# Hardie siding butt joi ts



## T-rum (Jan 29, 2011)

What are are you guys doing on re-paints regarding butt joints on cement board siding? I used to dig out old caulk and re caulk with quad. Now, I hear quad isn't recommended for expansion joins, so do you just use regular siliconized latex caulk or are you not caulking and leaving the gaps? 

I understand new building practices regarding cement board siding calls for an aluminum flashing underneath the butt joint and then not caulking, but on these older (10 year) builds I'm repainting there is no flashing underneath. 

So to caulk (and with what) or not caulk, thay is the question?


----------



## Joe67 (Aug 12, 2016)

Certainly the current "system" is to do the flashing and not caulk because caulk just doesn't hold up in those gaps. There's too much movement and the ends are basically dust. (Ideally if they were to get caulk for some reason the ends would get primer and paint to seal them up).


So if there's no flashing on this job, I'd say it does sort of leave you in a no win situation. I haven't yet gone behind a job without flashing, but I have needed to do some caulking on it, largely to cover up for bad cuts. So I make sure the ends get primer and paint and then caulk. My go to is Dynaflex 230 for all around performance, but others might have better suggestions.


I wonder whether there isn't a way to add flashing after the fact - cut down some flashing, get some manner of adhesive on the top edge and get it shoved up in there without making a mess. I'd likely try it. Worst that can happen is you don't make it work...


----------



## vwbowman (May 15, 2017)

Back int the day when I did the work rather than sell the paint, I used clear ProStretch, which is a private label for AllPro, made by TowerTech. Using a Mix-A-Color, I mixed in 10ml of paint and was careful not to overfill the cracks. Even with the movement over time, the color match was great. Typically the caulk had more sheen, but died down over the first few months. Customers loved the idea that they would not see white caulk in a couple years.


----------



## diT (Jul 24, 2019)

I've painted hundreds of big gable ends on apartment buildings that we're finished with Hardie.
If the Hardie is installed properly it should not move THAT much.
We caulk them with elastomeric caulking and paint them with minimal issues.
Most of the time they move when they are blind nailed.


----------



## Whiskey (Apr 10, 2019)

I am very interested in the responses as I just started the prep work on a house with the exact same scenario Hardie board butt joints with no flashing behind them. They had been caulked with some cheap caulking that had failed. My plan was to cut out all failed caulking, brush in loxon primer, caulk with OSI Quad or Sikaflex, wait 7 days to cure out, then prime again prior to painting. If there is a better way to do this I look forward to hearing about it.


----------



## RH (Sep 7, 2010)

Resided my own place with Hardi-Planks about 18 years ago. At the time, I think they may have actually recommended caulking butts joints. Anyway, I did all of them on my place using a good quality exterior caulk (not sure it was an elastomeric back then). Never had a bit of problem with them.

I suspect they may have come out with the non-caulk recommendations after getting burned by guys using cheap-assed caulk.


----------



## Woodco (Nov 19, 2016)

Whiskey said:


> I am very interested in the responses as I just started the prep work on a house with the exact same scenario Hardie board butt joints with no flashing behind them. They had been caulked with some cheap caulking that had failed. My plan was to cut out all failed caulking, brush in loxon primer, caulk with OSI Quad or Sikaflex, wait 7 days to cure out, then prime again prior to painting. If there is a better way to do this I look forward to hearing about it.


Good Lord, thats a lot of work...


----------



## Joe67 (Aug 12, 2016)

Woodco said:


> Good Lord, thats a lot of work...



Other than that I don't see a need to prime again after caulk, what other options are there? There are reasons that Hardie changed to "don't caulk butt joints" and among them is that they too often failed and then they're just plain ugly when they do. And then it's just a mess. When old caulk fails you start cutting and fixing.



(As RH surmises this might have all been due to people using shizzy caulk, but people coming behind it still have to figure out what to do).



So I'd skip the primer after caulk, but other than that, yeah. Cut out what you can without getting OCD about it. If it's loose get it out, and make yourself a gap. Prime the gaps trying to seal up the cuts. Caulk with an elastomeric. And hit it.


----------



## juanvaldez (Sep 7, 2019)

About 5 yrs back I talked to a rep on a job gone bad that I was pulled into with hardie and he said only caulk to verticals, (butt joints) and not the horizontal. It was a real pain to make it look good. 


Sent from my iPhone using Tapatalk


----------



## ParamountPaint (Aug 25, 2016)

Joe67 said:


> I wonder whether there isn't a way to add flashing after the fact - cut down some flashing, get some manner of adhesive on the top edge and get it shoved up in there without making a mess. I'd likely try it. Worst that can happen is you don't make it work...


I've done the scenario you describe, but slightly differently. We cut aluminum flashing slightly longer than the reveal of the siding, slide it in, and nail through the siding (as high as possible, angled under the overlap) with stainless steel nails in a trim gun (usually 18g, if I can hunt down the stainless nails). Stainless for 15g DA nails are widely available as a stock item here, so I use those if I haven't had the foresight to order the much cheaper 18g stainless.

If you aim right, you won't even need to fill the hole, but in any case it doesn't matter if you're repainting anyway. No big thing to use a little caulk on a tiny nail hole that you'd be hard-pressed to see from 3ft away.

If you want to be extra fancy, you can pick up black coil stock or paint the silver and it won't show. To be extra, extra fancy, you could potentially paint the flashing with the house color, but I've never done so, and doubt that it would make any noticeable difference. It might also screw over the next painter who is doing a drastic color change, but I've never went that far and have never seen it done, so who knows?


----------



## T-rum (Jan 29, 2011)

Thanks for all the replies. Well after hearing these suggestions, talking with my paint rep, and talking with the customer, I ended up digging out all old caulk and re-caulking with Shermax elastomeric. I informed the customer that these joints would be the first thing to fail on this paint job, but they just didn't like the idea of having exposed areas under the gaps and therefore opted for re-caulking even with the potential future cracking. I don't feel confident in my skills trying to put any flashing behind and just didn't want to go there. I do however feel confident that I ran a nice fat bead and that this will last a good 5 years at least (I hope) The only thing I wish I could have done is gotten some color matched caulk, I think the Pro Stretch offers it, but during this pandemic that's just wishful thinking. Anyways thanks everyone, this house is finished and I'm off to the next one!


----------



## Joe67 (Aug 12, 2016)

The Shermax will be great. You should sleep well at night.


----------



## fromthenorthwest (May 2, 2012)

I agree with the Shermax. I use Big Stretch for those butt joints, which is another elastomeric. I used to use Quad, and I still do in a lot of areas on re-paints, but I found that at least for the expansion joints Big Stretch holds up a lot better than quad


----------

