# Forum Home Renovation Cladding  How to make HardieFlex sealant joints inconspicuous?

## Chr1s

Hi,
I have a 6.7m x 1.1m (to the top of the fascia) section containing clerestory louvre windows above a laminated beam in the living room (BIG mistake), and while the actual louvre windows are fine, it has been impossible to maintain watertight seals around their timber frames and the surrounding Western Red Cedar weatherboards due to movement and ageing, and leaks are a major headache during storms. The only proper solution I can think of is to rip out and ditch all of the louvre windows, and have external cladding running across the entire section, as shown in the photo.  
Initially I thought of Duratex or HardieTex blue boards, but they require specialised joint reinforcement and a texture coat system, which sounds fiddly and expensive, and I'm sure they will develop cracks over time, so I figure that if I'm going to get cracks I might as well go for a cheaper option with simple sealant joints (rather than standard PVC joiners which I think look cheap and nasty). 
After considering a variety of options I think that three 2400 x 1200 x 6mm HardieFlex sheets cut down and butt jointed horizontally are probably the best solution. Weatherproofing is vital so my plan is to butt joint the sheets over the studs with 5mm polyurethane sealed expansion gaps, and with 230mm wide aluminium flashing and vapour permeable sarking behind. I'll use 50mm wide masking tape as the bond breaker behind the vertical joints. A continuous length of 230mm wide aluminium flashing will be run under the ridge capping tiles, over the fascia board and top tiles on the other side, which hopefully will complete the weatherproofing. There will be two vertical joints and I'm wondering if it's possible to make these joints inconspicuous after painting. 
Some of the fibre cement installation guides show butt joints as tight as 1mm, which would be good, but according to the Sikaflex guide, sealant joints should be about as wide as they are deep, so 5mm is probably as narrow as I can go with 6mm sheets. 
The HardieFlex guide says, "When filling joints with sealant, cut the nozzle of the cartridge to suit the specified gap between the sheets, weatherboards and planks. Mask the edges with easily removable masking tape. Then apply the sealant in an upward motion, pushing the sealant into the gap to fill it. Carry this operation out slowly to ensure the sealant completely fills the gap and bonds to the edges of the cladding. Run a spatula over the joint, carefully wiping away the excess sealant. Carefully remove the masking tape immediately after you complete the sealant application." 
Theoretically, 2.4m fibre cement sheets should only move by about 1mm over a 30 deg C temperature range, so if the polyurethane sealant is finished flat with a spatula and painted, how visible will the joints be from street level and can they be made invisible, and how stable in practice are butt joints between fibre cement sheets?

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## OBBob

Sounds challenging. I don't think it's the movement of the sheet you need to consider, rather the movement of the rest of the structure, which is supporting those sheets.

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## OBBob

What about something like Scyon Stria? It can be butt jointed off studs and if you stagger the joins theoretically the tounge and groove system should help the whole lot stay together.

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## Chr1s

OBBob thanks. I must confess I don't fully understand the mechanics of building structure movement, but assuming the 6mm HardieFlex sheets won't fracture or fail catastrophically in that situation, I was thinking that they should act as bracing to stabilize the frame up there shouldn't they? So presumably any movement would be essentially thermal expansion and contraction, and over 2.4m, the difference between timber and concrete expansion is theoretically only about 1mm per 10 deg C, which the sealant should be able to accommodate. 
At first I thought of using Western Red Cedar weatherboards, but their maximum length is 6m so there would be one joint per plank, however the disadvantages of timber had me thinking about FC alternatives. 
Scyon Linear 4.2m planks sounded good and they use tongue and groove joints but they're about 3 times the cost of HardieFlex and might have the same joint visibility problem, plus fiddly to have flashing behind each joint to protect against joint failure.
The Scyon Stria 4.2m planks would also have joints and the manual recommends 3mm gaps for sealant so presumably I would still have visible joints, although they could be staggered, but I'm not sure if they would be any better than the sheets and they're also about 3 times the cost. 
Do you see any problems with using HardieFlex sheets in this situation? My only experience with FC sheets is soffit linings and apart from the occasional nail popping, they seem to be stable and trouble free. Am I'm missing anything?

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## OBBob

I haven't done your particular scenario but I think trying for seamless joints without going down the full rendered path is likely to show over time. Some sort of architectural trim that covered the joints would be ideal if you could find something that would fit in with the look you are trying to achieve.

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## r3nov8or

I don't think you'll get a seamless finish, but with only two joins it'll be hardly worth worrying about. And yes in your situation over a large beam a rendered finish will likely crack on you. Go with the 5mm. Sealants only expand/contract x% of the width of the join. So for example 25% of 5mm is a lot more comparatively than 25% of 1mm

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## Chr1s

Yes, I agree that the two joints are only a minor issue and I was hoping there might be a trick of the trade to conceal them, but apparently not. The waterproofing is the major consideration and hopefully I've got that covered.
I can't think of an architectural trim that would suit, but I considered the Scyon Matrix idea with expressed joints every 1200mm ... so rather than try to hide the joints, make them a feature ... but while it looked good in their photos, it didn't work for me.
I saw a rendered wall at my local shopping center yesterday and for the first time noticed several cracks that I'd never noticed before. Sometimes you only notice these things when you go looking for them.
I suppose if the joints annoy me I could try painting the section with a darker colour that might make them less visible, but once the job is done I'll probably just stop fussing and learn to ignore them. Fingers crossed, thanks.  :Smilie:

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## OBBob

On newer houses they'd probably just use a plastic joiner trim, on older houses good probably put a 60mm x 10mm timber trim over it.

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## Chr1s

Yes I've seen the PVC jointers and also the timber trims. I was hoping I might be able to make the sealant joints less conspicuous.
With Hardie's PrimeLine weatherboards, the recommendation is for either a 3mm gap with sealant, or butt sheets together (presumably zero gap) without sealant, and no special joiner is shown, just Hardie's sarking.
BGC's Durasheet brochure shows butt joints with zero gap on soffit linings.
That suggests that thermal movement is not an issue. 
Sikaflex is supposed to be able to stretch 400% so maybe a tighter gap would work.
Even the manufacturers seem to be divided on gap width. All very confusing!  :Confused:

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## OBBob

It's just not likely to last. Happy to be proven wrong but in time it's likely to become visible.

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## gpkennedy

Hi Chr1s, you are replacing clerestory louvre windows with some sort of sheet. I have little experience with finishing external hardiboard. Have you considered replacing all the louvre windows with  another type of window? Those existing louvre windows must allow a fair bit of light into the rooms. Depending on the orientation of the sun, blanking out those windows may not be the best alternative

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## Chr1s

Hi gpkennedy, the louvre windows themselves are not the problem. They're watertight. The problem is the penetration of the sarking by the window frames and the impossibility of maintaining watertight seals between the frames and the external Western Red Cedar weatherboards ... too much timber and too much movement I think.
With normal windows I guess any water that seeps in usually runs down the cavity and out through the weepholes, but with clerestory windows it drips down onto the carpet inside.
I currently have all of the windows covered over with a sheet of black plastic and lighting is not a problem and there's plenty of light coming in through the other windows.
The clerestory windows were supposed to be for ventilating the hot air during summer, but they proved to be totally unnecessary and were a VERY bad idea!
Short of having the house rebuilt with a different roof line, I think the only solution is to have an unbroken run of sarking with impervious sheet cladding and good flashing from top to bottom. 
Maybe 3mm sealant gaps as per Hardie's recommendation might be the way to go. Zero gaps sounds risky and I think that whatever I do is going to be visible, so my aim will be just to make them as inconspicuous as possible.

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## OBBob

You could clad in cement sheet as you suggest and then clad over that in the diagonal cladding that is on the other section of the house?

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## Chr1s

This is the current sad state of affairs ... before being covered by the black plastic sheet.
The leaky sections were covered with strips of aluminium flashing as a temporary fix ... which hasn't always worked.
Too much sun was coming in so I stuck "Contact" over the glass, and that's now disintegrating.
All in all ... a bit of a disaster area!

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## Chr1s

OBBob, yes that's a thought, thanks.  :Smilie: 
That would certainly solve the problem of unsightly joins ... and be super waterproof! Cheers!

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## Chr1s

Certainly worth considering!  :Smilie:

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## OBBob

You can also get grooved ply or FC sheet. You could join at a groove to make it less obvious.

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## r3nov8or

> ...
> Sikaflex is supposed to be able to stretch 400% so maybe a tighter gap would work.
> ...

  I think you've taken 400% from 'Elongation at break' specs, which isn't the lateral movement

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## Chr1s

OBBob, thanks again. Another option I'm seriously considering is Duragroove with 150mm wide spaced grooves, which would match the spacing of the existing WRC weatherboards. It's twice the cost of HardieFlex, but I think it might look better than the plain sheets. I prefer horizontal grooves to vertical grooves.   
It is designed to be installed vertically and has shiplap joints, but they show an example of vertical butt joints so I was thinking that I should be able to install them horizontally, butt jointed as with the HardieFlex, and since the 1200 wide sheets exceed the height, there would be no horizontal joints to worry about. The EPDM Foam Gasket is expensive and sounds like overkill, and is probably there because of warranty considerations, so I might give it a miss and just rely on my 230mm aluminium flashing. Any thoughts on that?   
Walking to the polling booth yesterday, I noticed a large number of HardiPlank houses. Most of them had those ugly PVC jointers, but I saw a couple with long lengths of HardiPlanks and no visible joints and I'm guessing they might have been sealant joints. I might go back for a closer look and maybe speak to the owners, and if they are in fact sealant joints then that would be very encouraging.

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## Chr1s

> I think you've taken 400% from 'Elongation at break' specs, which isn't the lateral movement

  Yes I think the 400% refers to longitudinal tension. I'm assuming that longitudinal expansion/contraction is the major factor to consider.
If both sheets are nailed to the same, or adjoining studs, how much lateral shear would there be, given that the sheets will be acting as bracing for the area?
I imagine torsional flexing is not a concern.

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## r3nov8or

> Yes I think the 400% refers to longitudinal tension. I'm assuming that longitudinal expansion/contraction is the major factor to consider.
> If both sheets are nailed to the same, or adjoining studs, how much lateral shear would there be, given that the sheets will be acting as bracing for the area?
> I imagine torsional flexing is not a concern.

   The timber stud you are attaching both sheets to will swell and contract on its width ( across the grain ) with changes in moisture and temperature. This movement is enough to crack acrylic render in some circumsatnces. But your timber stud is very unlikley to get longer ( ie with the grain ) at any rate of any concern at all.

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## OBBob

You could call the JH technical help line and ask them. I'd be a bit concerned about using products in a way they weren't designed for... just in case you send up in the same situation you are now. I guess you just need to think it through carefully.

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## hotshot

I haven't read this whole thread so not sure if this has been suggested but have you considered a negative detail?

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## hotshot



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## Chr1s

r3nov8or, ahhh OK, yes I hadn't thought of that. Oh well, what will be will be, and I guess there's probably not much I can do about swelling except hope that the sealant will accommodate it. 
OBBob, yes that might be an idea. Perhaps I should shoot them an email with some photos so they can see what I'm planning ... might be better than trying to describe it over the phone. 
hotshot, if "negative detail" is the same as "express joint", yes I did consider that idea, thanks.

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## Chr1s

Thanks to everyone for your help and advice, so I thought I'd post a follow up to round off this thread. 
After much thought and consideration of the various fibre cement sheet and plank options, as well as Colorbond, etc, I decided to stick with the Western Red Cedar weatherboards, mainly because I had previously purchased six 6m boards several years ago and had them sitting in my garage, and I figured that since the WRC weatherboards elsewhere have stood the test of time quite well, if these boards were properly painted and installed they should be as durable as anything else. I'll just have to keep a closer eye on them in future. 
I needed to buy an additional 6m length and I then gave them all a generous coat of Dulux 1-Step oil based primer sealer undercoat on all surfaces, plus three generous coats of Wattyl Solagard Low Sheen white on the exposed surfaces. 
My carpenters dismantled the existing mess and discovered some rot in one of the rafters and a few studs, so they cut out the rot in the rafter and replaced the affected studs and then installed two layers of Ametalin SilverWrap breather medium duty sarking, and 300 x 300mm squares of 0.3mm aluminium flashing behind each of the mitred painted and sealed weatherboard joints. My thinking is that when the sealant inevitably fails, the moisture should then be stopped by the aluminium squares, but if they also fail then it will have to penetrate the two layers of sarking before it can cause me grief again. 
A continuous length of 230mm wide Aldamp Super Dampcourse was installed under the ridge tiles and over the fascia board, plus strips of 300mm wide aluminium flashing were installed at both ends of the section. Fingers crossed that my defense plan works and the section is now waterproof! 
The repairs took a full day from 7am to dusk and I think the carpenters did a beautiful job! 
Unfortunately, old Murphy played one of his nasty tricks, and after the job was completed, we then noticed some fine stress cracks in the original lead flashing, so the bottom weatherboard is now going to have to be removed so that we can install two lengths of 280mm Wakaflex underneath the lead. I figure I might as well retain the lead if possible, to protect the Wakaflex. 
Fortunately I was able to purchase the Wakaflex at a 15% discount at Masters (very sad to see them closing down!!!) and the carpenter thinks he should be able to remove the weatherboard intact, otherwise a new length will have to be purchased, painted and installed. Assuming that the flashing may require replacing at some point in the future, he's going to screw rather than nail the board in place this time to hopefully make it easier to remove next time. 
Here's how it should look upon completion.

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## OBBob

Looks good.

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