Slab and Stem Wall Treatment and Detailing

Concrete can act as a wick for ground mois­ture, thereby promoting water damage and fungal growth in other materials through moisture transfer. A layer of coarse gravel under the slab with no fines smaller than half an inch will break capillary action. A layer of continuous, unpunctured polyethylene di­rectly under the slab will help prevent water vapor and soil gases such as radon from find­ing their way through cracks in the slab. A fully cured slab can also be sealed to further prevent moisture and soil gases from enter­ing the building and to create a more finished floor surface. Some sealers are solvent based and should be avoided. The following sealers are more benign:

• AFM Safecoat CemBond Masonry Paint:

Water-resistant coating for cement, con­crete block, and masonry

• AFM Safecoat DecKote: Waterborne coat­ing for use on concrete, magnesite, walk­ways, breezeways, and patios

• AFM Safecoat MexeSeal, AFM Safecoat Penetrating Water stop: Water-based seal­ers and finish coats

• AFM Safecoat Watershield: Water repel­ling sealer for masonry and painted sur­faces

• AgriStain for Concrete: Sealer and stain for concrete, plaster, and porous tiles

• Vocomp-25: A solvent-reduced, water — based sealer

• Weather-Bos Masonry Boss Formula 9:

A water reducible sealer for all above — grade concrete and masonry surfaces; helps reduce dusting, powdering, efflores­cence, spalling, cracking, and freeze-thaw damage

• Xypex: A nontoxic (according to manu­facturer), zero-VOC chemical treatment for the creation of moisture resistance and the protection of concrete; creates a non­soluble crystalline structure that perma­nently plugs the pores and capillary tracts of concrete. Xypex concentrate DS-i and DS-2 are dry-shake formulations designed for horizontal surfaces.

Further Reading

Timusk, John. Slabs on Grade. National Building Envelope Council, Building Science Treatise, Construction Canada 92-07.