How to replace fibre cement expansion joints?

[reyemarr]

I’m trying to replace the expansion joints in the fiber cement boards on my alfresco ceiling/eaves. I purchased these PVC HardiePlank jointers from Bunnings (https://www.bunnings.com.au/james-hardie-300mm-smooth-pvc-hardieplank-jointer_p0712716), but I’m having trouble installing them as they’re not flexible enough to slide into the gaps between the boards.
Could you recommend either:
1. An alternative type of expansion joint that might be more flexible or easier to install
2. A specific technique for inserting these rigid PVC joints between already-installed boards
The current joints need replacement, but I can’t figure out how to get new ones in without damaging the existing boards. Any advice would be greatly appreciated.

[MitchellMc]

Hi @reyemarr,

These joining strips are designed to be installed while putting the boards up, not as a retrofitting solution. The jointer is pushed onto the exposed edge of the board, and then the next board is slid into it. The tongue on the back of the joiner makes it difficult to insert them into existing gaps between boards.

If the edges of your boards are well supported, one possible solution would be to cut off the rear tongue from the joiner. This would leave you with just the central piece, which you could then push into the gap from the front. You would need to glue the joiner into place to ensure it stays secure and doesn’t fall out over time.

Alternatively, if the current joiners are damaged and you want a different look, you could remove them entirely and adhere a cover strip bead over the joins. This would offer a clean finish and avoid the need for the joiner entirely.

You need to be aware that the joiners not only cover the joins, but also support the edges of the sheets. If you were to do any of the above, check that the sheets are nailed off securely on either side of the join.

Please let me know if you have any questions. 

Mitchell

[reyemarr]

Thanks, Mitchell — that’s really helpful and pretty much confirms what I was thinking. I am already securing the boards with screws, so we’re good on that front.

I do have a few follow-up questions:

1. I was under the impression that these joiners also act as expansion gap covers. If that’s the case, would gluing a cover strip bead directly over the joints cause any issues in terms of movement or expansion?

2. What’s the best method to ensure the cover strip beads are aligned neatly and held in place while the adhesive sets? I want to make sure the finish looks clean and consistent.

3. I also need to patch a couple of relatively large holes — around 10–20 mm in diameter. Given that the boards are only 4.5 mm thick, what’s the best product or technique for repairing holes of that size?

4. For finishing, I was planning to use drywall mud. Is that suitable for use on fibre cement boards, or would you recommend something else?

Thanks again for your time and advice.

Mario

[MitchellMc]

Hi @reyemarr,

The sheets are nailed off to the ceiling joists, so I don't think there would be much expansion going on as they are fixed in place. I'm not aware of the joints being expansion joints, moreso a neat way to join large boards.

Measuring well and tape the coverstip in place would be your best bet. If there is timber behind you can nail them in position.

You would need to glue timber of a board inside the sheets to provide a backing to be able to fill over. Otherwise, the filler would just get pushed inside the hole. You can use exterior Spakfilla.

Mitchell