How Do You Waterproof A New Basement?

A basement can be a great addition to any home, giving you extra space for storage, a home workshop, a gym or a private retreat. However, any basement is only as good as it is dry. Since basements are below ground structures, they can be subjected to moisture from both outsides, in the form of leakage and seepage or inside, in the form of humidity. Therefore, waterproofing a basement is tackling the problem from within and from without.

As a rule, waterproofing a basement is a job best left to the damp proofing experts, but there are many things you can do yourself to prevent or minimise the problem. Coldness and dampness are not a good combination for housing. An old basement, or one that hasn't been adequately maintained, will allow water to seep from the surrounding earth and wreak havoc with the foundations.

Failing to upkeep the waterproofing on any underground parts of your house will inevitably lead to an increase in mould, which can irritate or cause an increase in respiratory conditions and other ailments, as well as chip away at the structural integrity of your property. This can occur from even the smallest breach, so regular checks and maintenance are an absolute necessity. Fortunately, waterproofing your basement isn't nearly as daunting a procedure as it might seem. With some technical know-how and enough time to sink your teeth into a DIY project, anybody can ensure that their house remains secured against the elements.

Waterproofing A Basement From The Outside

Whether you notice leakage from near the floor of your basement or from around the windows, or elsewhere, improper drainage is usually a big part of the reason. As rainwater soaks into the soil, it gradually forms a water table deep beneath the soil. Your basement may be acting as a dam beneath the surface of the earth, preventing water from draining away. The hydrostatic pressure of this water forces it to seep into your basement wherever it can. The only way to prevent this from happening is by installing a drainage system that directs rainwater away from the house before it gets a chance to seep into the soil:

  • Check your gutters and downpipes regularly. Please make sure the gutters are clean and free of debris and that when water comes out of the downpipes, it is being directed well away from the sides of the house. If you are on a sloping block, ground-level drainage away from the house may nip the problem in the bud.
  • If you are on a level block, you may need to install below ground level drainage to direct the water well away from the house. It is better to get a damp proofing expert to help you with a job like this than to tackle it independently.

how do you waterproof a new basement (1)If you are building a new home, you have the opportunity to thoroughly waterproof your basement from the outside. Called "tanking" because it effectively turns your basement into a waterproof tank, this, combined with a drainage system, should ensure that your basement remains dry in even the wettest weather.

Waterproofing A Basement From The Inside

It is never advisable to waterproof a basement from the inside. However, if combined with good exterior drainage, using specially designed wall coatings on the basement walls will help protect the walls from rising damp or "weeping". A good hardware store near you may be able to supply you with the right sealers and fillers for keeping water seeping into your basement.

If the problem persists or has a severe problem with rising damp or leakage, get a damp proofing professional in your area to analyse and fix the problem for you. They have the expertise needed to get the job done right. Also, think about installing a dehumidifier in your basement. A basement is a tightly sealed environment that often has high moisture levels with no means of escape. This can create an unhealthy environment that allows allergens and other pollutants to thrive. However, between your waterproofing and your dehumidifier, you will end up with a basement that you can put to use and enjoy.

FAQs About How To Waterproof A New Basement

Firstly, you will have to choose between what kind of waterproofing solution you will be going for. We strongly recommend waterproofing from the outside to stop water at the source. That way, you also protect the building structure. We'll be covering external membrane installation in detail, as the others are mostly stopgap solutions or ways to alleviate excess moisture (but not effective long-term solutions in themselves). If the water has already penetrated your basement, you should think about doing these first steps:

  • Installing a sump pump
    • This is for cases where water has already entered the basement, and installing a sump pump will allow you to remove excess moisture before further waterproofing.
  • Waterproof paint
    • If you're getting a lot of seepage through the walls, you could consider painting your basement walls with waterproof paint. This is a stopgap solution, and while slowing moisture accumulation, it might not necessarily fix the problem.
  • Installing a dehumidifier
    • If you're dealing with a particularly humid basement, one easy solution is to suck the moisture out of the air, storing it in a reservoir that you can empty periodically.
  • Membranes
    • Suppose you're looking for a preventative solution to provide initial defence, as well as bolster any other waterproofing efforts. In that case, your best bet is in PVC (or PVC blend) membrane sheeting installed on the external walls of your basement.


Next, you'll need to choose which particular waterproofing system type you would like to have installed. Again, we recommend either Wolfin or Cosmofin.

Wolfin is first-in-class for membrane sheeting and affords extreme protection from the harsh Australian climate. It comes in either Wolfin IB, a standard multi-purpose loose-laid application, and Wolfin GWSK, an adhesive-backed bonded membrane form. However, the installation of Wolfin can only be done by an accredited Wolfin Applicator, making it unsuitable for DIY work unless that person already works in the industry. However, this is still the premium product in its class, so if you desire a truly quality installation that will stand the test of time, it's an excellent choice.

Cosmofin is an industry standard and is best used as a long-term solution as reliable as it is flexible. Cosmofin is used in everything from residential to maritime applications and is easily applicable for home DIY use, especially as it is versatile enough to be applied to almost any external building material, from concrete to timber. Cosmofin comes in both loose-laid, strip-bonded, and fully-bonded applications. The easiest to install is strip-bonded, as it comes with its adhesive as part of the package, while fully-bonded will require the use of traditional adhesives.


Here are the steps for installing Cosmofin and Wolfin:

  • Saw Cut Termination
    • The first step is to establish where the saw cut terminations are to be positioned and chalk the line base slab and wall terminations. It's important to remember that the wall terminations must be a minimum of 100mm above ground and backfill level. Mix and apply non-shrink grout to all the saw-cut terminations, then whilst still wet, embed the factory bonded membrane profiles into the grout, mechanically fastening the profile with Hilti nips at 150mm centres.
  • Preparing the membrane
    • Measure all the areas of the basement that need to be waterproofed, and cut the membrane to these specific required lengths and dimensions.
  • Installing the membrane
    • The membrane will be hot-air welded directly onto the top and the base terminating profiles, with the membrane having an overlap of 50mm where the sheets are joined together on the verticals.
  • Inspection
    • Inspect all the laps, seams and joints with a screwdriver to ensure waterproofing integrity. There should be no gaps, holes, or areas where the screwdriver can penetrate the membrane system's seam, lap, or joint.
  • Repairs
    • All laps, seams, or joints should be re-welded using the hot air gun to ensure that the membrane system is waterproof without gaps or breaches.
  • Backfilling
    • Before backfilling against the membrane, there are a couple of things to do first. You need to install A44 fabric directly against the membrane and install drainage cells (followed by another layer of fabric). This will protect the membrane and aid the drainage from these areas. The waterproofing contractor normally carries out these works to ensure the total integrity of the membrane system against potential damage.

Hydrostatic Pressure

Hydrostatic pressure occurs when water accumulates from rain or garden irrigation systems around your foundation. As gravity pushes down on that water, it will try to 

escape to relieve that pressure. As a result, the water will force its way through any cracks in your basement walls and floors. The pressure can get so strong that it will cause cracks.


Cracks in your basement walls, floors, and around windows or doors provide the perfect avenue through which water can flow. Water will always follow the path of least resistance, and these cracks make it easy for water to come inside.


Basements can be very damp places. When condensation occurs, it can bring mildew, mould, and potential damage along with it, which is a health hazard.

Methods To Fix Your Moisture Problem

Exterior Waterproofing

Exterior waterproofing is one of the biggest undertakings a homeowner can take. This usually means the excavation of the soil surrounding the home's foundation. As you can imagine, this can be a labour-intensive process, requiring heavy tools and machinery. The ideal solution would be to use a polymer-based sealant like our semco liquid membrane during the construction process of your home, and it could last you for the life of the building.

Interior Waterproofing

Interior waterproofing is the fastest and most cost-effective way to waterproof your basement. These typically begin with ensuring that any cracks or holes in your basement walls, floors, and around windows and doors are properly sealed and watertight. Water most frequently makes its way into your basement via these cracks. Therefore, properly sealing them is the first step towards ensuring your basement stays dry. Interior waterproofing methods, such as waterproof sealants, also do a good job at keeping humidity levels down, preventing condensation. In addition, these coatings can be put onto basement walls and floors, creating a waterproof barrier. 

Drainage Systems

The goal of these drainage systems is to direct water (whether it be groundwater or rainwater) away from the foundation of your home. However, this solution is more costly and time-consuming as it requires installation equipment. The best is to contact a local construction company to do the work. This section will look at the drainage options for new build basements in a bit more detail. With your external waterproofing system, you will need to provide a drainage system to remove water to an internal sump chamber or soak away point.

Land Drains And French Drains

To further protect your basement from water ingress, you should install a land drain, sometimes referred to as a French drain. These are laid around the perimeter of the basement at slab level. In essence, you have a trench around the perimeter, which contains a perforated pipe covered with gravel or crushed stone. Water that hits the external surface runs down the membrane through the gravel and is safely removed to a sump chamber, mains drain, or soakaway. This land should be wrapped in a geotextile membrane to stop fine sediments and debris blocking the pipe. Access points and jetting points should also be included for annual maintenance.

The ultimate goal is a dry internal environment in your basement or cellar. However, any walls in direct contact with the earth may experience hydrostatic water pressure. You, therefore, need to effectively deal with this pressure to stop water from entering the structure. You can tank the basement structure using conventional barrier tanking; however, any slight defect will be exploited if tanking is subjected to sufficient hydrostatic pressure. Also, barrier tanking is generally non-maintainable, increasing the risk of failure over time. A complete external waterproofing system, including an internal cavity membrane, is the best option for mitigating risk. 


It is important to consider your environment when installing a new-build basement. This will require a professional who can analyse the soil type, ground drainage, the presence of any potential contaminants (PermaSEAL Geodrain cavity drain membrane is resistant to all chemicals normally found in the ground), and the height of the water table. These should be considered in light of the intended use of your basement.

External Waterproofing Systems

With external waterproofing systems, we recommend combining a primary and secondary waterproofing system along with a priming stage.


The first step in external waterproofing in most cases is priming. Priming involves applying a specially-designed spray such as Kiesel Waterproofing Primer or Kiesol MB Primer to the external structure. This forces the masonry pores to narrow, creating a water-repellent surface. Primers are also designed to bond with the waterproof coating used in the primary waterproofing stage.

Primary Waterproofing 

Primary waterproofing involves applying a waterproof material directly to the external wall. It would be best to waterproof the substrate with a waterproofing compound such as Multi Tight. These specially-designed coatings have a high compression strength and are watertight even under aggressive pressure.  

Secondary Waterproofing – External Membranes 

You should install an external waterproofing membrane. This works as a drainage system to quickly remove any water and alleviate hydrostatic pressure against the building. As well as this, the membrane provides a protective layer for the primary waterproofing, especially during the backfilling process. It also acts as a slip membrane as the backfill settles. external cavity membrane

These membranes feature numerous studs (like an egg box), which create a cavity. This allows any water to drain freely down the cavity to a land drain or French drain. More information on drains can be found below. The drain channels the water to an appropriate evacuation point like a sump chamber with a pump, mains drain or soaks away. The water also passes through a filter (fabric or internal polypropylene layer, often called Geotex) in the membrane. 

This prevents fine particles from entering the drainage system and causing problems. You have both a primary and secondary waterproofing barrier by employing the above external waterproofing system. By using these methods together, you greatly minimise the risk of defects. Both methods are also highly flexible, giving you confidence that as the building settles or moves in the future, the external masonry waterproofing will move with it and remain watertight.

Sump And Pumpsump And Pump Piping

how do you waterproof a new basement (3)As detailed above, the Sump and Dual Pump systems are designed to remove groundwater from cavity drain membrane systems. They usually combine a sump chamber and a pump, often two pumps, in case one of them fails. Systems should also include a shut-off valve so that you can service the pumps. A battery backup also makes sense should electrics fail.


The biggest point of failure for waterproofing isn't in the initial installation but rather in letting the slow march of time allow water to slowly pool and reach through gaps in walls. Check your basement regularly for any excess humidity or dampness, and if you spot any mould, examine your entire waterproofing situation.

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