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How to Repair Leaks in Concrete Slabs
The wet
basement curse
Most homes develop basement leaks within 10 to 15 years. Over 60
percent of homes have a leaking basement. You are not alone - wet basements are
the most frequent complaint of homeowners.
Fixing cracks is relatively straightforward but once water starts
seeping through the concrete, the homeowner faces $1,000's in repair bills. If
you have a damp basement, musty odors, efflorescence ("white
powder"), or minor water leaks, fix it now before it gets worse and much
more expensive.
How to make
a wet basement dry
RadonSeal Penetrating Concrete Sealer
waterproofs leaky basements. It penetrates deep into concrete (up to 4"),
reacts with alkali, expands into pores, and hardens as a mineral. This seals
the concrete against water leaks and dampness.
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Waterproof & Color |
RadonSeal works inside the concrete. Unlike
waterproofing surface sealers, it cannot get lifted by efflorescence or water
pressure. And it cannot peel or wear off - once the concrete sealed, the seal
is permanent!
RadonSeal is non-toxic, nonflammable, and does
not contain chemical solvents or release VOCs. Its
spray-on application is quick and easy for contractors or homeowners.
RadonSeal seals bare (unpainted) cementitious materials:
Always seal the whole basement - both the floor and walls. If you
seal only the leaking area, water will find another way.
Leaking
poured concrete
Concrete usually starts leaking only intermittently after heavy
rains. Before sealing with RadonSeal, let the
concrete dry out to minimize dilution of the sealer in the water inside
concrete. First, wipe off or wet vac water from the
surface.
RadonSeal stops even active leaks under
hydrostatic pressure through sound concrete. It displaces water inside the
pores and hardens, gradually throttling off the seepage. But the leaky area
will require repeated applications. Let it partially cure for a day and then
apply additional applications, provided the concrete still absorbs it.
Try to make the area as dry as possible. If the area remains
continuously moist, RadonSeal cannot fully cure and
harden. Ventilate the area and install a fan or dehumidifier for several days
before and after the application.
Leaking
concrete blocks or cinder blocks
Blocks are very porous and only 1-1/4 inches separates the core
from the water outside. That's why 90 percent of basements with block walls
leak within 15 years. It is best to fill the cores with concrete during
construction.
If the seepage is intermittent, wait until it dries out before
spraying on RadonSeal Plus, in order to minimize
dilution of the sealer inside concrete. Ventilate the area or install a fan.
After the first 2 applications of RadonSeal Plus, let
it dry out and partially cure for a day or more to avoid pushing the
penetrating sealer into the cores. Then, apply 2 (3) more applications of RadonSeal. Cinder blocks are particularly porous and
typically need an extra application of RadonSeal
Plus.
Wet blocks are hard to seal. There is only a thin wall to seal and
unfilled hollow cores hold a column of water, which pushes it out under
pressure. Drain the water first - drill 1/4 or 3/8-inch holes in the bottom
blocks and let dry out for a couple of days. Ventilate the area to evaporate
water held in the pores of the blocks and then, to help RadonSeal
cure. Afterwards, caulk the drain holes.
Leached out
concrete or lightweight blocks
RadonSeal reacts chemically inside concrete with
alkalis and "free lime" (calcium hydroxide) produced during the
hydration of cement paste. But water gradually leaches out the free lime from
concrete subjected to continuous seepage. Lightweight CMU's (Concrete Masonry
Units), hadite blocks, and decorative splitface blocks are made with little or no cement, leaving
little for RadonSeal to react with. The pores in
concrete have to be first filled with a substitute.
Thoroughly mix baking soda (3 tablespoons per gallon) in a bucket
of hot water. Mix and let settle for a couple of hours. Leaving the sediment behind,
pour the solution into a pump garden sprayer and spray it on the concrete. Do
not flood, it should all seep into the concrete.
For large projects, purchase calcium hydroxide (hydrated lime)
from a local chemical company (below $20 for a 50-lb bag). Mix one cup per
5-gallon bucket, let settle for 24 hours, and spray on with a power washer.
Let dry. If there is residue left on the surface, wash it off with
water and a mop or brush. Apply RadonSeal Plus per
the application instructions.
Popcorn blocks
These are blocks made of a very course aggregate that have
straw-size holes. They can hardly slow down water or gases.
First, spray on 2 applications of RadonSeal
Plus. After it dries, trowel on a layer of Mapei
"Keraset Professional Grade Dry-Set Mortar."
It is easy to apply and will not shrink. It contains special resins, which make
it unsuitable for RadonSeal. Instead, use our
Ion-Bond Armor membrane sealer, which creates a subsurface water-repellent
membrane that resists negative side water pressure.
Leaky stone
foundations walls
The problem usually is water leaking through the mortar. First
scrape out and brush off with a stainless steel brush (no rusty specs) any
loose or soft mortar. Then, apply RadonSeal Plus. It
will leave a whitish film on the stones. If the wall is decorative, apply RadonSeal only on the mortar with a brush or sponge and
wipe off the stones with a wet rag within about 10 minutes.
Let dry out and cure for at least 3 days before re-pointing
(tuck-pointing). In addition to sealing the old mortar, RadonSeal
will improve the adhesion of the new mortar and by neutralizing alkali, protect
it against "cold joint" separation.
RadonSeal also seals porous limestone by
reacting with lime. If you have another type of porous stone that you would
like to seal, just consult us by e-mail or telephone.
Fixing
cracks or gaps
Before fixing cracks, seal the concrete with RadonSeal.
Any cracks help its penetration into the concrete.
RadonSeal is not a caulk and does not seal
cracks or defects in concrete. But when it cures and expands inside the
concrete, it tends to close off hairline cracks (thinner than a credit card).
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Seal cracks in poured concrete |
For larger cracks, you can hire a local waterproofing contractor
to repair them by injection.
Or you can fill cracks in slabs with self-leveling
polyurethane caulk, which is very "runny." It deep-fills the gap and resists
water pressure, is durable and remains elastic as the concrete moves. If the
crack is wet, use a marine caulk and adhesive. And if the crack is very wide,
use hydraulic cement but it lacks flexibility and gets loose after a couple of
years.
Before caulking, you have to open up the cracks. Instead of the
classic hammer and chisel" technique, rent a right-angle grinder with a
4-inch wheel for concrete or use a circular saw with a blade for concrete,
going about 1/2" deep. For hydraulic cement, the sides should be inverted
V-shape.
Other
waterproofing measures
Water can do much worse than seep into the basement - water
pressure can cause structural damage and buckle basement walls. Keep water away from
the foundation! Make sure that there is good drainage - footing drains, gravel
under the slab, a layer of gravel or drainage mats on
the walls to quickly take rainwater down to the footing drains, and drains from
window wells to footing drains.
The traditional approach is trying different remedies, proceeding
from the simpler to the elaborate and expensive. The following summarizes the
usual waterproofing methods, proceeding from the basic, common sense steps:
Rain gutters:
Maintain the gutters each spring to repair damage
from snow loads and each fall to clean out leaves and debris. Add extensions to
downspouts to take roof run-off water 10 ft. (min. 4 ft.) away from the
foundation. Install splash blocks.
Grading:
The soil should slope away from the house on
all sides of the foundation one inch per foot for 10 ft. (min. 4 ft.). You may
need a truckload of soil. Old concrete walkways, driveways or patios that slope
toward the foundation should be replaced.
Grass:
Remove flower beds, vegetable gardens, bushes
and trees from around the foundations and seed the area with grass.
Driveway:
Patch cracks in the driveway using cold-mix
asphalt patching compound.
Cracks:
Deep-fill all cracks and gaps with
self-leveling polyurethane caulk, which remains flexible and resists pressure.
If the crack is wet or larger than 1/4", use hydraulic cement. Or your
local waterproofing professional can fix structural cracks by injecting epoxy.
Condensation:
Excessive humidity from seeping water vapor
condenses on cold surfaces. Put insulation on cold water tanks, water piping,
and cold air ducts. Damp proof your basement with RadonSeal.
Dehumidifiers:
One or two good-capacity dehumidifiers will
reduce humidity. But the initial and operating costs are high. They also pull in
more moisture from the ground, which accelerates the deterioration of the
concrete.
Window wells:
If they drain poorly, install window well
covers. Or dig out and drain to footing drains.
Underground drainage systems:
Call a drain-and-sewer-cleaning contractor who
will use a long power snake to try to clear the lines. But often they just have
to be capped off at the surface and abandoned.
Curtain drains:
Excavate a trench alongside the house and fill
it with gravel to stop surface water from getting to the foundation. French
drain with a perforated PVC pipe in the gravel takes surface water away from
the house.
Dry wells for rainwater:
Install a 3 ft. deep hole filled with gravel
and wrapped with landscape fabric against silt at least 10 ft. from the house,
or a tank that allows run-off to soak into the ground. An
underground 4-in. PVC pipe brings the run-off from downspouts. Each well
can usually handle runoff from a 500 sq.ft. section of roof.
Sump pump:
Sump pumps relieve excessive water pressure.
Creating a sump and installing a sump pump costs $300 to $600. Install an
airtight cover to prevent the release of vapor and radon. Complete reliance on
a pump is unwise. Many sump pumps cannot handle large volumes of water in
severe storms, may burn out, be swamped, or the power may go off.
Interior gutters:
A plastic channel system collects water
seeping through the basement walls and routes it to a floor drain or sump pump.
It works after the water has entered and does not address dampness or seepage
through the floor. Usual cost $3,000 to $5,000.
Interior footing drains:
May be needed when
footing drains break or silt up. Perimeter drain system made of 4-in.
perforated PVC pipe laid in gravel under the floor inside foundation footings,
which carries water to a sump pump before it enters. Do not leave a gap next to
the walls - it would let in vapor and radon. It requires extensive jack
hammering and usually costs $3,000 to $8,000.
Exterior footing drains:
Installation requires removing landscaping,
excavating to expose the foundation down to the footings, waterproofing the
walls, and laying perimeter footing drains in a bed of gravel. Add fiberglass
fabric or polyethylene sheets on the coating for water barrier, because asphalt
coating on concrete cracks and deteriorates. The cost is $5,000 to $10,000, or
more.
RadonSeal waterproofs and damp proofs concrete
and will save you $1,000's on basement repairs. By bonding and
strengthening concrete, and encapsulating embedded steel, it also eliminates or
reduces cracking and preserves the concrete.