Re-laying slabs - How to re-lay slabs at the outer edges

[gmbodio]

Lovely website – congratulations!!

I have a patio at the back of the house ending with a drop of 50cm to the garden. It has 450mm square slabs all in good condition, the base is mostly very sound sand and cement but the middle of the base has collapsed a couple of inches or more. I am convinced that the collapse process took place some time ago and it’s not collapsing any more. The outer edge sits on a nice wall.

I am very happy to re-lay the slabs on a dry mix (10:1 or whatever you recommend) at the appropriate depth so they can again slope correctly down away from the house.

The only problem is that the outer edge of the patio-base is excellent and properly positioned, which means that I must use something like a powerful tile cement to secure the outer parts of the final, outer, row of slabs. If I don’t the alternative is to hack away at the sand and cement base in this large area, which would be a pity as the whole of the base there is in very good condition and at the correct level.

Is there a foolproof outdoor way of doing this? I don’t think that otherwise the outer slabs would be secured by pointing and they will only be affixed by a small amount of 10:1 mix (as the amount of collapse there is much less than in the couple of rows further in). Plus the outer slabs overhang the wall by about 3cm so are liable to be dislodged by the inevitable foot on the edge.

I would really appreciate your experienced view of whether there’s a suitable powerful adhesive for this.

Many thanks

Graham

[Tony McC]

Those outermost flags were probably laid onto a wet mortar and formed a decent bond to the wall beneath. The easiest option would be to break them loose by driving a bolster between the mortar and the underside of the flags, and then nobbling off all of the old mortar. When you re-lay the rest of the patio, the outermost flags can then be re-bedded, to a suitable line and level, using a good mortar. I recommend a 3:1 mix and it would do no harm to beef up the mortar with a splash or two of Ronafix/SBR