Guide for Use of Wood Preservatives in Historic Structures (2012-10)

This document provides guidance on wood preservation options in the context of historic preservation. Preserving wooden building materials is critical to historic preservation practitioners. Biodeterioration can be minimized through design, construction practices, maintenance, and, if neces¬sary, by use of wood preservatives. Moisture is the primary cause of biodeterioration, and if exposure to moisture cannot be prevented, the application of preservatives or use of pressure-treated wood may be warranted. The Secretary of Interior’s Standards for the Treatment of Historic Proper¬ties emphasize retaining the historic character of a property, including distinctive materials, features, and spatial relation¬ships. Existing conditions should be carefully evaluated to determine the appropriate level of intervention.

Wood preservatives are generally grouped into two cat¬egories: preservatives used for in-place field (remedial) treatment and preservatives used for pressure treatments. A limitation of in-place treatments is that they cannot be forced deeply into the wood under pressure. However, they can be applied into the center of large wooden members via treatment holes. These preservatives may be available as liquids, rods, or pastes. Pressure-treated wood has much deeper and more uniform preservative penetration than wood treated with other methods. The type of pressure-treated wood is often dependent on the requirements of the specific application. To guide selection of pressure-treated wood, the American Wood Protection Association developed Use Category System standards. Other preservative charac¬teristics, such as color, odor, and surface oiliness may also be relevant. Guidelines for selection and application of field treatments and for selection and specification of pressure-treated wood are provided in this document.