Figure 1. Detail of a cornice dentil shows the severe cracking and failure of paint finish. Photo: Alan O’Bright

On much of the projecting millwork, the final layers of paint had been applied so heavily that stalactites in excess of one-quarter inch were apparent due to paint dripping.

On one section of the building, constant moisture penetration from a poorly detailed sleeping porch floor deck had caused total paint failure. Rainwater had soaked wall cavities of a ground floor bathroom causing the paint to peel off in hand-size sheets. It was clear the exterior finishes had lost most, if not all, of their elastic integrity. In order to achieve a sound surface for painting, the decision was made to remove a majority of the exterior paint finishes to bare wood in preparation for a three-coat paint application.

Solution

As part of the planning required before the selection of the paint removal method, a physical investigation was conducted of the exterior structure to determine the method of construction and condition (see figure 2). This is particularly critical whenever paint removal is planned. Decisions as to which paint removal methods will be used—especially methods involving heat—are in part guided by the potential flammability of the wall material and debris in the wall cavity and cornices. Sections of lapped siding were carefully removed and the underlying board sheathing cut with a hole saw to reveal the wall cavities. Fortunately, the bulk of the balloon-framed structure was found to be in good condition and the project team believed that potential fire risks could be minimized. With the exception of the 1884 addition, all wall cavities had been filled from foundation sill to soffit with soft brick and mortar. A majority of the house was sheathed in white pine tongue-and-groove boards.

Figure 2. In assessing the safety of using thermal heat to remove paint from the siding, an investigation was performed to determine wall construction and condition. In this portion of the structure, there was no sheathing backing the siding but brick noggin extended from the foundation to the soffit. Photo: Alan O’Bright

Three methods of paint removal were considered: hand scraping and sanding, chemical strippers, and thermal removal. Prior experiences with hand scraping and sanding on a large scale had shown this method to be very damaging to wood surfaces and the workmanship was very difficult to control. Chemical strippers are very messy and difficult to control on exterior vertical surfaces. After application, the volatile chemicals usually need to be covered with sheet plastic to keep them from rapidly evaporating.

The use of propane torches to remove the paint was not considered because of the high risk of starting a fire or at least of scorching the wood. Two thermal paint removal techniques, however, were evaluated—radiant heat plates and heat guns. The radiant heat plate gives a consistent heat flow, but heat intensity is less controllable. The plate housing also obstructs the laborer’s view of the working surface, making it difficult to tell when the softened paint is ready to remove. If the paint is overheated, it can ignite and scorch the wood as the plate is withdrawn. The heat gun was chosen because of the following advantages: the heat is controllable; the working surface is exposed to view, allowing better control; and all layers of paint can be softened and removed down to the original surface in one pass without mechanical damage to wood.

Although chemicals and hand scraping were rejected as the primary paint removal method, chemicals and scrapers were used in other areas such as porch ceilings, soffits, windows, and brackets, where the working surface was too complex, or where there was a risk of overheating unexplored cavities. The majority of the exterior walls, sheathed or filled with brick noggin, apparently caused the radiant heat to dissipate considerably before reaching wall cavities. Furthermore, the sheathing formed a barrier protecting the wall cavities from direct hot air blast through cracks and joints in the siding and trim. Nevertheless, strict fire precautions still were taken throughout the project.