Since the 1960s, the majority of houses in the UK have been built without a cellar or basement space. The reasons for this vary but include the fact that this required deeper foundations and more excavation, which equals more labour and materials, and therefore more cost.
Also, due to our variable climate and frequent wet weather, cellars can be affected by moisture, mould and damp, which means that measures would have to be taken to keep the water out. Once again, more materials, more labour, and more expense.
Because of this, only 2% of homes in the UK have a level below ground, and most of those that do are older properties found in towns and cities, from the days where extra storage was needed for fuel coal and for perishable food that needed to be stored in a cool place.
These places were notoriously damp and musty, with damp walls and cellar floors. Over the years, many were abandoned and ignored.
However, new technology, materials and waterproofing methods introduced in the past few decades have made cellar conversions more feasible, with property owners transforming musty old cellars and basements into additional living spaces. New builds, including eco-projects creating underground homes or houses built into hillsides, are also taking advantage of these new ideas as people seek to make the most of the available space.
One of these waterproofing options is known as cellar tanking. If you're not familiar with the term, this guide will give you a basic idea of what's involved.
Any property with underground levels has an increased risk of becoming damp. The earth that pressed up against the external walls will carry varying amounts of water that can find its way inside through cracks or porous masonry or brickwork. Hydrostatic pressure, the sheer weight of water, pushes moisture through the walls, where it can cause mould and mildew. The local water table contributes to this, especially when it is high. Leaking downpipes and guttering, or faulty/damaged plumbing can also cause problems.
The water that enters the cellar often contains salts that leave a white, furry residue and stains on your walls. The walls are usually cold, which attracts even more moisture as it condenses on the cool surface causing condensation & mould, especially when there isn't adequate ventilation.
All of these factors mean that underground spaces need some form of protection against water ingress through permeable materials to keep them dry and usable. And this is where tanking comes into its own.
A tanking slurry is applied to the interior walls in your basement or cellar, forming a waterproof barrier that permanently stops water and damp. In case you were wondering, the word 'tanking' is simply another term for waterproofing, in the sense that you are creating a 'tank', in the sense of a sealed space or chamber.
Instead of tanking slurry, a damp-proof membrane or damp-proofing paint can be used. The latter is a far cheaper and easier alternative, but will only be effective for about 5 years. Damp-proof membranes, on the other hand, can last as much as 30 years as it is made from high-quality HDPE. This provides a waterproof barrier that allows moisture to evaporate.
Most basement conversion professionals will advise that if you opt for a damp-proof membrane that you also have a cavity drainage system installed, along with sump pumps and drainage channels.
There are various mixtures, depending on the company, but generally speaking, a slurry mix will be made from Portland cement, aggregates, and a selection of chemical modifiers. Acrylic polymer can also be included as it helps to form a stronger bond, improves overall strength, and gives a tough finish that is resistant to scuffs and scratches.
First, the walls and floor will need to be checked for any damage and the surface (substrate) will have to be prepared. Any fittings and fixtures will have to be removed to allow full access to the whole space, and any plaster or render will have to be removed to reveal the original masonry or brickwork. Any loose brick or stone will be cleared and mortar joints will be cleaned out. If there is a high level of salt presence visible on the walls, a salt inhibitor will be applied to prevent it from causing problems in the future. Sometimes, a curved joint is created to strengthen the wall-floor joint. A cut will be made about 20mm into the base of the wall. Once the debris is cleared, the tanking slurry will be applied up to about 100mm up the wall and along the floor, after which a sealant will be sprayed on.
The rest of the walls are then treated with the tanking slurry to form an impermeable barrier, with at least two coats applied, usually leaving 24 hours between each application.
The total cost of cellar waterproofing will obviously depend on the size of the space, the 'substrate' (the type of surface that the slurry will be applied to), and the type of mixture used. On average, this procedure will cost between £40 and £80 per square metre if you hire a professional to do the job for you.
The materials are available if you are brave enough to tackle the job yourself, cutting the cost to around £6 per square metre. While this might be tempting, applying a tanking slurry is not as simple as it sounds. First, you'll need to be sure to prepare the surface of the cellar walls properly. Secondly, you'll need to take safety precautions when handling and mixing the slurry. Many mixtures come in dry powder form that can be harmful to the eyes and skin and can even damage the lungs if breathed in. You'll need full protective gear, including goggles, gloves and facemask.
Mixing it can be a real chore as well, as any unused slurry will start to set after about 40 minutes and become unusable. The trick is to mix just enough and apply it before it starts to cure.
This is why most people leave it to the experts with the right knowledge and experience!
If you are considering a basement or cellar conversion, check out Damp Hero waterproofing specialists for a quote or advice. Our reputable company will find you the best and most cost-effective solution to transform your damp space into a dry, usable room, along with guarantees that will give you confidence and peace of mind.