Late Victorian Building
Construction
The
time was one of innovation and experimentation.
The
late 19th Century had seen the culmination of the replacement of
stone with brickwork as a primary unit of masonry construction and was most
dramatic in the development of Portland cement and its use, particularly, in
concrete and reinforced slabs, suspended between steelwork, also in its
infancy.
Portland Cement was
available from a number of developing suppliers, the most reliable company of
the time was J B White and Brothers of Swanscombe, Kent. Portland Cement was
invented in 1811 by Joseph Aspdin of Leeds, and met with considerable distrust
until the late 19th century, when it was then considered to have
resistive qualities in its use in forming reinforced concrete. Cement was not
as finely ground as was later recognised as being necessary to give a finer
spread of cement to the surfaces of the aggregate. There was also the
likelihood that cements were over-limed. Portland Cement consists of lime,
silica and alumina ( ie a calcareous and argillaceous mixture ) a mix of
chalk/limestone and clay/shale/marl. Mixing and testing in these early days was
rudimentary. Aeration of the mix on site was considered essential; it is now
considered that this “air-slaking” was injurious to the final strength.
Aggregate primarily
used was clinker and pulverised clinker dust mixed with mica based stone
particles. Cement was often so poorly set that moisture penetration in
subsequent years washed it out of the construction. This clinker is more
properly called “breeze”, as it contains material which is not fully burnt. The
unburnt portions include sulphur compounds, largely iron sulphates and iron
sulphides, more commonly known as pyrites, the agent instrumental in mundic
activity and decay of concrete and concrete blocks. The pyrites themselves do
not present an immediate problem, but when the concrete becomes wet. the action
is encouraged and continues until the whole of the wet/moist concrete has
decayed to a gravel, caused by the sulpho-aluminates of lime. The distortion
and de-lamination of the concrete is a primary indicator. Although the use of
lightweight aggregate reduces the weight, it also reduces the strength and it
is more fragile, more porous. It is therefore essential that buildings of this
age are protected fully against the penetration of water/moisture into the
fabric, and this includes prevention internally against pipe bursts, etc.,.
There is also a higher likelihood of the partially burnt material being more
susceptible to the effects of fire, and therefore greater reliance should be
placed upon fire protection systems and construction.
Steel beams and
reinforcement
Steel
at the end of the 19th century would have been produced by the
regenerative process of Pierre Martin, though it is more likely that they were
solely made in the Bessemer/Siemens processes. This steel would have been
placed ( unprotected and uncoated ) in the concrete ( this combination slab
technique was widespread ). The use of steel as reinforcement ( instead of
iron, which proved to be disastrous ) was not proposed until 1870, before which
time it was thought that the use of Portland Cement would inhibit the formation
of rust in iron.
Steelwork
of this time is prone to de-lamination and expansion when exposed to
water/moisture, lifting concrete, breaking down the concrete where it abuts the
steel, introducing stresses and fractures in the concrete slabs. Very little of
this is noticeable as Victorian floors were finished with a floating timber
floor, and the ceilings were often battened-off and plastered on lath. A keen
eye and vigilance is necessary.
If
we are to preserve the inheritance of these buildings, we need to be aware of
the construction and its susceptibilities and remedies.