Yes. Victorian bricks are generally quite soft. It is essential that in any
masonry structure that the mortar is softer than the masonry. Otherwise, the
masonry will crack or spall. Cement based mortars are very strong and
totally unsuited to Victorian brick.
Increasingly common from the early twentieth century, along with other
innovations like concrete blocks and plasterboard.
The Victorians did have cement mortar, but it was generally used for its
pozzolanic qualities for submerged work, such as sewers and bridges, along
with suitably hard bricks.
There are other issues of course. Lime mortar is lighter in appearance than
using cement to repoint bits of a lime mortar bulding will look ugly. Also,
it is said that
it is breathable, whereas cement is not, so a lime mortar render can let out
damp that enters
via a crack in the render, whereas damp that enters through a crack in
cement render is
stuck, causing penetrating damp and rot in the walls.
Old bricks are often soft and porous, while cement mortar is harder and
less permeable to moisture. The mortar should be the weak link in a
wall or the bricks may start to fail, or sometimes cement pointing will
just fall out in large pieces if the wall moves.
I remember a pair of semis being built across the road from my school
entrance and the kids had previously been used to walking across the
site as a short cut. There was a big pile of grey powder on the site
with a notice that said "This lime will burn your hands". It would
have been Ca. 1955 in Leeds
Portland Cement was too expensive for widespread use in general
mortar until 1920's, when it starts appearing near the production
sites initially, but took a long time to work its way across the
Well Ordinary Portland cement is what we would generically call cement,
although naturally occuring Pozzolana is also often called cement,
especially in historical contexts (i.e. Roman construction). Portland cement
is a manufactured material actually based on lime, but mixed up with clay
(or sand) and baked, to modify its qualities, making it much quicker
setting, non-porous and hydraulic (able to set under water quickly).
Some lime mortars have OPC in them, whilst some have lime only (plus sand,
of course). Even with OPC mixed in, they are much more porous and suitable
for older buildings, as they allow the building to move and prevent soft
bricks from cracking.
On Mon, 12 Sep 2005 13:50:26 +0100, "TheScullster"
Lime based mortar is softer than concrete and allows a certain amount
of movement in a wall.
In days gone by, pointing was intended to be a sacrificial
material-the intention was that it'd be replaced every 50 years or so.
Usually, modern builders/surveyors see weathered pointing as a fault
and replace the lime mortar with hard wearing cement based mortar.
This is a mistake.
Often, when walls are re-pointed with concrete you end up with cracks
in the softer bricks as the mortar has no 'give'. This leads to
moisture getting in, bricks having to be replaced etc..etc.
If you have lime based pointing and it's wearing away then it is doing
its job correctly. Have it re-pointed with more lime based mortar and
you will get no problems in the furure.
|| Usually, modern builders/surveyors see weathered pointing as a fault
|| and replace the lime mortar with hard wearing cement based mortar.
|| This is a mistake.
How can you tell which is which? Does it look different?
I have a 50's built semi and the front garden walls (like the rest of the
estate) are falling apart. The bricks are sound, but the motar between them
seems to have lost it's 'bond'. Its crumbly.
Some of this is due to no capping being used, just bricks on edge so the
failure is more pronounced where the weather gets to them.
If I rebuild the crumbling sections, should I use lime or cement?
The 'brick on edge' is refered to as the title suggests..
a brick....on its edge!!
Normally found on most 1 brick thick walls to finish it off the top
Walls are not normally terminated on a course of, errr, stretcher bon
for example, as the weather will penetrate and get up to its usua
Half brick thick walls sometimes have soldiers on the top but thes
walls are very flimsy and a quick boot can bring them down, especiall
with lime mortar :-
Chris Bacon wrote:
|| Is the wall still structurally sound? If not, pointing is point-less.
It's the top two or three courses that are unsound, the rest seems OK. I'm
talking about rebuilding rather than pointing.
|| Bricks on *edge*? Do you mean the top course?
||| If I rebuild the crumbling sections, should I use lime or cement?
What, cement mortar to rebuild & lime to point?
Lime mortar is usually white. It may have weathered a bit but it's still
lighter than portland cement. Scrape a bit off and look at an unweathered
surface, I've seen it look anywhere from off-white to creamy. Of course,
the type of sand or grit used with it might colour it slightly different
locale to locale.
Also there is the question of foundations and movement. 100 yr old
houses had very shallow foundations, and movement in these is normal.
With cement mortar, the weaker bricks break. With lime, the lime
cracks, but unlike cement it microcracks, then self heals. It reacts
with CO2 to grow hard crystals across the crack, so it heals itself,
with no damage done.
Also cement tends to pull the surfaces off the bricks in time, and this
loss of fireskin causes the brick to get wet, and crumble when it
freezes. Over the years bricks thus affected will slowly crumble away.
And finally theres damp. Water that gets into the wall, as is
inevitbale, evaporates out from lime mortar. It doesnt with cement, so
old walls built with porous bricks and no dpc are more prone to damp is
cement is used.
Note about cement lime mixes: almost all such mixes fail prematurely.
The only one that is ok is 1:1:6.
I would have said "cement pointing is much harder than the lime
the wall was originally built with; the excessive force on the
edges of the bricks causes spalling, which is exacerbated when
water is then allowed into the brick and is subject to the
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