Conservation via Reversible 'Waterproofing'

In Summer 2005, Trace wrote an article on reversible waterproofing in historic buildings, which was published in the PCA magazine ‘Property Care’.


In a recent issue of Preserve I commented on methods of re-plastering in barns and other ‘wet’ or salt contaminated properties. This issue is majoring on Heritage works, a byword of which is ‘reversible’ and one that I briefly mentioned and now elaborate further on here by showing case studies, and how using modern methods and cavity drain membranes, one can achieve that reversible objective and indeed safely deal with the many variations that the specialist contractor or consultant may be presented with.

showimageHigher Farm, Mottram: A centuries old farm house with 112.5mm brick panels within matching oak panels, with instructions among general damp proofing and treatment, to advise on how to protect against rain water penetrating through the oak, the brickwork and interfaces between once rebuilt, and how to prevent condensation occurring on the internal surfaces.

On the basis that the brick panels were to be rebuilt, this was achieved by (i) using Illmod 600, an expanding roll of foam larger than but similar to draught excluder, sat secretly at the oak and panel interface, ready to expand if becoming damp in the event of water attempting to penetrate, (ii) using Newton Slimline as a dpc at the brickwork to oak interfaces, extended into the property to later link to (iii) Newton meshed cavity drainage membrane that covered the internal face of the brick panels, and over which insulated plasterboard was dabbed. The Illmod 600 was positioned between the oak and Newton 500 and we plastered internally using lime plaster, with the latter also applied over many internal wattle and daub panels, many of which were conventionally re-formed from scratch. You can see the panels extending out internally in one of the photographs, this leaving the oak exposed while providing required U Values.

showimageA proviso was put on our liabilities in that we advised that because oak commonly cracks when a previously wet property is dried out, in the event of rain-water ever penetrating direct through the oak rather than through the panels and protected interfaces, we reserved the right to be paid to return to undertake further steps, such as filling sealing post completion integral cracks in the oak with Illmod 600 and resin. The purchaser and NHBC required an insured guarantee on this specific work, so we arranged ten year cover from GPI at a greatly increased premium over the norm.

The Stables, Didsbury: A listed complex around a courtyard, including stabling, shippons and housing, being converted into offices, with conservation precluding the use of direct applied plaster over painted brick walls or disturbing of original tiled and stone flag floors. Our instructions were to advise how to allow the walls to be plastered and the floors covered, while leaving all reversible and meeting required U values.

showimageThis involved lining over the floors with a cavity drain dpm, part screeded over and part with floating timber, with the walls covered in ThermalDry cavity drainage membrane, battens and plasterboard. Targeted wall areas adjacent to where the profiles of retained listed joinery were present, were covered with meshed membrane to limit the impact of plastering.

showimageWhile walls in areas were clearly effected by salts and ‘rising dampness’, particularly where animals were once housed and where ground levels marginally breached floor levels, we were able to advise that a remedial dpc could be omitted because the degree of dampness would simply equalize behind the membranes and that forming a wall and floor joint between the wall and floor membranes would design out problems associated to slightly high ground.

The system was basically the same as Type C Drained Protection waterproofing, but installed above ground, so not requiring planned associated drainage. This was a very simple yet safe and successful solution.

The following text was submitted but not included within the magazine because of limitation on space:

showimageManor House, Herefordshire: In association with forming a reversible Type C Drained Protection waterproofing system throughout extensive basements within this former Knights Templar Chapter House, the requirement to protect but leave exposed internally this 800 year old stone arch, called for meshed cavity drainage membrane to be carefully applied over the surrounding stone. A bay was being added above at ground floor to the rear of the arch, so the ground was excavated externally, with the local structure inspected and recorded by a conservation archeologist and then before backfilling occurred, we applied cavity drainage membrane to dry down the structure from the outside. The internal and external wall membranes and a cavity drainage dpm, along with drainage channels, have all acted to dry out what was once a very wet basement area, allowing the arch to be left on view.  As a telling aside, when the stone flags were excavated in this 800 year old basement, a blocked but planned system of drainage channels was present, draining down the hillside with gravity, and yes complying with BS8102. They knew how to do it safely then, whereas today most buildings with basements are protected with Type A, Tanked Protection.


showimageListed Barrel Arch, Stockport: A large brick barrel arch supporting a road bridge and open cobbled market over, with the instructions to design waterproofing to allow the arch to be converted into a hairdressing salon while leaving the whole process reversible. The vertical walls were damp in areas but asphalt present below the cobbles over had largely limited water penetration through the arch proper. Heat reflective Basement Systems ThermalDry cavity drainage membrane, battens and plasterboard were applied to the vertical walls and limited targeted areas of the arch proper, with Delta MS-20 cavity drainage membrane and a screed over the existing stone flag floor, the latter only disturbed to install Basement Systems WaterGuard drainage channels. Other works in proposed service areas included fitting cavity drainage membranes below adjacent weather exposed stone steps where water from above continuously dripped through with every rain.


London Manor House: This Georgian house reportedly benefits from the second largest garden in London, and while we were solving problems of standing water in the retrofit new build and existing basements where other measures had failed, we were asked to quote for lime replastering in the dining room where a leaking pipe above had caused Dry Rot, previously treated by others. Whereas lath and plaster had originally been present, to limit the risk presented by applying new laths on battens, we instead applied  Delta PT meshed cavity drainage membrane, with lime plaster over.

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