# Caulked Butt Joints on Cement Siding



## nkpaintingvt (Dec 1, 2015)

I'm doing a repaint on cement siding in which the butt joints were all caulked years ago. Now the caulk is mostly dried out and there are gaps at most joints with a few broken corners near the nail. I cleaned out a few joints and it there's flashing. 

Question is - what do I do now? As I understand it, cement board butt joints aren't meant to be caulked, hence the flashing, but I have an entire exterior with failed caulk on every joint. On those few sample joints I cleaned out, it was damn near impossible to get through that hard, old caulk without scoring the flashing behind it with my blade or multi-tool.


Leaving it the way it is is unsightly. Recaulking would temporarily clean it up but the problem would persists, and removing all the old stuff would be super time consuming and I'd likely damage a bunch of flashing in the process. 


Thoughts?


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## kmp (Jan 30, 2011)

I have done projects like this before and just re caulked the joints because it takes too much time to dig them out. Use a better grade of caulk on them when you do it. I really do not know why the plastic h shaped spacers that can be put between the butt joints are not used all the time on houses with siding.


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## SemiproJohn (Jul 29, 2013)

I'm assuming this is Hardie siding. If you go back in time far enough, James Hardie recommended butting the siding together with "moderate contact," or leaving a maximum 1/8'' gap which was to be caulked (even though many caulk manufacturers recommend at least a 1/4'' gap).


The good news for you (actually for the homeowner): you found joint flashing, which is now what James Hardie requires for proper installation. That flashing should by itself prevent water problems (and the wrapping used before installation of flashing and siding). However, for aesthetic and maintenance reasons, that caulk should never have been applied. 



All I can suggest is you talk with your customer and explain the situation to him/her. If they want it caulked again, I would not try digging out all the old caulk. I understand removal of the old caulk would be optimal, but as you stated, very time consuming and potentially damaging to some of the siding. I would just use a really top-notch caulk over the existing like Tower Tech II, or SherMax...something with great elastic properties. The re-caulking may hold up reasonably close (over time) to that of the new paint job. Maybe not, but since it was caulked, this will be a recurring issue over time. Thus, Hardie became of the issue and no longer recommends caulking the butt joints.


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## RH (Sep 7, 2010)

18 years or so ago I resided with Hardie and there was no mention of *not* caulking butt joints. So I did and have never had an issue. 

I have to wonder if they had problems with guys using caulk that hardened up like cement in climates where the siding did achieve potential maximum expansion and then buckling and warping occurred. So now, larger gaps and no caulk are SOP in order to cover their azzes.


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## lilpaintchic (Jul 9, 2014)

They aren't meant to be caulked. The cracked corners are one example of the expansion and contraction that the boards are designed to have. In the fall, the gap will go away again. I'd caulk whatever needs it around the front and in high viz areas and leave the rest alone. 


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## nkpaintingvt (Dec 1, 2015)

Many thanks for all the good input. 



Sounds like I'm re-caulking. John mentioned TowerTech/Shermax - any other strong opinions on type? 



I'm going to power wash the house, so considering that those joints might change with water absorption, how long would you wait to recaulk?


Could measuring some of the wider gaps and only caulking once they've returned to the original width be a good gauge? How about moisture content? I know how to use my moisture meter with regards to wood, but this is my first cement board house. 


Thanks again!


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## ParamountPaint (Aug 25, 2016)

I like osi quad, but it has a decent cure time. Npc solar seal is better yet, imo.

These are "real" sealants with a learning curve. There is an art to that, which is why glaziers are paid pretty well.


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## RH (Sep 7, 2010)

I like and use the Tower Tech 2. 

I can’t see where measuring and then waiting for the optimal time for gaps to close up before recaulking would be a feasible plan. Just use a caulk with good adhesion and flexibility.


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## Mr Smith (Mar 11, 2016)

I remember working with a contractor who was doing some Hardie Board Siding repairs a few years ago. He gave me some specialized caulking that is used specifically with Hardie Board. It was super sticky and difficult to apply, unlike the usual acrylic caulking that we are all used to using. Apparently, it stays flexible and doesn't dry in a typical fashion. I forget the name of that caulking. I'm sure any Hardie dealer will give you the name.

I can tell you that it was difficult cleaning that caulking off my hands!!

I'd just apply more of this on top of the old caulking and call it a day. Removing the old caulk would destroy the siding.


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