AUTHENTIC LIME TECHNOLOGY FOR THE MODERN WORLD

Project: Roedean School

Client: Sidell Gibson Architects, London

Introduction

Sidell Gibson Architects in London are retained by Roedean School, an impressive 125-year old building in a stunning East Sussex location that is situated 250 yards from the sea on rising ground, overlooking the English Channel. Part of the architect’s wide renovation remit, was to address a perennial and long term water ingress problem. This water ingress, combined with the associated sea salt was causing extraordinary corrosion to the structural floor steel work; (being the worlds’ first ‘I’ beam and block floor construction). This corrosion was literally threatening the future of the building and in a very short period of time.

The Brief

The client was seeking a combined specifier and applicator, an expert single-source provider and Lime Works were consulted to discuss the dampness issues and advise on the best practice, economic solution. Following consultation meetings, we recommended a materials and application solution that would be based on the results of an exhaustive series of on-site trials and monitoring of results.

The Trials

The first and primary question was, “If we remove the existing render, what on earth do we replace it with?” The second question was “Can we keep the existing render but make it work – albeit an unusual approach to the problem?” Our testing process was primarily to prove whether we indeed, needed to remove existing cement or hydraulic set renders. At the same time, it was considered important to establish a secure and breathable process as a possible alternative, using Lime Works specially formulated non-hydraulic lime slurry and lime wash finishes. The latter question/solution would negate the damage and expense caused by the removal and re-rendering of the building.

We installed a series of humidity sensor probes into walls strategically across four 70m2 sections of wall on the most exposed South West corner of the main building – a total of 280m² and 240 electronic RH sensors. The first acted as the control panel being simply monitored but left, otherwise untouched, a modern cement render. In the second area we retained existing ‘modern’ concrete render and applied specially prescribed Lime Works Slurry Coat and Limewash finish. The existing concrete render was removed in the third area where we re-rendered using the original 19th Century render recipe, then applied our own-manufactured slurry coat and lime wash. The final test area had original 19th century render in place and we applied the same slurry coating and lime wash layers.

All the sensors were wired back to an on-site computer which then took a reading from each sensor, every hour for a continuous 18 months, two winters and one summer from 2006 to 2008. We also installed an on-site weather station, above the test panels to analyse and make comparisons of the weather and moisture ingress readings. Then through a remote desktop broadband link to our offices in Gloucestershire, we created an analysis programme to interpret the readings.

The Result

The results of each of the test area trial was analysed and proved that the unique Lime Works Slurry Coat prescribed, had excellent weather proofing and drying properties. The third and fourth test panels successfully proved that we could indeed keep the existing render in place and this in turn led to financial savings and a lack of consequential damage to the building substrate.

We had carefully considered the local and regional environmental with an open hilltop location; the pressure effects of prevailing winds; and the continual sea salt on the massive external areas of the building. We had also taken into account the high costs involved in removing the original cement render, which could affect the building integrity and lead to more issues and extensive additional costs. The monitoring programme proved that, in this circumstance, our method and materials worked. As a result of those findings, with a small improvement in exact method and material, we have now steadily been coating the entire range of buildings at Roedean.

The performance of the applications have now proved even more extraordinary and even better than hoped; with walls measuring 100% moisture-free dry! The building is breathing and dry. We contributed to a saving of millions of pounds, more than enough to cover the costs of new structural steel repairs, which will be bedded into dry walls. Our clients are delighted with the aesthetic finish too and Roedean as a major heritage building, proudly displays a beautiful new glow. Natural lime-based materials have unique properties and the process of maturing and weathering will actually continue to improve the patina for decades to come.

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