I need to rebuild a Bulwell stone wall which consists of a skin of rectangular stones and behind that irregular stones in layers to make the double skin. The wall in question is a retaining wall approx 2.5m high by 3m long and behind that will be soil/hardcore. Questions are: What type of mortar mix should I be using? It was suggested I use a 5:1:1 building sand:lime:cement mix but they were not sure. What type of lime should I use?
Secondly, what type of drainage do I need behind the wall?
Bulwell is a limestone, and soft mortars are important for such stone to avoid damage to the stone. 3:1 sand to lime putty is the stuff to use. 1:1:6 cement:bagged lime:sand also gets used, but with such soft stone I'd go with the lime. Those are the only 2 mixes recommendable.
Propping that earth up while you work will be fun.
I would strongly advise doing what I did, and making the unseen underground bit out of concrete blocks, tied together at every course and every block with 'bow tie' ties..and then link that to the facing layer of stone with a few more. I infilled the gap between with scrap mortar and rubble. (the mortar that is past its sell by date)
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is a place to have a look, but in my case I put some plastic pipe through the wall base at 2m intervals, and backfilled behind the wall with shingle and rubble, so the actual clay itself (in my case) sloped down to the wall base at about 40 degrees.
I have no experience with limsetone for building, but I used a mixture of hydrated lime and white cement in about equal amounts and about 4 times as much sharpish sand (I liked the look of sharp sand) for my show face brickwork. The concrete blocks were laid with 3:1 grey portland and builders sand.
This gave a fairly hard mortar on the show face, but not as hard as a straight strong cement one on the rear.
I topped the wall both sides with bricks. For appearance.
Trouble with these hard mixes is that when the mortar eventually deteriorates, as it will, it pulls away from the stone pulling the surface and corners off the stone with it. The other issue is that if there's any movement, the weaker stone breaks, whereas one wants the mortar to break instead. This is achieved by using softer mortar than the stone. The other plus with lime mortar is it micro-cracks and self heals, whereas cement does neither during movement.
a concrete base with 3:1 should reduce your odds of movement, but doesnt eliminate it.
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