The Evolution of Lath and Plaster

FROM THE FOUNDATION The Evolution of Lath and Plaster By Gary J. Maylon Alabama Metal Industries Corporation that five new manufacturers of metal lath have entered the market in the last eight years. These manufactur- Metal Lath ers have invested millions of dol- lars in what was perceived to be a and dying industry not too many years ago. Plaster Series Early in this period the EIFS (Ex- terior Insulation and Finish Sys- tems) werebeing introduced to this The Foundation of the Wall and A new type of mesh lath assured improved Ceiling Industry will sponsor a country from Europe. These sys- mechanical bond for the stucco finish of tems, though initially controversial, series of articles exploring the this upscale Hilton Head, SC home. evolution of the lath and plaster have steadily grown in popularity, industry from what it was for uses, and in the number of manu- many years, to what it is today. facturers producing them. I can re- Many very talented individuals, call many discussions with mem- who are extremely well versed in bers of the lath and plaster industry these systems, have volunteered about EIFS, and what its influence to share their knowledge with might be on our industry. Early on, us through these articles. everyone wanted to believe that sus- Through this series we hope ceptibility to damage was inherent to cover every aspect of both in these systems which would deem them to be short lived and unsuc- gypsum cement plaster and Multiple colors were used to define the cessful. Many people overlooked portland cement stucco. Though quoins and other decorative features of the problems we were having in our the articles may not occur in any this home. particular order, it is our plan to own system, namely, cracking prob- assemble these articles in a lems, poor color selection and per- compendium or primer (as was There have been many changes formance, the lack of freedom of- recently completed for in the lath and plaster trade during fered for architectural creativity, light gage steel framing) for my 20 years in the industry. In 1972, and last but not least, the shortage publication and sale to the we were still shipping rail carloads of qualified craftsmenand mechan- construction industry. of expanded metal lath to contrac- ics, which has led to poor installa- If there is a particular subject tors who were doing jobs that took tion practices. matter you would like to see months, even years to complete. All of the above led to a market addressed, or if you feel that you However, during the 70s and 80s that was ripe for change. Many in- would like to contribute an we saw at least five metal lath manu- dustry leaders, including some in article on a particular subject, facturers leave the business, con- our company, believed that lath and please contact The Foundation of siderably reducing production ca- plaster was dying a slow and pain- the Wall and Ceiling Industry at pacity of our industry. In this article ful death, as evidenced by the de- (703) 548-0374 I will relate what has happened to mise of such industry leaders as revitalize our industry to the extent Inryco, Ceco and Wheeling. Construction Dimensions/November 1992 17 The diamond mesh used on this job is lighter, stronger and has larger diameter openings than traditional mesh. What has happened to bring this industry back from the grave? Simply, it is a willingness to admit that problems did exist and to make positive changes. Also we are an industry that has used modern technology to incorporate the best of both worlds (EIFS and stucco) to create a system that should endure for many years to come. Let’s examine what exactly has evolved to fix the problems listed earlier. The largest perceived problem with lath and plaster is maintenance due to cracking. This problem has been greatly reduced by innovations that have come indirectly from the EIFS industry. Many contractors now add chopped alkali resistant fibers and acrylic modifiers to the scratch and brown coats of stucco, to add strength to these coats and to slow the curing process. This creates a stronger, more crack- resistant membrane which requires less curing time between coats. Since time is money, this results in cost savings. Additionally new expanded metal lathing products have been developed that are lighter, stronger, larger and have greater diameter openings. These larger openings allow the fiberglass fibers to embed and key into each opening to assure excellent mechanical bond. Regular diamond mesh lath tends to cause lamination of the fibers on the surface of the lath rather than total embedment; woven wire mesh, which has larger holes, is much harder to keep flat and smooth on the wall. It also has fewer keys to offer structural support. Additionally, many new accessory products have been introduced to the market. Primary among these are vinyl accessories. Rusty galvanized beads have long been a concern in exterior stucco work. This concern previously was solved by the use of zincalloy (99% pure zinc) accessories. These products have become so ex- pensive in recent years that many contractors and specifiers have preferred to risk the consequences of 18 November 1992/Construction Dimensions The plastering contractor installed paper-backed mesh on Figure 1 this residential job. using galvanized beads. Vinyl accessories have pro- Products such as the vinyl foundation weep screed vided a much more affordable alternative by providing (recommended in ASTM C 926 for use at the base of all very effective functional products, at one third the cost, exterior stucco walls) can now be produced inexpen- that will not rust. New weather-resistant vinyls are sively in vinyl. This screed (see Figure 1) allows mois- available that will endure for many years. ture to escape the wall cavity rather than get trapped in Construction Dimensions/November 1992 19 the casing bead at the base of the added to it. The color selection was providing an answer to these prob- wall. somewhat limited, the colors were lems. Knowledgeable contractors Previously, three-coat stucco generally pastel, not bright and vi- are now finishing their three-coat would have been finished with a brant, and often these colors faded, system with the same acrylic fin- portland cement stucco finish coat even becoming chalky after only a ishes that are used to finish soft coat applied approximately 1/8 in. thick. relatively short time. Once again EIFS. Often this coat would have color we can thank the EIFS industry for Why is this anadvantage? These finishes offer movement and an elon- gation ratio far greater than portland cement. Portland cement is restricted in movement; that is, de- For decades beautiful architectural decorations such as quoins, cornices, keystones and beautiful window details were molded in stucco by the craftsmen and artisans of our industry. Unfortunately, the number of mechanics qualified to do this work has dwindled . flection is limited to L over 360. In plain English, portland cement will crack if deflections are greater than mere fractions of an inch. For this reason, many industry experts believed that cracking, either minor shrinkage cracking or even some structural cracking, was inevitable. Though we still witness some mi- nor amounts of cracking withacrylic coating, the amount is greatly re- 20 November 1992/Construction Dimensions and owners now have hundreds of colors to choose from, and mul- tiples of these colors can be com- bined on the same job to add architectural relief and design. This leads to another evolution. For decades beautiful architectural decorations such as quoins (comer stones), cornices, keys tones and beautiful window details were molded in stucco by the craftsmen and artisans of our industry. Unfor- tunately, the number of mechanics qualified to do this work has dwindled, while the cost has risen greatly, to a point that very little new work is being performed in this field. However, this void has been filled by the EIFS industry. Newproducts and installation innovations have helped revive the lath andplaster Once the brown coat has been fin- market. ished to a relatively smooth coat duced and generally deemed very tion ratios in excess of 300%) are and allowed to cure for a period of acceptable. now becoming available. These coat- time, foam shapes (available in a Recently developed paint applied ings will do even more to enhance large number of configurations to and trowel applied elastomeric coat- the beauty and durability of stucco. fit almost any need) are then pre- ings (some of which have elonga- As an added benefit, architects pared for finish by first applying Construction Dimensions/November 1992 21 alkali resistant fiberglass mesh fied, fiber-added portland cement this system even more acceptable. which is embedded in an acrylic stucco and finally an acrylic finish We are seeing one-coat systems, base coat, and prepared to accept coat. This system eliminates one of currently manufactured by a num- an acrylic finish coat. As stated ear- ber of the EIFS manufacturers, lier, the acrylic finish coat is then steadily growing in popularity. This applied directly to the brown coat is particularly true in the residential and the prepared shapes. Multiple The newest housing markets of the southeast, colors are often used to define the innovation to the southwest and the west coast. architectural reliefs from the field The lath and plaster industry has of the walls. our industry much for which to thank the EIFS The newest innovation to our industry. because of shared tech- industry takes all of the previously takes all of the nology, and the increased prefer- mentioned innovations one step ence for the aesthetic beauty of further.

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