Easiest was to level a exterior patio slab for tiling

[stone tiler]

Evening all,

I'm pricing an exterior patio where the concrete pad has been laid by the homeowner to save costs. It's 10mt x 4mt, has no fall away from the house, is very rough and has several belly's and dips - approx 5-8mm max. I've only got 10-15mm to play with or the tiles will be higher than the bi-folds once fitted. Tiles to be fitted are 900 x 600 x 20mm granite slabs in b/b.

Now obviously I've got to raise the patio on the house edge to get a fall but whats going to be the best/easiest way of doing this? I was thinking its too thin for re-screeding. I was chatting to the client and said I could kinda re-screed it - form straight edges front and back with cement boards cut down into 6inch strips, get the correct fall on them and then fill in with rapid flexi with a mixed in 5mm agg but in my head that sounds a bit bodge to me. Told him I'd have a think over the weekend and get back to him monday. I see dpf has a similar project but he has more height/depth to play with.

Spent the weekend thinking about it but no ideas so far so I'm throwing it on here to pick your brains guys. How would you go about it? Am I missing the obvious?

 

[Spud]

how wide are the bi folds ?

 

[Diggy]

I think Ardex do an exterior SLC K301?

Never used it so I don't know what it flows like or how it would behave for putting in a fall on the patio.
Sure someone will have done something similar , will be interested to know a product for myself.


Diggy

 

[Diggy]

You aint gonna get much of a fall though over 4 LM from a height of 15mm , unless he's at least put something there already?

Diggy

 

[stone tiler]

The bi-folds are on the long edge of the slab. 2 sets of 5 doors so guessing about 3mt ish each.

Yeah I said he's cocked it up and I cant get much of a fall on it. He said he didn't want much of a slope anyway as it's for summer dinner parties and he doesn't want a sloping table, just keep the water away from the house! am tempted to ramp the 1st row or 2 of tiles and then tiles almost level and let the water sit if it wants to

 

[Spud]

biggest problem you have will be bonding directly to the slab with the slab being level any water that get through the tile will stay where it is regardless of the fall at the surface this will cause the tile to blow when the cold weather eventually comes if you do manage to get a fall you will need need to protect the subfloor from water ingress ,the water will then drain away and your tiles will be less likely to be damaged from the frost options you have is thinner material ,surface prep by scabbling off the concrete for the fall, ditra drainage matting then tile waht ever way you go it will be expensive for the customer but dont be tempted to cut corners as it always comes back and bites you on the ars

 

[Colour Republic]

As has been said 15mm over 4m is nothing what i'd do in this situation is bash the customers over the head whilst repeating 'You skin flint '****s' your penny piniching ways are going to cost you double now with the balls up you've made'

 

[stone tiler]

How much fall would you recommend for it? Is the drainage matting expensive? I've seen it but never used it

 

[Spud]

from the top of my head 80mm is 1;50 cant remember if its 1;80 or 1;50 either way between 50mm-80mm

 

[Diggy]

Well According to this:

For commercial or specification paving projects, the minimum recommended falls for flag paving as stated in BS 7533:4 are 1:80 longitudinal and 1:40 transverse.


Then this from the paving site:

On private patio and driveway projects, a fall of approximately 1:60 is usually adequate.




Then this calculator gives - for your input of 15mm by 4000mm - well a lot less than 1:100

Gradient, Slope, Grade, Pitch, Rise Over Run Ratio Calculator

Wish him good luck a bid him farewell , IMHO.

He might say he isn't worried about falls , but if you lay it , he gets a downpour and it floods back over DPC , I bet I know who he'd ring.


Diggy

 

[White Room]

How thick is the concrete slab....

 

[stone tiler]

Yeah thats what I'm thinking. Is it really worth the grief if/when it goes wrong. Could cost me a few quid in the long run and you know even though he says yeah go with it, I want hold you responsible if it went wrong my phone wouldn't stop ringing.

I can't grind that much off the screed either to get the falls - it'd take forever!

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I think he said 6 inch but not 100%