Hi I have been fighting the calking on my house .the house is new and all the siding is not done yet ,but the areas on the butts of the hardy board expands and contracts enough that in the hot summer the boards expand and push the calk out of the butt joint ,and in the winter they shrink enough that it pulled the calk apart and I can see the tyvex through the crack . The joins at the trim at the corners of the walls look perfect still.are my butt joins to tight ? I have used elastic type latex calk ,is there a better calk that bonds better to the boards and follows the expan.and contract. Of the boards... thanks much , can reply to [email protected]

Have you tried silicone chaulk? It can be messy to work with but worth the effort.

It would be good to know just what product you have. The stuff made by the James Hardie Company is called Hardieplank, they also make Hariebacker for sub flooring. To my knowledge Hardieplank does not expand and contract but maybe your house does.

I just read the hardie directions. There are two ways of installation: moderate contact butt joints with no caulk or 'leave appropriate gap and then caulk' The important thing on 'moderate contact' butt joints is to use the factory edge at the joint so that it is properly sealed.
http://www.jameshardie.com/pdf/install/install_plank_north.pdf

I don't think hardieplanks will expand much, but if it is a moderate contact joint, any expansion would definitely squeeze caulking out. If it is a 1/8" gap, then you wouldn't have a problem because the caulking would compress. I think that is why you are not having trouble with the joints at the trim.

I wonder if the solution is to remove the caulking on the butt joints, because it does not appear that you need it. Perhaps the painters put it on by mistake?

Oh - and I wouldn't recommend silicone under anything that is painted. It'll change the sheen of the paint after a while and look peculiar.

When considering the use of silicone remember that paint will not adhere to silicone.

When it comes to hardi - board silicon is NOT an option. I have installed around 75,000 square feet of hardi-board siding and I use nothing but QUAD sealant by OSI. You can order it at construction adhesive manufacturers - adhesives - sealants - OSI Pro-Series® (http://www.osiproseries.com). It comes in many different colors and is by far the best product I have found for hardi-plank. If the caulk is being pushed out of the joints in the summer... it was installed with out enough expaintion room... Hardi-plank WILL expanded and contract. Hardi-plank requires a minimum of 3/16" for expansion.
Mike