How to replace fibre cement sheets with chamfer boards?

[matzpersson]

Morning community,

I have a little DIY project that I have been meaning to complete for a while now. I have a fibre cement sheet wall at the end of an former carport that I would like to replace with Bunnings 138mm chamfer boards. See picture below. Was hoping for a little bit of advise/tips of how I am planning to go about doing this.

My plan is to remove the fibre cement sheets leaving a 40-50mm fibre cement strip at the bottom touching the slab as this is already sealed and then start the first chamfer board above that strip so the chamfer boards does not sit in any rainwater.

Once i have removed the sheets, I was going to ensure that I have minimum 600m centres studs for the chamfer boards. Not sure what is behind there yet.

I was going to use nails to fasten the boards onto the studs building the chamfer boards from the bottom up. Once boards are in place, i was going to use an external, paintable no-gap sealant under joins and paint the pre-primed boards.

So my questions are:

• Does this sound like a reasonable approach?
• Are there special nails i should be using for this?
• Does the 138mm height measurement on the Bunnings page: https://www.bunnings.com.au/138-x-19mm-5-4m-chamfer-board-h3-treated-pine-primed-fj-126mm-cover-losp... represent "visible area" of the board and does not include any overhangs?... or is this 126mm visible area? Probably sounds like a silly question but my existing boards around the corner have a visible area of 138mm. Seems too coincidental.
• Any other gotchas i wonder?

Appreciate any advise,

Thanx,

Matz

[MitchellMc]

Hi @matzpersson,

Your approach seems reasonable and well-thought-out. Leaving a 40-50mm strip of fibre cement at the bottom is a smart idea, as it helps keep the chamfer boards from sitting directly on the slab, which can prevent water damage. Once you’ve removed the fibre cement sheets, check what’s behind them. If there’s no moisture barrier in place, you’ll need to install one before fixing the chamfer boards. A breathable wall wrap will help prevent moisture from getting into the frame while allowing the wall to breathe.

When it comes to fixing the boards, it’s essential to use nails that are durable enough to withstand the elements. Galvanised nails are the best choice to prevent rust and corrosion, and bullet head nails work well for this kind of project. If you’re using a nail gun, ensure you use galvanised or stainless steel brads or finishing nails designed for exterior use. Regarding the board dimensions, the 138mm listed on Bunnings refers to the overall height of the board. Once installed, considering the overlap, you’ll have roughly 126mm of visible coverage per board. 

Leave a small gap at the ends where the boards meet another surface to allow for expansion. Don’t forget to apply a paintable gap sealant on the joins to prevent water ingress, and make sure to prime and paint any cut ends of the boards before installation to increase their durability.

I just wanted to point out that asbestos was used to clad on older dwellings. So, if you have any doubt about what it is, it's best to have the sheeting tested before beginning work.

Please let me know if you have any questions.

Mitchell

[matzpersson]

Morning Mitchell,

Thank you for the advise. Will make sure I put a wall wrap on if missing. In regards to leaving a gap at the ends, will 4-5mm on each end be enough?

Thanx again,

Matz

[JacobZ]

Hi Matz (@matzpersson),

4-5mm on each side will be fine. This will allow for that little bit of expansion that can be easily covered with a gap filler like this Selleys White No More Gaps Exterior Gap Filler.

Let us know if you have any further questions.

Jacob

[matzpersson]

Hello again,

After closer inspection of existing cladding wall around the corner from the project wall (which i am trying to match), i discovered that they are infact NOT 138mm chamfer board but weatherboard panels like this one: https://www.bunnings.com.au/weathertex-3660-x-300mm-colonial-smooth-selflok-weatherboard_p0241450.

As these weatherboard panels are much thinner, I could potentially fit them over of the existing fibre cement boards but I am not sure if that is a good idea? Does moisture get trapped between the sheets and panels? Thoughts?

Am I still better of removing those fibresheets, put a wall wrap up and then fit the Weathertex panels?

Thanx again for your help,

Matz

[EricL]

Hello @matzpersson 

Installing the Weathertex 3660 x 300mm Colonial Smooth Selflok Weatherboard over cement sheet might be possible, but please allow us to double check with our supplier. As soon as we have more information, we'll get back to you. However, if the cement sheet is no longer in good condition or has been infested with mould and mildew then it would be best to remove it rather than installing over it. 

Here is a link to the Weathertex Brochure: Selflok Weatherboards Installation Manual.

If you have any other questions we can help with, please let us know.

Eric

[MitchellMc]

Hi @matzpersson,

There is a provision for the Weathertex boards to be installed over a masonry wall. However, 70 x 35mm batons must first be attached to the wall for the boards to be fixed onto. You'd also need a dampcourse to prevent moisture in the masonry from penetrating the timber. That method is for solid concrete walls, but in your situation, it would be similar as the timber Weathertex boards can't be installed over a flat surface. Any moisture that gets in behind it will be trapped and cause accelerated decay. A gap must be provided with batons to allow airflow.

Please let me know if you have any questions.

Mitchell

[matzpersson]

Morning Mitchell,

I suspected that was the case. I will remove the fibre cement sheets and make sure to use a wall wrap.

Thank you for the advise,

Matz