MASONRY VENEER/STEEL STUD WALLS
1. INTRODUCTION. This document defines the criteria to be used when designing curtain wall
masonry veneer on steel studs. These walls are to be designed to resist out-of-plane lateral
loads due to wind and seismic forces. Also, the wall system must collect, direct and remove
water from the wall cavity to properly control moisture, prevent efflorescence, and control
corrosion of the steel system. These curtain wall steel stud systems will not carry building dead
or live loads, nor provide lateral resistance to the building system.
2. GENERAL DESCRIPTION OF WALL SYSTEM. This wall system consists of a masonry
veneer exterior wythe connected by anchors to a steel stud backup wall. The steel studs will be
mechanically braced until the sheathing and wallboard are placed on the studs. Sheathing is
placed on the cavity face of the stud and the wallboard material is placed on the inside face of the
studs. A cavity space is provided between the masonry veneer and the steel stud wall to allow
moisture to migrate down the inside face of the cavity, brace the masonry veneer laterally and
transfer the horizontally applied loads to the steel studs. The masonry wythe will be isolated on
three sides to assure that it will only carry its own weight.
3. REQUIREMENTS FOR WALL COMPONENTS AND DETAILS. See Appendix G for typical
Masonry Veneer / Steel Stud details.
a. Masonry Wythe.
(1) Masonry Units. Dimensional and physical requirements of the masonry units
are given in TM 5-809-3/NAVFAC DM-2.09/AFM 88-3, Chapter 3. Masonry units used in
veneer walls will be solid.
(2) Mortar. Four types of mortar are specified in ASTM C270, they are M, S, N,
and O. While Types S and N may be used for masonry veneer systems; Type S mortar
has higher strength and good workability and can be used above and below grade, Type
N has a lower strength, better workability is more water tight and can only be used above
grade. The lower strength of Type N mortar allows cracking in the masonry wythe at
relatively low load levels. Masonry cracking will result in more uniformly distributed
anchor forces. Conversely, vertical beam action of the uncracked masonry wythe causes
nonuniform distribution of loads to the wall anchors. Those wall anchors near the top of
the uncracked masonry wythe have much higher loads than those in the lower half of the
wythe. Type S mortar is recommended for the design of masonry veneer steel stud
systems. Two strength properties of mortars are measurable: the bond strength in
accordance with ASTM C 1072 and the compressive strength in accordance with ASTM
C 780. Of these two strengths bond is more important in veneer walls and compression
is more important in bearing walls. Type S mortar has the highest compressive and bond
strengths and can be achieved with either portland cement-lime or masonry cement.
However, since masonry cements include premixed workability and air-content additives
the bond strengths are reduced. In order to achieve good bond strengths the maximum
air-content of the cement must be limited to 12 %. Since every manufacturer of masonry
cement uses different additives and a different air-content, care should be used when
specifying masonry cements for veneer walls. To assure a bond strength comparable to
a portland cement lime mortar, a comparative bond strength test between the masonry
cement proposed for the job and a corresponding type of portland cement mortar needs
to be completed to demonstrate equivalent or better bond and compressive strengths for
the masonry cement mortars. The contractor will be required to perform the ASTM C
1072 and C 780 tests on their proposed mortars. Masonry units for the bond strength
test will be the same as proposed for the project.