How to Prepare a Cinder Block Basement for Framing Home Guides

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Framing your basement adds tremendous value to your home. Not only does it increase the usable square footage, but it makes the area look and feel warmer and more homey. Cinder block basement walls are actually a form of concrete and are framed identically to poured concrete basement foundation walls. If the job is performed properly, the result is walls that will not transfer moisture to the interior wall framing and sheathing. Wet wood, insulation and sheathing leads to the growth of unsightly and unhealthy mold and mildew, with eventual rot and wall failure.

Water Leaks Check the basement walls for evidence of moisture, leaks, standing water or mold and mildew growth before framing the walls. Concrete is porous, so any moisture in the ground outside will naturally leach into the concrete and gradually dissipate throughout the wall. This accounts for the faintly musty smell in some basements. Isolated areas of darkened concrete indicate a leak, however. Leaks, standing water and severe cracks should be repaired before framing any walls. Washing the walls with a mixture of borax and water will kill mold and mildew. Mix 1 cup of borax with 1 gallon of hot water. Spray on the walls to weight down the mold or mildew spores, scrub, then wipe to remove loosened debris. Once dry, the borax residue continues to inhibit new growth.

Waterproofing Waterproofing cinder block or concrete basement walls is an option when preparing your walls for framing. Waterproofing products fall into four general categories: waterproof masonry cement, plastic sheeting or panels, waterproofing paint, plastic sheeting or panels, or silicate-based concrete sealers, sometimes called densifiers. While the use of certain insulation types eliminates the need for waterproofing, the addition never hurts. Read the product directions and specifications to ensure it suits your wall conditions and determine how to apply it.

Insulation The most common type of insulation used for framing a concrete basement is rigid foam insulation since it resists moisture. Extruded polystyrene foam board insulation -- the blue or pink board so commonly seen -- has an R value of about 5 per inch of thickness. Rigid foam insulation is glued to the concrete walls using an adhesive designated as safe for foam. Other adhesives may eat through it. Some builders suggest lining the walls with a layer of foam then placing the framing on top of the foam. Additional layers of foam, enough to meet your required R value, can then be pushed in between the wall studs. Or use fiberglass batts. Another option is to use fiberglass alone, but only if the walls are properly waterproofed.

Vapor Barrier Strictly speaking, after waterproofing the walls or installing rigid foam insulation -- or both in combination -- the walls should not experience moisture or air wicking through the concrete to the interior. Foam insulation is considered a vapor barrier in addition to its moisture resistance, as long as every seam is taped with foil insulation tape. Consider stapling a vapor barrier to the face of the wall framing studs for extra protection, regardless of the products used. Plain plastic sheeting works well.

Framing You have a couple of options for framing the wall. Either attach furring strips -- thin strips of wood -- or build a 2-by-4 or 2-by-6 stud wall. Furring strips take up less room, since they aren't as thick, but 2-by-6 provides the most insulation depth. Use your previous product choices to guide you. For instance, a thin layer of foam works well with furring strips, but foam plus fiberglass benefits from thicker studs. Use treated lumber wherever wood rests against bare concrete to avoid rot.

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