How to Waterproof Basement or Cellar Using Tanking
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What Is Cellar Tanking?

Cellar tanking (also known as Basement tanking) is the term used for the process of applying a waterproof layer that acts as a coating on the walls and floor of a cellar or basement. This waterproof layer acts as a water repellant that completely waterproofs your cellar, allowing it to remain dry when exposed to wet and moist conditions. Cellar and Basement tanking is a great way to waterproof your basement, If you ever decide to go through with a cellar conversion (or basement conversion).

Cellar tanking makes your cellar waterproof, which is important if you want to use the room for any living activities. Tanking a basement reduces any negative health conditions you or your family may be exposed to if you plan on using your room for anything which will have people in there for long periods of time.

There are multiple ways on how to tank a cellar. Tanking slurry blocks have been described as one of the best and efficient basement tanking systems, as they block water and any other moisture from entering the basement, as opposed to other methods which only redirect the flow of water.

BDS Drainage offers a premium cellar and basement tanking service. Visit our basement tanking London page today to arrange your free basement tanking valuation today.

Why should you get Cellar Tanking?

Cellar Tanking is a very important process that you should consider if you are thinking about investing in a basement conversion. It is extremely common to experience damp conditions in the basement/cellar of your home, especially in the seasons of the year where rain and the heavy downpour is common. The process on how to get rid of damp on the walls is a long and tedious one, which is why it is heavily recommended that you get cellar tanking as soon as possible. Tanking a Cellar acts as treatment, and a repellant for damp conditions, which is great if you have planned on using those areas of your home for practical reasons.

The reason why your basement walls are so prone to damp conditions is that the walls of your basement/ cellar are below the level of the ground. This means that the moisture from the ground transfers through the semipermeable surface (the walls of your basement) in a process very similar to filtration or osmosis. Once the moisture has entered your basement, the walls get damp, which makes them the perfect breeding ground for fungi and bacteria. Conditions like this encourage the growth of mould in your property. Once the walls in your basement become damp, they become cold which allows the moisture in the air to condensate on the walls, creating wet walls, which also encourages mould growth.

Having a basement conversion (cellar conversion) increases the immediate living space your property has, which allows you to do so much more with your home. But it’s important to always try and get the best standard of living you possibly can get. Basement Tanking allows you to enhance your home, without experiencing any of the health hazards that damp and mouldy conditions can put you though. Basement damp proofing is a great way to counteract these hazards, which will allow you to get the most out of your new cellar conversion.

How does Cellar tanking work?

There are multiple methods you can pursue when it comes to waterproofing a basement. The two options that are most common involve using a cavity drainage system, and basement tanking (also known as Cellar tanking). The method that we are going to explore in this post will be that of Cellar tanking.

The aim of cellar tanking is to keep the basement or cellar as dry as possible but not allowing any moisture in from the outside. It also helps the cellar walls and floor remain warm enough to minimise any form of condensation, which will cause moisture to form on the inside of the basement.

Basement tanking is known to be a prefered option compared to using a cavity drainage system when it comes to waterproofing a cellar. This is because it completely prevents water from entering, rather than just transporting the water to a different location.

How To Mix Tanking Slurry

When mixing tanking slurry, it is important to keep yourself protected at all times, as getting tanking slurry in your eyes can cause unwanted issues. The tanking slurry has a dangerous level of alkalinity, and when it’s in its powdered state, it is easy for it to make contact with your eyes and skin. Make sure you are wearing goggles, gloves, a full cover facemask and appropriate protective clothing. Do not inhale the tanking slurry powder either, as it may cause complications with your lungs.

A high number of tanking slurries comes in a powdered state, which requires you to mix on site. It’s important to follow the manufacturer’s instructions when mixing the slurry, as each slurry has different requirements and prerequisites. Tanking Slurry, when not used becomes unusable after around 40-50 minutes, so it’s important to only mix an amount that can be used within this time constraint.

When Tanking cellar walls, it is important to start by adding the necessary quantity of water to a good, sturdy mixing vessel. It is important not to use a cement mixer, as this does not get you the right texture of slurry for tanking cellar walls.

Steadily add the slurry powder to the water in the mixing vessel, whilst you are mixing the water. Once the powder has been added, continue mixing for around 3 minutes using a plaster mixer, to give it a consistent rotation, giving you the desired texture. You should expect the texture of the slurry to come out like a batter like substance. Let the slurry set for approximately 1 minute, before remixing.

Cellar/ Basement Tanking Process using tanking Slurry Explained

Stage 1

Prepare the surfaces

The first stage of using the tanking slurry to waterproof a house involves preparing the targeted surfaces before any slurry is applied. You will also need to make sure there are no items obstructing the walls, so you’ll need to move all the items that may be obstructing your accessibility. This includes old dressers, shelves, wardrobes and other miscellaneous items.

Once this is done, you will need to remove any plaster and other previous coatings such as paint, wallpaper, insulation etc. This should take you to the original wall (masonry), which is where the process of slurrying will start.

Make sure there is no unwanted residue like dust, debris and make sure to fill in any existing holes you encounter. Doing this makes the process of applying the layers easier and means that you are less likely to encounter any issues when carrying out your basement tanking.

It has been recommended that, if you have, or are experiencing any issues due to excessive levels of salt (from rain and the soil), that you should use a “salt inhibitor” on the afflicted areas. Salt inhibitors are additives added to mixes when applying plaster or slurry to a wall which has been affected by damp. The salt inhibitor acts as a remedial damp proofing solution, which helps hinder natural salts from compromising the basement tanking.

Stage 2

Observe wall for any seepages

When you have stripped the wall of all materials, you’ll need to keep an eye out for any water or moisture seeping through the walls. If you notice any water seepage, or any other liquid or moisture seeping through the surface, then you will need to stop the flow by filling in the source.

Stage 3

Create a reinforced junction between the wall and floor

When tanking a basement, it is always important to apply the basement tanking coating as if you were creating a completely waterproof and water resistant box that prevents water from coming into the cellar. It has been noted that from this waterproof box, the areas where the wall and floor create an angle are the weakest part of the coating.

The best way to tackle the weaker areas of the slurry coating is to create a wall floor junction. The best and easiest way to do this is to:

At the junction between the wall and floor, chase out the ground surface to a minimum of around 20mm x 20mm, cutting into the wall if you can. Flush the chase and remove any debris that is left over. Whilst the chase is still fairly damp, apply a single coat of basement tanking slurry around 100mm on the wall vertically, and the same across the floor. As the tanking slurry is setting, apply “Fillet Seal” over the slurry and chase you created, which should create a concave arch-like surface, spreading from the wall to the floor.

Applying Cellar Tanking to a wall

It is important to remember to apply your cellar slurry to surfaces which are damp, and to avoid applying it directly to a dry surface. If the walls in your basement or cellar are dry, make sure to make them damp. You could do this by spraying water onto the surfaces, make sure the wall isn’t dripping wet, however.

With basement tanking slurry, it is recommended to use at least 2 layers of the slurry to get the best results. The first layer needs to be applied directly to the bare brick walls (masonry), and the second layer should be applied approximately 2-24 hours.before you apply this coat, however, it is important to make sure that the first layer is dry enough to be able to apply a layer on top of it without it peeling off. The layers should be applied on opposite strokes to the layer beneath ( first layer horizontal, second layer vertical). It is important that the second layer is applied within 24 hours of the first coating, even if the first layer still has a damp feel towards it.

Applying Cellar Tanking to a Floor

Applying cellar tanking (basement tanking) to a floor is similar, but a different process to applying it to a wall. It has been strongly recommended that you always tank the basement floor after you tank the basement walls.

Applying slurry to the basement/cellar floor is similar to the walls, applying two layers and making sure you alternate the stroke direction between them. The main difference comes when you finish tanking a basement floor. It is always important to protect the basement tanking coating. This can be done by applying “floor screed” to the surface.

Cellar Tanking Slurry Curing

Once you have applied the second layer of the basement tanking slurry, it is important to let that layer cure properly. This process can take around 24 to 72 hours to fully cure. Sweating is a process that you may experience when allowing your slurry to dry. What this is, is water vapour condensing on the cold surface of the dry slurry. It’s nothing to worry about, it’s just something that can happen in regards to the amount of ventilation the basement or cellar has.

Cellar tanking decoration

Once you have applied and let your basement tanking slurry dry, you can now look to getting the room decorated. It is important to add a render to the basement 24 hours after the slurry dries before you continue with the decorations, however. We recommend using PermaSEAL tanking and PermaSEAL renovating plaster. Once the render coat has been added, you are now able to use plasterboard, and in some cases, a multi finish can be also used. Although you can, BDS Drainage and other credible sources do not recommend painting directly onto the tanking.

BDS Drainage recommends that you avoid using any Gloss paints, wallpapers, and Vinyl emulsions, as these all can trap moisture underneath, which stops the basement tanking (cellar Tanking) from doing its job. This can cause further problems.

How much does Basement Tanking Cost?

Basement tanking costs do vary depending on multiple factors. One of these factors includes the size of the room you plan on tanking. Another factor that could affect cellar tanking costs could be the extent of the amount of mould that is currently present in your cellar or basement.

PermaSEAL tanking slurry is an effective product that is highly recommended at BDS Drainage. It comes in 25 kg buckets and costs around £30-£35 depending on what type you get. With this amount, you can expect to cover around 12m squared. For a DIY basement tanking job, you are probably looking at a ballpark figure of around £500-£600. If you wish to enlist the help of a professional slacking company, contact BDS drainage today! Contact us today to receive a free basement tanking quote tailored to your property now!