In making repairs and renewals to timber bridges—and, in fact, all bridges—the bridge gangs formerly were usually equipped with only hand tools; but, now that the cost of labor is so much greater, it is economical to replace manual labor as far as possible with machines. A light derrick car equipped with a hoisting engine or a locomotive crane will save the work of many men in handling heavy bridge material. On timber structures a large part of the labor consists of boring holes for bolts and fastenings. Repair gangs should be equipped with boring machines operated by either air or electricity, in order to do this work economically. The magnitude of the task will determine whether machinery or hand labor is the more economical. On very small jobs it will be more costly to set up the equipment than it would be to do the work with hand tools; however, the tendency is to make more and more use of machines instead of manual labor.

The preservation of timber, in order to increase its life and reduce the necessary maintenance, has been mentioned. Formerly timber highway bridges were commonly covered by roofs and siding to protect the frame work from the weather; and such structures lasted for a long period of years, several notable wooden bridges in this country having reached an age of nearly 100 years. This sort of bridge accumulated a great deal of dirt and was very dark at night, and the roof, housing, and floor naturally required considerable maintenance.

The question of fire protection should also receive proper attention in connection with timber bridges. The expense caused by a burned bridge in some cases far exceeds the value of the structure itself, as, for instance, on a railway where the traffic is stopped on this account. On railways, timber trestles are frequently partially protected from fire by covering the deck with sheet metal or with stone or gravel, so that sparks from a defective engine will not set it ablaze. Sometimes fire-proof paints are used. Some of these paints are very effective for several years, and at the same time are good timber preservers; hence, if properly selected, they will be economical from a maintenance standpoint as well as in respect to protection from fire. The timber floors on highway bridges and the ties on railway bridges are subject to wear, and are usually worn out before they rot out. In cases of very heavy traffic, bridge floors should be constructed of more permanent material than planks; and the ties on railroad bridges should be protected with tie plates.

Old stone piers and abutments often show open seams where the mortar has fallen out of the joints. If these receive attention in time, it will usually be sufficient to dig the old mortar out of the seams and repoint them, thus protecting the interior of the structure from moisture; but in some cases more work than that is necessary. On high structures, especially over rivers, it is very costly to put the spans on falsework in order to repair or rebuild piers, hence  other  expedients  are  resorted  to,  in  order  to  avoid  this