Sealing / Water Proofing Basements
written by: Joe Cumpelik, Novion Inc. http://www.RadonSeal.com
The No. 1 Enemy of Finished Basements - Moisture
Finished walls and floor covering trap moisture, which accumulates and causes molds and mildew. The musty odor found in many basements is the telltale sign of molds, which may be growing inside the carpeting or walls,
or in upholstered furniture.
As houses age, most basements start seeping water through the concrete or cracks after a heavy rain or snowmelt. The walls, carpets and furniture get wet and molds start growing in just several days. Moldy drywall, carpeting and furnishings have to be discarded.
Why to risk your basement remodeling investment (typically $30,000) and more importantly, the health of your family? Before finishing the basement, seal it against moisture!
Basements as a Source of Moisture
Sooner or later, most basements develop water seepage. At first, it is just intermittent after a heavy storm or snowmelt raises the groundwater level but over time, the leaks become more and more frequent.
All houses settle and stress cracks may develop in the slabs or the walls. The floor-to-wall joint opens up and expansion control joints in the floor crack, as designed. Exterior waterproofing coating deteriorates and the
drainage system may silt up. Hydrostatic pressure then pushes water through any cracks or right through the concrete.
However, most moisture infiltrates into basements in the form of water vapor, which is invisible, unlike steam condensing above a pot with boiling water. Low air pressure inside buildings draws in soil gas with water vapor
from the ground through all openings and pores in the concrete.
Basements are the largest source of moisture in homes and typically, let in over 15 gallons of moisture each day! That is much more than cooking and showering combined (3-5 gallons per day).
Concrete is Very Porous
Concrete cures by cement reacting with water (hydration). But concrete mixes contain much more water than needed, in order to make them easily ³workable.² Almost half of the water is surplus and has to evaporate as
concrete cures. While water pushes through the concrete to the surface, it leaves behind a network of tiny capillaries (pores), much smaller than a human hair.
As a result, concrete is more porous than Swiss cheese residential concrete contains 12 to 20 percent air! Gases and vapor (water molecules) flow easily through the pores. But liquid water has is tougher the water molecules are held back in a ³blob² by surface tension until the pore surface gets wet. Then, liquid water starts seeping through the wet pores in concrete (capillary seepage). Moreover, the pores draw in water like a sponge by capillary action water comes up through a concrete slab against gravity.
Sealing the Sources of Moisture:
Eliminate internal sources of moisture:
* vent the clothes dryer to the outside
* insulate air-conditioning ducts against condensation
Keep Rainwater away from the Foundation:
* proper gutters and downspout extensions
* properly sloped grading around the foundation
* shallow swales or French drains to steer rainwater away
Seal All Openings:
* cover the sump pit airtight
* tape a plastic sheet to isolate the crawlspace
* cover airtight the gravel bathroom rough-in
* install check valves in floor drains to stop vapor
* seal open cores in block walls with expandable foam
* similarly, seal hollow lolly (support) columns
Caulk All Gaps:
* the floor-to-wall joint
* expansion control joints (straight cuts in the slab)
* caulk around all penetrations
Fixing Concrete Cracks:
1. Hydraulic cement is often used for cracks, but it has no ³give² and as the concrete constantly moves, expands and shrinks, it gets loose and the crack starts leaking again.
2. Caulk does not penetrate the full depth of the crack and as water continues to deteriorate the concrete inside the crack, the caulk tends to get loose.
3. You can hire a contractor to inject the crack with epoxy or polymer
4. Or purchase a do-it-yourself foundation crack repair kit to seal the
whole crack with low-pressure injection.
However, still does not seal perhaps the largest source of moisture the
Sealing Concrete against Water and Vapor:
Homeowners often paint walls with a store-bought waterproofing sealer, which is merely a latex-based paint. Sooner or later, it will crack and peel under the attack of lime from the concrete (saponification). And it cannot hold back efflorescence (³whit powder²) or a high negative side water pressure. More importantly, it is porous and cannot stop water vapor or most of the moisture seeping through the concrete.
Some cover the concrete with plastic sheets or use plastic covered insulation ³pillows² on the walls. But this traps any moisture coming through the concrete and is known for causing severe mold and mildew problems. We strongly recommend against trapping moisture - all moisture coming through the concrete should be allowed to evaporate.
Floor slabs are usually poured on a plastic sheet a ³vapor barrier.² But it gets usually punctured during construction and over the years, it slowly disintegrates under the attack of lime in the concrete.
To stop water vapor, concrete slabs are sometimes painted with epoxy or urethane paints, which are impermeable to vapor. They trap all the moisture for a while, but after several years, the paint starts bubbling or cracking
and loses its purpose.
We strongly recommend sealing the concrete with a top-quality silicate-based penetrating sealer. It penetrates deep into the pores in concrete, reacts with lime and alkalis, expands and hardens, which bonds and seals the
Seal the Concrete before Finishing the Basement:
Concrete is not a rock! It is porous and it ages, becoming more and more porous. Just like wood, it needs a sealer - protection against water and deterioration.
Seal the concrete before finishing the basement, enclosing the walls or covering the slab, or just painting concrete. It is a simple do-it-yourself project and avoids putting your basement remodeling investment, as well as
your family¹s health, at risk.
RadonSeal penetrating sealers, available at radonseal.com, seal concrete
not only against water seepage, but also against water vapor and even radon
gas. RadonSeal foundation crack repair kits allow homeowners to fix
foundation cracks like a pro.
Joe Cumpelik, Novion inc.