Back-Plastered Metal Lath for Home Building
DEVELOPMENT of metal lath as a basic exterior wall material has been one of the remarkable features of recent progress. Its easy adaptability to every kind of building has led to its wide use and the attendant evolution from crude to perfect construction has brought forth several distinct types of exterior wall, of which the back-plastered form has been found by actual tests to be the most efficient.
In back-plastered construction the studs are erected as usual, but no sheathing is used. Furring strips (metal preferred) are placed along the studs and the metal lath attached at once. The metal lath is placed with the long dimensions (8 ft.) across the supports and fastened by nailing or stapling every 6 ins.
The first exterior stucco coat is applied as usual and the plasterer goes to the inside of the house and plasters with the same material between the studs on to the keys of the exterior coat. This positively imbeds the lath and forms a reinforced monolithic coat of cement which common sense and many tests tell us is far stronger than sheathing.
After the back-plastered coat has been completed the next step is the insulation. Satisfactory results have generally been obtained without paper insulation of any kind. It is wise, however, to provide a safeguard against extremes of weather. Ordinary building paper, doubled, forms a satisfactory and inexpensive insulating medium. The paper is cut in between the studs and fastened by nailing wood strips over the folded edges of the material and so placed as to leave about 1 inch air space between it and the stucco.
All that remains to complete the black-plastered exterior wall is the lathing and plastering of the interior side of the wall. In a general way the operations are identical with those described for the exterior wall. Furring, however, is usually dispensed with and a lighter lath is used, 2.3 Ibs. per square yard being the minimum weight recommended. Back plastering of this side of the wall is of course mechanically impossible. If care is taken in applying the plaster a perfect and satisfactory key is attained.
When the exterior is decided upon the next consideration is the permanency and safety of the interior. Cracks in plaster are the most objectionable and unsightly evidence of thoughtlessness in construction. They are nearly always unnecessary and can be avoided if metal lath is used as a base and reinforcement for the plaster. It is not necessary to use this modern lathing material throughout; the expense is negligible when its use is confined to the places where cracks are most unsightly or where they are most likely to occur.
Common sense dictates these positions:
A. On ceilings of prominent rooms, because the living room, dining room and hall are seen by most visitors.
B. Lapped 6 inches on either side of wall angles and around doors, because these places are certain to crack unless reinforced.
C. Back of wainscots and tile mantels, because the constant changes of moisture and temperature affect ordinary lath and cracks are unsanitary or unsafe here.
D. Across the plumbing pipes and heat ducts, for the same reasons.
Metal lath is made from steel sheets so expanded or punched that the myriad of holes allows the plaster to push through and form an unbreakable bond or "key." The metal mesh reinforces the plaster and prevents cracks and dislodgments, usually caused by warping, vibrations and ordinary settlement.
Metal lath does not warp, twist, expand, contract or stain the plaster it will not burn and will reinforce the plaster under most ordinary circumstances which will completely wreck the finish on other material. Repairs and redecoration costs are minimized and the home will always bring a high value on sale as there is no evidence of deterioration.
All fire prevention engineers realize that over 90% of all residence fires start inside the house. These are from electricity, either crossed wires, misuse of appliances or other causes, or from over-heated flues, coal-bin fires or spontaneous combustion, actual carelessness or accident.
As these are constant and recurrent, about $63,000,000 loss is suffered each year to say nothing of the 23,000 people burned to death. It is best to be sure—fight fire where it starts. As the greatest danger of fires is at certain points, metal lath can be used there only and safety is assured for the family.
The "five vulnerable points" at which good sense dictates the use of metal lath are:
1. All bearing partitions, and studs in exterior walls, including a basket to hold incombustible material as a fire stop.
2. Ceilings under inhabited floors, especially over heating plants and coal bins.
3. At chimney-breasts, around flues and back of kitchen ranges.
4. Stair-wells and under stairs.
5. As a base and reinforcement for exterior stucco.
Choose from these points and talk with your architect and contractor so that your home will be permanently beautiful, inside as well as outside, and the lives of its occupants safe from fire.
Source: "Home Builders Plan Book" 1921