cause the least 

 possible damage to the surface. No precautions, however, can relieve such piling from 

 the danger of storm battering. It has also been found that in many cases failure was 

 due to the exposure of unprotected wood as a result of the rotting and disintegration 

 of the burlap. This apparently is likely to happen much less quickly when the paint or 

 other compound is applied to the burlap cold than when it is applied hot. In the latter 

 case there is danger of the burlap being burned, and its rotting or disintegration is 

 hastened by the degree to which its fibres are thus injured. When hot asphaltic or 

 bituminous compounds are applied to w'et piling, as they often have been in some of 

 these processes, no sufficient adhesion is secured and they are in danger of peeling 

 ofi as soon as the surface is broken. 



A further factor affecting the \alue of these coatings, which is common to all 

 external coatings applied to only a part of the pile, is the danger of unprotected wood 

 being exposed to borer attack at the bottom. This may happen either by a mis- 

 calculation of the necessary length of driving, and therefore of protection, or by chang- 

 ing currents subsequently scouring the bottom away to a point below the protection. 

 The latter may easily occur without being obser^'ed and the untreated wood thus 

 exposed be damaged to a dangerous extent without warning. 



The Northwestern Pacific Railroad in 1920 installed about 250 piles protected by 

 the paint and batten process in a bridge trestle across Petaluma Creek under conditions 

 which illustrate the practical applicability of this type. These, briefly stated, were: 

 (1) lower initial cost as compared with creosoted piles; (2) possibility of salinity being 

 so reduced by a return of wet years, and increased fresh water flow, as to kill oft marine 

 pests; (3) possibility of structure becoming obsolete before the expected life of pile 

 would be reached; (4) sheltered location. 



DUR.\BILITY 



The records of the thirty years or more during which piling protected with paint 

 and batten coatings has been used in this region should give considerable information 

 as to their effectiveness. Unfortunately, however, most of the installations of piles of 

 this type which should give this information have been removed for other causes 

 than failure, without records being kept which would permit of adequately following 

 them up in new locations where many of them have been driven. Accurate data are 



