How Much DRYLOK Do I Need?

1. The Two-Coat Rule That Halves Every Number on the Label

Start here, because it is the single most common reason people underbuy. DRYLOK's waterproofing warranty is conditional on two coats. Not two coats if you feel like it, not two coats on the bad wall: two coats everywhere, brushed into the pores on the first pass. One coat is paint. Two coats is a waterproofing system, and the manufacturer is explicit that the performance claim applies to the latter.

The coverage figure printed on the can is per coat. So when a gallon claims to cover 75 to 100 square feet, the number you should be working with for a real basement job is 37 to 50 square feet of finished wall per gallon. Everyone reads the first number and plans around it, and that is where the shortfall comes from.

There is a second reason the first coat goes further than you expect and the second coat goes less far than you expect, which confuses people mid-job. The first coat is absorbed into open masonry pores and disappears fast. The second coat sits on a partially sealed surface and covers considerably more area per gallon. If you budget both coats at the same rate you will over-buy slightly, which is the correct direction to be wrong in.

The application method matters to the warranty as well. The first coat has to be worked into the surface with a stiff brush rather than rolled on, because the product waterproofs by filling and bridging the pores rather than by forming a film on top. Rolling the first coat leaves the pores open behind a skin, which is exactly the failure people describe when they say the coating bubbled off after a season.

2. Measuring the Wall Properly

The arithmetic is simple and people still get it wrong, usually by measuring the floor instead of the walls.

You want wall area, not floor area. Measure the perimeter of the basement, in feet, and multiply by the height you are coating. For a rectangular basement the perimeter is twice the length plus twice the width. A 30 by 24 foot basement has a perimeter of 108 feet. At a full 8-foot wall height, that is 864 square feet of wall, which at 50 square feet per gallon of two-coat coverage is about 17 gallons. That is a substantially larger number than most people expect, and it is why the job is usually bought in five-gallon pails rather than gallons.

Decide the height honestly before you measure. Many people only coat the lower half of the wall, because that is where the damp is, and that is a legitimate choice for a damp-proofing job on a wall that is dry above grade. It is not legitimate if you want an even appearance, because the line where the coating stops is permanently visible. Coat to a natural break, such as the underside of the joists or a clean horizontal line you have chalked, rather than to the top of the damp.

Subtract openings only if they are large. A standard basement window is about 8 square feet, and three of them come to 24 square feet, or roughly half a gallon. That is inside your rounding error and it is not worth the arithmetic. A walk-out door or a large window well opening is worth subtracting. Do not subtract for the area behind the furnace or the shelving you plan to move, because you will coat it anyway and you will be glad you did.

Add area for anything the tape does not capture. A basement with pilasters, a chimney breast, or a bulkhead stairwell has meaningfully more surface than its perimeter suggests. Walk the room and add a rough square footage for each projection. Ten percent is a reasonable blanket allowance in an older house with an irregular foundation.

3. Surface Type Changes the Answer More Than Size Does

Two basements of identical area can need substantially different quantities, and the variable is texture. Coating fills pores and voids, so the rougher and more open the masonry, the more it drinks.

A rough block wall can take nearly twice as much material as smooth poured concrete over the same area. If your basement is split-face block or old rubble stone with deep mortar joints, plan from the bottom of that table and expect to be at the pessimistic end. The mortar joints alone on an old stone wall can account for a surprising share of the total, because they are both recessed and porous.

Surface preparation changes the rate too, in both directions. Wire-brushing off loose material and efflorescence opens the pores and increases consumption on the first coat, which feels like a penalty and is actually the product doing its job. Skipping that preparation reduces consumption and also guarantees the coating fails, because it will not bond through a layer of powder. Our guide on efflorescence explains why that white bloom has to come off rather than be painted over.

One surface where the calculation does not apply at all: previously painted walls. DRYLOK and similar masonry waterproofers need bare, clean masonry to bond and to fill the pores. Over existing paint they behave as a topcoat with no waterproofing function, and the warranty does not apply. If your walls are painted, the honest answer is that you are looking at a stripping job first, or a different product entirely.

Temperature and humidity matter less for coverage than for cure, but they do matter for workability. Coating applied in a cold basement is stiffer, goes on thicker, and covers less. The label conditions are typically above 50 degrees, and working below that both reduces coverage and compromises the cure.

4. Which DRYLOK You Actually Bought

The range is wider than people notice on the shelf, and the products are not interchangeable. The coverage differs, the price differs by a lot, and one of them is not a wall product at all.

DRYLOK Original Masonry Waterproofer

The entry product, latex-based, typically quoted around 100 square feet per gallon per coat on smooth masonry. It carries a shorter warranty than Extreme and a lower hydrostatic pressure rating. For a basement that is damp rather than actively seeping, it is adequate, and it is meaningfully cheaper per gallon.

DRYLOK Extreme

The one most people should buy for a basement. Higher hydrostatic pressure rating, longer warranty, better mildew resistance in the film. Coverage is broadly similar to Original, in the 90 to 100 square foot range per coat on smooth masonry, so switching up does not change your gallon count much. The price difference is real but modest against the labour you are about to spend.

DRYLOK Floor & Wall

Different product for a different job. It is formulated to take foot traffic, which the wall products are not, and the coverage rate is different again. Do not buy it to save money on walls, and do not put a wall product on a floor and expect it to survive being walked on. Our basement floor sealer guide covers what actually belongs down there.

The Fast Plug Confusion

DRYLOK Fast Plug is hydraulic cement, not a coating. It comes in a tub, it sets in minutes, and it is for plugging an active leak or filling a hole before you coat. It is a consumable you will probably need and it does not go into the coverage calculation. Our hydraulic cement guide covers using it properly, because it is the product people most often ruin by mixing too much at once.

Buy all of your coating in one purchase and check the batch or lot numbers match where you can. Masonry waterproofers vary slightly between production batches, and a wall finished from a different batch can show a visible difference in a raking light. Boxing the material, which means combining all of it in a larger container and stirring before you start, eliminates the problem entirely and takes five minutes.

5. Three Worked Examples, End to End

The method is clearer applied than described.

Example 1: Small Poured Basement, Full Height

A 20 by 24 foot basement with smooth poured walls, coating the full 7-foot height. Perimeter is 88 feet, wall area is 616 square feet. Smooth poured concrete gives roughly 55 square feet per gallon across two coats. That is 11.2 gallons, and rounding up for two pilasters and the chimney breast puts it at 12. Buy two five-gallon pails and two single gallons, which gives 12 gallons with a little margin.

Example 2: Mid-Size Block Basement, Full Height

A 24 by 30 foot basement in standard concrete block, full 8-foot height. Perimeter is 108 feet, wall area 864 square feet. Standard block gives about 43 square feet per gallon across two coats, so 20.1 gallons. Add ten percent for an irregular older foundation and you are at 22. That is four five-gallon pails plus two gallons. This is the case where people buy three pails, run out on the last wall, and discover the batch difference.

Example 3: Rough Block, Lower Band Only

A 28 by 36 foot basement in rough split-face block, coating only the lower 4 feet where the damp is. Perimeter is 128 feet, so the band is 512 square feet. Rough block is the expensive surface at roughly 34 square feet per gallon across two coats, giving 15.1 gallons, call it 16. Note that coating a quarter of the wall height in a large rough-block basement still costs more material than coating a small poured basement from floor to ceiling.

6. What Else the Job Consumes

Coating is the headline cost and it is not the whole shopping list. Missing one of these mid-job is the usual reason a weekend becomes two weekends.

Brushes are a genuine consumable here, not a tool you keep. The first coat has to be scrubbed into masonry, which destroys a brush quickly, and masonry waterproofer is hard on bristles. Buy proper stiff-bristle masonry brushes and buy more than one. A 4-inch block brush is the usual choice; some people prefer a 6-inch for open walls and a smaller one for corners and joints.

You will need a wire brush or a drill-mounted wire cup for preparation, and it is worth having both. Efflorescence, loose mortar and old flaking paint all have to come off, and the drill attachment turns a miserable day into a manageable one. Add a shop vac, because the dust from that preparation is considerable and it will otherwise end up in your coating.

Hydraulic cement for holes and active leaks, in a small tub, is close to mandatory. So is a masonry crack filler or an injection kit if you have a crack rather than general dampness. Coating over an unrepaired crack does not stop the crack, and the coating will fail there first. Our basement crack repair guide covers which repair suits which crack.

Then the ordinary consumables: drop sheets, because this product is difficult to remove once dry; a paint scraper; rags; and eye protection, which matters more than usual because you are scrubbing a stiff brush overhead into masonry. Add a respirator rated for the dust if you are doing significant wire brushing.

Budget a full day for preparation on an average basement before a drop of coating is opened. That ratio surprises people, but the preparation is what decides whether the coating holds, and it is the step that gets compressed when the schedule slips. Our full basement waterproofing supplies checklist lists everything in one place.

7. Buying, Rounding, and What to Do With the Leftovers

A few practical decisions at the till that save money or trouble.

Always round up, and round up to the next pail rather than the next gallon if you are within about three gallons of a pail. Five-gallon pails are consistently cheaper per gallon than singles, often by a wide margin, and the marginal cost of having a gallon left over is far lower than the cost of a second trip plus a batch mismatch on a visible wall.

Box the material before you start. Combine the pails in a clean larger container, or at minimum pour a portion of each into a working bucket and top it up alternately, so that any batch variation is distributed evenly across the whole basement rather than concentrated on one wall. This is standard practice in the trades and almost unknown among homeowners.

Do not thin it. Masonry waterproofer is formulated to be applied at full body, and thinning it to stretch coverage or make brushing easier defeats the pore-filling mechanism that makes it a waterproofer rather than a paint. If it is too stiff to work, the basement is too cold, and the answer is to wait for warmer weather or heat the space.

Leftovers store reasonably well in a sealed container kept from freezing, which a basement usually provides. Keep at least a gallon for touch-ups, because you will find spots you missed once the walls dry and the colour evens out. Label it with the date and the room, since an unmarked pail in a basement in three years is a mystery nobody solves.

Finally, do not treat the coating as the whole project. A masonry waterproofer manages dampness and minor seepage on the inside face of a wall. It does not stop water arriving under hydrostatic pressure, and it does not address the reason water is at the wall in the first place. Extending downspouts and correcting the grade outside costs almost nothing and reduces the load on everything you are about to apply.