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lathnet-with-code-overlapAdhered masonry veneer can be installed using five different building techniques

An adhered masonry veneer is a cost-effective way for a home owner or commercial property owner to keep the appearance of masonry in the façade, even when budgets or design considerations don’t allow the use of full-sized masonry units. However, veneer installation is based on recommendations of the specific product and system chosen for your project. With that in mind, here’s a breakdown of basic installation using five standard building techniques that can help you in your next project.

 

  1. Weep Screed

The purpose of the weep screed is to provide drainage for the system. It typically is a galvanized metal or a durable plastic strip placed at the base of the wall and, in some cases, at each floor level of a large veneer. The galvanized weep screed must be at least 26 gauge (0.018 inches) thick. The plastic weep screed must be a minimum thickness of 0.05 inch, and both products must extend up the wall a minimum of 3.5 inches. They both must also be fastened to a stud in frame construction, or directly to the concrete or concrete masonry unit (CMU) substrate.

To function properly, weep screeds should be a minimum of four inches above grade and two inches above a roof line. If applying veneer to a CMU or cast-in-place grade or foundation wall, the minimum tolerance is two inches from a sidewalk or driveway surface. This placement will reduce the possibility of the weeps becoming clogged with debris that splashes on the wall. Attach your weep screed prior to placing the weather resistant barrier (WRB) on your project, since it is easier to install the overlap when the weep screed is in place. Many building code officials have become more rigid on the enforcement of these standards in recent years.

  1. Weather Resistant Barrier (WRB)

The WRB sheds the moisture that passes through the veneer away from the substrate and allows drainage to the weep screed or flashings. Two individual layers of house wrap or building felt sealed with tape surrounding the structure typically are required. When a drainage mat is used directly against the lath as part of the wall system, one layer of WRB is eliminated (check local codes). When a drainage mat is used, air and moisture can move with significantly less resistance behind the veneer, and the wall is usually dryer than one without a drainage mat. The WRB is installed after the weep screed is in place, and must drape over the weep screed to allow moisture to be channeled past the face of the wall.

  1. Continuous Insulation

Continuous insulation, or rigid insulation, has become increasingly popular, and the installation of adhered masonry veneers on the exterior side of the insulation is allowed as a non-engineered system for insulation that is a thickness of ½ inch or less. Designs using insulation greater than ½ inch in thickness require an engineered anchoring system. Specialty washers for anchoring lath over rigid insulation are available where you purchase your insulation or from the rigid insulation manufacturers. There are several options, and the manufacturers can guide easily you in the right direction when specifying or constructing a project with the thicker insulation.

Continuous insulation, when placed as the outermost layer on the structure prior to lath installation, can eliminate the need for a second layer of WRB. The inner layer of WRB must have all of the joints sealed and taped for the system to work properly.

  1. Fasteners

Adhered masonry veneers can be applied to concrete, CMU, steel stud and wood stud substrates. The allowable non-corrosive or corrosion-resistant anchors used for anchoring lath or lath systems are as follows:

Wood frame: Staples, roofing nails and screws can be used. The minimum embedment is ¾ inch, but a minimum of one inch is a good practice to follow.

Steel stud: The only anchor recommended for steel stud is the self-tapping screw or hex head anchor with a neoprene washer attached to the anchor. Minimum embedment is 3/8 inch, but again, a greater depth will increase your odds of success.

Concrete or concrete masonry units: Powder actuated fasteners, also known as cap anchors, are allowable for this installation. Powder actuated anchors do not need pilot holes, but are not used commonly. Concrete masonry screws are a good choice as they can be monitored for embedment; will not blow through the substrate; and typically are more economical.

Innovations in lath during the last several years have opened the market to different ideas, when thinking about the lath that is integral to adhered masonry systems.

  1. Metal Lath

Metal Lath is manufactured by several outstanding domestic manufacturers. Metal lath used today is a galvanized, self-furring, dimpled product that allows the lath to project ¼ inch out from the substrate, so the base or scratch coat mortar can fully encapsulate the lath. Lath weight is expressed in pounds per square yard, and is offered in three different weights: 1.75 pounds, 2.5 pounds and 3.4 pounds. The most common is 2.5, but, in some areas, all of the specifications are written for 3.4 material.

Lath placement or orientation is no longer stipulated by local codes. It is still most productive to install lath horizontally – one over two for example – and the days of “cups up, smooth down” have been eliminated. Do not terminate lath at a corner. Always extend the lath past an outside corner a minimum of 12 inches. Lath can be terminated at an inside corner. Anchor lath a minimum of every seven inches vertically, and at every stud, or 16 inches on center.

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