A basement waterproofing membrane is a continuous, bonded layer that stops liquid water from passing through a foundation wall. Rubberized asphalt, self-adhering sheet and cured liquid-applied membranes can do this when they are installed on a clean, sound wall. Dimple board is different. It drains water away but does not block it. Always ask which of the two jobs your contractor is selling.
Why the word “membrane” causes confusion
Contractors use “membrane” for several products that do different jobs. A true waterproofing membrane is a barrier. It bonds to the concrete or block, covers cracks and joints without gaps, and resists water pressure. A drainage membrane, such as dimple board, is a plastic sheet with raised studs. It leaves an air gap and sends water to the drain.
Both are useful. They are not the same thing. A quote that says “membrane” with no product name, no thickness and no description of the surface preparation does not tell you which one you are buying.
Ontario homes add some pressure to this question. Much of the Toronto and Vaughan area sits on clay-rich glacial till. Clay holds water against a foundation for long periods. Spring melt and heavy rain raise the load on the wall, and freeze and thaw cycles open small cracks. The Ontario Building Code generally calls for dampproofing on foundation walls below grade, and for waterproofing where groundwater can build up pressure against the wall. Dampproofing resists soil moisture. It is not built to hold back pressurized water. Check the current code requirements for your house with your municipal building department.
The four membrane types
Rubberized asphalt
Rubberized asphalt is asphalt blended with polymer rubber. Contractors apply it two ways: as a hot or cold spray-applied liquid that cures into a seamless coat, or as a self-adhering sheet with a sticky back. It is a common choice for exterior work because it bonds to the wall, stretches a little over hairline movement, and has no seams when sprayed.
Points to ask about:
- Surface preparation. The wall must be clean, dry enough for the product and primed if the maker requires it.
- Coat thickness. Spray products depend on correct wet and dry film thickness. Ask for the product data sheet.
- Protection. Asphalt coatings can be damaged by backfill. A protection board or drainage layer usually goes over them.
- Temperature limits. Many products have minimum application temperatures. Late fall and winter excavations in Ontario can be a problem.
Self-adhering and other sheet membranes
Sheet membranes come in rolls. Common types are rubberized asphalt on a plastic film backing, and bentonite clay panels that swell when wet. The rolls are laid in overlapping courses, lapped and rolled out so no air is trapped. Their main advantage is a factory-controlled thickness. Their main weakness is the seams, corners, pipe penetrations and the top and bottom terminations. Most sheet failures start at a detail, not in the middle of the roll.
Liquid-applied membranes
Liquid-applied membranes are brushed, rolled or sprayed on and then cure. They include polyurethane, acrylic and polymer-modified cementitious coatings. They can be used inside or outside, and they are easy to apply around odd shapes. Quality depends heavily on the surface and on the coat thickness. Some products need a set number of coats and a cure time between them. A thin, single-coat application is a common cause of failure.
Cementitious crystalline products work differently. They react with moisture and cement to form crystals in the pores of the concrete. They suit concrete that is in good condition. They do not bridge a moving crack.
Dimple board (drainage membrane)
Dimple board is high-density polyethylene with raised studs, typically about 8 mm tall. It is fixed to the wall and leaves an air space. Water that gets behind it runs down to the footing drain or to an interior drain channel. It is also called a drainage mat, a drainage membrane or a cavity membrane.
On the outside of a foundation, dimple board is usually laid over a real waterproofing layer to drain water away and protect the coating from backfill. On the inside, dimple board is part of a drainage system. It catches water that has already come through the wall and guides it to a sump pit. In both cases, dimple board is a drainage layer. It does not seal the wall.
Comparison: which layer does which job?
| Type | Real waterproofing layer? | Usual position | Main strength | Main weak point |
|---|---|---|---|---|
| Rubberized asphalt (sprayed) | Yes, when applied to the right thickness | Exterior | Seamless, flexes over small cracks | Needs clean, primed wall and protection from backfill |
| Self-adhering sheet | Yes, if seams and terminations are sealed | Exterior | Controlled factory thickness | Laps, corners and pipe penetrations |
| Liquid-applied (polyurethane, acrylic) | Yes, if enough coats at full thickness | Exterior or interior | Fits irregular surfaces | Thin coats, poor surface prep, cure time |
| Cementitious crystalline | Partly, as a pore blocker in sound concrete | Interior or exterior | Works in the concrete itself | Does not bridge moving cracks |
| Dimple board (HDPE) | No, it is drainage | Interior or exterior | Moves water to a drain; protects coatings | Does not stop water entering the wall |
Positive side or negative side
A membrane on the outside of the wall is on the positive side, where the water pressure is. The pressure presses the membrane onto the wall and helps it stay in place. This is why exterior membranes hold well.
A membrane on the inside is on the negative side. Water pressure tries to push it off. Interior coatings often work on damp walls and light seepage. They are less dependable against steady pressure. For that reason interior work in most Ontario basements is built around drainage: a drain channel at the footing, dimple board on the wall, and a sump pump. The water is managed, not blocked.
Exterior work means digging down to the footing, which costs more and disturbs landscaping, decks and walkways. In the older neighbourhoods of Toronto the lot may be narrow, with a neighbour’s wall close by. Many homeowners go with interior drainage for this reason. It is a trade-off, and contractors may disagree about which approach suits a given house. Ask for the reason behind a recommendation.
How to choose by situation
| Situation | What usually fits | What to ask |
|---|---|---|
| Damp walls, no active leak, interior finish planned | Interior coating or dimple board with a drain | Is the source of the moisture identified? |
| Water seeping at the floor and wall joint | Interior drain channel, dimple board, sump pump | Where does the water discharge? |
| Active leak or hydrostatic pressure through the wall | Exterior excavation with a bonded membrane and drainage | Which membrane product, and what thickness? |
| Cracked foundation wall | Crack repair first, then membrane or drainage | Is the crack still moving? |
| New build or addition | Membrane applied before backfill, with drainage layer | Is it a waterproofing or dampproofing system? |
Costs depend on the length of wall, the depth of the excavation, access, wall condition, the product chosen and whether landscaping must be restored. Exterior work costs more than interior work because of the digging. We do not give a price here, because no single figure fits all houses. Get at least two written quotes that name the product and the scope.
What to ask a contractor about the membrane
- Which product is it? Get the brand and the product name. Then read the manufacturer’s technical data sheet.
- Is it a barrier or drainage? A contractor who calls dimple board “waterproofing” should explain how the wall is sealed.
- How is the wall prepared? Look for cleaning, patching of holes and cracks, a cove at the footing and priming where the maker requires it.
- What thickness or number of coats? Liquid products depend on this.
- How are the details handled? Ask about corners, penetrations and the top edge above grade.
- What protects the membrane at backfill? Look for a drainage board or protection board.
- What does the warranty cover? Read whether it covers the membrane, the labour, the drain and the sump pump, and whether it transfers to a new owner.
A written scope that answers these points makes quotes easier to compare. If a quote is vague, ask for a revised version.
What our boards show for Toronto and Vaughan
The data below is for September 2026 and comes from our own ranked boards. It shows Google ratings and review counts. It is not a recommendation of any company, and it does not measure the quality of the membrane work.
In Toronto, the basement waterproofing companies in Toronto board ranks 20 companies. The median rating is 5.0 and the median review count is 100. The 20 companies have 3,989 reviews between them, and none has fewer than 20 reviews. The waterproofing contractors in Toronto board also ranks 20 companies, with a median rating of 5.0, a median of 100 reviews and 3,899 reviews in total. One company on that board has fewer than 20 reviews.
In Vaughan, the basement waterproofing companies in Vaughan board ranks 20 companies with a median rating of 4.95 and a median of 77.5 reviews. The total is 3,463 reviews, and 4 companies have fewer than 20. The waterproofing contractors in Vaughan board ranks 20 companies, with a median rating of 5.0, a median of 87.5 reviews and 3,402 reviews in total. On that board, 5 companies have fewer than 20 reviews.
What this means when you choose:
- Ratings cluster near the top. With medians at or near 5.0, the rating alone does not separate companies. The review count helps more. A 5.0 from a handful of reviews is a thin signal.
- Vaughan has more thinly reviewed companies. On the Vaughan waterproofing contractor board, 5 of 20 have fewer than 20 reviews. On the Toronto basement waterproofing board, none do. A smaller count is not a mark against a company. It means there is less public evidence to read.
- Several companies serve both towns. The top of the Toronto and Vaughan boards shares companies, such as Aquatech Basement Waterproofing Toronto with 867 reviews at a 5.0 rating, and RCC Waterproofing Toronto with 794 reviews at a 4.8 rating. This is data from the boards, not an endorsement.
- Reviews do not name the membrane. Most reviews describe service, tidiness and price. Use them to judge communication and follow through, and use the written scope to judge the product.
If your problem is a cracked wall, see the foundation repair companies in Toronto. If it is a damp smell or visible growth, see the mold removal companies in Toronto. To see more cities, visit the waterproofing contractor hub.
A short checklist before you sign
- Confirm the source of the water: surface runoff, a high water table, a failed drain, a cracked wall or condensation.
- Ask whether the quote is for a barrier, a drainage system or both.
- Get the product name and read the data sheet.
- Compare at least two written quotes on the same scope.
- Check Google ratings together with review counts, and read the recent reviews.
- Keep the warranty document and the product details with your house records.
Frequently asked questions
Is dimple board a waterproofing membrane?
Dimple board is a drainage layer, not a true waterproofing barrier. Its studs hold the sheet off the wall and let water run down to a drain. It works well with a perimeter drain, but it does not stop water from entering the wall.
Which basement waterproofing membrane is used on the outside of a foundation?
Exterior work usually uses a rubberized asphalt or self-adhering sheet membrane, or a spray-applied membrane, on the cleaned and primed wall. A dimple board layer often goes over it for drainage and protection. Exact products vary by contractor and by wall condition.
Can I paint a liquid membrane on the inside of my basement wall?
You can, but an interior coating fights water pressure from the wrong side. It may hold back light seepage and damp, but pressure can push it off the wall. Active leaks usually need drainage or exterior work, so ask a contractor to assess the cause first.
How do I compare waterproofing contractors in Toronto or Vaughan?
Check the Google rating together with the review count, and read how the written scope names the membrane product, the thickness or layers, and the warranty. A high rating from a small number of reviews tells you less than a high rating across hundreds.