Why You Should Never Caulk Fiber Cement Butt Joints
Fiber cement is one of the few exterior cladding products that can actually act as a water infiltration barrier. It is a common misconception that fiber cement butt joints should be caulked. These are the reason why you should never caulk the butt joints of fiber cement and use some kind of flashing sheet instead.
- Fiber Cement Shrinks – Yes, fiber cement does shrink once you install it. It will not shrink a lot, but in some cases it will shrink just enough to pull lose from the caulking.
- Walls Move – Everyone knows that homes and buildings shift and settle during different times of the year. When a building shifts, so does the fiber cement. A large enough shift can cause joints to separate away from the caulking you installed.
- It Looks Unsightly Over Time – No matter how hard you try, the colored caulking you use will never completely match the color of your fiber cement. It might look great at first, but in 8 to 12 months it is very likely that the fiber cement and caulking will weather differently and the colors won’t match like they did in the beginning.
It doesn’t matter how hard you try to match the caulk and fiber cement paint color, you will eventually see streaks.
The absolute best way to flash fiber cement butt joints is to use some kind of flashing sheet or tape behind every joint.