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California Preservation Foundation

2005 Preservation Design Awards

Description of the Project: The Gamble House Exterior Conservation Project

The David B. Gamble House, a historic house museum designed by Charles and Henry Greene, is listed as a National Historic Landmark. The Gamble House represents a high-water mark of the “craftsman” architectural idiom which spread through neighborhoods across the country. The project sought to maintain the highest conservation values, and standards of science and artisanship. The project criteria were the Secretary of the Interior’s Standards for Preservation and the Ethics of the American Institute for Conservation. The Historic Structure Report completed in 2000 established the need for the project. The analysis and treatments were reviewed by the Getty Grant program staff, peer reviewers, SHPO, City staff, and National Park Service.

Flat steel plates were installed in the basement in order to connect the wood framed house to the brick basement walls that support the structure. The exposed plates were designed to be compatible in shape and finish with the house’s original iron straps.

The replacement roof is a durable contemporary product that is visually compatible with the original material. Products that use hot tar adhesives were specified in order to eliminate the need for open flame “torch-down” on the building. Metal flashings (copper and lead-coated copper) were added under roofing and at locations not visible to visitors.

Exterior wood and finishes were categorized into thirteen conditions. A sample of each condition was analyzed by the project scientist, conservator, and historic architect. The exterior wood surfaces were not “restored” to the finish or appearance of the 1908 conditions. Restoration would have required removal of 1930s paint and original plant-based creosote dip to recover a bare wood surface, destroying prior finishes and causing impacts on the surface profile of the wood. Painted wood surfaces were cleaned; a clear resin-based coating that consolidates failing wood consolidating paint was applied. The surfaces recovered the original darker green hue. Unpainted surfaces such as windows, posts, and railings were “cleaned” using a gentle stripper (N-methyl pyrolidone) that does not profile the surface wood, and then coated with protectant. The weathered color and value relationships in the house were restored to those designed by the architects; i.e., before treatment the walls were blanched to a yellowish green hue and wood trims were dark brown; after conservation the walls returned to a darker hue, while windows, and doors regained a light yellow glow.

There is a history of dry rot at gable beams and rafter tails. More than twenty years ago epoxy fillers were used to replace rotten wood, and Dutchman patches replaced some rafter tails on the garage. The investigation during the preparation of the Historic Structure Report found rotten wood below the earlier patches. The old epoxy and rotten wood were removed, retaining all good material. Wood was treated with borate fungicides in solution, liquid epoxy consolidants, and borates injected in gels to prevent fungal growth. New permeable epoxy fillers were used to replace lost wood. The replacement epoxy was tinted with mineral-based pigment, sculpted, and stained to blend visually with adjacent wood when viewed from the ground.

There is efflorescence of salts at the interior of brick basement walls, some of which are finished with gypsum plaster. Both plaster and brick are damaged by moisture migrating through basement walls. Exterior foundation walls were excavated wherever they were accessible, down to the bottom of the footings. A footing drainage system and outside-applied wall membranes were installed.

The protection plan was a critical part of the project. Crew training for safety and corrective action was required throughout the construction. Scaffolding was self-supporting and clear distance away from the structures. A fire and blast shield was built the full height of the house at the southeast corner during the period that compressed gas was stored and used for heating roof tar.

The Gamble House, USC, will make all information about the assessments and treatment methods and materials available to everyone. Portions of the project documentation will be accessible on their website so the even private homeowners can learn about exterior wood treatments.