Caulking For Fiber Cement Siding

Dap alex plus 12 pack 10 1 oz white paintable latex caulk.

Caulking for fiber cement siding.

2 house built before 2008 so has no flashing okay to caulk. Fiber cement boards don t expand and contract much but leave a little room for expansion at the end joints and then fill the gap with caulk. Applying caulk to the butt joint is ineffective because the gap is not large enough to accommodate the sealant. We only caulk butt joints on cedar siding if previously caulked.

Many professionals like those at james hardie also agree that you should not use caulk on fiber cement siding unless there is no metal flashing underneath. 1 i chose this caulk because it has 25 flexibility compared to silicone based caulk. Caulk is usually used with fiber cement siding to prevent water intrusion at the butt joints. Flashing acts as a waterproofing layer for this type of siding and caulking will prevent the flashing from doing its job.

Trim boards wood windows. When james hardie siding products butt into wood based materials a 1 8 gap will allow for expansion and contraction of the wood based product. Fiber cement boards are caulked only when there is no metal flashing behind them. The specification to omit caulk at siding butt joints is for new installations and is discussed in detail by the manufacturer.

So what i would tell you to do is to use a colored caulk to choose the caulk in the color of the siding. Some manufacturers do not require the metal flashing therefore we caulk the butt joint to keep the pieces together and also prevent moisture. Do not caulk fiber cement butt joints edges. Caulking around windows doors eaves and trim edges gives added insurance that leaks will not occur.

However this detail may not be effective at sealing the ends allowing water to be absorbed and swell the board ends.