Pool shell · SEMCO Liquid Membrane
Projects › Swimming Pools
A pool shell never gets to dry out. Most finishes aren't built for that.
Permanently submerged, chemically treated, and moving with the ground it sits in. Three coats at 60 mil, a full cure, and chemistry kept where it should be — that's what holds water without replastering.
A long weekend, then patience
Four steps. The last one decides it.
A pool is the hardest thing this product does: permanently submerged, chemically treated, and large enough that a thin spot anywhere becomes the leak.
Drain and dry the shell
Empty it, remove failed plaster or coating, and let the shell dry properly. Concrete that has held water for years holds it in the pores too.
Prep D, then reinforce
Nu-Lift lifts scale and waterline deposits, Stone Soap clears the residue and rebalances the surface pH. Fabric Reinforcement into cracks over ¼" and at the floor-to-wall cove.
Three coats plus pigment
Three thin coats at 20 mil, 60 mil total. Color Activator goes into every container — submerged color needs it to stay true.
Cure fully, then fill and balance
At least 7 days, longer with thick coats or humidity. Fill, then bring the chemistry to normal levels before anyone swims.
Keep your chlorine at normal levels — high concentrations can discolor the finishThe cured film is designed for treated water at standard pool chemistry. Shocking heavily, letting free chlorine run high, or letting undissolved tablets or granules sit directly on the surface can bleach or discolor the coating in that spot. Dose through the skimmer or a floater, never onto the shell, and keep chlorine and pH within normal ranges. This affects appearance rather than waterproofing — but it is not reversible.
Your pool
What does your pool need?
Submerged work takes three coats, so a gallon covers about 100 sq ft rather than 200. Color Activator is added automatically, one per container.
What is the shell made of?
Gunite and plaster are the common ones. Fiberglass works too, with different prep.
How big is the wetted area?
Floor plus all four walls. Rough guide: a 16 × 32 ft pool with an average depth of 5 ft is about 1,000 sq ft.
Not sure? Floor (length × width) + walls (perimeter × average depth).
Tell us the shell material and the wetted area — we’ll size the whole job.
Untick anything you already have. Quantities are editable.
Will it work on mine?
Shells, spas and everything that holds treated water.
The standard in-ground shell. Porous by nature, which is why plaster goes over it and why it leaks once the plaster fails.
Prep D: Nu-Lift + Stone SoapChalking, crazing or patchy plaster that no longer holds. Coat over sound plaster rather than replastering the whole shell.
Prep D: Nu-Lift + Stone SoapIncluding gelcoat that has gone chalky. Sand the whole surface with 60-grit first so the coating has something to key into.
Prep B: Power Cleaner + Stone SoapSmall enough to do in a day. Same three coats, same cure — and the same rule about keeping chlorine at normal levels.
Prep D: Nu-Lift + Stone SoapCommon on older pools. Treat the old coating as unknown, use the heavy-duty pair, and test a patch if there is any chance of silicone.
Prep C: Power Cleaner + Nu-LiftA shell with structural cracks, movement or a failed bond beam, and vinyl-liner pools. Structural work comes first — a coating seals a surface, it can’t hold one together.
Real water
Shells that hold their level.
Pools, ponds and large water features, in the owners’ own words.
“Not only does it work flawlessly, it’s also beautiful.”
I used two gallons of this (Rockslide Grey) to seal the mortar on my 1600 gallon pond project and not only does it work flawlessly, but it’s also beautiful. Highly recommended!
“The pond was newly constructed and I cured it by letting it rest for a month.”
I applied the Liquid Membrane on my 12’ x 8’ koi pond in mid-September upon the advice of my cousins. The pond was newly constructed and I cured it by letting it rest for a month.
“My prior failure was due to inadequate curing time.”
I had struggled for years attempting to seal my cement fish pond with water stop cement. In addition I had tried using rubberized paint one year with no success. After researching the use of rubber paint in fish ponds I realized that my prior failure with the rubber paint was due to inadequate curing time.
“The prep work requires a degree in chemical engineering.”
Used this product 6 years ago to seal a concrete boulder pond. The other product, pond armor, lasted ten years for the same pond but WAY more expensive and the prep work requires a degree in chemical engineering. So for the price and ease of use I will go with another 6 years.
“Curing takes about 7 days before I filled it with water.”
Used it for an old concrete fountain that had multiple hairline cracks. I applied 3 coats and had no issues with any leaks afterwards. I pressure washed the concrete and used SEMCOworks Stone Soap cleaner the day before applying it. No issues with it adhering to the bare concrete. Curing takes about 7 days before I filled the fountain with water.
“The pond would not stay full and needed topping off daily.”
I use the Liquid Membrane for an outdoor concrete in-ground waterfall pond. The walls and bottom of the pond leaked due to cracks and the porous cement. The pond would not stay full and needed topping off daily, a waste of water. No more water loss after applying the sealant and allowing the recommended cure time.
Why pools are the hard case
Permanently wet, chemically treated, and always moving.
A pool shell never dries out. It sits under constant hydrostatic pressure from the inside, and from the outside too whenever the water table rises. It carries treated water that is deliberately aggressive. And it moves — ground shifts, temperatures swing, and a shell that big flexes more than people expect.
That combination is why rigid finishes craze and why patched plaster keeps failing next to the last patch. A film with 1,300% elongation moves with the shell instead of cracking across it. What it asks in return is the full three coats, the full cure, and water chemistry kept where it should be.
The full version
Detailed application instructions.
01 Drain, strip and dry
- Drain fully. Check with a pool professional first if your water table is high — an empty shell can float.
- Remove failed plaster, chalking gelcoat or any coating that is letting go.
- Let the shell dry out properly. Days, not hours.
02 Clean and reinforce
You’ll need: Nu-Lift Cleaner · Stone Soap · Fabric Reinforcement
- Apply Nu-Lift Cleaner to lift scale, waterline deposits and calcium. Rinse.
- Follow with Stone Soap to clear the residue and rebalance the surface pH. Rinse again.
- Coat cracks over ¼" and the floor-to-wall cove, lay in Fabric Reinforcement, wait 10–15 minutes, coat over it.
- Let everything dry before the field coats.
03 Three coats with Color Activator
- Stir the membrane well, then mix in one Color Activator per container — matched to the same size and color.
- Roller on the flat, brush into the cove, corners and around fittings.
- Recoat when it holds no fingerprint. Three thin coats, roughly 20 mil each, 60 mil total.
- Inspect for pinholes and thin spots before you stop — on a shell this size one missed patch is the leak.
04 Cure, fill, then balance
Initial cure is at least 7 days, and longer if the coats went on thick or the air is humid. Fill only after that.
| Coverage, submerged | ~100 sq ft per gallon at 3 coats |
| Film thickness | ~20 mil per coat · 60 mil total |
| Color Activator | One per membrane container, same size and color |
| Cure before filling | 7 days minimum · longer if thick or humid |
| Chlorine | Normal levels — high concentrations can discolor |
| Temperature | 50–90°F · not in direct afternoon sun or over 85°F |
Pool questions
The ones worth asking.
Will chlorine damage it?
At normal pool chemistry, no. What can cause a problem is concentration — heavy shocking, free chlorine allowed to run high, or undissolved tablets and granules sitting directly on the surface. That can bleach or discolor the coating in that spot, and it isn’t reversible. Dose through the skimmer or a floater and keep chlorine and pH in their normal ranges.
Why does it need Color Activator?
Submerged color behaves differently from color on a wall. The Activator is mixed into the membrane before you roll it, one container per container of membrane, matched to the same size and color. The calculator adds it automatically.
How many coats, and how much?
Three coats at roughly 20 mil each, 60 mil total. That means a gallon covers about 100 sq ft rather than the 200 you’d get on a wall. A typical 16 × 32 ft pool is around 1,000 sq ft of wetted area.
How long before I can fill it?
At least 7 days, and longer if the coats went on thick or the weather is humid. Filling early is the most common way this job fails.
Can I coat over old plaster?
Over sound plaster, yes — that’s one of its better uses, since it avoids a full replaster. Remove anything chalking or delaminating first; the membrane bonds to what’s solid, not to plaster that’s already letting go.
What about a fiberglass shell?
Sand the whole surface with 60-grit first, then Prep B. Chalky gelcoat needs taking back before you coat.
My shell has a structural crack. Will this fix it?
No. Structural cracking, shell movement or a failed bond beam all need proper repair first. This seals a sound surface — it can’t hold one together. It also isn’t for vinyl-liner pools.
Not sure about your shell? Call 1-833-211-2297 — the team will tell you honestly if yours needs a pool contractor instead.
Before you start
Additional information.
The manufacturer notes that decide whether this goes well. Most of the problems people report trace back to one of these.
Stop chasing the level. Seal the shell.
Three coats, seven days, chemistry where it should be — and the water stays where you put it.
Size my pool