Paving steps - Paving over concrete blocks.

DUNSTABLE DUNCE · Mon Mar 17, 2014 1:42 am

Hi, I have 6 steps built out of concrete blocks that I intend to pave with slabs. I have cut them to size and they are ready to lay. They are manufactured ones all of 50mm thickness.
My main question is how to lay the risers so they don't come off.
I have been looking around and it seems that most are laid behind the tred on the same level and with a gap to the tred above/overhanging. The gap is then filled along with all the other gaps afterwards.
Is this the best way?
Secondly, should I mix some sbr bond with the mortar mix to make the risers stick and should I use sharpe sand for the mix?
Thanks for any help.

Post: # 96355Post **Tony McC** Mon Mar 17, 2014 10:08 am

The usual method when you have the former in place (the concrete blocks, in your case) is to affix the risers first and then fit the treads, starting at the top and working your way down.

There are some specialist fixing mortars, such as Ardex, which is really an outdoor grade tile adhesive, that can be used, but with your pieces being a chunky 50mm thick, you'd need to check the strength first. The alternative would be a 3:1 mix using building sand with SBR and a SBR slurry bond bridge just to play it safe.

DUNSTABLE DUNCE · Mon Mar 17, 2014 12:13 pm

Thanks for that. How deep should the mortar bed be for risers?

DUNSTABLE DUNCE · Mon Mar 17, 2014 12:26 pm

and should I leave a pointing gap at top of riser/under tread?

London Stone Paving · Mon Mar 17, 2014 3:04 pm

if you are using mortar as Tony suggest the bed should be 15-20mm.

A pointing gap is required at the bottom but the top is optional IMO.

Although the picture hasn't been pointed yet it does give the idea of how a step would look when the top and bottom is to be pointed

DUNSTABLE DUNCE · Mon Mar 17, 2014 3:25 pm

Thanks for all your help, one last question - I see you have put your risers on top of the treads. I was going to put them down behind the tread. Does it matter which way I do this and would you agree with Tony that SBR mortar and a mortar bond is best? What did you use on ones in pic?
Thanks.

London Stone Paving · Mon Mar 17, 2014 5:45 pm

The mix Tony recommends is spot on.
The riser should site on top of the step IMO

Post: # 96393Post **Tony McC** Tue Mar 18, 2014 9:55 am

The position of the riser depends on the type of material being used and the method of step construction being used.

With 'free-form' construction where the whole shebang is constructed as you go, placing the risers so that they sit on the tread below makes a sort of sense because the tread helps spread the load. You can only work from the bottom upwards and you are at risk of having to work from newly placed treads.

However, when a concrete or block former exists and is effectively being 'clad' with the risers and treads, I prefer to get all my risers fixed in place first, as they are carried by the con/block sub-structure, and that then allows you to lay treads from the top down. By laying from the top down, you never have to work from freshly placed paving and it's so much easier to keep your work meticulously clean as to work your way down.

When you have a completely free choice, and even when working with the 'bottom up' method, the choice of riser on or behind the preceding tread is purely aesthetic. Which do you prefer?