Damp coming through a floor is quite common. Especially with solid concrete floors in your property. Some common places you may find this issue are:
- Downstairs rooms with solid concrete floors
- Garages and sheds
- Basements and cellars
These are all areas where water can penetrate through the concrete and result in damp on the surface.
Tanking slurry can be used to stop damp coming through a floor. In most cases it is a very effective solution. However, if the surface is not prepared correctly and the tanking slurry is applied poorly, then it could fail at a later date.
Why does damp come through a concrete floor?
An issue with the existing DPM (damp proof membrane) is the most common reason for rising damp in a concrete slab. In some cases, a DPM may not have been installed at all.
A damp proof membrane is a waterproof barrier, it is installed below the concrete to stop water from rising into the slab. This is usually made of a durable and completely water resistant polyethylene sheet.
The material is usually intended to last the lifetime of a building, but as with anything, it can degrade slightly over time. Plus, there is always a chance that the membrane suffered some form of damage during the building process, which has caused it to fail later.
One potential solution when your DPM fails, is to dig up the concrete slab and insert a new DPM. However, this is a big job, and you will need to completely remove the existing concrete slab to add a new DPM.
In most cases this is a job for a professional. Once concrete is fully cured, ripping it up is no small task. Expect this to be a lot of work and expense.
How to use tanking slurry on your floor
The good news is that something like tanking slurry is far more simple. You will not need to dig up the existing floor to replace the DPM. Instead the tanking slurry will form a waterproof barrier on the surface.
Before you apply tanking slurry to your floor, it is important that you prepare the surface thoroughly. There should be no dust and debris on the surface, and if you are applying the slurry to smooth concrete, it is advised that you use a primer.
Priming the surface will enable the tanking slurry to get a good key. This will stop it from lifting and cracking.
The best option here is a SBR primer (Styrene Butadiene Rubber) this will prime the surface and allow a better adhesion for the tanking slurry.
It is recommended to use a mixture of 1 part SBR to 2 parts clean water. This will create a good key. It will also be dilute enough to allow silica from the slurry to penetrate the concrete.
Applying tanking slurry to your floor
Tanking slurry is relatively easy to apply. It usually comes in powder form, so you will need to mix the slurry yourself.
You should mix your tanking slurry in a clean bucket with clean water. It is also advised that you use some form of mechanical mixing. A good option here is a drill with a mixing paddle attachment. You can see a good example of a mixing paddle by clicking here – amzn.to/3jhwO4f
The problem with mixing tanking slurry by hand, is it will be very difficult to achieve a fully mixed and smooth finish. By using a mixing attachment and a drill, you can easily get a nice smooth, lump free finish.
Once your tanking slurry is fully mixed you can start to apply it to the floor. To do this, simply pour some of the slurry onto a section of the floor from the bucket, next spread the mixture with a brush. You can use a masonry paint brush, or if you prefer to stand up a soft sweeping brush is also a good option.
You will need to apply two coats of the tanking slurry to achieve the best results. Each coat should be applied in different directions to achieve the best finish.
For example, if your first coat is brushed lengthways, then the second coat should be applied across the width of the room.
Generally, the second coat can be applied after around two hours. At this point the first coat should be dry to the touch. Before you apply the second coat you should spray a fine mist of water onto the first coat.
Following the second coat your floor should be fully covered with the tanking slurry. Once the job is finished you should leave it for 24-48 hours, this will allow the mixture to completely go off. At this point the floor should be fully damp proofed. This will mean previous damp problems are no longer an issue.
Tanking slurry can be a great way to waterproof a floor. It is also very effective on walls and is an affordable way of adding a waterproof barrier to a room.
Its ease of application and low cost make it very popular DIY damp solution. It does not really require any technical knowledge. If you can follow simple instructions on the container and operate a whisk and a brush you should be good to go.
To learn more about tanking slurry you can read our full tanking slurry case study here.
In this article, we walk through a case study of tanking a small outbuilding (floors and walls). This includes the full process from start to finish. As well as our favourite tanking slurry to use.