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Title: In-Place Preservative Treatments for Covered Bridges

Author: Lebow, Stan; Morrell, Jeff;

Date: 2014

Source: Guide for In-Place Preservative Treatment of Covered Bridges. Proceedings, Second National Covered Bridge Conference. June 5 – 8., 2013. Dayton, OH. 2014; 32 p.

Publication Series: Full Proceedings

Description: Covered bridges can be vulnerable to damage from fungal decay and insect attack. This paper describes procedures for selecting and applying in-place treatments to prevent or arrest biodegradation, and summarizes recent research evaluating some of these treatments. Wood moisture is the key to decay and termite attack, and the first line of defense against biodeterioration is to minimize moisture intrusion through prompt maintenance and repair. Biodeterioration will tend to be more prevalent wherever members contact abutments, are near the ends of bridges subject to wetting from splashing, or are below windows or other openings that allow entry of wind-blown precipitation. In-place preservative applications can help limit deterioration when moisture cannot be eliminated. The goal of in-place treatment is to distribute preservative into areas of a structure that are vulnerable to moisture accumulation. In-place treatments include surface coatings, pastes, rods, gels and fumigants. Some preservative treatments may cause a color change in the treated wood and/or present safety and handling concerns. One limitation of all these 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 and can move through the wood by vaporization or diffusion. Laboratory research compared the movement of 7 water diffusible treatments and 3 fumigant treatments as a function of moisture content, wood species and dosage. Field research evaluated the mobility of two water diffusible treatments and two fumigants placed into timbers in 5 covered bridges. The wood in many covered bridge timbers was too dry to promote diffusion. Water diffusible treatments must be applied in locations where moisture accumulation is suspected. Fumigants have greater potential for movement in dry bridge timbers and refractory wood species.

Keywords: covered bridges, decay, termites, wood preservatives, in-place treatments

Publication Notes:

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  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.



Lebow, Stan; Morrell, Jeff 2014. In-Place Preservative Treatments for Covered Bridges. Guide for In-Place Preservative Treatment of Covered Bridges. Proceedings, Second National Covered Bridge Conference. June 5 – 8., 2013. Dayton, OH. 2014; 32 p.


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