Hydraulic or "normal" lime mortar for retaining wall.

[gsport george]

Have moved a BIG pile of stone to find that it was either hiding or shoring up a collapsing bit of retaining wall, so I have the fun of re-building it.. smartish as it looks very precarious (centre of gravity looks well out from the foundation and part looks like it has already collapsed and been repaired) Only about 10feet needs doing, but the ground level behind ranges from 3 to 6 feet. as does the wall.

Do I need to use hydraulic lime?

Can I use some non-hydraulic lime mortar (from putty) I mixed up about 18months ago that has been sitting in a fairly air tight container and "looks OK"?

Can I mix up lime mortar with smooth pebbley gravel and rock to make a sort of concrete to shove behind as a kind of back-fill or will it never set?

The wall is overhanging the area where I am going to build the "deck" for children to play on so I really dont want to risk leaving it.

 

[andrew gayton]

non-hydraulic mortar relies on carbonation to set whilst hydraulic mortar will set via a chemical reaction - the former requires exposure to air, the latter exposure to water only. so, where you have a retaining wall situation, I would advocate the use of hydraulic (either from the bag or non hydraulic made hydraulic by the inclusion of burnt clay)

be aware that the usual rule of thumb for fully bonded walling in this situation, is that the walling must be a 1/4 thickness of overall height, i.e. 1600mm tall, 400mm thick etc.

so, as this is a 'modern' wall - exposed only on one side, retaining and needing therefore to be stable - you could always build a backing wall of brickwork then face up with stone?

 

[gsport george]

I am pretty sure it will set OK. My plan was to remove the soil from behind and build it as an ordinary wall, then replace the soil after a few weeks when the mortar should be dry. But does non-hydraulic lime behave the same as hydraulic once set but in wet conditions?

I assume that the 1:4 ratio is a minimum? I was intending to build it a lot thicker than this to ensure stability and resist pressure. I was also going to let it overhang on the back slightly to shift the centre of gravity back and pre-stress it against the soil pressure.

 

[andrew gayton]

I am pretty sure it will set OK. My plan was to remove the soil from behind and build it as an ordinary wall, then replace the soil after a few weeks when the mortar should be dry. But does non-hydraulic lime behave the same as hydraulic once set but in wet conditions?

Leave it for at least a month then you will be ok. non-hydraulic lime is a better overall solution where carbonation is possible

I assume that the 1:4 ratio is a minimum? I was intending to build it a lot thicker than this to ensure stability and resist pressure. I was also going to let it overhang on the back slightly to shift the centre of gravity back and pre-stress it against the soil pressure.

A minimum, yes - but for bonded walling as opposed to rubble - so go as thick as possible. 'overhanging' may not be th ebest approach as you may well introduce a hinge-point............ better to build a consistant thickness in section and/or batter the wall slightly so it leans into the retention.

 

[chuckey]

I had a earth retaining wall built and it leaks ground water, so its all damp and green. It all depends on your soil type and rainfall, how much ground water you have, sounds as though yours is dry.
Frank

 

[gsport george]

Any guidance on whether the old lime mortar from putty will still be safe to use? It looks OK, but could it be too old now (18months plus stored outside in a relatively airtight bin)? I have been shifting big stones all day and dont want to do it again if it isnt.. then again it is probably 2 less bags of mortar to shift if I CAN use it...

 

[Nemesis]

Non-hydraulic putty? It will be fine - it gets better with maturity!