I am replacing some rotted cedar T1-11 8" O.C. grooved 4' x 8' sheets with Certainteeds 8" O.C. Cement Fiber 4' x 8' siding. It won't ever rot.  It hasn't arrived yet, so I may send it back.  The Certainteed guy who just called me up said "you butt the sheets together along the 8' edges". If that is so, the butt seam will leak with the kind of weather we have unless the edges are caulked as they go up. He said he thought Certainteed did not recommend caulk.  Yikes, am I in the hand of amateurs, or what?  Anybody else had experience installing this product?  I need information.

I have not used that name but have hung plenty of cement board and I have butted them together with caulk and overlapped them to give them a ridged look when going horizontally. I dont know why they would say no caulk.

Some of those products have a preapplied resin along the joint edge that melts together after you install them, so before you decide to calk it, or not, check on that first.
Only siliconized rubber caulkings will stick to cement products for any length of time, they are expensive, but they will work ok for most things.
But... remember, you aren't building an aquarium, you are supposed to have the barrier layer *under* the siding, not make the siding into one, water trapped under the siding that can't escape  will eat the structure...

Cant paint silicone so something else to consider

I use Hardiplank and Hardiesiding, and both have an overlap joint. Hardiesiding that I use is manufactured like T111 siding, designed to overlap. Hardieplank is installed like shiplap, making an automatic overlap. I have used silicone in a few spots that I thought weren't sealing well.

Quote from: Wrenchmensch on September 19, 2011, 05:20:57 PM
I am replacing some rotted cedar T1-11 8" O.C. grooved 4' x 8' sheets with Certainteeds 8" O.C. Cement Fiber 4' x 8' siding. It won't ever rot.  It hasn't arrived yet, so I may send it back.  The Certainteed guy who just called me up said "you butt the sheets together along the 8' edges". If that is so, the butt seam will leak with the kind of weather we have unless the edges are caulked as they go up. He said he thought Certainteed did not recommend caulk.  Yikes, am I in the hand of amateurs, or what?  Anybody else had experience installing this product?  I need information.

From what I know about ya, you're pretty smart.... could be wrong!  I've heard a lot of mixed reviews about that stuff. So, find someone that knows what they're talking about (IE--- NOT ME)... because they're definitely mixed reviews about that stuff. all the best and such
cheers, bird

Quote from: 1930 on September 19, 2011, 07:09:51 PM
Cant paint silicone so something else to consider

Marine grade caulk.   I used to buy it from a wooden boat repair shop.  They carried a 3-M product (#2000?) that worked wonders.  More expensive, and takes longer to harden enough to paint, but it really does the work.  It's permanent and paint-able. 

5200. you do NOT want to know what that stuff costs !
It is a polyurethane based sealant, and onlyt paintable with certain types of paint.
Last time i looked it was over $3/oz
It is also not rated for concrete....

The installation manual does *not* recomment horizontal board to board caulking, it is a breathable system. Trim caulking is recommended, and latex compatable caulking seems to be ok...

The installation manual is online btw... http://www.certainteed.com/resources/fc017.pdf
(yeah,yeah, real men don't read the instructions...)

The need for sealing the 8-foot vertical butt seam between adjoining 4 x 8 panels was discussed at Bible Study this a.m. and then with a Certainteed Consumer Rep this p.m. The consensus is: use 15# felt strips 6" wide and 8' long behind each butt seam. I am not going to use the 5/16" furring strips as they will create cavities between cement fiber panels and the aluminum-clad 1" foam sheathing. Into such cavities local vermin, arachnids, and insects will crawl and nest, which is undesirable.  I will use a z-strip along the lower edge of the installation, with a horizontal clearance of 1 inch from the bottom of the cement fiber panel.  This has been unanticipated learning curve.  The reassuring news from Certainteed is that their product is tougher, more resistant to damage than the comparable James Hardy product.  The reason, they say, is that Certainteed use fly ash.  Full report to come when I get the 28 linear feet of new exterior weatherboarding in.  Stay tuned!