Where is the water coming from?

Whatever your problem, the main thing is to determine the source of the water. This is often very difficult but you may be able to at least isolate the suspect area by judicious water testing. Such tests are essentially static and it is difficult to simulate conditions such as wind driven rain which may be the cause.

Tiled Decks and Balconies

The first thing is to try and establish whether the membrane system has failed or whether it is being bypassed. Perhaps a flashing has been missed or the cavity in the brickwork has become blocked or bridged.

Once everything is dry, try blocking the drain and flooding the area. If it then leaks, then the membrane is highly suspect. It is however possible that water is still bypassing because the membrane was applied to a rendered surface and not the structural elements, which is what should happen,and was not applied high enough on the wall. This can be checked by first sealing the perimeter with Wrimco ealant and brushing Wrimco/Duroseal AR say 50mm up the wall and re-testing.

If this suggests that it definitely is the membrane, then the best solution is to remove the tiles and re-waterproof. This is of course expensive and may create a disposal problem. You should therefore first try caulking the perimeter and then coating the entire area with.

If you decide to re-waterproof, it is best to remove the old membrane as much as possible. Since Kanga hammers are normally used, the pock marks in the slab will need to be filled to make a level surface with Wrimco/Screedbond mortar. If the wall is rendered, remove say 75mm from above the slab in order to bring the new membrane onto the structural wall and at least 25mm above the height of the tiles.

Since it is often difficult to remove 100% of the old membrane, it will be safest to use a water based membrane such as Wrimco SBS/Duroflex P15 or Wrimco/Durabit EF as the solvent in solvent based urethane is likely to interact and cause blisters and bubbling. Best of all would be an SBS sheet membrane Wrimco SBS/Sopralene Flam 180 which is ideal for such remedial work.

Retaining walls

When dampness appears on the inside of a retaining wall, water testing to help locate the source is impossible while excavating is often not an option. Normal waterproofing materials will seldom work when there is water pressure in the wall since it causes them to lose adhesion.

If the wall is less than 2-3 months old, then Wrimco Foundation is an excellent solution.

If the wall is quite old, it is likely to be saturated with salts in which case the Wrimco/Maxseal Flex is preferred.

If the wall is rendered, it is best to remove the render, apply the Wrimco/Maxseal Flex and re-render. Otherwise there is a risk that the render will lose adhesion to the structural elements of the building because the water is then trapped within the render.

An alternative system that may be used is a water based epoxy such as Wrimco/Duropoxy WBE.


If the membrane roof is loose laid or semi-loose laid, water can track between the membrane and the slab so it makes it virtually impossible to determine the source of the leak. It could well be that the water is bypassing the membrane system so the first thing to do is to carry out a very careful inspection of all constructions above the roof and particularly the flashings.

Water testing could be carried out after a period of dry weather and when there is no dampness beneath. If this proves positive, then it is most likely that the membrane should be replaced. It must be remembered, however, that static water testing does not simulate the dynamic conditions of wind driven rain which may well cause water to bypass the membrane system.

It is not a good idea to simply cover the existing membrane with a much better one such as torch applied elastomeric Wrimco SBS Granules. It is always best to remove the old membrane so you can benefit from a fully bonded system that will not allow water to track.

Naturally there are exceptions to every rule and for difficult to remove materials such as acrylic, it is sufficient to remove the blisters and torch over with Wrimco SBS Granules, assuming that it is exposed.

If there are pavers on “Polypad” supports, then the Wrimco SBS Granules should be used for fire protection. If there is insulating foam and pebbles, then Wrimco SBS plain is sufficient.

Leaks around drains are frequently the cause of problems as are blocked drains that allow water to bank up and go over the membrane upstand. Naturally you should look for any work that may have been carried out such as fitting TV aerials, securing heater coils or installing air conditioning units.

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