Exterior foundation · SEMCO Liquid Membrane
Projects › Foundations
Seal it from the outside and the water never reaches the wall.
Interior sealing stops water after it has already soaked into the concrete. Coating the positive side stops it entering at all — and if the trench is already open, that's a weekend rather than a contract.
While the trench is open
Four steps. Then backfill.
If you’ve excavated, or you’re building, this is the moment. Sealing the positive side stops water before it ever reaches the wall.
Expose and clean the wall
Clear soil, roots and old coating back to sound substrate. Prep D on concrete, block, stone and stucco — Nu-Lift then Stone Soap.
Fill, then bridge
Foam or hydraulic filler into anything large. The membrane spans cracks up to ¼" on its own — wider than that takes Fabric Reinforcement.
Two to three coats
½" nap roller on the flat, masonry brush into the texture. Two coats on smooth concrete, three on block, stone or anything rough.
Cure hard, then backfill
At least 7 days before soil goes back. Pair it with a French drain and free-draining fill and you’ve solved the problem rather than moved it.
Get a second quote before you accept a foundation repair numberOne homeowner was quoted $40,000 for the garage alone on a 3,100 sq ft house. He sought a second and third opinion — minor repair work and a concrete sealer was all it actually needed. Another declined a second major renovation after the first hadn’t worked and sealed it himself.
Your foundation
What does your wall need?
The material decides the prep, the coats and how much the surface drinks. Rough and irregular walls use noticeably more.
What is the wall made of?
Stone and block have far more real surface than their face measurement suggests.
How big is the wall?
Length of wall × the height you’re coating. For a crawl space, add the floor if you’re sealing that too.
Tell us the material and the area — we’ll work out exactly what the job needs.
Untick anything you already have. Quantities are editable.
Will it work on mine?
Poured, block, stone and everything below grade.
The common cases. A customer coated an entire east elevation with a masonry brush; another did exterior block and waited for the weather before backfilling.
Prep D: Nu-Lift + Stone SoapOlder homes with stone walls. Three customers specifically coated stone foundation walls from outside — the brush matters more than the roller here.
Prep D · three coatsLow, awkward and enclosed. One owner sealed a crawl space she could never find the leak in; another chose it specifically because there was no smell to ventilate.
Prep D · low odor at 14 g/LBonds to the styrofoam face. Pre-fill large gaps with caulk, build up four to five coats, then a dimpled membrane over the top before backfill.
No cleaner · four coatsIt sticks to what’s already there. One customer coated over original tar-based waterproofing; another over a ground-smooth epoxy foundation repair.
Prep C: Power Cleaner + Nu-LiftThe junctions people miss. Customers have sealed where the sill plate was never properly sealed during construction, and leaking bulkhead surrounds.
Fabric Reinforcement at jointsReal foundations
Walls sealed from the side that matters.
Selected from 53 foundation and crawl space reviews.
“I was shocked with a $40k estimate — for the garage alone.”
I noticed some degradation on my concrete foundation so I contacted a company specializing in foundation repair. I was shocked with a $40k estimate… for the garage alone. I have a 3100 sq ft house and I knew there were other areas. I sought a second and third opinion. Some minor repair work and concrete sealer was all it needed.
“It looked translucent when I applied it but dried darker.”
Just used this over my exterior foundation epoxy repair. Had a contractor grind the epoxy and concrete foundation smooth. I then applied 2 coats of Rockslide Grey. It looked translucent when I applied it but dried darker. Looks fantastic. I am highly impressed. The coverage was great too — I had about 100 linear feet.
“We dug out a trench around the outside.”
Used this to seal a partially below grade cement wall in our house that was leaking. We used about three coats of this on the outside of the wall and added a French drain to get water away from the wall. Both worked nicely, no more water seeping in. But it was a lot of work — we dug out a trench around the outside.
“What a relief — I also saved money there.”
Excellent product. I excavated a section of my foundation and wanted to add cement in a hairline crack, when I learnt that SEMCO Liquid Membrane can bridge cracks up to ¼". What a relief, as I also saved money there. Applied it with a ½" nap roller. Made sure the surface was clean and dry, 2 coats applied with a waiting time between.
“I could never locate the source of water — only the general area.”
I purchased this product to waterproof a small section of a concrete crawl space. I could not be more pleased. This process was out of desperation because I could never locate the source of water, only the general area. I brushed on a thick coat.
“Covers well on styrofoam.”
Used to waterproof ICF foundation forms. Covers well on styrofoam — better if you pre-fill any large cracks first with a caulking. I used two coats and it looks ok. Better as recommended to use 4 to 5 coats, but I didn’t have time for more. Then covered it with dimpled membrane before backfilling.
“It goes on like paint, but dries to a rubber coating.”
This product goes on like paint, but when it dries it leaves a rubber coating that prevents water from penetrating. I highly recommend it. I used it to coat the exterior of my foundation walls, which are made of stone.
“I didn’t have to worry about ventilation.”
I used something like this before. I hate its smell! However, this liquid membrane is different — I used it on my crawl space and I didn’t have to worry about ventilation.
Positive side vs negative side
Sealing the outside is the permanent version.
Water pushes inward. Seal the interior face and you’re stopping it after it has already entered and saturated the wall — which works, and which thousands of people do, but the wall stays wet and the pressure stays behind the coating. Seal the exterior and the water never gets into the concrete at all. That’s the positive side, and it’s why contractors excavate.
The catch has always been cost. Excavating a foundation is real work, and once the trench is open the quotes get large. But if you’re already digging — for a drain, for a repair, or because you’re building — the coating itself is a few hundred dollars and a weekend. Two customers dug their own trench, coated the wall, added a French drain and stopped the seepage entirely.
The full version
Detailed application instructions.
01 Expose, clean and dry
You’ll need: Nu-Lift Cleaner · Stone Soap
- Excavate to the footing where you can, or as deep as the problem goes.
- Remove soil, roots, loose mortar and anything flaking. Old tar can stay if it’s sound.
- Apply Nu-Lift Cleaner, work it in with a stiff brush, rinse.
- Follow with Stone Soap to clear the residue and rebalance the surface pH, then rinse again.
- Let it dry completely. A wall that has been underground holds moisture — give it more time than you think.
02 Fill and reinforce
You’ll need: filler · Fabric Reinforcement · Liquid Membrane
- Fill large voids with foam or hydraulic filler and let it cure.
- Cracks up to ¼" the membrane bridges on its own — a customer about to buy cement for a hairline crack found he didn’t need it.
- Anything wider, or any joint that moves: coat, lay in Fabric Reinforcement, wait 10–15 minutes, coat over it.
- Do the same at the footing junction, around bulkheads and along the sill plate line.
03 Coat the wall
- Stir well — pigments settle and unstirred product gives uneven color.
- ½" nap roller on flat concrete; a masonry brush for block, stone and stucco.
- Two coats on smooth poured concrete, three on block or stone, four to five on ICF foam.
- Recoat when it holds no fingerprint — a day apart is common in cool weather.
04 Cure, drain, backfill
Initial cure is at least 7 days, and longer if the coats went on thick or the air is humid.
| Poured concrete | ~200 sq ft per gallon at 2 coats |
| Block | ~150 sq ft per gallon at 3 coats |
| Stone or rubble | ~120 sq ft per gallon at 3 coats |
| ICF foam forms | ~100 sq ft per gallon at 4 coats |
| Bridges cracks up to | ¼" without fabric |
| Cure before backfill | 7 days minimum · longer if humid |
Foundation questions
The ones worth asking.
Outside or inside — which should I seal?
Outside, if you can get to it. That’s the positive side: water never enters the wall at all. Interior sealing works and is often the only practical option, but the wall stays saturated. If you’re already excavating for a drain or a repair, do it while the trench is open.
Do I still need a French drain?
If the soil around your foundation stays saturated, yes. The coating stops water entering the wall; the drain takes it away from the wall. Customers who did both report the problem solved rather than moved.
Will it go over the old tar?
Yes, provided it’s sound. One customer coated over original tar-based waterproofing and reported it adhered and dried well; another went over a ground-smooth epoxy repair. Remove anything loose first.
How wide a crack will it bridge?
Up to ¼" on its own. Wider than that, fill it first and reinforce with fabric. One customer bought filler for a hairline crack and then found he didn’t need it.
Can I use it in a crawl space?
Yes, and it’s a common use. At 14 g/L VOC there’s effectively no fume issue in an enclosed space — one customer chose it specifically so she wouldn’t have to worry about ventilation down there.
When can I backfill?
After the full cure, at least 7 days and longer in humid weather. Wet soil against an uncured film damages it. On ICF, add a dimpled membrane over the cured coating before the fill goes back.
My wall is bowing. Will this fix it?
No. Bowing, shearing or displaced block is structural and needs an engineer. A coating seals a surface — it can’t hold soil back. Get the structure sorted, then seal it.
Been quoted for foundation work? Call 1-833-211-2297 before you commit — the team will tell you honestly whether this is the right fix or whether you need a contractor.
Seal it from the outside. Then backfill and forget it.
If the trench is already open, the coating is a few hundred dollars and a weekend — and it stops the water before it ever reaches the wall.
Size my foundation