TANKING (STRUCTURAL WATERPROOFING)
Many holder properties have external walls where the internal floor levels are below the external ground levels, these walls are generally described as soil bearing.
There are also many situations where the internal floor levels between adjoining properties vary and where internal floor levels vary within a property.
Some properties with basements have pavement bridges or vaulting abutting the walls at ground floor levels.
In all these situations moisture, from within the ground, can enter the walls due to lateral penetration or in some cases by hydrostatic pressure.
In such positions an injected damp proof course is an unsuitable method of damp control.
To prevent moisture penetration it is necessary to provide a waterproof barrier, this is generally referred to as Tanking or Structural Waterproofing.
TIMBER DECAY TREATMENT LIMITED CAN OFFER A NUMBER OF DIFFERENT TANKING SYSTEMS TO SUIT THE VARYING NEEDS OF INDIVIDUAL SITUATIONS.
Our Surveyors will visit the site, inspect the problem and offer a suitable damp control method. It should be understood that ideally external ground levels should be no higher than 150mm below internal floor levels and if external ground levels can be reduced, this should be the first option.
Improved land and rainwater system drainage should also be considered. Often, old underground rainwater drains become silted up and rainwater collected from gutters etc is discharged through the downpipes into mysterious holes in the ground only to add increased water into the soil which eventually shows itself in the form of damp on the internal wall faces.
Land which slopes down to a wall with no relieving lateral drain can add significantly to wet walls.
The client or his builder should address themselves to improving such situations.
Tanking can only improve the environment within the building, it cannot provide an entire solution, this can only be achieved by correct design, difficult, we appreciate, on buildings constructed centuries ago.
Once a tanking system has been introduced, care must still be exercised in the treatment of a wall. Plastering specifications are critical, only cementitious renovating plasters should be used, this can be bonded using Styrene Butadiene Resin. PVA bonding agents and lightweight gypsum plasters must not be used under any circumstances.
Any puncturing of the tanking membrane will immediately allow entry of moisture. Positioning of electric sockets, radiators and other fixings should be avoided on tanked walls. Skirtings should be stuck onto the plastered face and not screwed or nailed.
The use of impermeable decorating materials such as vinyls should be avoided and it is recommended that items of furniture such as cupboards are not pushed back against tanked walls.
Condensation is another hazard as the tanked wall, being soil bearing, is often cold, therefore surplus airborne moisture will tend to be deposited on its surface in the form of condensation.
Another important consideration is the joint between a solid floor damp proof membrane and the vertical wall tanking membrane. The two systems should be bonded and lapped, it is for this reason liquid applied systems are superior to polythene membranes in these situations.
TIMBER DECAY TREATMENT LIMITED CAN ALSO APPLY 12MM WATERPROOF SCREEDS ONTO SUITABLE SURFACES, WHICH WILL PROVIDE AN HOMOGENOUS BARRIER OVER WALL AND FLOOR, again our Surveyor can advise on this matter.
Where practical a tanked wall should have a separate, detached lining wall of concrete blockwork, or similar, introduced across its face, this will overcome or ease many of the potential problems previously detailed.
Similarly, styrene thermal board linings are an ideal method of reducing subsequent problems. We can supply ad fix these materials if required.
In poorly ventilated areas, often the case with high external ground level situations, additional environmental control aids are necessary. Dehumidifies, condensation control units, humidistat controlled extractor fans and dry background heating can usually assist in the relief of these problems.
Finally it must be once more emphasized that taking makes the “best of a bad job”, modern buildings in subterranean situations are built to prevent moisture entering their structure, in old buildings the structure remains damp or wet, tanking does no more than provide a dry surface.
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