INSTALLATION GUIDE - continued

3. INSTALLATIONS OF HARDWOOD FLOORING OVER A CONCRETE SLAB.

Hardwood flooring can be installed successfully over a slab which is on-grade or above grade heart level. Below-grade installations are not recommended but still are possible with the right techniques and flooring materials a lots of hardwood flooring installation have occur on concrete slabs like in the cities of san Jose California, Santa Clara California, Pacifica and san Francisco. The slab must be constructed properly Watch out for water wood and water are no a good combination. New concrete is heavy with moisture, an inherent enemy of wood no matter if the hardwood floor is pre-finish, side nail or staple, unfinished or have aluminum oxide finish. Proper on-grade slab construction requires a vapor retarder such as 6 mil polyethylene film between the gravel fill and the slab. Test for dryness, even if the slab has been in place over 22 months. Slabs younger than 2 months are generally too wet for hardwood flooring installation places in the bay area are very high on moisture like the city of san Francisco and south san Francisco, also the cities in the east bay area, like Oakland, Berkeley north and the Berkeley hills.

4. TESTING CONCRETE FOR EXCESSIVE MOISTURE.
NOTE: Make tests in several areas of each room you don’t want to have a problem with the beautiful hardwood floor. When tests indicate excessive 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 remember always to test the moisture contents again doing this will save you money in wood floor materials waste or loss.
1. The Rubber Mat Test. For this test you need to 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 about 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, mean excess moisture is present.

5. SLAB PREPARATION.
The slab where the floors are going to be installed must be dry and flat. To prepare the slab grind off any high spots, fill low spots, clean up grease or anything that you think can interfere with the integrity of the installation make sure to sweep and vacuum the area before the installation all need to be nice and clean for the new hardwood floors.
6. VAPOR RETARDER.
To be certain normal slab moisture does not reach the finished floor, a proper vapor retarder must be used on top of the slab. The vapor retarder must have perm rating of less than 1 perm. 6 mil polyethylene films have a 0.04 perm rating and is considered a good choice. With 3⁄4" plywood used as a nailing base, the recommended vapor retarders are affixed to the slab. These systems may be either 2 membrane asphalt felt/building paper or mastic or a 4-6 mil polyethylene film or an equivalent system as described below.
Two membrane asphalt felt or building paper system.
Prime and apply cold cut-back asphalt mastic with a hardwood floor stain notched trowel at the rate of 50 sq. ft per gallon. Let set 2 hours. Roll out 15 lb. asphalt felt/building paper over the hardwood floor installation, lapping edges 4". Butt ends. Over this apply a second similar coating of mastic and roll out a second layer of asphalt or sometimes wood felt/building paper. Lay both layers of felt in the same direction, but stagger the overlaps to achieve a more even thickness.
Polyethylene method. This is not the oil base that we use in the hardwood floor refinish in the bay area we are talking about another polyurethane When slabs are well above grade and the expected annual rainfall is light to moderate, cover the entire slab with 4- to 6-mil polyethylene film, overlapping edges 4-6" and allowing enough to extend under the baseboard on all sides.
Where moisture conditions are considered more severe, prime and apply* cold-type cut-back asphalt mastic with a straight-edge or fine tooth trowel over the entire slab surface (100 sq. ft. per gal.). Allow to dry about 1 hour. Lay the 4-6 mil polyethylene film over the slab, covering the entire area and lapping edges 4-6". “Walk in” or roll in the film, stepping on every square inch of the floor to insure proper adhesion. This test is very successful in the bay area from any hardwood floor installation in San Leandro California to a refinish wood floor in the city of San Lorenzo California , Small bubbles are of no concern, and may be punctured to allow captive air to escape.