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How to Damp Proof Your Basement

Do you have a basement which is damp, mouldy and uninviting? Then read this helpful article to discover ways to waterproof this room and help turn it into a usable area of your home, as well as adding value to your property.


Why does damp occur in the basement?

The problem is that the cellar walls are usually sited below ground so they are beneath the waterproof layer which acts as a building’s damp proof course. Consequently, these walls are surrounded by conditions which favour penetrating dampness and they have no protection. 

Problems caused by the damp

Dampness needs to be addressed as it causes many problems. It is an invitation to mould, fungus and mildew, which not only look unsightly but also have associated health issues. In addition, salts are often contained within the water. As the water moves through the wall it brings the salts with it and these salts cause damage which you often see at the surface as efflorescence or white dusty powder. There are also various structural problems associated with dampness. 

Ways to Waterproof your Basement

To waterproof your basement and eliminate the associated problems of dampness it is necessary to prevent moisture in the walls and floors from migrating to the internal wall surfaces. Since no two basements are the same there is a range of suitable waterproofing solutions. However, the two most common are cavity drain tanking membrane (Tanking Membrane) and structural waterproofing (tanking slurry).

Tanking Membranes

This method is done by lining the basement walls and floors with robust, dimpled, waterproof membranes which can be applied to nearly all underground building structures. The high density polyethylene membranes provide an air gap between the membranes and the wall, which permits water drainage and air circulation and allows the underlying substrate to both drain and breathe. The water can pass into specially constructed drainage channels and sumps in the floor of the basement, where it is silently pumped away.  Please note that your basement floor must be angled toward the sump pump so that any water that enters the cavity will run into the pump.

The membrane is typically fixed to the original sound wall surfaces using special plastic plugs (please see SkilledBuild’s wide range of high quality and inexpensive DPM fixings and accessories). Plasterboard can be fixed to the membrane or alternatively a wet plaster can be applied.

There are various types of membranes and the final choice will be determined by both the finish required and the anticipated flow rate.

Please read our Tanking Membrane sheets on the respective product pages for more information.

Benefits of Cavity Drain Membranes:

  • Lightweight.
  • Quick to install.
  • Non destructive to the structure.
  • Insulating and sound absorbing.
  • Conducive to a dry, high quality environment.
  • The 21st century solution to basement conversion.

However, Please Note: If the electricity goes out the system will not work because the pump will shut down. In addition, the honeycomb membranes are susceptible to mould and mildew spores over time.

Tanking Slurry

Tanking slurry is a particularly appealing option as it is not only cost effective but also time proven, having been used since the 1950s.

Once applied the tanking slurry, such as HydraBloc + Tanking (Product Code: N00090), is able to withstand external water pressure and maintain a dry environment by creating a physical barrier to water entering the basement area through the walls. It is simple to apply you just need to mix the tanking formula, which is supplied as powder, to water to make the cementitious slurry compound that sets to make a completely waterproof barrier over a masonry wall surface.

Please read our Tanking slurry Information sheets on the HydraBloc+ product page for more information.

Other Methods

There are also other steps you can take to help waterproof your basement.

Check Guttering etc.

It should be recognized that the majority of all basement waterproofing problems occur because of water pooling near your home’s foundation. Therefore, the first steps you should take to waterproof your basement are actually outside.

Start by checking your gutters and their downspouts. Ensure that they are not plugged, rusted or leaking, and fix these problems if necessary. The perfect time to check the water flow through your gutter is when it is raining, especially with a moderate to heavy downpour.

Since the guttering is typically made of a continuous metal seamless design, unless there is rusting or other punctuated areas, there should not be leaking around the main lengths of your guttering. You will want to check the connection points closely, as it is here where there is most chance of leakage occurring. This is where your downspouts connect perpendicularly with your main gutter runs. It is important that you fix any leaks you find here. It may be as simple as tightening the connector elbows of your downspouts. A touch of caulk (Product Code:N02130) or the addition of gutter screws can help to secure the  connections and prevent leaks.

If there is a leak and water is not flowing through the downspouts, then most likely you have a clog. A range of debris, including leaves, pine needles, and dirt can become trapped in the gutters and will need to be removed to restore proper water flow. Alternatively, you can invest in a gutter guard to help prevent this from happening again.

It would also be useful to ensure that water run-off is diverted away from the home and subsequently the basement. In order to accomplish this, ensure that that the angle of the soil is flowing downhill away from the house (this only needs to be minor in steepness)

You can also place gutter splash block pans at the bottom of downspouts which will also help to guide the flow of water away from your basement.


Please be aware that the moisture within the basement may in fact be condensation, not lateral damp. To verify if this is the case use our humidity sensor to test if humidity is present. If you unable to find a humidity sensor than there is a DIY alternative. All you need to do is place a 12” x 12” section of aluminum foil on the basement wall and tape each side with duct tape. Leave this in place until moisture develops; this could take hours or even a few days. If you find moisture on the outside surface of the foil then the likely cause is condensation. However, if moisture is not visible on the outside of the foil, then penetrating damp is the culprit.

If your basement does suffer from condensation, you should focus on sources inside the basement. Dryers are normally a key source of condensation so please ensure your dryer is properly vented; ideally to the exterior. You may want to employ a dehumidifier to remove moisture from the room. You can purchase a small portable dehumidifier or even consider a larger whole house unit. If you do have a condensation problem please read our in depth condensation article for more causes and suitable solutions.