Hundred year old lime mortar. If the load on a part of a wall made from such mortar is removed, can the underlying section of wall heave upwards. So later problems if load reapplied and spread over that section of wall and an adjascent section that remained loaded.
If this effect exists, is it less likely to occur with modern mortar?
My appreciation of a local architect
vitually incompressible. However, if the wall is on a clay soil then there could be some heave as water is re-absorbed into it.
I'm not quite sure what the second sentence means. But, lime mortar can 'move' so i would guess that the wall might flex and take up a new position. perhaps frost heave would be the most likely thing to cause this since these walls often have shallow foundations, or none at all.
Robert
AIUI heave is a ground condition, not a masonry condition.
Whilst ground heave may cause masonry built with portland cement to crack, cracking may be reduced with lime mortar - as it has some ability to withstand movement.
No. Heave happens because the ground swells. Most usually because ground
-= especially c;lay - that was dry, becomes wet. Thi sis typoically enciountred when a patch of groujd taht a tree has extesnive root systems in, and thius sucks water out of, is used to build on. The rottes are destroyed, and te soil expnads.
Its very little to do with loading.
Mortar doesn't affect the heave, it affects how the structure will behave when it does. Lime mortar is just a crude friable gap filler that will shift and move so you wont get overt cracks. Portland is tough and hard, and cracks instead.
In the end its a style choice. Crap foundations and a building that can accomodate movement, or modern foundations and a building that doesn't need to.
The secret is depth. Go deep enough beyond tree roots and into the subsoil with strip or piled foundations, and you get a stable foundation. Then use a raised floor so surface heave wont crack it.
If you have heave, underpin. Go deep, and fix the foundations. Then the mortar you use is irrelevant.
We are in the throes of building an extension to a cottage which was originally built in the 1920s - lime mortar, imperial brick, tiny foundations by modern standards. The extension, of course, is built up to modern standards - deep foundations, DPC, modern cement mortar.
There has been an amount of movement to the existing structure. I don't think, though, that I've noticed any effect as you describe.
The main issue with lime mortar as I see it is that if you cut a hole (say to insert a lintel at an external brick corner) the area of brick above the cut is much more likely to settle downwards slightly and cause cracking than with modern cement mortar. I don't think our builder really made any concessions to this - perhaps he should have.
Similar sort of situation , decades ago and level change was apparent soon after leading to a crack. De-Mec/Dmec ? points glued across the emergent crack and separation noted a couple of times a year. Changes up and down presumably with weather a bit over the years but otherwise stable and no shift in the sense that all brick surfaces are still co-planar so load is still vertical
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