In theory, a basement built in decent, free-draining ground conditions will stay dry. But if there’s a build-up of water in the ground surrounding the basement, the water will penetrate the floor and walls through any cracks, joints or structural weaknesses in the basement. This water ingress can lead to mould growth, decay and leaking.
For obvious reasons, a basement needs some form of waterproofing to prevent damp-related issues that could lead to more serious structural problems.
The easiest known method of basement waterproofing is applying an external membrane or liquid coating on the outside and/or inside of the wall to create a hydrophobic barrier.
Some waterproofing membranes are “stick-on” plastic sheets that are inexpensive and quite simple to apply. However, these membranes can easily lose adhesion when things get wet on site or when there is high humidity during application. These can also be damaged during backfilling operation or incorrectly installed by the contractor. A better option is a “paint-on” waterproofing membrane, which has less room for builder error and last a long time. These tanking membranes can be easily applied using a paint brush, roller or trowel.
Just like paint, there are different types of waterproofing membranes made for different structures and soil conditions.
For example, Cemix Crystalproof is a crystalline material which waterproofs and protects concrete in-depth. It can be used for both internal and external waterproofing of any structurally sound concrete (new or old), including moist or green concrete. Its ultra-strength bond ensures long-term protection even when subjected to high water pressure.
On the other hand, Aquastop is best used for concrete, block and masonry surfaces. It’s most suited for inside concrete block basements as it can withstand pressure from a head of water (hydrostatic pressure) and keeps internal areas dry, though it can also be applied externally.
For concrete block walls, retaining walls and timber posts, a stable flexible bituminous emulsion like Bituproof Plus works best as it does not creep under heat or slump in vertical surfaces. However, this product is only suitable for use on the positive side of the wall where water or moisture can enter the structure.
Elastomeric membranes like Cemix Rubberguard are an innovative waterproofing solution that offers the best durability. When applied systematically and allowed to cure completely, these membranes make basement walls impermeable to water, chemical vapours and subterranean gases. Rubberguard, in particular, has excellent adhesion properties over concrete, masonry, cement sheeting, renders, plaster board and wet area sheet surfaces.
Sealants and Joint Treatments
Other considerations in using basement tanking membranes are sealing active leaks or cracks and ensuring the corners and joints are also protected.
Crystalproof and Aquastop can both be used to seal minor cracks up to 0.4mm. Bigger cracks can be filled with the Cemix Quick Patch repair mortar. Block walls and floors with rising damp can be cured instantly using a nano-technology sealer like Cemprotect, which penetrates hydrophobic protection treatment for all cementitious substrates including natural and artificial stone. It’s designed to protect concrete from gradual water damage and enhance the effectiveness of the waterproofing membrane.
For the corners, pipes and joints, there are elastic bands and seal tapes specifically made for these volatile areas. The ones from Cemix Safeguard range are high-strength and tear resistant, offering long-term sealing protection.
Are Paint-on Tanking Membranes the Solution?
Paint-on membranes have the advantage of low in-place cost, quick application and excellent elongation. When applied correctly, they can last for decades. The chief disadvantage to them is the possible inconsistency in coverage. It takes careful application to achieve the minimum coverage thickness of 60mils.
Moreover, it’s good to remember that these cheap methods only manage the symptom rather than treat the cause. If you don’t solve the root of the problem, groundwater will still seep into anything that’s not 100% structurally perfect, including a tanking membrane that has not been applied properly.
So what’s a good basement waterproofing design?
It should include a system for removing excess water from the soil surrounding your property. An effective yet unobtrusive method is to install subsoil drainage, wherein drainage pipes are installed underground to intercept and convey subsurface or seepage water.
Benefits of subsoil drainage:
- Protection from water damage
- Increases stability of the ground and soil strength
- Reduces foundation movements caused by the variations in the soil moisture content
The subsoil drainage system is ideally installed around the perimeter of your home so that the water gets drained before it reaches the foundation. If you have a retaining wall, it’s a good idea to locate the drainage pipe behind it to relieve hydrostatic pressure. The important thing to remember is to place the system above the natural water table so you’ll drain away the surface water, instead of groundwater.
The most common type of subsoil drainage is a special geotextile-covered pipe. The pipe has a number of perforations which allows water to be drained away to enter. The geotextile covering stops soil and other particles from going into the pipe and clogging it up. A simpler type of subsoil drainage is buried rocks or pebbles, which acts as a free draining system. The subsoil drainage must discharge water into a cesspit or holding pit, where any debris is cleaned out, before overflowing into an approved point of outfall such as soakholes, a curb discharge or an existing stormwater system.
To prevent clogging, the drain pipes should be at least 7.5mm in diameter and the trenches should be 300mm-wide at the very least. Drain envelopes are installed around a subsoil drain to provide structural bedding for the pipe and increase the effective surface area of the drain.
Basement waterproofing membranes are great if you need a quick fix that is inexpensive. But the fact is they don’t solve the problem at all and there’s still a risk of running into bigger problems later that costs more to repair.
Installing a subsoil drainage system should tackle the problem at its roots. If you need more information about it, call us on 0800 372 465.