Making a 9" hole in patio?

[Gadgetbazza]

Hi,

I want to install a bottle gulley at a low point in my patio that collects water. I have everything planned out regarding the route of the drainage etc. I've picked up a bottle gully drain from screw fix which connects to standard 110mm (4") underground drainage. However, I'm trying to work out how I can make a suitable hole in a patio slab to accommodate this. The top grate area requires a 9" circular hole. At his point I can only think to cut a square out of the corner of a slab and position it there and infill with pointing but can't help but think it will look a bit crap.

Any ideas on how best to effectively make a 9" round hole?

Thanks

 

[JohnD]

core drill from tool-hire shop

edit
sorry my mistake. I was thinking 4" not 9"

 

[Pigeon85]

Would take a bit of time but I would use a small angle grinder to give the shape then chisel out.

 

[Mursal]

The supplier may have one off slabs with a cut out available?

Or use a slab as a template for a simple timber mold? We usually place a piece of plastic on a flat surface (this will be the base of the slab) and drop the 4 sided mound on top. find a circular object that the drain will fit into and use for the center. Fill with a good strong mix of sharp sand cement and 13mm stone chip, float to a smooth finish. You wont need very much with a great big hole in the middle. Spend a bit of time on the outside top edge to get it rounded like the proper slabs. If you feel the need sprinkle a bit of neat cement on the top as it dries and float it in to get that white finish on the top to match the other new slabs.

 

[Gadgetbazza]

Thanks for the reply guys.

I should have mentioned, the slabs have a textured dark slate finish, so making something up in cement will be fairly obvious even tough we do have colouring for the pointing.

I was thinking I might use my 4" core drill to make 4 holes next to each other as the bulk of the cut out for the drain and then maybe follow Pigeon85's comment and smooth it out with an angle grinder.

I checked to see if there is a 9" core drill, the only ones I can find are in a jig, presumably because a 9" core drill will likely break you wrist in a drill! I did find a 6" one, but that's not really any better. Might try the tool hire shop to see what they have.

One final thought, is there such a thing as a stone blade for a jigsaw???!

Cheers

 

[Jackrae]

Rather than cutting a large hole in a single slab you might want to consider placing the drain in the corner of 4 separate slabs (or 3 if they are lap jointed). That way you are scalloping out a segment of the corners rather than endeavouring the exceedingly difficult.

 

[LastMagicBean]

Draw the 9" circle on the slab, get a 6mm masonry drill and drill a succession of holes on the outside edge of the line.
Tap with a hammer, done job.

 

[r896neo]

A stone flag will delaminate if you try to stitch drill it. Its possible to make a good job of it using a 5inch grinder.

a combination of overcuts from the back and nibbling with chisel. It takes a bit of practise but i know pavers who can cut a hole out for a rodding eye.

Make sure you have a few spare flags.

 

[WabbitPoo]

Maybe I am being thick, but if the patio is already down, how are you going to run pipe to the new trap anyway without lifting other slabs?

 

[Gadgetbazza]

Yep, the patio is already down. I will only need to lift a short run of 3 slabs to get to a drainage channel, so no big deal there.

I have a few spares so I will try the multiple holes and tap with a hammer approach first to see what happens. I'll likely mark the cut out while the slabs are in place but not make the cut until they're removed. I am planning on fitting it across the joint of 3 slabs.

I don't think it will delaminate, the slabs are concrete castings with a natural stone effect rather than genuine stone.

Thanks all for the replies.

 

[Jackrae]

When you're hammering the centre out of the slab I'd suggest laying it on a thick bed of damp sand such that the whole area of the slab is supported. This may prevent unwanted stresses resulting in the slab splitting. With luck you'll see the fracture line develop as intended.

 

[LastMagicBean]

Its possible to make a good job of it using a 5inch grinder.

Never in a million years.

 

[freddiemercurystwin]

Why not core drill a 250mm hole and just mortar the remaining gap.

 

[Gadgetbazza]

Because I don't have a 250mm core drill! Not have I found anything bigger than 6". I haven't tried the tool hire place yet though...

Cheers

 

[r896neo]

It will be cheaper to buy a new gulley with a square grid rather than hire stuff