Structural Work
The most major element of the 2013 project was structural repairs in the basement of the building. There were two elements to this; the replacement of pillars that support the ground floor, and repairs to ailing concrete on the soffit, or the underside of the ground floor.
The Pillars
Three
deteriorating brick-built pillars, that support the floors above, were
replaced. The ground floor of the museum is a suspended floor constructed in
1904-6 from steel beams and concrete. It is supported on eight pillars,
originally all brick-built, mounted on the top edges of the two ice wells, four
per well. The first floor is supported on pillars too, and these are also
seated on the edge of the wells and pass through the ground floor. You can see
the supports for the first floor when you are walking around the ground floor
of the museum.
The three pillars on the north side of the western ice well were showing signs of deterioration and one in particular was beginning to crumble and crack. In the long term, if not remedied, this would have led to a serious structural failure. The cause of the deterioration is not known with 100% certainty but is thought most likely to have been due to sulphate expansion of the mortar. The mortar may have had a high sulphite content exmpanded as damp penetrated the piers over many years. The damp is due to slow but stready leakage from the canal into the wells - a separate problem that must also be addressed in the future.
The 2013 project saw the three piers or pillars that
were in the greatest need of replacement demolished and replaced. Two were
replaced by brick-clad re-inforced concrete piers that were pre-cast, with
steel reinforcement, on site close to their final location. The huge beams
above were supported with large props and a hydraulic ram, and then the old
brickwork was demolished. The new concrete piers were slid into place and
mortared in. Then the propping could be removed, and finally, brickwork was
built to give the new installation a similar appearance to the old.
The Soffit
"Soffit"
means the underside of the ground floor. If it were plastered and finished we
would call it a ceiling. We needed to do some work on this because this iwas
also affected by the damp conditions in the wells. Over many years, damp has
penetrated into the concrete and this has caused corrosion and expansion on the
surface of the steel beams and joists that are components of the floor itself.
The expansion forced the concrete to crack and pieces had broken off and
fallen into the ice well below. Our project removed the loose concrete, cut it
back as necessary, and cleaned and treated the steelwork that was exposed.
Rather than applying new concrete we left the steel exposed and treated it with
a preservative coating based on zinc.
