# To prime or not to prime? "Pre-Primed" hardie



## Asmith1776 (Feb 10, 2021)

Brother in law called me last week to paint his house and its hardie board. The hardie is going to be of course the yellow board. So I figured I would go with a one coat prime, Loxon C&M P/S, one-two finish coat, Exterior Duration. So in regards to prep does it need primed other than the "pre-prime". I've read all the post on here regarding the issues that have stemmed from the board after the fact so I want to do my due diligence before the fact. Just extra reassurance from you guys that I need to prime the home for proper adhesion of the finish coat.


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## Joe67 (Aug 12, 2016)

I have never re-primed pre-primed Hardie and have never had a problem. The Hardie co. is pretty serious about what they do, including maintaining a good, quality rep. If I wanted to know the best way to prime it, I'd ask them. I've just always had the impression that they really know what they're doing.


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## Holland (Feb 18, 2011)

Asmith1776 said:


> Brother in law called me last week to paint his house and its hardie board. The hardie is going to be of course the yellow board. So I figured I would go with a one coat prime, Loxon C&M P/S, one-two finish coat, Exterior Duration. So in regards to prep does it need primed other than the "pre-prime". I've read all the post on here regarding the issues that have stemmed from the board after the fact so I want to do my due diligence before the fact. Just extra reassurance from you guys that I need to prime the home for proper adhesion of the finish coat.


Is it new construction? Other than any “raw cement board” you do not need to prime anything. If it is new construction, make sure the backs are primed, and any cuts during installation.

If it’s a re-paint, it just needs to be cleaned (lightly pressure washed) beforehand if needed, and top coated with Exterior Duration.

Most pre-painted Hardiboard comes from the factory with 100% Acrylic Exterior Paint (eg., Exterior Duration). If it is just pre-primed you should be fine to topcoat w/ Duration.


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## RH (Sep 7, 2010)

Put up a fair amount of it. Only primed cut ends.


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## Asmith1776 (Feb 10, 2021)

Joe67 said:


> I have never re-primed pre-primed Hardie and have never had a problem. The Hardie co. is pretty serious about what they do, including maintaining a good, quality rep. If I wanted to know the best way to prime it, I'd ask them. I've just always had the impression that they really know what they're doing.


Awesome I just needed some validation. I explained to him that I needed manufacturing info and a pds on what they used for primer. I wasn’t sure if anyone had any issues I needed to know about before hand.


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## Asmith1776 (Feb 10, 2021)

Holland said:


> Is it new construction? Other than any “raw cement board” you do not need to prime anything. If it is new construction, make sure the backs are primed, and any cuts during installation.
> 
> Should be cleaned (lightly pressure washed) beforehand if needed, and top coated with Exterior Duration.
> 
> Most pre-painted Hardiboard comes from the factory with 100% Acrylic Exterior Paint (eg., Exterior Duration). If it is just pre-primed you should be fine to topcoat w/ Duration.


It’s a new construction, yes. The boards are supposedly just primed yellow unsure of the backs at this time. I’ve had good luck with Duration so I’m probably going to stick with that series for all the jobs I can.


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## Joe67 (Aug 12, 2016)

Not sure why anyone would prime the backs, but happy to hear a reasoning. I'll back-prime wood siding to help protect it. But Hardie isn't going to rot.


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## Asmith1776 (Feb 10, 2021)

RH said:


> Put up a fair amount of it. Only primed cut ends.


I’m coming from an industrial and automotive background, bare with me. 
would you in your PO do a 100% caulk around doors and windows? With metal we do 100% if it’s not welded to ensure rust and any delaminations due to water between coat and substrate.


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## Holland (Feb 18, 2011)

Asmith1776 said:


> It’s a new construction, yes. The boards are supposedly just primed yellow unsure of the backs at this time. I’ve had good luck with Duration so I’m probably going to stick with that series for all the jobs I can.


Cement transmits moisture.

Off-brands don’t always prime the backs, and it causes premature paint failure.
Important to prime raw cement during install. Will last a lot longer.

I believe water-based primers are recommended with cement board, but not positive.


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## Asmith1776 (Feb 10, 2021)

Holland said:


> Cement transmits moisture.
> 
> Off-brands don’t always prime the backs, and it causes premature paint failure.
> Important to prime raw cement during install. Will last a lot longer.
> ...


Good to know. I’ll be sure and check it out before hand. The project is mid-April so I still have plenty of time.


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## Gymschu (Mar 11, 2011)

I re-sided my garage about 10 years ago. I've since moved. Did not re-prime even though many painters will say you should. Literally, the paint looks as good as the day it was applied. I used SuperPaint Satin. I was very much impressed with how well it took paint, how easy it was to paint, and, a big factor for me was that my garage had no gutters so rainwater would splash onto the lower pieces. This may have done a bit of fading to those pieces, but, no rot, not peeling. It's a great product just the way it is, IMO.


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## Asmith1776 (Feb 10, 2021)

Gymschu said:


> I re-sided my garage about 10 years ago. I've since moved. Did not re-prime even though many painters will say you should. Literally, the paint looks as good as the day it was applied. I used SuperPaint Satin. I was very much impressed with how well it took paint, how easy it was to paint, and, a big factor for me was that my garage had no gutters so rainwater would splash onto the lower pieces. This may have done a bit of fading to those pieces, but, no rot, not peeling. It's a great product just the way it is, IMO.


Awesome, I haven’t had good luck with Superpaint (interior). By not good luck I mean just not good coverage. I need to look into the exterior


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## Joe67 (Aug 12, 2016)

Asmith1776 said:


> I’m coming from an industrial and automotive background, bare with me.
> would you in your PO do a 100% caulk around doors and windows? With metal we do 100% if it’s not welded to ensure rust and any delaminations due to water between coat and substrate.


I caulk around doors and windows, and that's when it's most important to have the cut ends primed. (It's concrete board so the cut ends will basically be dust. A primer can basically soak in and - more or less - "glue" it all down so that you're not putting caulk on dust). Hardie does not recommend caulking the butt joints where siding meets siding, but those need some manner of flashing behind them on install to protect from moisture intrusion.


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## Asmith1776 (Feb 10, 2021)

Joe67 said:


> I caulk around doors and windows, and that's when it's most important to have the cut ends primed. (It's concrete board so the cut ends will basically be dust. A primer can basically soak in and - more or less - "glue" it all down so that you're not putting caulk on dust). Hardie does not recommend caulking the butt joints where siding meets siding, but those need some manner of flashing behind them on install to protect from moisture intrusion.


I definitely understand the moisture intrusion and the effects on untreated surfaces. Good catch on the board ends also and thanks for the insight. I could use all the insight I can get.


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## RH (Sep 7, 2010)

When I first put a bunch up (my own house) twenty plus years ago they didn’t recommend _not_ caulking the butt joints so I did it and have never had an issue. Seven years ago we had a substantial addition put on and the siding contractor left the gaps uncaulked as per instructions. Looks terrible IMO, guess that’s the painter in me seeing a gap and thinking “caulk”. Going to repaint that area in a few years and debating whether to caulk the joints there or not. Personally, as long as you leave the required gap and use a caulk with decent adhesion as well as good give and take (I use Tower Tech II), I feel it comes down to personal preference. Though Hardie may disagree if there was an issue and a claim needed to be filed.


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## Joe67 (Aug 12, 2016)

RH said:


> When I first put a bunch up (my own house) twenty plus years ago they didn’t recommend _not_ caulking the butt joints so I did it and have never had an issue. Seven years ago we had a substantial addition put on and the siding contractor left the gaps uncaulked as per instructions. Looks terrible IMO, guess that’s the painter in me seeing a gap and thinking “caulk”. Going to repaint that area in a few years and debating whether to caulk the joints there or not. Personally, as long as you leave the required gap and use a caulk with decent adhesion as well as good give and take (I use Tower Tech II), I feel it comes down to personal preference. Though Hardie may disagree if there was an issue and a claim needed to be filed.


As I understand it, they went to this recommendation of not caulking the joints was because of so many failures. But I'm inclined to see the problem as having been mostly about install of siding and the caulk. Butt joints that are too tight, for example, leave the unsightly seam, but don't give you anyplace to lay in a suitable bead. (I like to have something like an 1/8"). And then there's priming the ends. And then there's just plain old lousy caulk. If your ends are sealed up and you use the Tower, I'm sure it will hold up just fine.


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## RH (Sep 7, 2010)

I agree. I think the biggest issue would be if the recommended gap wasn’t allowed for - regardless of caulking or not.


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## Holland (Feb 18, 2011)

I called HardiBoard on this issue a couple years ago. Apparently, the main concern is 'buckling'. 
Cement board expands and contracts A LOT! Many caulks harden, and would thus crack-out under the stress, or the opposite, they may cause the planks to buckle and wave. 

I have caulked a few in the past under homeowner's insistence, and have not noticed any issues. Think RH's caulk suggestion may be a good one.


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## cocomonkeynuts (Apr 14, 2017)

RH said:


> When I first put a bunch up (my own house) twenty plus years ago they didn’t recommend _not_ caulking the butt joints so I did it and have never had an issue. Seven years ago we had a substantial addition put on and the siding contractor left the gaps uncaulked as per instructions. Looks terrible IMO, guess that’s the painter in me seeing a gap and thinking “caulk”. Going to repaint that area in a few years and debating whether to caulk the joints there or not. Personally, as long as you leave the required gap and use a caulk with decent adhesion as well as good give and take (I use Tower Tech II), I feel it comes down to personal preference. Though Hardie may disagree if there was an issue and a claim needed to be filed.


Doesn't hardie recommend to install H flashing instead?


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## RH (Sep 7, 2010)

Now they do. I have wondered if that wasn’t a result of poor siding installations combined with poor caulking with poor caulk.


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## stelzerpaintinginc. (May 9, 2012)

The only time pre-primed Hardi would need re-primed is if it were installed more than 5-6 months prior and subjected to exposure, thereby degrading the existing primer coating. For all other occasions, I could think of no reason to prime it again. As far as what to caulk, I think it's a bit debatable, especially given the fact that even Hardi has changed what they claim should and shouldn't be caulked. I'm on the side of NOT wanting to see butt-joint shadows from the street, so in most cases, I caulk them, whether they've been flashed or not. I'm often back at homes that I painted well over 15 years ago and I can't see where me initially caulking the butt joints did anything but good. I think a lot of it comes down to proper installation of the siding initially as well as using high quality caulk.


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## ParamountPaint (Aug 25, 2016)

We had a batch of Hardi that needed "re-primed" once, but we didn't realize until after the 2nd finish coat dried and it was all splotchy. Maybe it was old stuff that was laying in a lumberyard for awhile...it didn't look any different than any of the other.

Could have just been a bad batch of Hardi...who knows?

Since we were using a lift, it wasn't a big thing to spray the whole house again with another coat of finish (Manor Hall). The HO paid for the extra work and materials. This was late November and nobody was going to wait and see how all the chips fell with warranty claims and what not...it just needed finished before the snow started blowing. The place still looks good and it has to have been 8 or 9 years ago.

Despite that particular instance, we've never had any particular problem since, using 2 finish coats.


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## Asmith1776 (Feb 10, 2021)

Holland said:


> I called HardiBoard on this issue a couple years ago. Apparently, the main concern is 'buckling'.
> Cement board expands and contracts A LOT! Many caulks harden, and would thus crack-out under the stress, or the opposite, they may cause the planks to buckle and wave.
> 
> I have caulked a few in the past under homeowner's insistence, and have not noticed any issues. Think RH's caulk suggestion may be a good one.


Would that caulking be better or would a loxon caulking?


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## Holland (Feb 18, 2011)

Asmith1776 said:


> Would that caulking be better or would a loxon caulking?


I'm not sure which caulk would be better, I don't use them often enough to say for sure. I think the important thing is that they don't harden as they age, like traditional painters caulks. My guess is probably either Loxon or Tower Tech would be better than painters caulk for that. 

( Loxon is paintable after full cure- Some Polyurethane caulks can take a week or longer to cure). 

*As other posters stated Hardi-Board does not advise using caulk, they currently recommend H-channels ( I've never liked the look of H-channels, they are too "obvious" imo, but warranty may require them).


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## kentdalimp (Aug 15, 2013)

Asmith1776 said:


> Would that caulking be better or would a loxon caulking?


If by Loxon Caulking you mean SW Loxon Urethane Urethane sealant  is always going to be more durable, especially on an exterior. But it's not as cheap, user friendly, and I have yet to find one that doesn't require a minimum 7 days to off-gas before painting. In some instances it would be overkill, but for exterior siding, it would be hard to beat performance wise.


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## Ramus8T (Jan 14, 2020)

kentdalimp said:


> If by Loxon Caulking you mean SW Loxon Urethane Urethane sealant  is always going to be more durable, especially on an exterior. But it's not as cheap, user friendly, and I have yet to find one that doesn't require a minimum 7 days to off-gas before painting. In some instances it would be overkill, but for exterior siding, it would be hard to beat performance wise.


Shermax caulk is pretty awesome and Solar Seal as well. Although I think Solar Seal can bubble at times. 


Sent from my iPhone using Tapatalk


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## finishesbykevyn (Apr 14, 2010)

I wouldn't re-prime or caulk butt joins. Around windows and doors, yes. It's not really necessary. Plus if the caulk does fail, it is a nightmare to repair on hardy and looks horrible.


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## 54pontiac (Jan 7, 2014)

Holland said:


> I called HardiBoard on this issue a couple years ago. Apparently, the main concern is 'buckling'.
> Cement board expands and contracts A LOT! Many caulks harden, and would thus crack-out under the stress, or the opposite, they may cause the planks to buckle and wave.
> 
> I have caulked a few in the past under homeowner's insistence, and have not noticed any issues. Think RH's caulk suggestion may be a good one.


I am shocked to hear that hardiboard expands and contracts a lot. I thought that was one of its selling points, that paint would adhere longer because cement board (like asbestos shingle) does not expand and contract like wood. Can this be true?


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## RH (Sep 7, 2010)

54pontiac said:


> I am shocked to hear that hardiboard expands and contracts a lot. I thought that was one of its selling points, that paint would adhere longer because cement board (like asbestos shingle) does not expand and contract like wood. Can this be true?


Any expansion or contraction is very minimal where we live and under our regular weather conditions so to say "a lot' would be an extreme exaggeration IMO. In fact, if it does occur at all on our house, it's so slight as to be virtually unnoticeable. 

However, in other areas it may be more of an issue. I just think that they want those minimal gaps in place as a precaution against all sorts of temperature and humidity ranges.


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## Holland (Feb 18, 2011)

54pontiac said:


> I am shocked to hear that hardiboard expands and contracts a lot. I thought that was one of its selling points, that paint would adhere longer because cement board (like asbestos shingle) does not expand and contract like wood. Can this be true?


I could be wrong.

However, I have seen hardboard gap up to easily 3/8 to almost 1/2" between boards at some homes. I don't think it was installed that way. 

Hardiboard told me the reason they do not suggest caulking is because of buckling.
You are welcome to verify that info with the manufacturer.


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## ParamountPaint (Aug 25, 2016)

I believe most everything expands and contracts to some extent. I've witnessed Hardi that I installed contract in winter. They have gapping recommendations for installation based on temperature.

If you were to install it when it was hot and caulk the joints with some good stuff, it wouldn't necessarily cause any buckling, but it might pull your caulk joint apart when it was cold.

It's probably not an issue if you live in a happy place where the temperature stays relatively consistent, but we get below zero to near 100 in a year's time...this is the kinda place where you gotta think about such things.


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## kentdalimp (Aug 15, 2013)

My understanding is that they no longer recommend caulking Hardie Siding joints. And it has more to do with Building science than with maintenance of the caulking. 

Currently the science behind Air/Moisture Barriers is that you want the interior walls to be completely sealed and the Exterior walls to be breathable. Because if (when) water get into the wall cavity, they want it to exit to the outside of the building, NOT the inside. 

The idea is by layering multiple layers on the exterior, they can direct water down the wall and away from the structure. 


So the first layer is typically some type of OSB Sheeting. (Which is more of a structural thing that a Moisture/Air thing, but it serves two purposes. 
Then comes a layer of Tyvec or similar, which is designed to be breathable but also keep as much water out as possible. (So that Air/Water in the cavity can exit to outside the structure) 
After that it can be any type of cladding material. In this case it's hardi siding. The recommendation is to use Joint flashings to keep water from flowing into the joints and behind the siding. If you completely seal up the Siding, then any water that finds entry into the cavity will Never Dry. The Moisture cant escape and the is no airflow to assist with drying what does get behind it.
Now there are plenty of reasons to paint the siding! Especially the edges that got cut. The reasoning being that Hardi Siding can hold up to 30% of its weight in water. So if the siding is not "sealed" (Primed/Painted) then it can gather moisture and weigh down the building and allow the moisture to transfer towards the building instead of away from it

Its similar to why you want a breathable coating on CMU block. If you coat it with Elastomeric or something and water can find intrusion it will remain inside the block and lead to failures. Imagine water stuck in the CMU behind the paint then undergoing a winter below freezing. 

There is an awesome Instagram account: BuildingScienceFightClub (Christine Williamson) [LINK] who is an expert in this field and constantly covers it in her feed. 

The more you know! 



> Why does James Hardie recommend using flashing instead of caulk or “H” - Jointers? Experts across the industry recognize flashings as an effective and responsible method for draining a wall system:
> 
> 1. Moisture management –Inherent in lap siding design is the provision of drainage at the laps and drying through the airspace that exists behind each plank. In line with this and fundamental water management principles, joint flashing behind field butt joints provides a physical layer that directs water down and out away from the wall cavity. Caulking at the horizontal overlaps is not recommended because it impedes these drainage and drying mechanisms inherent to lap siding. “The fundamental principle of water management is to shed water by layering materials in such a way that water is directed downwards and outwards out of the building or away from the building. The key to this fundamental principle is drainage. The most elegant expression of this concept is flashing. Flashings are the most under-rated building enclosure component and arguably the most important. ” EEBA (Energy & Environmental Building Association™) Water Management Guide by Joseph W. Lstriburek, Ph.D., P.eng. June 2004.
> 
> ...


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## Paintgirl27 (7 d ago)

Asmith1776 said:


> It’s a new construction, yes. The boards are supposedly just primed yellow unsure of the backs at this time. I’ve had good luck with Duration so I’m probably going to stick with that series for all the jobs I can.


 Exactly, "pre-primed" that's funny. That cement board will suck paint up if not. Also that yellow will bleed through on certain colors.


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