Laying slabs on a mortar bed

[A Dillon]

Hi there,

Thanks very much for all your help. I would like to ask you a bit more though. I have so far removed my old patio and sub base entirely. It was ok in some parts but not in t'other parts. I have now layed a new sub base of approx 65mm, this was 5:1 Ballast to cement. I am now faced with the tough question of going for a mortar bedding or a sand bedding layer?? My slabs are 450mm x 450mm. I dont know which to go for. Also I would like to know whether I could screed the mortar in the same way that sand would be screeded, obviously only one length at a time. Is it worth the extra hassle. I am a bit cautious about a sand bedding layer because i know someone who's sand bedding has failed.
Which is the preferred and more durable method?? Any tips are greatfully appreciated.

[A Dillon]

PS I forgot to ask how thick in mm should the mortar bed be? The slabs are 32mm thick.

Many Thnaks

[84-1093879891]

Use a 10:1 bedding mix of grit sand with cement, as described on the Patio page. It can be screeded, if that's how you want to work, and it should be 35-50mm thick when consolidated.

[A Dillon]

Tony,

Before I ask any more, I think your site is really helpful and informative, thanks for all the good work.
I am building some steps and as they are quite large, I have used concrete blocks and bedded them down onto the sub base with sharp sand and cement mortar. Is this the right way, you advise the use of bricks for steps, are concrete blocks ok , breeze blocks, for use in the building of a step.

Thanks for all your help.

[84-1093879891]

CMUs, or Breeze Blocks as they are still referred to in some parts, are fine for constructing the risers for steps - they're not the prettiest of materials, but there's nowt wrong with them, structurally.

I'd normally bed them onto a 100mm layer of concrete, but laying them on mortar is fine, as long as the sub-base is sound.

[A Dillon]

Many thanks Tony, I will do that and let you know how I get on.

Cheers!