Stucco on a home’s exterior adds a classic and luxurious touch to the general aesthetics. However, the lines of an expansion joint disrupt the continuity of the stucco, which may look unattractive to you. So, can you stucco over expansion joints?
Based on most building codes, the acceptable standard is to have expansion joints in your stucco (especially if you stucco over lath). However, you can stucco over expansion joints if you agree to handle the cracks it causes.
This article considers if stucco expands and contracts and whether you can stucco over expansion joints. I also explore the possibility of putting lath over expansion joints and if you can stucco without lath. To conclude, I describe the differences between expansion and control joints.
Stucco contracts and expands with temperature changes, and it causes no problems. Issues arise in the stucco when your home consists of different materials with varying properties.
Different parts of a house heat up and cool down at different rates, causing each material to contract and expand. All these differences can lead to cracking and delamination of the stucco.
Additionally, the stucco breaks away from adjacent surfaces, leaving a free path for water intrusion. The water exposure causes moisture damage to the home’s frame and substrate (sheathing).
A seamless appearance completes stucco’s appeal, but how gorgeous will the stucco look with cracks popping out everywhere? You sign up for an increased risk of cracking when you stucco over expansion joints.
Your builder will probably insist you put expansion joints in your stucco, especially if you’re stuccoing over lath. If you decide to stucco over the joints, you may have to sign a waiver absolving the builders of responsibility for any cracks.
Expansion joints usually cut across the surface of a stucco finish building—vertically and horizontally. However, with the development of architectural styles, you can now place them in creative ways, making them a part of the building’s design.
Some people don’t want to see those crisscrossing lines on their stucco finish, regardless of their protective features. Another reason for choosing stucco over expansion joints is the aesthetic appeal of hairline cracks. Natural hairline cracks may occur in your stucco with age if you forego expansion joints.
Alternatively, you can install laths directly without expansion joints or apply stucco directly on the substrate (without lath).
As mentioned earlier, stucco contracts and expands with temperature changes. Expansion joints prevent the stucco from cracking randomly, especially at the corners of doors and windows.
Simply put, expansion joints are like pre-cracking your stucco to maintain the pristine look of the rest of the surface. Unfortunately, these noticeable cracks at your door and window corners may alter the perfect finesse you want without these joints.
Again, you risk exposing your house and building materials to moisture and the damages it brings. These may include damages like mold and mildew.
Stucco expansion joints serve an important purpose. It’s up to you to use them as a preventive measure against cracks or embrace organic hairline fractures. Whatever you choose, a stucco house is beautiful, and if installed correctly, the stucco is relatively easy to maintain.
Lathing over expansion joints negates the purpose of expansion joints in a structure. Expansion joints are put in buildings to make room for contraction and expansion. Covering the joint with any material predisposes your stucco finish to cracks.
The international building code states that you must cut the lath behind the joint and tie its wires to the sides of the joint. Doing this ensures that your stucco finish doesn’t cross the expansion joint.
You can stucco without lath, and you’ll have no issues if you do it right. The proper procedure involves a well-preferred substrate surface or plumb wall. Applying stucco on this substrate produces a mass wall and minimizes the risk of water intrusion.
An undulating wall will cause you to apply the stucco at different thicknesses, resulting in a removal of the bond. Many people believe that stucco used without lath cracks easily and falls off. This is not true, and architects and owners prefer stucco with lath for a reason.
Stucco on the lath creates a drainage plane behind the cladding for water removal. However, a mass wall made by a well-applied stucco on a substrate doesn’t need a drainage plane. Sometimes, using stucco on lath instead of putting it directly on substrate causes significant cracking.
One scenario that demands stucco over lath is when an older block building is involved. You cannot abandon a metal lath here because there are too many variables from all the time the structure’s been standing.
Expansion and control joints are essential in building materials and construction. Control or contraction joints find application in concrete or masonry (CMU, brick, etc.). Curing or small expansion and contraction movements occur in concrete and masonry, causing shrinkage.
Ultimately, shrinkage causes small amounts of movements that stress the structure. Control joints serve to relieve this stress and maintain the integrity of the building. They usually run vertically on the building, have a bond breaker on one end, and are filled with mortar.
The control joint mortar contracts and expands with the masonry, absorbing the stresses. Hence, the surface of the masonry stays free from cracks.
Expansion joints are horizontal or vertical joints used in masonry or stucco. Unlike control joints, they have no mortar filling. They provide room for contraction and expansion due to moisture and thermal issues.
Expansion joints are also designed and sized to separate building elements and accommodate expected movements in the building materials it separates. The building design team prescribes the size and width of these joints.
They also use a joint expansion system to seal and bridge the expansion joints. A joint expansion system is selected to perform any or all functions, including:
- Handling movements—seismic, thermal, etc.
- Supporting traffic from pedestrians, high-point-load rolling equipment, and vehicles.
Finally, you can create control joints when you place the building material or after placing the material. Place a saw-cut control joint in the concrete to induce cracking in a controlled manner. The usual depth is half an inch or 12 mm.
Careful preparation of stucco finishes can minimize undesirable cracks, but cracks can still develop because of the following:
1. Weak sections due to cross-section changes, like openings
2. Building movements
3. Pilasters, intersecting walls or ceilings, and corners
4. Settling foundations.
5. Restraints from plumbing and light fixtures
6. Shrinkage stress
It’s impossible to prevent all cracks, but metal control joints significantly contribute to their control. Therefore, it would be best to install stucco control joints directly over existing control joints—in the underlying structure.
To meet the proper standards, a building must have control and expansion joints. They maintain the building’s integrity and help prevent unwanted cracks. Weigh the pros and cons before including or excluding one of these joints.