Expert: Stephen Major (Owner--Major Design Group) - 6/3/2007

Question
I am using 8.25 inch x 12 foot hardi plank with a 7 inch exposure. It is proper to caulk the horizontal laps between each board. I understand the need to caulk and butt joints, and areas where the " skin " has been broken. But I am getting much conflicting advise on the caulking of the lap joints. Some say it will void the warranty, or it will not let the material breath and the moisture drain, others say just the opposite. An e-mail to the James Hardie site remains unanswered. Your timely advise would be greatly appreciated since I start painting tomorrow.  

Answer
Richard,

There is no need to caulk the horizontal laps.  The lap is what sheds the water.  Caulking this area is a waste of time, and can, under some circumstances, cause water to be trapped behind the siding.

Please let me know if you need additional information.

--Steve Major