Archive for November, 2012

Waterproofing a historic building on the Scilly Isles

Friday, November 16th, 2012
Refurbishment of Porthcressa Library

The 150 year old building stands on the sea front

Triton approved contractor, ISCA Preservation, has installed waterproofing systems from Triton to protect a historical stone building on the seafront at Porthcressa on the Isles of Scilly.

The granite and lime mortar building was constructed around 150 years ago and has been used in the past as agricultural and boat storage, a lifeboat station and a registry office!  It is now being converted to a public library as part of the Porthcressa Regeneration Scheme.

Main contractors, Kier Construction and Exeter based Grainge Architects, asked ISCA Preservation to recommend a method of protecting the new dry lined interior from the invasion of sea salts, rising damp and lateral penetration from high external ground levels. In view of the building’s location, the building’s heavy salt contamination and risk of Radon gas ingress also had to be taken into account when specifying an effective solution – as did shipping costs to the remote island.


In view of its position, the building was heavily contaminated by salt!

Following site visits and working in conjunction with Triton, ISCA proposed using a combination of BS 8201 Type A and Type C waterproofing systems. The solution comprised Platon cavity drain membranes sealed with butyl rubber products and a liquid applied membrane which together provided a fully sealed system to the building requiring minimal preparation or disturbance to the original substrate.

Platon P5 cavity drain membrane was installed to the full height of the walls, and linked to the internal drainage channels.  All joints were sealed using a double system of butyl sealing rope and over tape. Cavity drain membranes work by allowing moisture to continue to penetrate the substrate but then control it in the air gap formed by their studded profile and direct it down to perimeter drainage channels.

The floor area was protected by Platon Multi membrane, a BBA certified product which is impermeable to water, gas and water vapour. Any moisture entering via the new slab is again drained to the perimeter channels. Platon Stop membrane was then laid over the insulation layer and sealed to the wall membranes with Triton’s Corner Strip, providing a completely sealed system behind the insulated dry lining.

In the entrance foyer, a different approach was taken as the client wanted to install granite sets to the floor. Here, the new slab was sealed with Triton’s liquid applied water and gas barrier, TT Vapour Membrane, a Type A system that will form a traditional water and gas proof tanking layer. The sets originally formed two cart tracks through the entire length of the building to allow boats to be dragged in and out.

Upon completion of the works by ISCA, an insurance backed guarantee was issued to the client.