Sandstone paving steps within gravel - what's going wrong?

[fathertobe]

Hi,

I've got several sandstone slabs standing within gravel - on mortar* bases. They were done as part of work on our garden two years back.
The problem is that they're coming (cleanly) loose. Here's an example:

View media item 75980
The stones receive above average traffic in comparison with most gardens but nothing crazy.

Can anyone help me with what the problem is? And how I rectify it?

Thank you!

*I say mortar but really I have no details on the base used.

 

[footprints]

I would suspect the mortar was too dry when the slab was laid or the slab was dry and dusty.

I think I would try dampening both surfaces and a fairly wet mix of sand/cement to try and get a bond without raising the level too much but I have never tried it.

 

[fathertobe]

Thanks for this. Any guidance on the mixture of sand/cement?

 

[footprints]

I would think somethig not too hard maybe 1 of cement to 5 sand I might use builders sand instead of the normal sharp sand used on slabs as it might bed down a little better in a thin layer.

 

[r896neo]

use exterior grade tile cement, that way you dont raise the level too much and it will give much stronger adhesion

 

[xdave]

In situations like this where I cannot raise the level and it is not worth removing the old mortar and replacing then I have found that a suitable two-part epoxy applied neat to the entire contact area provides a very strong bond (I use West System 105/205 but most would likely be fine). I've used it to re-fix floor tiles and coping stones and none have moved since. Both surfaces must be porous, dry and dust free.