Many people think installing fiber cement boards is simple-just nail them on. But honestly, after so many years in this industry, I've seen far too many failures: cracked boards, bulging joints, and even entire walls becoming loose after a few years. Where does the problem lie? Nine times out of ten, it's in the "unseen places"-the joists and the joints.
First, don't install them rigidly onto metal joists.
Despite having good structural integrity, one of the main characteristics of fiber cement boards is that they will expand or contract due to changes in temperature. Although they have a lower shrinkage rate than both wood and plastic (with many material types), any variation in temperature can cause internal stresses in fiber cement boards.
Many installers, to save time, screw the boards tightly onto the joists, using a dense fastening pattern-almost like sewing a garment. The result? In the summer heat, the boards have no room to expand and end up cracking at the joints.
My advice is: give the boards some "flexibility." Use galvanized light steel keels, as their stability is far superior to that of wooden ones (which can warp when damp-a "killer" for cement boards). During installation, screws should not be driven too close to the edge of the board; leave at least 10–15 mm of clearance. It's like fastening a belt-if it's too tight, it becomes uncomfortable; a little slack makes it more secure.
Secondly, for joint treatment, don't rely on "putty as a cure-all."
Overseas projects often take place in regions with significant climate differences, such as the hot deserts of the Middle East or the icy conditions of Northern Europe. In such environments, if you simply fill the gap between two boards with ordinary putty, the joint will likely become visible like a "scar" within six months.
We always emphasize to our clients: joints are not just "filled"-they must be properly treated.
Use only dedicated mesh or elastic joint compound. The correct way to do it is to first "bevel" the joint into a V, then fill the joint with joint compound and apply the mesh tape immediately while the compound is still "slightly wet." After adding another layer of compound to level out the surface, you will have an elastically buffered joint.
Similar to the sewing of an elastic waistband onto a garment, your boards can move slightly due to temperature changes; however, because there is an elastic buffer between the two pieces of wood at the joint, the joints will not crack.
Third, don't forget about waterproofing.
Fiber cement board is water resistant, and can be submerged without causing damage to itself; however, moisture can damage the joists and rust out the screws.
When doing work in bathrooms, on exterior walls, and in wet basements I have observed many instances where there was a need for rework because the previously mentioned items were not taken into consideration during installation.
Keep the joists off the ground: The ground is the most humid area. When installing partition walls, place a rubber pad or PVC strip between the bottom joist and the floor. Do not allow the cement board and joists to come into direct contact with the ground. Even raising them by just 5 millimeters can extend the wall's lifespan by several years.
Use corrosion-resistant screws: You should never use regular self-tapping screws. Use stainless steel screws or double-cell threaded nails with a corrosion resistant coating. Also, when using screws as mounting hardware, the screw head should be slightly recessed into the surface of the board and the hole filled with epoxied resin texture so that water cannot penetrate through these locations.