TEC HydraFlex Coverage Calculator: How Many Gallons?

TEC HydraFlex coverage

Source: TEC Product Data Sheet: HydraFlex Waterproofing Crack Isolation Membrane (316), DS316_R0925-20, updated September 2025, read 2026-10-26.

How the calculation works

gallons = area × (1 + waste ÷ 100) × coats ÷ sq ft per gallon per coat

Every coat goes over the whole area, so two coats at 80 sq ft per gallon use as much liquid as one coat at 40. The rate depends on what the membrane is for: the data sheet lists a heavier rate for code-listed waterproofing than for crack prevention alone. The calculator then picks the fewest pails that cover the job without leaving more than one small pail of liquid unused, so a job needing 3 gallons gets one 3.5 gallon pail rather than three 1 gallon pails. Extra passes over corners, seams, drains and pipe penetrations are not included; raise the waste figure if you have many of them.

Worked example

A 100 sq ft area, Waterproofing (ANSI A118.10): 2 coats x 25 mils wet, 50 sq ft per gallon, with 10% extra: 100 × 1.1 = 110 sq ft. The data sheet calls for 2 coats at 100 sq ft per gallon each, so 110 × 2 ÷ 100 = 2.2 gallons (8.3 L). In the pail sizes on sale, buy 3 × 1 gal pails (3 gal).

TEC HydraFlex key specs

What HydraFlex is

HydraFlex from TEC is a ready-to-use liquid membrane that you roll, trowel or spray onto a floor, wall or ceiling before setting ceramic tile or stone. It is an acrylic emulsion modified with a polyurethane dispersion, and it dries to a smooth, seamless, flexible film that does two jobs: it keeps water out of the substrate in showers, tub surrounds and wet areas, and it stops small in-plane cracks in the slab from telegraphing up through the tile. It goes on light purple and turns dark purple as it dries, which is how you tell when it is ready for the next step.

TEC's product data sheet 316 (revision DS316_R0925-20, updated September 2025) says HydraFlex exceeds ANSI A118.10 for waterproof membranes and ANSI A118.12 for crack isolation membranes at the high performance level, is IAPMO approved, and can be used inside and outside on residential through extra heavy commercial floors, depending on the substrate. Mesh is not needed in the field; TEC's 6 inch waterproofing mesh is optional at corners, changes of plane and joints between different materials. Tile can usually be set 1 to 3 hours after the membrane goes on.

What the data sheet says about coverage

The coverage table in the data sheet gives four rates per US gallon, each tied to a number of coats and a wet film thickness:

• Crack isolation over cracks up to 1/8 inch: one coat at 25 mils wet, 100 sq ft (9.29 m²) per gallon.
• Crack isolation over cracks up to 1/4 inch: one coat at 50 mils wet, 50 sq ft (4.65 m²) per gallon.
• Waterproofing: two coats at 25 mils wet each, 50 sq ft (4.65 m²) per gallon.
• Steam rooms: two coats at 30 mils wet each, 40 sq ft (3.72 m²) per gallon.

The pattern is simple. The thinner job uses half the liquid of the thicker one, and the waterproofing rate is the same as the heavy crack isolation rate because both put about 50 mils of wet membrane on the surface, once in one pass and once in two. The calculator stores each setting as coverage per coat times the number of coats, so the waterproofing setting is two coats at 100 sq ft per gallon each and the steam room setting is two coats at 80.

The same data sheet also describes the film. For waterproofing you need a continuous membrane of at least 46 to 50 mils wet over the whole surface, applied in two coats of about 25 mils, which cures to about 30 mils dry. For steam showers built to SR613 and SR614 the target is two coats of 30 mils wet, 60 mils combined, curing to at least 36 mils dry. If you have no wet film gauge, TEC suggests a coin check: a 50 mil film is about the thickness of a dime lying flat, and a 30 mil coat about the thickness of a penny.

A check on the numbers

A US gallon is 231 cubic inches. Spread 25 mils (0.025 inch) thick, it covers 231 ÷ 0.025 ÷ 144, or about 64 sq ft, not the 100 sq ft in the table. The same arithmetic gives about 32 sq ft per gallon for 50 mils and for two 25 mil coats, against 50 in the table, and about 27 for the steam room film against 40. The table is roughly 55 percent more generous than a straight volume calculation in every row.

The data sheet does not explain the gap. Membrane tables often assume real-world films that average a little under the target, and a wet film gauge reading is taken where the film is checked, not as an average over the floor. Still, if you plan to roll every coat to the full stated thickness, the table can leave you short. The calculator's fifth setting, "Waterproofing by volume", uses two coats at 64 sq ft per gallon, about 32 sq ft finished per gallon. Treat it as the cautious upper end for a shower; the default follows TEC's own figure.

How the calculator works

Enter the area in square feet or square meters, choose the job and set a waste allowance. The calculator multiplies the area by one plus the waste, multiplies by the number of coats and divides by the coverage per coat, which gives the gallons of HydraFlex you need. It then picks pails from the three sizes TEC sells: the fewest pails that hold enough, as long as you are not left with more than one 1 gallon pail of extra liquid. A job that needs 3 gallons is shown as one 3.5 gallon pail rather than three 1 gallon pails, and a job that needs 4.6 gallons as one 5 gallon pail.

The pre-fill of cracks, plywood gaps and control joints, and the extra membrane used to embed mesh at corners and drains, are not in the table. On a small shower with many corners, a niche and a bench, raise the waste figure to 15 or 20 percent.

Measuring a shower or floor

For a shower, measure every surface that will get membrane: the floor, each wall up to the height you waterproof (TEC follows the usual practice of at least the shower head height, and steam showers need the ceiling too), both faces and the top of the curb, and every face of a niche or bench. A 3 x 5 ft alcove with three walls coated to 7 ft has 15 sq ft of floor and 77 sq ft of wall, 92 sq ft in all. With 10 percent waste and the default waterproofing rate that is about 2 gallons, and the calculator suggests three 1 gallon pails because 2.02 gallons is just over two.

For a crack isolation floor, measure the room. If you only need to protect individual cracks, TEC has a separate technical bulletin for treating single cracks, and the whole-floor rates here will overstate what you need.

Application notes from the data sheet

Store and install between 50 and 90°F (10 and 32°C), with the substrate at least 43°F (6°C). New concrete must be at least 3 days old; plywood needs two layers, at least 1 1/8 inch thick in total, and a coat of TEC Multipurpose Primer, and is for interior floors only. Pre-fill cracks and gaps up to 1/8 inch with membrane first. Apply the first coat, let it dry about an hour until semi-transparent, then apply the second coat at right angles. At drains, take the membrane down to the bottom of the drain flange without covering the weep holes. Flood test once the second coat is dark purple everywhere, usually 2 to 12 hours after application, for 24 hours.

HydraFlex is not a wear surface, should not go on wet substrates, and is not for particle board, pressboard, lauan, hardboard or fiberglass, or for hydrostatic pressure from beneath the membrane. Keep it from freezing; unopened pails last a year.

Check before you buy

TEC says its data sheets are valid for 90 days from the date printed, so check the current version on the product page before a large order. Coverage on rough or porous concrete, or when spraying, will be lower than the table. For a shower, buying one extra 1 gallon pail is cheap insurance against running out between coats.

FAQ

How many square feet does a gallon of HydraFlex cover?

It depends on the job. TEC's data sheet gives 50 sq ft per gallon for waterproofing, which is two coats at 25 mils wet each, and 40 sq ft per gallon for steam rooms, two coats at 30 mils. For crack isolation only, one coat covers 100 sq ft per gallon at 25 mils wet over cracks up to 1/8 inch, or 50 sq ft at 50 mils over cracks up to 1/4 inch. So a 5 gallon pail is about 250 sq ft of shower waterproofing or 500 sq ft of light crack isolation.

How much HydraFlex do I need for a shower?

Add up the floor, every wall you will waterproof, the curb and any niche or bench. A 3 x 5 ft alcove with three walls coated to 7 ft is 15 sq ft of floor and 77 sq ft of walls, 92 sq ft in total. With 10 percent extra that is about 101 sq ft, and at 50 sq ft per gallon it comes to just over 2 gallons, so three 1 gallon pails. For a steam shower at 40 sq ft per gallon the same room needs about 2.5 gallons.

Why is there a heavier "by volume" setting?

Because the table and the film thickness in the same data sheet do not quite agree. A US gallon is 231 cubic inches; spread 25 mils (0.025 inch) thick it covers 231 ÷ 0.025 ÷ 144, about 64 sq ft, not 100. Two full 25 mil coats therefore come to about 32 sq ft per gallon rather than 50. If you check every coat with a wet film gauge and roll it on at the full thickness, the heavier setting is the safer estimate. The default follows TEC's table.

Do I need two coats for crack isolation?

No. TEC says the membrane may be applied in one coat for crack isolation: 25 mils wet over cracks up to 1/8 inch, or 50 mils wet over cracks up to 1/4 inch. Two coats are required only when HydraFlex is the waterproofing layer, as in a shower, tub surround or wet room, and for steam rooms.

How long before I can tile or flood test?

Let the first coat dry about an hour, until it turns semi-transparent, before the second coat. Tile can usually go on 1 to 3 hours after the membrane at 70°F and 50 percent relative humidity. Wait to flood test until the second coat is dark purple with no light purple left, which TEC puts at 2 hours in ideal conditions and up to 12 hours when it is cool, humid or the substrate is dense. Then plug the drain and leave water in for 24 hours.

TEC and TEC HydraFlex are trademarks of their owner. This page is an independent estimate based on the published data sheet; check the bag label before mixing.