BUILT WITH LIMETEC HYDRAULIC LIME MORTAR

St Pancras Station

Limetec, working with English Heritage, produced over 150 different mortar samples to try to meet the challenging specification of matching the original: a good visual match in terms of both colour and texture, and workability with new bricks – which may be a good visual match to the originals, but still have different build characteristics.

YEAR

2006-2009

LOCATION

London, United Kingdom 

CATEGORY

Grade 1 Listed Building

ARCHITECTS

Alistair Lansley

ENVIRONMENT

Grade 1 Listed Building

When the original mortar was analysed, it was realised that the lime and sand that had been used was no longer available: with thousands of limeworks in the Victorian era contracting to just a handful, the closest match found was a French hydraulic lime, distributed in the UK by Castle Cement.

We eventually narrowed down the 150 samples to around 20 variants that were used in test panels, before the final selection was made. For the fine gauged arch work, however, we had to produce a pure lime putty, with no sand at all. The closest match for colour and coarseness came from a works in Shillingstone, Dorset, which went out of business some six years ago. Luckily, we still had 30 tons of it in stock, which we were able to utilise!

Once the final specifications were agreed and approved the various preblended dry mortars were manufactured in the industrial quantities required, the first time on such a major commercial development. It was then delivered in tankers and put into mobile silos on-site.

Before any building work could begin, sample panels had to be produced and approved for quality control purposes. One of the biggest questions to be answered was, “What exactly are we replicating?” The original Gilbert Scott designed building is over 150 years old, so should it be a match to what is there now, or what we think was there originally?

Given that modern brick-making techniques – even hand-made ones – make an exact match an impossibility, an element of compromise in the eventual decisions made was inevitable.Take the main facing bricks as an example: St Pancras was built by Midlands industrialists, and the original product came from two independent brickworks: Thomas Gripper’s Nottingham Patent Brickworks, and when they could not keep up with demand, Tuckers in Shepshed, Leicestershire (whom Gripper’s eventually acquired). Finding the right Keuper Marl clay with which to make them was not the difficult part: finding a company that could match the shape, colour and texture most definitely was.

Apart from the fact that it was an unusual size brick (229 x 69mm, compared with current UK standard of 215 x 65mm), weathering over the years had badly affected the original brickwork, leaving a textured surface that made a facsimile match virtually impossible.

Extensive investigations were carried out throughout the industry, to try to solve the problem and develop a specification and brief; brick factors, James & Taylor, working with brick consultant Philip Mason, made recommendations on which companies were best placed to fulfil all the key criteria – not just the technical excellence of the product, but also the ability to produce a hand-made product in very large quantities, to unforgiving schedules.

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