New Construction: Measures for Minimizing Radon Pathways 

A gas-tight barrier could be placed between the soil and foundation to eliminate radon entry from below. The types of mechanical barriers that have been suggested for radon control fit into one of the following three categories:
bullet Foundation materials
bullet Coatings
bullet Membranes

 

FOUNDATION MATERIALS
The materials used to construct a foundation can often be used as an effective barrier to the entry of radon-laden soil gas. Below-grade walls may be constructed of poured concrete, masonry, or other materials such as pressure treated wood or stone. Poured concrete and masonry block are the most common materials in new construction.

In residential buildings, the foundation walls and floor made of poured concrete are generally constructed to a compressive strength of 2,500 to 3,000 psi. A poured concrete wall is a good barrier to radon transport. The major points of radon entry are the cracks, joints and other penetrations. It is these openings in the walls that allow soil gas to enter the building.

Residential foundation walls built of concrete masonry (concrete block) may have open cores, filled cores or cores closed at the top course. Masonry walls are frequently coated with an exterior layer of cementitious material, referred to as "parging," for water control. This coating is usually covered at the bottom of the wall to make a good exterior seal at the joint between the footing and the block wall, thus preventing the entry of radon into the house. Research indicates that homes with concrete-block foundation walls typically have twice the radon level as homes with poured-concrete foundations.

 

COATINGS
Waterproofing and damp-proofing are effective methods of sealing the joints and thus preventing the entry of radon. The most common damp-proofing treatment for residential foundation walls is an exterior parge coat of bituminous asphalt. The parge coat is used for concrete masonry walls but is not necessary for poured concrete.

The following are some of the damp-proofing/waterproofing systems suitable for radon barriers.
bullet Coal tar polyurethane
Coal tar-modified polyurethane is a cold-applied liquid waterproofing system. It is applied as a liquid at the rate of 10-15 mils/coat. The coating dries hard, but has some elasticity. This material may be attacked by acids in groundwater but can be defended by a protection board.
 
bullet Polymer-modified asphalt
Polymer-modified asphalt is a cold-applied liquid waterproofing system, but it is difficult to achieve an even coating on a vertical surface. High grade polymer-modified asphalt is superior to coal tar-modified polyurethane in elasticity, crack-spanning ability, and resealability, but inferior in its resistance to chemicals.
 
bullet Membrane waterproofing systems
Waterproofing applied as a solid-sheet membrane has an advantage over liquid-applied systems in that quality control over thickness is ensured by the manufacturing process. Most membrane systems are chemically stable and have good crack-spanning ability. Thermoplastic membranes may be applied in various ways: affixed to walls, or laid beneath slabs. Thermoplastic membranes are rated for resistance to chemicals and longevity. Seals and overlaps must be carefully and completely closed in order for membranes to function as radon barriers.
 
bullet Bentonite
Bentonite clay expands when moist and thereby creates a waterproof barrier. Bentonite is not as resistant to chemicals as the thermoplastic membranes. The major flaw of this material as a radon barrier, however, is that it is only expanded when wet. This is acceptable for a waterproofing material, but not for a gas barrier.
 
bullet Cementitious waterproofing
A number of additives can be incorporated in concrete to create cementitious "waterproofing." This type of waterproofing is appropriate only for interior applications because it is inelastic, does not have good crack-spanning ability, and cannot resist hydrostatic pressure.

 

MEMBRANES
Membranes of plastic or rubber are used to control water penetration and water vapor diffusion but are also effective at controlling air movement as well.

Types of membranes available: 
bullet Polyethylene film.
bullet High-strength bubble-pack with aluminum foil.
bullet Aluminum foil over a core of glass scrim webbing.
bullet PVC sheets.

 

 

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