Moisture Testing In Wood Floors

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Installation: Moisture Testing

Some of the first steps to successful wood flooring installation are the most important.

Here’s some information on moisture guideline testing and vapor retarders.

Reference to ASTM Standard revisions: ASTM Standards listed are most recent revisions or use ASTM Standard in effect at time of installation.


Part I

Moisture Testing for Wood Flooring and Wood Subfloors

Determining moisture content is an essential part of quality control within the flooring installation process. Flooring Installers must know the moisture content of the wood flooring, as well as the subfloor.

A. The most accurate measurement for moisture content in wood is the oven-bake-out method. However, it is not widely used because the cost and difficulty of performing the test on-site is not practical.

B. Hand-held electrical tools, called moistur e meters, should be part of the toolbox of every flooring contractor for measuring moisture in subfloors and floors. Moisture meters have many purposes. They can be used to determine if floor boards are dry enough for an installation to proceed, they can check subfloors and concrete for high moisture levels, they can determine when a second coat of finish can be applied and they can assess water damage.

There are two main types of meters for testing wood: probe and pinless.

1. The probe type measures electrical resistance across opposed sets of pins, which are pushed into the wood. All probes should be inserted parallel with the grain or as instructed by the meter manufacturer. An advantage of probe type meters is that those with insulated pins are able to measure moisture content at varying depths; for example, you can determine whether the moisture content near the bottom of the board is higher than near the top.

2. The pinless, dielectric type employs signal penetration at one inch or more for both hardwood and softwood. The meter can be moved across the surface to identify pockets of moisture. It is relatively unaffected by temperature. Rough surfaces have very little effect on the reading. Measurements can also be taken through coatings, varnish or paint without damage to the surface. Newer pinless meters can be adjusted to depth desired. Older models may read deeper into flooring systems and not give an accurate reading of wood flooring only.

3. Follow the meter manufacturer’s recommendations to get an ac curate reading from the wood floor. One effective testing method is to remove a sample board and get a reading with air space beneath it.

4. It is important that the meter you chose offers the following:

a. A wide moisture content range from at least 6 percent to 30 percent.

b. The necessary adjustment tables, conversion charts or settings for various species. Test for moisture at several locations in the room – a minimum of 20 per 1,000 square feet – and average the results. Document all results. A high reading in one area indicates a problem that must be corrected. Pay special attention to exterior and plumbing walls.


Part II

Moisture Testing for Concrete Slabs

Note: All tests give a result – at the time the test is done – and in general give you the ability to start or not start a job. These tests do not give a permanent condition of your substrate, but merely a “at the time the test was performed” indication.

Testing Requirements
Before moisture testing begins, the concrete slab must be a minimum of 30 days old.

Qualitative Moisture Tests – Electrical Impedance Test and Electrical Resistance Test (Moisture Meter) Follow meter manufacturer’s instructions.

1. Use moisture meters designed specifically for concrete moisture testing.

2. Test within the body of the slab (electrical resistance), as well as at the surface (electrical impedance).

3. These testing methods are not recognized by any standard and should not be used for the purpose of accepting or rejecting a floor. These electronic tests are useful survey tools to broadly evaluate the relative moisture conditions of a slab and to select locations for quantitative moisture tests.

4. If the moisture meters indicate the presence of excessive moisture, as per wood flooring or meter manufacturer’s recommenda tions, further testing is required using relative-humidity testing (ASTM F2170), calcium chloride testing (ASTM F1869) or calcium carbide (CM) testing (ASTM D4944 and MilSpec CRD-C154-77).

Quantitative Moisture Tests

1. ASTM F1869 – Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor using Anhydrous Calcium Chloride.

a. This test method covers the quantitative determination of the rate of moisture vapor emitted from below-grade, on-grade, and above-grade (suspended) bare concrete floors.

2. ASTM F2170 – Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs using in Situ Probes.

a. This test method covers the quantitative determination of percent relative humidity in concrete slabs for field or laboratory tests.

3. ASTM F2659 – Standard Guide for Preliminary Evaluation of Comparative Moisture Condition of Concrete, Gypsum Cement and Other Floor Slabs and Screeds Using a Non-Destructive Electronic Moisture Meter.

a. This guide focuses on obtaining the comparative moisture condition within the upper 1″ (25.4 mm) stratum in concrete, gypsum, anhydrite floor slabs and screeds for field tests. Due to the wide variation of material mixtures and additives used in floor slabs and screeds, this methodology may not be appropriate for all applications. See 1.2 through 1.8 and Section 11 of ASTM F2659. Where appropriate, or when specified, use further testing as outlined in Test Methods F1869, F2170 or F2420 before installing a resilient floor covering.

4. ASTM F2420 – Standard Test Method for Determining Relative Humidity on the Surface of Concrete Floor Slabs Using Relative Humidity Probe Measurement and Insulated Hood.

a. This test method covers the quantitative determination of percent relative humidity above the surface of concrete floor slabs for field or laboratory tests.

5. Relative Humidity Testing – ASTM F2170 (Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes).

a. Select test locations to provide information about moisture distribution across the entire concrete floor slab. For slabs on grade and below grade, include a test location within three feet of each exterior wall.

b. Perform three tests for the first 1,000 square feet and one test for every additional 1,000 square feet thereafter.

c. At least 48 hours before test is placed, concrete floor slabs should be at the same temperature and humidity that is expected during service conditions.

d. Use a rotary hammer-drill to drill holes in the concrete slab; 40% depth of slab is required for the holes when concrete is drying from one side and 20% when drying from both sides. Follow manufacturer’s instructions provided with test kits.

e. Allow 72 hours to achieve moisture equilibrium within the hole before making relative humidity measurements. Follow manufacturer’s instructions provided with test kits.

f. ASTM F710 provides installation guidelines for acceptance of hardwood flooring using relative humidity testing. Typical limits for wood and wood-based products are 75% relative humidity. When getting readings over 75%, you must use a proper vapor retarder, based on the flooring manufacturer’s recommendations, or wait for further concrete curing.

6. Calcium Chloride Test – ASTM F1869 (Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride).

a. Select test locations to provide information about moisture distribution across the entire concrete floor slab.

b. Perform three tests per 1,000 square feet of surface area. Add one additional test for each 1,000 square feet thereafter. At least 48 hours before test is placed, concrete floor slabs should be at the same temperature and humidity expected during service conditions.

d. The actual test area shall be clean and free of all foreign substances. Use approved OSHA work practices for removal of all existing flooring materials and debris.

e. Blast or grind a minimum area of 20 inches by 20 inches and let stand for a minimum period of 24 hours prior to setting test.

f. Follow manufacturer’s instructions for properly placing tests onto concrete.

g. Tests are to be covered and left in place for 60 to 72 hours. Follow manufacturer’s instructions for labeling and recording time and date of test.

h. Send the test to a certified laboratory for results and documentation, or perform the measurements as per ASTM F1869.

i. Always follow the flooring manufacturer’s guidelines and specifications to determine when the concrete slab is ready for installation.

j. ASTM F710 provides installation guidelines for acceptance of hardwood flooring using alciumchloride testing. Typical limit for direct glue-down wood flooring is 3lbs/1000sf/24hr. When getting readings over 3lbs and up to 7lbs, you must use a vapor retarder. A reading over 7lbs may not be acceptable for wood flooring installation. Follow the wood flooring manufacturer’s recommendations. In the case of a glue-down installation, the adhesive manufacturer may also have recommendations. Note: For information on the tests listed above, contact your distributor or call NWFA at 800.422.4556 (USA or Canada) or 636.519.9663 for the source nearest you.

7. Calcium Carbide (CM) Test – ASTM (modified) D4944, MilSpec CRD-C154-77.

a. The calcium carbide test, also known as the CM test or calcium carbide bomb, is more widely used in Europe than in the United States. It is a gas-pressure test in which moisture in the concrete reacts with calcium carbide crystals to create acetylene gas, and the gas pressure produced is measured to provide a moisture content reading, expressed as a percentage of moisture. Follow the directions provided by the test-kit manufacturer. A reading of more than 2.5% requires use of a vapor retarder. A reading of more than 4% may not be acceptable for wood flooring installation. Follow the wood flooring manufacturer’s recommendations. In the case of a glue-down installation, the adhesive manufacturer may also have recommendations.


Part III

Acceptable Vapor Retarders Over Wood Subfloors

A. Always follow local codes and manufacturer’s instructions for acceptable vapor retarders. Note: The 2012 IBC defines three classes of vapor retarders:

1. Class I 0.1 perm or less.

2. Class II 0.1 perm less than or equal to 1.0 perm.

3. Class III 1.0 perm less than or equal to 10 perm. When tested in accordance with ASTM E96 Method A.

B. An acceptable vapor retarder is a vapor resistant material, membrane or covering with a vapor permeance (perm rating) of greater than or equal to .7 and less than or equal to 10 when tested in accordance with ASTM E96 Method A. Installation of a vapor retarder reduces the potential for moisture or vapor related problems, but does not guarantee elimination of moisture or vapor related problems. Install a vapor retarder over wood panel or board subfloors prior to installing nail down solid strip or plank flooring. Overlap seams a minimum of 4 inches or more as required by manufacturer or specifier and local building codes.

Some examples of acceptable vapor retarders over wood subfloors include:

1. An asphalt laminated paper meeting UU-B-790a, Grade B, Type I, Style 1a.

2. Asphalt-saturated kraft paper or #15 or #30 felt paper meeting ASTM Standard D4869 or UU-B-790.

Note:
1. A vapor retarder has some extra benefits in that it eliminates wood-on-wood contact, wood strips slide more easily when positioned, it minimizes the impact of seasonal humidity change and it may reduce dust and noise levels.

2. However, by today’s standards, asphalt saturated kraft or felt paper may not be an effective vapor retarder, with a Class III perm rating of 1.0 perm <10, in all applications. Consult local codes.

3. Over a wood subfloor, do not use an impermeable vapor retarder material with a perm rating of .7 or less, such as 6 mil polyethylene film or other polymer materials, as it may trap moisture on or in the wood subfloor. Such impermeable material may be used if recommended by the wood flooring manufacturer as such materials have been measured for vapor transmission due to fastener penetration or include special backing to dissipate vapor horizontally.


Part IV

Acceptable Vapor Retarders Over Concrete

A. Always follow local codes and manufacturer’s instructions for acceptable vapor retarders.

B. Test concrete for moisture. For concrete slabs with a calcium chloride reading of greater than 3lbs, a relative humidity reading of greater than 75%, or a calcium carbide (CM) rating of greater than 2.5%, install an impermeable vapor retarder with a perm rating of less than .15 perm. Adding a vapor retarder is not required on installations over slabs with a calcium chloride reading of 3lbs or less, a humidity reading of 75% or less, or a calcium carbide (CM) rating of 2.5% or less. However, in on-grade and below-grade applications, adding a vapor retarder is always recommended.

C. The 2012 IBC defines three classes of vapor retarders:

1. Class I 0.1 perm or less.

2. Class II 0.1 perm less than or equal to 1.0 perm.

3. Class III 1.0 perm less than or equal to 10 perm. When tested in accordance with ASTM E96 Method A.

D. The NWFA recommends an “impermeable” vapor retarder with a perm rating of less than or equal to .15, thereby limiting the passage of moisture to near zero.

E. Some acceptable vapor retarders over concrete include:

1. A minimum 6 mil construction grade polyethylene film or other impermeable material with a perm of .15 or less is recommended. A premium polymer material meeting ASTM E1745 for concrete with higher tensile, tear and puncture resistance is highly desirable.

2. Double felt: Two layers of #15 asphalt saturated felt paper that meets ASTM Standard D4869, with the first layer adhered to the slap in a skim coat of appropriate asphalt mastic type adhesive recommended by manufacturer, and a second layer felt adhered to the first layer with same appropriate adhesive.

3. A chemical retarder or urethane membrane, as recommended by the adhesive or wood flooring manufacturer. These are usually in the form of a liquid-applied or trowel-applied membrane dispensed from a bucket following manufacturer recommendations.

4. Installation membrane: a permanently elastic, cross linked, closed cell polyethylene membrane. Follow membrane manufacturer instructions.

5. A loose laid or mechanically fastened plastic, waterproof, dimple type membrane, providing a thermal air gap separating finished floor from concrete. Follow membrane and floor manufacturer installation instructions.

6. An elastomeric, fully adhered or mechanically fastened membrane with seams sealed. Follow membrane manufacturer installation recommendations.


Part V

Dimensional Change of Coefficients

A. See Solid Strip and Plank Flooring Installation, for dimensional change of coefficients.

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