Hardie butt joints can be filled in with some good caulk that can expand and contract. Hardie does not recommend filling on Hardie Plus lap. Elastomeric Joint Sealant complying with ASTM C920 Grade NS, Class 25 or higher, or a Latex Joint Sealant complying with ASTM C834 are allowed. Your hardie lap is not installed properly as it requires a min 6" above the ground.

Thank you for your comment. It looks to me like a bondo or wood filler was used. If it is, will it crack when the siding expands and contracts?

Yes.

Correct, whatever is used to fill joints like that needs to be able to expand and contract with the material (i.e. something like a silicone a sealant). Anything without that ability to move will crack.

But the other concern that others and myself included have is that the siding is extending down to and below grade. In addition to the manufacture's recommendations for the siding material itself, it makes me wonder to what it is attached? Does your framing extend down to grade? Even if it doesn't, then the siding is on some sort of wood nailer? Has your builder left your home vulnerable to water, or depending upon your location to termites?

If Hardie Siding is not installed 100% according to their instruction there is no warranty.

If the lowest board is over concrete, all that will happen is the paint will eventually peel at your expense and if it is on strapping (doesn't look like it), the strapping might rot if its not pressure treated. If the boards bow outward later, you'll need to remove the gap filler.

If the joints were properly flashed, they do not need sealant.

On top of your joint problem, Hardi Siding coming in contact with the soil is a problem too.

Based on Hardie installation directions, the end joints do not need any sealer, but that assumes the installer got the boards close enough so that there is minimal gap and it looks good. I prefer to use flashing behind (as shown) and also add a bead of caulk between the board ends, even though its not required for water resistance reasons.

Bruce

This is not a hardy installation.

Thank you for the information. I attached a picture of the side of the house before the siding was installed. I don't know how they attached the siding to the concrete blocks.

It looks like they used treated wood to attach the siding to the concrete blocks.

The foundation height above grade at the front was not maintained in the rear forcing the top of it and the bottom of the siding too close to the ground. I hope the strapping is pressure treated and you're not in a termite or snow zone. Not much that can be done except avoid vegetation against the house and install gravel. You might consider replacing part of the siding with cementitious parging.