Bed too deep

[mo-uk]

I am laying 450x450 concrete flags

I am aware the guidance on this site suggests up to a 50mm bedding layer of sharp sand concrete

There are a few sections in my garden where the depth is going to be more - possibly up to 90mm

I had a go yesterday with a wet mix and found when hitting with a rubber mallet the mix would start squishing out of the edges

I am going to try a drier mix tomorrow in the hope that I can get it right with trial and error.

Is there any scientific reason as to why it would be harder to lay onto a deeper bed? I am thinking, would there be less 'given' on a deeper bed as oppose to a less deep bed?

I have enough sand on site that I can always bed down a first layer to make it so I only need a 50mm depth but I was hoping to make up the height in one go

I am aware I could have sued MOT Type 1 but havent for various reasons! I don't mind mixing up sharp sand/cement even if it costs more money as I already have it and would have sued it anyway whetehr I do it in 1 stage or 2.

[ahfix]

I'm a diy'er, but my take is deeper the bed the more movent it has due to the fluidity. Mix some pea gravel in and make a concrete base for your lower 50-70mm. Allow it to set to give you a firm base and mortar on top of that.

ah

[mo-uk]

Ive decided I am going to 'double layer' it

I might spend an evening or two doing it but I feel I will save myself a lot of aggro fighting to put down 100+ slabs on possibly a very deep bed.

Also give me the chance to chuck in some hardcore

That said, the 6:1 sharp sand/cement combo has gone pretty rock hard so I would not really worry about it moving much. I chuck in 200ml of SBR per 10litre of cement for the hell of it - dunno if it makes a difference but makes me feel good.

[Tony McC]

Apologies for being late to this - had all sorts of health issues with angina during the heatwave and now an arthritic knee that is driving me mad with pain.


If the laying course (bed) is too deep, then the regulating should be done with the sub-base, not by building-up mortar on top of mortar on top of more mortar.

Loosen the surface of the existing sub-base; add further type 1 or Type 2, spread, level and compact to refusal so that you will end up using a 25-40mm bed depth.