Sawn sandstone mortar not sticking to slabs - help

[Rossoliver]

Hi,

I've recently started laying 22mm calibrated sawn sandstone after reading up on this website I'm using a 3:1 sharp sand cement mix - laying -4cm depth on 150mm compacted hardcore - full mortar bed. I wet the back of the slabs before placing onto the mortar bed although I haven't used sbr for fear of getting it on the slabs and not working quick enough to lay before it hardens.

A week has gone by and I've noticed the first slabs I placed lift up relatively easily - although not all of them. It's mainly the first ones I laid and I believe it was because my mix was too dry (I went to a wetter mix latterly finding it easier to place the flags).

The ones I lifted up weren't rocking but if I tapped them I could hear them clicking - they must be moving about a fifth of a mm. I lifted and coated the back with sbr and relayed on the same bed and they seem solid now. There are three larger ones that don't rock but click if I tap or step lightly on a certain corner. My question is should I lift and stick these down also or is the pointing likely to sort this kind of issue? The larger ones (900 x 600) will be tricky to lift so I'm wondering if it is really necessary or if pointing tightens them up at all?

I know I should probably relay on a new bed with sbr (and going forward I will be using the stuff), but the mortar is rock hard and I now struggle to chisel it up - I have one 'rocker' that I am relaying on a new bed and the old mortar is hard as nails to pick out.

On a related note, some of my slabs have grooves on the back that look like it will aid holding them into the mortar but some are as smooth on the back as the front - is this typical or have I got a dodgy product?

Thanks for taking the time to read all that!

Ross

[lutonlagerlout]

some have grooves some dont
wet mix all the way for calibrated stone IMHO

sbr doesnt go off that quick,as long as you use a gauge in half an hour to an hour its fine

LLL

[Rossoliver]

Thanks for the info - any tips on the larger flags that have very minimal movement? In that if you tap them you can hear it but can't see/feel it moving... I may be mistaken but I think I read somewhere you can make a very runny sbr mix and pour it down the joint so it seeps in and stabilised the flag - is that an option or total rubbish? Obviously I would need to be careful not to stain the top of the flags...

The turn in the weather for the weekend has also given me another question - will my unpointed, few days old patio be fine exposed to the elements for a week or so until I get around to pointing it or is it best covered?

Thanks again!

[lutonlagerlout]

cover it if possible ross
water in the joints is a PITA
LLL

ps you could try the slurry trick but best practise is to relay

[Rossoliver]

Cheers, will do!