Basement Waterproofing
Transform your damp basement into a dry, usable space
Your basement has huge potential, but groundwater and heavy rainfall are a constant threat. When moisture gets through foundation walls, it causes structural damage and unhealthy mould, and it stops you using the space at all. At Crystal Damp Proofing & Basements we provide robust, guaranteed basement waterproofing that keeps moisture out for good.
Our expert waterproofing systems
Every property is different, so our specialists tailor the waterproofing method to your building and its surroundings. We mainly use three proven methods, often combined.
1. Cavity drain membrane systems (our most popular solution)
Instead of just trying to hold water back, this system manages it. We fix specialist studded membranes across the walls and floor. Any groundwater that gets through the outer masonry is caught behind the membrane, channelled into a hidden drainage system and quietly pumped away by a high-performance sump pump.
The result is a dry, warm space that is ready straight away for plastering, decoration or a full conversion. Under BS 8102:2022 this is known as Type C (drained) protection.
2. Structural tanking (slurry coatings)
Where the structure calls for it, we apply advanced tanking slurries that form a tough, waterproof barrier directly on the masonry. Under BS 8102:2022 this is Type A (barrier) protection. Standard slurry can fail if micro-cracks are ignored, so we follow a careful process:
- We strip, clean and prepare the walls back to the bare substrate.
- We repair all visible cracks and mortar defects.
- We apply specialist primers to stabilise the surface.
We apply several precise coats of waterproof tanking render to form a continuous seal against moisture.
3. Spray-applied tanking and bitumen coatings
For larger areas and external structures we also use spray-applied tanking. Spraying lays the material down evenly at a consistent thickness, with no gaps or thin spots, even on uneven or hard-to-reach surfaces.
- Proper preparation. Before spraying, we level and repair the substrate with specialist levelling and repair mortars, such as universal mortar. This gives the coating a sound, even surface, so we can be sure it has been applied correctly and will perform as intended.
- Bitumen coatings on external structures. We spray bituminous waterproofing coatings, especially on the outer face of retaining walls and other earth-retaining structures, before backfilling. This stops groundwater at the outside of the wall, before it reaches the structure.
Part of a two-layer system. External spray-applied tanking can be combined with a cavity drain membrane inside, giving full A + C protection.
Why do we use these two systems below ground?
Below ground level, walls and floors are in constant contact with damp soil. After heavy rain, or where the water table is high, water also pushes against the structure under pressure (hydrostatic pressure). Ordinary damp proofing is designed for above-ground walls and cannot resist this. That is why BS 8102:2022, the British standard for protecting below-ground structures, sets out dedicated waterproofing systems.
- Cavity drain membranes don’t fight the water pressure. They give water a controlled route out, so pressure never builds up against your finished walls. This makes them the safest choice for habitable rooms and areas with a high water table.
- Tanking slurry bonds directly to the masonry and blocks water at the surface. It works well on sound, solid walls, in lower-risk areas, on lightwells and on external walls, and where every millimetre of room space matters.
Combined systems (A + C). In many basements, especially new builds and full conversions, we use both. The slurry forms the first line of defence and the membrane is a back-up if water ever gets past it. BS 8102 recommends this kind of combined protection where the risk is higher or the space will be lived in.
How durable are these systems, and how long do they last?
- Cavity drain membranes are made from high-density polyethylene (HDPE), which doesn’t rot and resists chemicals, salts and mould. Once installed correctly, the membrane is designed to last for the life of the building.
- Sump pumps are mechanical parts, so they need looking after. We recommend a service every 12 months. A well-maintained pump normally lasts many years, and a battery back-up or dual pump keeps the system running during a power cut.
- Tanking slurry is a cement-based system that lasts for decades when it’s applied to a properly prepared, stable wall. Its lifespan depends on the condition of the substrate. That is why we spend so much time on preparation and crack repair before the first coat goes on.
- Sprayed bitumen coatings on external walls are protected by the backfill once the ground is reinstated. With a protection board in place, they last for decades without maintenance.
Regular checks and pump servicing are what keep a waterproofing system working as well in 20 years as it does on day one. We offer aftercare packages for this.
How do these systems affect below-ground walls and floors?
- A cavity drain membrane doesn’t dry out the masonry behind it. Instead it separates it from your living space. The air gap behind the membrane lets any moisture drain away safely, so no water pressure builds up and there’s no risk of the membrane being pushed off the wall. The membrane can take plasterboard on battens or dot-and-dab, or it can be plastered directly using mesh membranes.
- A floor membrane is laid over the existing slab and connected to perimeter drainage channels. It is then finished with a screed or a floating floor, ready for tiles, laminate or carpet. The whole build-up usually takes only a few centimetres of height, which we plan for at the survey stage.
- Tanking slurry on walls. The slurry becomes part of the wall and adds almost no thickness. Because it holds water back at the surface, it relies on sound masonry. That is why we repair cracks and defects before applying it.
- The structure itself. Both systems protect the building from ongoing water damage:
rusting steel, frost damage, salt staining and mould. They also make the space suitable for insulation and a warm, healthy finish.
Can I get a guarantee, how long does it last, and what types are there?
Yes. Every waterproofing system we install comes with a guarantee, and you can choose extra protection:
- Company workmanship guarantee. Our written guarantee covers the installation for 10 years.
- Insurance Backed Guarantee (IBG). This insurance policy protects your guarantee even if the installing company stops trading. It usually lasts 10 years, can pass to a new owner if you sell your home, and is often asked for by mortgage lenders and buyers’ surveyors.
- Manufacturer’s product warranty. Membranes, drainage and pumps carry the manufacturer’s own warranty on the materials.
- Sump pump warranty and service plan. The pump is covered by the manufacturer’s warranty. Keeping up the annual service keeps both the pump warranty and your system guarantee valid.
We explain exactly which guarantees apply to your project in your written quotation, so you know what is covered from day one.
Powered by premium products from leading manufacturers
We never compromise on quality when protecting your home. That’s why Crystal Damp Proofing & Basements works only with proven products from leading manufacturers:
- Cavity drain membranes, sump pumps and tanking slurries.
- High-performance studded membranes for walls and floors.
- Waterproofing coatings, levelling and repair mortars.
- Damp proofing and property protection products.
Each project gets the products best suited to the building, rather than one system for everything. By combining our installation expertise with these manufacturers’ technology, we deliver a dry, secure basement that will stand the test of time.
Is it time to waterproof your basement?
Don’t wait for damp to cause expensive structural problems. If you live in an older property with no protection in the foundations, or in an area with a high water table, your home could be at risk.
Warning signs include a musty smell, peeling paint, salt marks on the walls or water pooling on the floor. If you notice any of them, we can help. Our specialists will find the root cause, from poor insulation to bad rainwater drainage, and put in the right solution.
Take the first step towards a completely dry basement. Fill in our quick form to book your damp survey, or call our specialists today on 020 8432 3350 or 07720 752231.
Qualified Specialists & a 10-Year Guarantee
Our family-run team holds CSSW qualifications, with a minimum of 10 years’ experience each. We back our work with a 10-year guarantee covering workmanship, plus a QANW Insurance Backed Guarantee that transfers to the new owner if you sell your property. Based in Croydon, we work on domestic and commercial properties across London and the South East.
See What Our Clients Say
We are proud of our 5-star Google rating: see our reviews. If your basement is damp or takes in water, book a survey in our Booking Survey section, or call or message our fully qualified advisors.
