nonslip nosing of steel, brass, bronze, aluminum, and molded hard rubber is commercially available and should be applied according to the manufacturer's recommendations.

EXTERIOR WALLS

Exterior walls fall into three structural categories: load-bearing walls (carrying structural loads); nonbearing walls (carrying only their own weight); and supported or enclosed walls, sometimes called curtain walls (with their weight supported by structural members).

Exterior walls are made of a wide variety of materials, such as the following:

Wood (shingles, weather-board siding, plywood)

Concrete and masonry (brick, concrete or cinder block, reinforced or nonreinforced concrete, structural clay tile, stone, stucco)

Metal (corrugated iron or steel, aluminum, enamel-coated steel, protected metals)

Mineral products (asbestos shingles, asbestos-cement sheets, and glass block)

Wood Exteriors

Wood exteriors should be regularly inspected for damage from wear, accidents, and the elements. They should also be inspected for damage resulting from insect pests. This may be done by tapping the wood with an object. A dull or hollow sound is an indication of damaged wood, which may be the result of insect pests. Painting and surface treatments should be inspected quarterly for deterioration; exteriors should be inspected for loose, warped, cracked, or broken boards or shingles.

Moisture is the most prevalent cause of failure of exterior walls. Stains, paint deterioration, and rot are usual signs of moisture damage. Condensation within and behind walls is a less obvious but equally damaging factor. Insufficient, loose, or displaced nailing produces separations and cracks that admit moisture and reduce the stability of wood walls.

Foundation settlement or displacement may cause misalignment of framing members and consequent damage to walls, including cracks in siding and breaking or displacement of boards or shingles. Make a careful check to determine that existing structural, functional, and material conditions warrant repair to the existing wall, rather than complete residing, insulating, or other overall repair or rehabilitation. Where existing situations are satisfactory, replace damaged material with like material. Cut back sufficient areas beyond the damaged part to obtain good jointing and sound nailing. Tighten nails in existing material to be left in place. Be sure that material receiving the new nailed pieces of sections are sound and true. Cover replacement wood with treatment and/or paint matching the original design. When "as-built" plans are available, it is well to examine the original construction detail for assurance that out-of-vision construction and utilities will not be damaged. Warped, split, or curled shingles should be removed with a ripper and replaced in a similar manner as roofing shingles. Panel siding should be periodically checked for looseness and faulty caulking. It is usually more economical and satisfactory to replace damaged or deteriorated panels than to attempt patching.

Concrete and Masonry Exteriors

Concrete and masonry exteriors, such as concrete block, cinder block, and brick, require less frequent maintenance than most outside materials, but some failures are common. Exteriors should be inspected quarterly for structural cracks, open-mortar joints, condensation in weep holes, settlement, efflorescence, stains, and deterioration of paint or other surface covering.

The most common fault found in block and brick walls is defective mortar joints. These defective joints can be corrected by re-pointing. The steps for the procedure are as follows:

1. Cut out cracked open-mortar joints to a depth of at least one-half inch. (Cutting can be done by hand, but if large areas are involved, it is usually cheaper to use power tools.) Take care not to damage brickwork during the cutting process.

2. Remove all dust and loose material with brushes, compressed air, or a water jet. If water is used, no further wetting of the joints may be needed unless the work is delayed.

3. Repair the joints by tuck pointing.

4. Use mortar of about the same density as the original mortar, if it can be determined; otherwise, use a prehydrated mortar mix in the following proportions by volume: 1 part of portland cement, 1 part of lime putty or hydrated lime, and 6 parts of sand.