Agriculture Reference
In-Depth Information
at all! Think hard on this. You only have multiple joints in brickwork because of
how brickwork through the basic brick size has evolved down through the ages.
Think also of a column of stone (few joints), or of iron (no joints), also of con-
crete blocks (again fewer joints), and pre-cast concrete wall panels. You will see
how joints have begun to disappear.
The 'infinite brick' concept by itself is obviously absurd, yet serves to illustrate
one way to avoid worrying about the influence of joints. This is very desirable
when estimating the magnitude of direct load that completed brickwork can
stand. In the real world of brickwork, however, the way one can get to perfection
in jointing, is to go for the thinnest joint you can make, by first shaping the most
accurate brick, which is perfectly possible with a top craftsman cutting and rub-
bing bricks post-fired. Then to mix a screened slaked lime mortar, of the appro-
priate class for function, with the right amount and micron size of sand, that is
used to fill the bed and cross joints completely between the dampened bricks, let
it all set and stand back and admire the finished result! Built by craftsmen who
are fully competent the result will be strong, robust and durable as historic exam-
ples have shown.
Experience and numerous scientific tests down the years have demonstrated
how little influence the compressive strength of mortar has on the weight carry-
ing ability of brick walls, this being dictated more by the crushing strength of the
brick itself. One just needs to study the modern 'Structural Code for Masonry' to
confirm the lack of effect of mortar mixes for normal situations in practical situ-
ations of brickwork. This should eliminate concern over a moderately weak brick,
thin joint and modest mortar concept, and worry over replicating the details
found with this type of gauged brickwork during repair and restoration work,
once you know how.
I have been fortunate in my career to have met numerous and diverse situations
in old and historic buildings. This has shaped my view of what factors are impor-
tant in Building Conservation. This may seem extraordinary, but tests carried
out by Professor A.W. Hendry in Edinburgh in the 1970's, showed that masonry
made with joints of only sand with no lime, or Cement, binder, could stand up
and be counted.
Finally, on the question of loading capacity, it is a fact that most traditional
buildings experience no greater stress than about 0.8N per sq. mm in the wall
construction that is relatively insignificant compared to their crushing strengths.
When even 3N concrete blockwork is considered to be loadbearing then the
softer rubbing brick does not necessarily imply an unacceptable weakness.
Converting the figures for the crushing strengths of red rubbers, in Table col-
umns 3 and 4 in the chart, Mitchell & Mitchell, (1904, 327-28) the structure first
cracked at a brick stress of 3.5 N/sq.mm then crushed at 6.6 N/sq.mm. From this
you could say the controlling stress is 3 N/sq.mm. Column 4, where it states, 'red
rubbers three in a column, bedded in putty', shows the weakest crushing strength
as 2.4N/sq.mm. This is pretty good. After all, timber has a good crushing
