Caulking Lap Siding Bottom Edge

The worst failure we have seen yet.

Caulking lap siding bottom edge.

Wherever hardie siding meets a trim board the company recommends you leave a 1 8 gap between the siding and the trim and apply a 3 8 bead of approved caulking to protect and seal the edge of the siding. Pull the tip of the caulk tube slowly along the joint of the window trim and the siding holding the caulk gun at a. How to caulk the window trim on lap siding 1. After the paint dries apply caulk and then paint the rest of the siding.

Bottom of siding boards should not be caulked. Water is meant to exit through the bottom of each board. The bottom edge of lp lap siding is where the failure is first evident. While paint does tend to somewhat glue these pieces together caulking them is never advised and can cause permanent damage.

Lp siding products also come in sheets in when water runs down the face of the siding it tends to hang on the bottom edge wicking up and causing the bottom edges to swell and delaminate. It needs to move and breathe. It is generally not a good idea to use caulking on wood siding. In my opinion caulking between the seams in any lapped siding either horizontal or vertical is not good practice but not just because of any potential vapor barrier effect.

When deciding how to use caulk on your siding however it is generally more important to consider where you should not use it. If overused or incorrectly placed siding caulk can cause more damage to your exterior than good. Also avoid caulking tongue and groove siding boards together. If you prefer to caulk before painting you should still paint the cut ends first.

The siding expands and contracts with temperature and humidity.