routing in fibre cement

[havabeer69]

VERY left of field question...

has anyone ever tried routing fibre cement sheeting. A decking product i'm using is a glorified fibre cement sheet 30mm thick which has a tongue and grove profile to lock its self together. its normally meant to go as a subfloor in bathroom rooms etc but we're attempting to use it as a deck.

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ALPHAFLOOR | XCEM (https://www.xcem.com.au/alphafloor)



how ever the edges of the tongue and groove are a bit ratty and I'd like to fill them with silicon to help with waterproofing and look a bit nicer.

my rough thoughts where to get a fibre cement saw and cut a bevel on the ratty edges at 45 degree's both ways (creating a V) and filling that with silicon.... then I stumbled along a $50ish diamond coated V router bit. it'll do 11mm deep which should be more then enough but wasn't sure about longevity. How ever it doesn't seem like a very common practice so trying to search info about it isn't great.


TruaCut Vacuum Brazed Diamond Router Bits -Vee Grooving Bit - 11mm Dep — ConFit Australia (https://confitaustralia.com.au/products/copy-of-truacut-vacuum-brazed-diamond-router-bits-3-2mm-rounding-over-bit?_pos=20&_sid=fb98f3517&_ss=r)

[droog]

Have used an angle grinder to add a recessed edge to fibre cement sheet for jointing and finishing, don’t think you would have much success trying to re-create tongue and groove connection, but then have not used one of those bits.

Just add a waterproof membrane over the entire surface after it is laid.

[ian]

I've used a Makita dustless [saw] cutter to cut 20mm FC sheeting -- it gave a very nice clean cut.
Kennards have the same saw for hire.

Given the low cost of the diamond coated router bits (AUD <$40), you could try using a straight edge and dustless saw to cut off the "ratty" edges of the 30mm thick sheet, and then use the diamond router bits to recreate the T&G -- say a tongue around 12 mm thick going into a groove say 14 mm wide.
Should be a bit neater than filling a 45 degree channel with goo

[havabeer69]

I think I've given off the wrong question.

I'm not trying to reproduce the tongue and groove, just route (or cut) out the top 3 - 5mm of the sheet so I can shove some sealant/silicon in there.




how ever I suddenly realised the samples I was sent already have this feature and unsure why my sheets are a different profile. So contacting the manufacturer tomorrow to see whats goings on.

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[Skew ChiDAMN!!]

Ah, you don't have the bevel.

In the past I've never thought twice about using an angle-grinder on the stuff, but I'm doubtful about it routing out cleanly enough for long enough to finish the job before the bit(s) blunted.

Still, if you can source them economically...

[droog]

Filling a gap with silicon will not help to waterproof the floor, the compressed cement sheet products are not waterproof by themselves.
To waterproof the floor a waterproofing membrane is overlaid including bandages over any joints in the sheet.
Where there is a requirement for expansion joints a gap between sheets is often specified and silicon may be used in the gap as part of a bond breaker, or a bandage with integrated bond breaker is used.

[ian]

What I'm curious about is the purpose of the ~5mm deep recess on the underside (?) of the join.
Is it intended to sit on a steel joist so that the joint is reinforced from below?

https://www.woodworkforums.com/attachment.php?attachmentid=535075&d=1707039573


also see Droog's comment re the sheets needing to be waterproofed with a membrane, and then faced with covered with tiles or similar.

[mic-d]

I did a bit of reading about this product because it interested me for some jobs I have. It is not a fibre reinforced cement sheet, ie a FC sheet like the traditional subfloor panels, it is concrete. Still needs to be waterproofed to standard. I like that it does not contain crystalline silica, but use dust suppression anyway. Ian, I think the rebate is to prevent fouling the joints (when joints are perpendicular to joists) when they're pressed home and to give a bit of play when aligning. Specifically there is a diagram showing to pack shims under if a joint happens to align with a joist (when running parallel)

[ian]

Ian, I think the rebate is to prevent fouling the joints (when joints are perpendicular to joists) when they're pressed home and to give a bit of play when aligning. Specifically there is a diagram showing to pack shims under if a joint happens to align with a joist (when running parallel)
thank you for this clarification

[havabeer69]

I did a bit of reading about this product because it interested me for some jobs I have. It is not a fibre reinforced cement sheet, ie a FC sheet like the traditional subfloor panels, it is concrete. Still needs to be waterproofed to standard. I like that it does not contain crystalline silica, but use dust suppression anyway. Ian, I think the rebate is to prevent fouling the joints (when joints are perpendicular to joists) when they're pressed home and to give a bit of play when aligning. Specifically there is a diagram showing to pack shims under if a joint happens to align with a joist (when running parallel)

It definitely has fibres in it. Its part of my complaint to the manufacturer, that they're hanging out everywhere

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