This from installation instructions.
Caulking siding joints.
When to use caulk on exterior siding siding caulk can be used on several different areas of your exterior siding to help prevent water damage and moisture buildup.
Use sanded caulk any time you use sanded grout and in joints 1 8 inch or wider.
Another critical place is where the siding butts together in the middle of the wall.
Sanded caulk has particles in it that help it adhere to wet surfaces and expand in larger gaps without cracking.
25 4 mm on overlap no caulk figure 1.
A high quality paintable caulk is recommended.
This is a must do for all houses.
Moisture can still seep in at butt joints the places where the ends of two pieces of siding meet and where siding meets trim.
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There s no way around regular maintenance of those siding butt joints unless you want to completely remove the siding and install joint flashing.
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These siding joints can be caulked successfully if the gap is wide enough for the caulk to get into the crack.
What must be caulked caulking corners.
Unsanded caulk has a smooth appearance and texture.
For regular hardiplank lap siding the kind you paint after installation caulking at butt joints is optional.
152 4 mm wide 1 in.
Dap cedar acrylic latex caulk with silicone.
Caulk can be either sanded or unsanded.
Moisture likes to hide in corners edges and under ledges.
Butt joints but not all butt joints.
This allows for the caulk to get in and fill the gap correctly.
To avoid leakage these seams should be sealed with caulk.
Some of the most commonly caulked areas of siding include both corners and crevices as well as some butt joints and window and door trim boards.
Sometimes the old caulk in the siding joint is cracked and you need to cut the old caulk out with a razor knife.
Joint flashing butt joint horizontal lap treatment june 2014 james hardie does not recommend caulking butt joints or the horizontal overlaps joint flashing 6 in.
Caulking your home s siding is a simple process but not necessarily a foolproof one.
If the siding joint is so tight that the caulk only bridges the gap it may split again.
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Where two pieces of siding meet.
Those joints need to be protected somehow.
It has a grainy texture and appearance.
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James hardie also does not recommend applying caulk to the horizontal overlap between siding planks see figure 2.