Pool skimmer mouth repaired with Epoxybond putty, water still at its normal level against a blue pebble finish

Atlas Minerals & Chemicals, Mertztown PA

The pool stays full

Epoxybond hardens under water. Cut off what the crack needs, knead it until the color goes even, press it in and hold it there. No draining, no plaster drying for a week.

Work out what you need See the three sizes

Rated 4.5 out of 5 across 5,024 ratings on the listings we link to.

Customer photo from the listing: putty packed around a skimmer mouth with the water left where it was.

8,000 psi: compressive strength once it is cured
5 to 15 min: working life on the sticks before they stiffen
1/8 inch: thinnest fill that still holds
11.7 cu in: mixed putty out of the 14 oz set

Every number here comes off our own data sheets. The first epoxy mortar sold in this country came out of the Mertztown lab in 1949, and we have been mixing repair putties on the same site since 1917. Where the putty is the wrong tool, that is on this page too.

Three sizes, and the only real question is how much void you are filling

Same chemistry in all three. The sticks put resin and hardener in one extruded rod with the hardener as a core, so a slice off the end carries the right ratio with it. The 2-part set is two 7 oz cartridges you cut equal lengths from.

Cubic inches matter more than ounces here, because a crack is a volume. The 14 oz set yields 11.7 cubic inches of mixed putty. The 4 oz stick yields 3.66. The 2 oz stick yields 1.83.

2 oz Single-Stick
Hairline cracks, chips, a loose tile, the seam round a light ring. One stick covers a repair of about a cubic inch and a half.
Yield
1.83 cu in
Set time
20 to 30 min
Compressive
8,000 psi
$11.45
4 oz Single-Stick
Open cracks, skimmer throats, return fittings. Twice the stick for the jobs where a 2 oz runs out halfway.
Yield
3.66 cu in
Set time
20 to 30 min
Compressive
8,000 psi
$15.25
14 oz 2-Part Set
Step treads, spa floors, spalled patches bigger than your hand. Two cartridges, cut equal lengths from each.
Yield
11.7 cu in
Set time
2 hours at 70F
Compressive
8,000 psi
$20.49

Prices come from the listing and move without warning. What you see when you land there is what counts.

How long you have, and what the water temperature does to it

Two clocks run at once. Working life is how long the mixed putty stays soft enough to shape. Set time is when it stops taking an impression. The sticks give you 5 to 15 minutes of working life and set in 20 to 30 minutes, with full cure in one to two hours.

The 2-part set is slower and more temperature dependent, which is why we publish the whole curve instead of one number. Warm water is not gentler. It is faster, and it will catch you out at the far end of a long crack.

Set time for the 14 oz 2-part set, measured at temperature
Water or air temperature	Set time	What that is in a pool
60 °F	3 hours 30 minutes	Spring or a shaded north-facing shell
70 °F	2 hours	The number the data sheet is usually quoted from
80 °F	80 minutes	A typical summer pool
90 °F	55 to 60 minutes	Warm pool, hot deck
100 °F	40 to 45 minutes	Spa temperature
120 °F	20 to 25 minutes	Equipment pad in full sun

Reading the table on the pool deck

Pool water in high summer sits near 80 to 86 degrees F. That is 80 minutes or less on the set, not the two hours people quote from the 70 degree row.
A spa at 100 degrees F drops you to 40 to 45 minutes. Mix half a batch at a time.
Spring water at 60 degrees F stretches the set to three and a half hours. The patch is not broken. It is cold.
The sticks are far less sensitive, which is the argument for using them on small repairs regardless of season.

What it bonds to

Bond strength on the set is rated at 400 psi to concrete. The list below is the substrate side of that, plus the prep each one needs. Every surface wants the same starting condition: clean, sound, and rough enough to key into.

ConcreteThe substrate the putty was formulated around. Open the crack, wire-brush it, fill.
GuniteSprayed concrete shell. Same preparation as poured concrete, get back to sound material first.
PlasterMarcite and pebble finishes hold well. A white patch will read lighter than aged plaster.
FiberglassScuff the gelcoat dull before you apply. Glossy gelcoat is the one surface people skip prep on.
Ceramic tileChipped tile and failed grout lines. Bonds to the biscuit as well as the glaze.
MetalLadder anchors, light-ring screws, steel fittings. Clean to bright metal.
PVC and most plasticsReturn fittings, skimmer throats, conduit. Abrade the surface, PVC is slick from the mold.
WoodDry rot in decking and trim around the pool, not in the water.
Vinyl linerA rigid epoxy on a membrane under tension is the wrong pairing. The liner keeps moving; the patch does not. Use a vinyl patch kit.

One exception, and we would rather say it here than have you find out in August.

The underwater repair, step by step

Nothing below needs a pump, a gun, or a mixing tip. Goggles and a pair of gloves cover it. If the repair is deeper than you can reach comfortably, a mask and snorkel beat holding your breath over an open crack.

Open the crack up
A hairline you can barely see has nowhere for putty to go. Run a scraper or a grinder along it until you have a channel at least an eighth of an inch deep. That eighth is the minimum application thickness on the data sheet, and a patch thinner than that has no body to hold with.
Get back to sound material
Wire-brush the channel and a couple of inches either side. Loose plaster, scale and algae film all come off. Underwater, brush slowly so the debris drifts clear instead of settling straight back into the groove.
Cut and mix
Slice a piece off the stick, or equal lengths off both halves of the set. Knead it in gloved fingers for four to five minutes until there is no marbling left and the color is uniform. Streaks mean unmixed hardener, and unmixed hardener never gets hard.
Press it in
Roll a rope for a crack, a ball for a chip. Take it down and push it into the channel hard enough to displace the water sitting in there. Work from one end so the water has somewhere to go. Overfill slightly.
Smooth it and leave it
Wet-gloved fingers or a small trowel will feather the edge flush. Then stop touching it. Every time you go back to tidy a patch that has started to set you break the bond it was forming.

Yes, you mix it with your hands

Cartridge systems in this category sell hard against hand mixing. Messy, they say, and prone to a bad ratio. The mess part is fair. The ratio part is worth a closer look.

A stick carries its hardener as a core inside the resin. Cut across it and the slice holds the ratio the extruder built in, whatever length you cut. The 2-part set is two cartridges of equal diameter, so equal lengths give equal volumes. You are not guessing at proportions, you are cutting them.

Hand mixing has one real demand: four to five minutes of honest kneading. Cut that short and you get a soft patch that crumbles in a month. That is the whole trade.

No applicator gun to buy, and none to leave in the shed with a cartridge cured inside it.
No static mixing tips. Those get thrown away after every interruption, and a pool repair is mostly interruptions.
You cut two cubic inches when the job is two cubic inches. Opened sticks keep, with a stated shelf life of twelve months on the set.
The cost of the tooling is a pair of nitrile gloves.

How much putty a crack actually takes

Measure the channel after you have opened it out, not before. Length by width by depth in inches gives cubic inches, and cubic inches is the number the packaging can answer.

The result adds 15 percent over the raw void. Some putty stays on your gloves, some gets pressed out past the edges, and running short halfway through a set is worse than having a stub left over.

Open the calculator on its own page

What it will not fix

The technical data sheet says it in four words: not intended for structural applications. Below is what that rules out in a pool.

A structural crack. If the shell has moved, putty rides along with it and opens again. The data sheet says it plainly: not intended for structural applications.
A pressurized line. Water under pressure pushes the patch out before it sets. Shut the line down and repair the pipe.
An expansion joint. Joints are supposed to move. Fill one with epoxy and you move the crack somewhere else.
A vinyl liner. A rigid patch on a flexing membrane is a temporary fix at best.
A pool that drops inches a day. That is plumbing or a structural failure, and no amount of putty finds it for you.

Nothing on that list is a defect in the putty. They are jobs for a different trade, and a patch that fails in six weeks costs more than the honest answer does now.

The 35-second spot from the listing

We made this clip, and it is an advertisement. A swimmer, the logo, the line about stopping leaks without draining, and three small tiles reading cut, mix, fix.

What it never shows is a repair. No crack, no hand holding putty against a wall while it stiffens, no skimmer throat. That part is the steps section above and the repair notes below.

Manufacturer video from the product listing, re-encoded smaller for this page. It runs 35 seconds and has sound.

Repair notes

Longer write-ups on the parts that go wrong: temperature, prep, the surfaces that argue back, and the repairs worth handing to somebody else.

Repairing a pool crack without draining the water
Why an empty shell is the riskier option, and the order of work for a repair done with the pool full.
Working time, set time and full cure, and what water temperature does to all three
Three different clocks, one temperature curve, and the mistake people make quoting the 70 degree number in August.
Concrete, gunite, plaster, fiberglass and tile: what the putty bonds to
Prep for each substrate, and why gelcoat is the surface people skip preparation on.

All repair notes

Questions we get asked

Can I really repair it without draining the pool?

Yes, that is what the formulation is for. The putty displaces water as you press it into the channel and cures submerged. Draining a pool to reach a crack brings its own risk, since an empty shell in wet ground can float or crack further.

Mix above the water, then take the mixed putty down. Kneading underwater traps water in the mix.

How long before the pool is usable?

The sticks set in 20 to 30 minutes and reach full cure in one to two hours. The 2-part set follows the temperature table on this page, from 20 minutes at 120 degrees F out to three and a half hours at 60.

Set means it no longer takes an impression. Give it the full cure window before anything scrubs or presses against the repair.

Will the patch show?

On aged plaster, yes. The cured putty is white and older marcite has drifted gray or tan, so the repair reads lighter for a season until it weathers in.

The listings describe the sticks as yellow. Cured color is white, and it is formulated to hold that color rather than yellow with age.

Can I tile or paint over it?

Once fully cured, yes. Sand it flush, clean the dust off, and treat it as you would the surrounding substrate. The set carries 8,000 psi compressive strength, so it takes a tile bed without moving.

What about a vinyl liner?

A rigid epoxy on a membrane under tension is a mismatch. The liner keeps flexing with temperature and water level, the patch does not, and the bond opens at the edges. A vinyl patch kit is the right tool, and we do not make one.

How cold or hot can the repair get?

The sticks are rated for continuous service from minus 40 up to 250 degrees F, and 300 degrees F intermittently. The 2-part set is rated to 150 degrees F continuous and 200 intermittent.

Pool and spa temperatures sit nowhere near those limits. The numbers matter when the same putty goes on a hot water line or an equipment pad.

Does an opened stick keep?

Shelf life on the 2-part set is twelve months. Reseal what you cut from, keep it out of direct sun, and check that the material still kneads soft before you rely on it for a repair.

Who makes it?

Atlas Minerals & Chemicals in Mertztown, Pennsylvania. The company was founded in 1892 grinding red shale for pigment, moved to Mertztown in 1917, introduced the first epoxy mortar sold in the United States in 1949, and has been owned by its employees since 1978. The pool putty tubes came first. The Single-Stick format arrived in 2021 for smaller repairs.

The pool stays full

Three sizes, and the only real question is how much void you are filling

2 oz Single-Stick

4 oz Single-Stick

14 oz 2-Part Set