Fountain basin · SEMCO Liquid Membrane
Projects › Fountains & Ponds
If you're topping it up every morning, the concrete is the leak.
Cement is porous, and a fountain never gets to dry out. Three thin coats and a full cure is what holds water — and once cured it's inert enough that customers keep koi in ponds sealed with it.
An afternoon, then patience
Four steps. The last one is waiting.
Submerged work is different from everything else: three coats instead of two, and a full cure before water goes back in. Rushing that is the one thing that ruins the job.
Drain and dry it out
Empty it, remove any failed coating, and let the concrete dry properly. One owner let an eroded fountain dry for a month before starting.
Clean to bare substrate
Prep D on concrete and cast stone — Nu-Lift lifts mineral deposits, Stone Soap clears the residue and rebalances the surface pH.
Three thin coats
Not two, and not one thick one. As one customer put it: your coats shouldn’t be too thick — that’s the secret. Work into every crack and corner.
Cure seven days, then fill
At least seven days before water goes in — longer if you applied thick coats or the weather is humid. Owners who filled early are the ones who had to redo it — one traced his earlier failure with a different product to exactly that.
Safe for fish, birds and pets once curedIt’s water-based, low-VOC at 14 g/L and cures to an inert film. Customers use it in koi ponds, on birdbaths, and on a cat fountain their animals drink from daily. What matters is the full cure — give it the seven days before anything lives in it.
Your water feature
What does your fountain need?
Everything submerged takes three coats, so coverage halves. Tell us the material and the wetted area.
What is it made of?
Concrete and cast stone are the common ones. Fiberglass and metal both work with different prep.
How big is the wetted area?
Base plus all the sides that hold water. Rough guides: a birdbath is around 6–10 sq ft, a fountain bowl 20–40, a 5 × 9 ft pond about 90 including the walls.
Tell us the material and the wetted area — we’ll work out exactly what the job needs.
Untick anything you already have. Quantities are editable.
Will it work on mine?
Birdbaths to koi ponds. Same product.
The most common repair. Hairline cracks, eroded bases, and porous cement that loses water overnight.
Prep D: Nu-Lift + Stone SoapIncluding mortared stone and boulder ponds. Customers have sealed 1,600-gallon ponds and 12 × 8 ft koi ponds with it.
Prep D: Nu-Lift + Stone SoapSmall enough that a pint does it. One owner brushed on seven or eight coats over two concrete birdbaths.
Prep D: Nu-Lift + Stone SoapDecorative fountains and statuary basins. One customer sealed a cast stone fountain with a serious leak; another a new plaster garden fountain.
Prep D: Nu-Lift + Stone SoapFiberglass fountains once sanded, and galvanized tubs used as ponds — Nu-Lift etches the metal so the film has something to grip.
Sand or etch, then cleanA basin that has broken through structurally, or one you can’t drain and dry out. It has to go on dry substrate and cure dry before it sees water.
Real water features
Fountains that hold water again.
Selected from 72 fountain and pond reviews, with the owners’ own photos.
“Nothing worked until I came across SEMCO.”
I have tried many different products to seal my yard fountain. It is cement and developed cracks. Nothing worked until I came across SEMCO. Now the water is retained in its ponds. I gave it 3 coats and it’s working and retaining water perfectly.
“Thin enough to get into all cracks and crevices.”
Rubber membrane applies very nice over substrates. It is thin enough to get into all cracks and crevices. It dries fairly quick for multiple coats where needed. We just finished the interior of a fountain with it.
“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 sealant had to be non-toxic.”
Used this to repair an Angel water fountain that leaked. My precious kitties literally drink from this fountain so the sealant had to be non-toxic! Allowed 3 days cure time and it certainly seriously worked like a charm. Cats have been drinking from it for weeks with no problems!
“Several full length cracks but still structurally sound.”
Our 55" fountain bowl had several full length cracks but still structurally sound. We used Nu-Lift Cleaner and Stone Soap to prep the surface then 2 coats of Liquid Membrane and it worked perfectly, super easy application — I am not a pro. Also the customer service on SEMCO chat is phenomenal, they are extremely helpful and knowledgeable.
“Applied with a brush; about seven or eight coats.”
Easy to apply. Great sticktion. Used on two concrete birdbaths. Applied with a brush; about 7 or 8 coats. Looks great.
Why the last five things failed
Submerged is a different problem. Most products aren’t built for it.
A coating on a wall dries out between rain. A coating in a fountain never does — it sits under constant hydrostatic pressure from the inside, through freeze-thaw in winter and UV on the waterline in summer. That’s a far harder job than the aerosol sealers and rubberised paints in the hardware aisle were designed for, which is why they crack and craze within a season or two.
The other half of the problem is cure time. Rubberised coatings need to cure fully before they go under water, and almost nobody waits. One customer traced his own earlier failure to exactly that — not the product, the impatience.
The full version
Detailed application instructions.
01 Drain, strip and dry
- Drain it fully. If there are fish, move them before you start.
- Remove any failed coating — the membrane bonds to sound substrate, not to something already letting go.
- Let it dry out properly. Concrete that has held water for years holds it in the pores too. Days, not hours.
02 Clean the surface
You’ll need: Nu-Lift Cleaner · Stone Soap
- Pressure wash if the surface takes it.
- Apply Nu-Lift Cleaner and work it in to lift mineral deposits and old waterline staining. Rinse.
- Follow with Stone Soap to clear the residue and rebalance the surface pH. Rinse again.
- Let it dry completely before coating.
03 Three thin coats
- Stir well — pigments settle and unstirred product gives uneven color.
- Roller on the flat, brush into corners, cracks and around any fittings.
- Recoat when it holds no fingerprint. Three coats for submerged work.
- Check the waterline and the base especially — those are where leaks reappear.
04 Cure — then fill
Initial cure is at least 7 days, and longer if the coats went on thick or the air is humid. Owners who waited report no leaks; the ones who rushed are the ones who redid it.
| Coverage, submerged | ~100 sq ft per gallon at 3 coats |
| Coats | 3 — thin, not thick |
| Cure before filling | 7 days minimum · longer if thick or humid |
| New concrete | Let it cure ~1 month before coating |
| Temperature | 50–90°F · not in direct afternoon sun or over 85°F |
| Prep | D on concrete · sand fiberglass first |
Fountain questions
The ones worth asking.
Is it safe for fish and birds?
Once fully cured, yes. It’s water-based and low-VOC at 14 g/L and cures to an inert film. Customers keep koi in ponds sealed with it, use it on birdbaths, and one has cats that drink daily from a fountain coated with it. The condition is the full cure — at least 7 days before anything lives in it, and longer in humid weather.
How many coats?
Three for anything submerged. That’s the single most repeated number in these reviews, and it’s why coverage is 100 sq ft per gallon rather than 200.
How long before I can fill it?
At least seven days, and longer if the coats went on thick or the weather is humid. Every owner who reports a failure filled early, and one traced his previous failure with a different product to exactly that.
My fountain has cracks. Will it bridge them?
Hairline cracks, yes — several customers sealed multi-crack concrete fountains with three coats. Anything over ¼" gets Fabric Reinforcement first. A basin that has broken structurally needs repair before coating.
Will it stick to fiberglass?
Yes, once sanded with 60-grit. One customer fixed a crack in a fiberglass fountain he didn’t think was repairable, with three coats.
What about a galvanized tub or an old liner?
Galvanized takes Nu-Lift, which etches the metal. Customers have converted galvanized garden tubs into fish ponds with it, and one sealed a pond that had both rubber liner and stonework — it bonded to both.
Can I use it on an irregular shape a liner won’t fit?
That’s one of its better uses. Two customers built irregular ponds where a bought liner leaked, and coated the form instead.
Not sure about your feature? Call 1-833-211-2297 or use live chat — reviewers single out the chat team as genuinely knowledgeable.
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 topping it up every morning. Seal it once.
Three coats, seven days, and the water stays where you put it.
Size my fountain