Negative side waterproofing is used when moisture is going to come through the walls of a basement for example and the waterproofing is carried out from the inside. Negative side waterproofing means that the waterproofing membrane is applied to the side of the construction member which is opposite to the side with direct contact to the water. Negative side waterproofing is more difficult than positive side waterproofing because the water/moisture penetrates through the construction member behind the waterproofing material and tries “to push it off” the substrate.

 

Ideally you would waterproof on the positive side first, but if the positive side is not accessible then negative side waterproofing is necessary. It is also used when the positive side has failed and this is your last attempt. 

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Some examples of negative side waterproofing • underside of leaking ceilings • inside of tunnels • inside of lift pits • outside of water tanks or potable water tanks • leaking side of retaining walls • inside of basements • Rising Damp • Moisture coming from brick walls.

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Some Information on Rising Damp

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What is the rising damp by definition?

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Rising damp (dampness) is ground moisture containing salts rising up a foundation/Concrete Slab/Masonry walls.

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What can cause rising damp to occur?

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Rising damp can occur as a result of a suction of moisture below substrate into porous masonry building materials such as Concrete slabs, brick, stones, earth and mortar. The moisture evaporates from either face of the wall (inside or outside), creating a flow of suction allowing more to be drawn from below. The height to which the moisture will rise is determined by the evaporation rate and materials surrounding the area. The normal limit for rising damp ranges from 0.5 to 1.5 metres above ground level.

 

What are the signs of rising damp?

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Rising damp can look like a high-tide-like stain on wallpaper and other interior finishes, in severe cases as blistering of paint and loss of plaster and walls bowing. Damp walls will encourage the growth of mould which with an average to high humidity can lead to health problems for home owners. Externally, a damp area may be evident to the base of walls with associated fretting and crumbling of the masonry.

Some of the below symptoms may be present.

Internal walls: rotting timber skirting boards, bubbling paint, bubbling plaster-work, water tidemark, efflorescence, paint deterioration.

External walls:  water tidemark, fretting brickwork, crumbling mortar, damp patches or stains at low level (less than 1.2-1.5m), White floury salts (efflorescence) in the form of nitrates, chlorides and sulphates on the wall, high moisture readings.

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Does rising damp affect the value of my house?

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High chance it will as when it comes time to sell the prospective buyers will order a building inspection which will reveal the problem using there moisture meter, even if it has been covered up. This discovery results in the loss of the sale or at least a heavily discounted price on your property.

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