Solve backwards
How much tile floor will my rolls of crack isolation membrane cover?
- 4 rollsThe example worked below
- Floor Crack Isolation Membrane Coverage CalculatorEvery figure is its own
You have
How much crack isolation membrane?
Worked by the Floor Crack Isolation Membrane Coverage Calculator at the settings below.
The settings it uses
- Roll coverage area
- 100 sq ft
What it will do
400 sq ft of tile floor
37.2 m²
One tile floor. Enough for a tile floor about 20 × 20 ft.
Or several. About 1 tile floor of the size the Floor Crack Isolation Membrane Coverage Calculator opens on: a tile floor about 17.9 × 17.9 ft.
Check it forwards
- Floor Area
- 400 sq ft
- It asks for
- 4 rolls
- You have
- 4 rolls
The Floor Crack Isolation Membrane Coverage Calculator asks for 4 rolls at that size, and 5 rolls one step larger.
If you had more, or less
Around your amount
Each worked by the Floor Crack Isolation Membrane Coverage Calculator at the same settings.
Half
2 rolls
200 sq ft
a tile floor about 14.1 × 14.1 ft
Yours
4 rolls
400 sq ft
a tile floor about 20 × 20 ft
Half as much again
6 rolls
600 sq ft
a tile floor about 24.5 × 24.5 ft
Double
8 rolls
800 sq ft
a tile floor about 28.3 × 28.3 ft
Common amounts
What each amount of crack isolation membrane covers
The sizes it is usually sold in, each worked by the Floor Crack Isolation Membrane Coverage Calculator at the settings above.
| You have | It covers | As one tile floor | Average tile floors |
|---|---|---|---|
| 1 roll | 100 sq ft(9.29 m²) | a tile floor about 10 × 10 ft | under 1 |
| 2 rolls | 200 sq ft(18.6 m²) | a tile floor about 14.1 × 14.1 ft | under 1 |
| 4 rolls | 400 sq ft(37.2 m²) | a tile floor about 20 × 20 ft | 1 |
| 8 rolls | 800 sq ft(74.3 m²) | a tile floor about 28.3 × 28.3 ft | 2 |
A roll's face, not its floor
The calculator divides the floor by each roll's rated coverage and rounds up; read backwards, four rolls at 100 square feet cover 400 (37.2 m²), a floor 20 feet (6.1 m) square. That is face area. Sheet membranes lap at every seam and turn up at the wall base, and each doorway, column and pipe takes an offcut, so a large floor loses several per cent of every roll to laps the division never sees.
Rated for a width of crack
A membrane is rated to bridge a crack of a stated width in a slab that has stopped moving, and nothing here checks either condition. A crack from settlement, a slab still giving up its shrinkage, or a joint that opens and closes with the seasons keeps moving under the tile, and the product's rating — not its coverage — decides whether it telegraphs through. Liquid-applied versions carry their own coverage ratings.
Carry the joint through
Covering a control joint with membrane is not the same as carrying it through. A joint in the slab still has to reappear as a soft movement joint in the tile above, filled with sealant rather than grout, and a full-floor membrane under an unbroken field of tile leaves the slab's joint nowhere to go — which is where tile lifts. Protection is often concentrated over known cracks and joints rather than the whole floor.
How the answer is worked
Nothing here is a second formula. The Floor Crack Isolation Membrane Coverage Calculator runs forwards — a size in, a quantity out — and this page grows its own starting tile floor in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Floor Crack Isolation Membrane Coverage Calculator
runs it forwardsCalculate how many rolls of crack isolation membrane are needed beneath a tile floor over a concrete slab.
Work out what to buy insteadSolve backwards
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Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much tile floor does 4 rolls of crack isolation membrane cover?
- At the Floor Crack Isolation Membrane Coverage Calculator's own settings, 400 sq ft (37.2 m²) — a tile floor about 20 × 20 ft. That is about 1 tile floor of the size the calculator opens on: a tile floor about 17.9 × 17.9 ft. Every figure follows the settings, which you can change in the calculator.
- Do I need crack isolation membrane over the whole floor?
- Not always. The calculator's own guidance is that protection is typically concentrated over known or suspected slab control joints and cracks. Whole-floor coverage is a choice some installers and makers prefer; either way, the slab's movement joints must continue up through the tile as soft joints filled with sealant.
- How many square feet does a roll of crack isolation membrane cover?
- Common rolls are sold to cover roughly 100 square feet (9.3 m²), the calculator's default. Sheet products differ in width and length, and liquid-applied products carry their own coverage ratings, so check yours. The rated figure is the roll's face: laps at the seams and turn-ups at the walls come out of it.
- Will crack isolation membrane stop a moving crack?
- Only within its rating. A membrane is rated to bridge a crack up to a stated width in a slab that has stopped moving. A crack still moving from settlement, shrinkage or seasonal change keeps working under the tile, so find out why it moves before tiling over it, whatever the roll count.