Types of Stucco Control Joints
Stucco control joints are introduced normally to limit plaster cracking. Control joints in stucco can be used to separate different textures, different colors or when different materials are used. Plaster is so thin that must be divided into sections to reduce crack due to volume changes. Depending on the type of movement expected, the joint must be able to move also in different directions. The joints could be specified to move in only one direction or two directions by using some combinations of materials, or by prefabricating those joint at the jobsite. Stucco joint are commonly available as one piece joints or two piece joints.
Stucco Control Joints: One Piece Joint
A one piece joint are normally classified as control joints. This joint normally deals with the contraction of the mortar mix and minor expansion and contraction. Shaped as a ‘V’or ‘M’, normally are fabricated with expanded flanges to increase bonding characteristic. The ‘M’ type provides movement control but also gives the appearance of a narrow reveal. The ‘V’ type joint is used normally when the area is larger than 144 square feet. Vertical joints should be attached to a stud where necessary. A one piece joint is limited in the amount of movement it can handle and it can only move in one plane.
‘J’ control joints are normally manufactured with expanded flanges o that the crack is less likely to occur or be exposed. The design of J joints provides locking of the stucco to the edge of the joints and reduces stucco separation at the edge of the joint. The plaster most force stucco under the upside down J shape in order for this bead to perform optimally. They are normally manufactured with tape over the groove so it can be cleaned faster and easier.
Stucco Control Joints: Two Piece Joint
A two piece expansion joint is normally one that could slide in different planes. These are normally located through wall expansions, using a female expansion over a flexible membrane. This membrane will prevent leakage, something that is quite normal in these beads. They can also be formed by using back to back casing beads mounted over a flexible membrane. The benefit of using this method is that the joint is filled with backer rod and silicone caulking that will work better than the flexible standard membrane. A two piece joint will manage some larger movements in the range from 1/4 inch to just under 1/2 inch.
There are also three piece joints, rarely used, that could be installed at outside corners and soffit vent expansions. Stucco control and expansion joints are available in roll formed galvanized steel, zinc alloys and polyvinyl chloride (PVC)
Stucco Control Joints: Joint Spacing
The use and spacing of stucco control joints will depend on several factors: type of materials, orientation of the building and the type of surface. Stucco can be applied over concrete and masonry surfaces and will only require joints where there is a change in material or over concrete joints. If stucco is applied using metal lath, joint spacing are implemented by following Portland Cement Plaster/Stucco Manual, EB049, are based on ASTM C1063, Standard Specification for the Installation of Lathing and Furring to Receive Interior and Exterior Portland-Cement Based Plaster requirements.
Generally joint spacing should meet these general criteria:
- Joint spacing should not be greater than 18 feet.
- No panel should exceed 144 sq.ft. on vertical applications.
- No panel should exceed 100sq. ft. over curved or angular sections.
- No length-to-width ratio should exceed 2 ½ to 1 in any given panel.