Guide for In-Place Treatment of Wood in Historic Covered and Modern Bridges

This guide is another fine product written by the Forest Service’s Forest Products Laboratory, in cooperation with the US-DOT, Federal Highways Administration.  The publication’s abstract gives great description of the book;

“Historic covered bridges and current timber bridges can be  vulnerable to damage from biodeterioration or fire. This  guide describes procedures for selecting and applying inplace treatments to prevent or arrest these forms of degradation. Vulnerable areas for biodeterioration in covered bridges include members contacting abutments, members near  the ends of bridges subject to wetting from splashing and  members below windows or other openings that allow entry  of wind-blown precipitation. Pressure-treated timber bridge  members can be vulnerable when untreated wood is exposed  by field fabrication or by the development of drying checks.  The objective of an in-place preservative treatment is to  distribute preservative into areas of a structure that are  vulnerable to moisture accumulation and/or not protected  by the original pressure treatment. Types of field treatments  range from finishes, to boron rods or pastes, to fumigants.  A limitation of in-place treatments is that they cannot be  forced deeply into the wood as is done in pressure-treatment  processes. However, some can be applied into the center  of large members via treatment holes. These preservatives  may be available as liquids, rods or pastes. Bridge members  can be treated with fire retardants to delay ignition, reduce  heat release, and slow the spread of flames. In-place coating  products are available to reduce surface flammability, but
these coatings may need to be reapplied on a regular basis if  exposed to weathering. For more integrated protection, fire  retardant treatment of bridge members may be combined  with other forms of protection such as lights, alarms, sprinklers and monitoring systems.”

So if you are working with wooden bridges of any kind, then this guide is defiantly worth the read. It can be downloaded from the Forest Products Laboratory’s website at this link.


National Center for Preservation Technology and Training
645 University Parkway
Natchitoches, LA 71457

Email: ncptt[at]
Phone: (318) 356-7444
Fax: (318) 356-9119