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Testing Concrete for Excessive Moisture

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hen testing your concrete slab, make tests in several areas of each room on both old and new slabs. When tests indicate too much moisture in the slab, do not install hardwood floors. For a moist slab, wait until it dries naturally, or accelerate drying with heat and ventilation then test again.

1) The Rubber Mat Test. Lay a smooth, non-corrugated rubber mat on the slab, place a weight on top to prevent moisture from escaping, and allow the mat to remain 24 hours. If the covered area shows water marks when the mat is removed too much moisture is present. This test is worthless if the slab surface is other than light in color originally.

2) The Polyethylene Film Test. Tape a one-foot square of 6 mil clear polyethylene film to the slab, sealing all edges with plastic moisture resistant tape. If, after 24 hours, there is no "clouding" or drops of moisture on the underside of the film, the slab can be considered dry enough to install wood floors.

3) The Calcium Chloride Test. Place a quarter teaspoonful of dry (anhydrous) Calcium Chloride crystals inside a 3-inch diameter putty ring on the slab. Cover with a glass so the crystals are totally sealed off from the air. If the crystals dissolve within 12 hours the slab is too wet.

4) The Phenolphthalein Test. Put several drops of a 3% Phenolphthalein solution in grain alcohol at various spots on the slab. If a red color develops in a few minutes, too much moisture is present.

Flooring Installation Guide :: Index
1) Installation Introduction
2) Handling & Storage
3) Job Site Conditions
3.1) Installing over Concrete
3.2) Testing Concrete for Excessive Moisture
3.3) Concrete Slab Preparation Prior to Installation
4) Laying & Fastening
5) Plank Flooring
6) Laying a New Strip Floor Over an Old Floor
7) Parquet, Block Herringbone & Similar Flooring
8) Special Construction Situations
9) Tips for Easier & Better Flooring Installations
10) Strip Flooring on Walls & Ceilings
11) Installation of Gymnasium Floors over a Concrete Slab


Installation content courtesy of NOFMA. FloorMall.com is a Proud Member of NWFA.

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