It is my understanding that "big strecth" is designed or used for large gaps and / or for very "dynamic" substrates where extreme expansion and contraction would be a problem. In my experience, regular painters caulk works fine...But this is working under the assumption that the gaps are "normal sized" about 1/8 " or less.
The official position from James Hardie is that these joints are NOT caulked but "flashed". They even go on to say that caulking the painted product will void the warranty. The use of caulk on "primed" material does not void the warranty.
Correcto, this siding expands and contracts too much for any caulking not to break. Since the joints should be flashed behind, the only purpose the caulk serves is for aesthetics. Just know that you have to put up with looking at the gaps.
I have tried priming the inside edges and then using a superior caulk; it still cracked out, not a pretty picture )-:
Most manufacturer warranties are written by lawyers and cover about zero...most installers void the hardie warranty...including HandyANDY. It's a great product. Hardie recommends that joints be sealed with their own proprietary patch...we've never used it. I wouldn't use BigStretch....it's great for interior problem areas and is awesome around crown & trim to avoid the gaps that appear during the heating season. We use Duron Maxflex on our hardie jobs and it hold up great. You can purchase it as Sherwin Williams...it's the best caulk we've ever used and have been doing so for years. We haven't seen much cracking and we have a lifetime warranty on our siding work and 5 to lifetime on painting...depending what we're doing
I'm Charis w/ Sashco, makers of Big Stretch. Please do NOT use Big Stretch on HardiPlank butt joints! It won't work (nor will most caulks). Those joints are simply too small to accomodate proper joint design and a good amount of caulk, and then they move too much (as a percentage) to allow any caulk to hold its seal. If you must seal them (because the HardiPlank is already installed), feel free to use Big Stretch. Just know that you'll have to replace it over the years.
Hardi has new recommendations for sealing butt joints in their installation instructions that Sashco actually helped them form because of our knowledge about butt joints and how they move. Do a search on their website to find out more.
Hey Sashco....Welcome to Hometalk...it is always nice to see another Coloradan on board.