Moisture Test! Water & Wood Don’t Mix


Approximately 85% of all installation failures are resulting from moisture problems. Therefore, the purpose of this post is to outline typical moisture testing, planning and procedures designed to help your installation be a successful one.

The installation of Lumber Liquidators, Inc.("LLI") wood flooring should not commence until conditions are determined to be "dry" according to industry moisture testing standards. Testing is to include, (a) the new wood flooring, (b) the wood subfloor or cement slab.

It is the responsibility of the professional flooring contractor or the Do-It-Yourselfer (DIY) to inspect and test jobsite moisture conditions prior to the commencement of any flooring system to ensure compliance with established hardwood industry standards. It is understood that moisture testing only establishes the existence of moisture at the time of testing and does not forecast future moisture issues. Installers would not be held responsible for moisture problems arising after the installation providing testing was conducted and normal moisture remediation was completed before installation. The point of moisture testing is to establish when the new flooring and substrate is actually ready for installation or the need to reschedule the work until conditions are acceptable.

Testing concrete

Common testing methods for moisture




Testing new wood flooring and subfloors

Moisture Meters: probe and pinless

Testing concrete
LLI does not recommend installation of any flooring system over a newly-installed concrete slab within 60 days of pour. Concrete slab drying time is affected by the type of construction, concrete formulation, location of the building and climatic/environmental conditions. Vapor barriers or under-slab membranes, while recommended, can increase slab-drying times, therefore accurate testing should not commence until after some 90 days of cure time. When conducting slab moisture testing, conduct tests in several areas regardless of the age of the slab. If the test(s) indicate a wet slab, document the results and delay installation of the flooring until corrected.
The use of an electronic concrete moisture meter to determine slab moisture emission is not reliable nor recommended. This is because electronic meters measure moisture content in the slab, usually in terms of an overall percentage and register moisture content only at 1% of the surface, while other meters register an average only in a vertical downward direction where placed. Metered moisture content values may indicate degree of saturation of a slab, but not the on-going emission rate that is occurring at the time.

The Following are several industry-recognized concrete slab moisture tests that provide quantitative measurements of moisture emission. All tests should be conducted at several different locations in a room–typically along exterior walls and walls with plumbing enclosures.

Common testing methods for moisture

THE CALCIUM CHLORIDE TEST: The calcium chloride test is one of the oldest and most legally recognized concrete moisture tests. This test has been used most often by flooring retailers and contractors. The cost can run about $50 or $60 per test. Depending on the kit purchased results can be acquired immediately, or sent away for documentation and reading. The calcium chloride test works by measuring changes in weight of anhydrous calcium chloride crystals.

Typical procedure: a small plastic dish of anhydrous calcium crystals is weighed to determine moisture content. 1st, after sanding or scarifying the cement surface (fig 1) the entire dish is weighed on a gram scale prior to placement and the weight, date and time the test was started must be recorded. The lid is then opened, and the dish of crystals is carefully set down on the concrete for 60 to 72 hours. The dish is enclosed within a 7-by-10-inch cover, which is then sealed with plastic tape to the concrete (fig 2). During this time, the only source of moisture being absorbed by the anhydrous crystals is what can evaporate out of the covered concrete surface area. A note of caution: Use care in lid dealing and removal of the dish, and weighing as exposure to atmosphere will dramatically effect the results.

At the end of the test, the dome is removed and the lid is placed back on the dish and sealed. Again the dish is weighed on the gram scale and the date and time are marked. The change in weight is multiplied by a constant and divided by hours to provide an estimated rate of evaporation, in pounds.

(fig1) Fig 1 Moisture
(fig2) Fig 2 Moisture

For example, water weighs 8.3 pounds per gallon. Pounds, is the equivalent weight of water that evaporates out of a 1,000-square foot surface area during 24 hours. If the test reports 8.3 pounds emission, then one-gallon of water is leaving a 1,000 square foot surface area in 24 hours. A conservative but generally recommended allowable amount of moisture emission as expressed by the calcium chloride test is 3.0 pounds per 1,000 square feet per 24 hours at the time of the installation of the flooring.

THE POLYFILM TEST: Several pieces of plastic film, 18″?- 24″? squares of are placed at key points on the cement, seal all four sides with silver duct tape. After 24 hours, the plastic film is removed and inspected for signs of condensation. If beads of water are found on the subfloor or the concrete appears darker this is a heads-up that further testing is necessary. If there is no indication of moisture under the plastic film, one can assume the installation may proceed. The reading is valid at 24 hours, but it’s even better if the test can stay in place until 72 hours have passed. The plastic film test can also be "accelerated" by using a heat source such as a 40 to 60 watt light bulb safely placed 18″? above the plastic.

Fig 3 Moisture

PHENOLPHTHALEIN TEST: This moisture test uses a 3 percent phenolphthalein solution (fig1) in water-free ethyl alcohol. Dime sized holes,1/4-inch deep, are drilled in various areas of the slab, particularly around walls. Then two drops of the solution are applied into each of the drilled areas. If there’s no color change in the solution, there should not be enough moisture and the alkalinity is not high enough to affect the installation. But if the phenolphthalein turns pink or dark red within five minutes and the pH is 9.0 or higher, further testing must be done with a more precise method. This should NOT be the only method used for testing moisture. Color of concrete surfaces: The "proper" color of concrete should be a light yellowish-grey (similar to limestone) not sugar white. In fact, a sugar-white surface usually means the concrete was improperly cured and can create a severe moisture problem later on (usually months later). This is due to the poor hydration of cement within the surface, creating a disproportionately high water to cement ratio…that appears white.
(fig1) Fig 4 Moisture
(fig2) Fig 5 Moisture

pH paper or litmus paper test:
Both the phenolphthalein and litmus paper tests measure the alkalinity of the surface of the concrete. Determining if cement is alkali free is important for glue down installations on concrete. Excess alkalinity(salts) can contribute to adhesive failure. Alkali can be visible as a white powder on the surface of the concrete. However, it is the excess salt contained within the concrete that can cause adhesive failure over time. This problem is magnified if moisture is present and passing through the concrete, as this condition will deposit the excess salt on the concrete surface. A simple pH test (fig2) will determine the presence of alkali on a slab surface. Apply a few drops of distilled water to a small thoroughly clean and scraped concrete surface area and apply a strip of pH paper to the wetted area. The paper will change color within 5 minutes. Compare the color change to the chart standard supplied with the paper to indicate the pH of degree of alkalinity. A pH range from 5 to 10 is acceptable. Corrective measures must be taken with any concrete slab that measures a pH reading above10.

Testing new wood flooring and subfloors

Moisture Meters: probe and pinless Probe or pin-type meters (fig1) are fast and easy to use. They come with different measurement indicators. The lower-cost units have L.E.D. display lights indicating different moisture levels; the better-quality units have analog or digital displays and provision for different species and wood temperatures.

The pinless meters (fig2) are also referred to as "non-destructive" because these don’t leave small testing holes in the wood. Signal penetration for pinless meters is up to 1 inch for both hardwood and softwood. The meter can be moved across the surface to identify pockets of moisture in a wood block or plank. It is relatively unaffected by temperature. Rough surfaces have very little effect on the reading. Measurements can also be taken through coating, varnish or paint without damage to the surface.

One advantage of probe type meters is that those with insulated pins can measure moisture content at varying depths–you can tell whether the moisture content near the bottom of a board is higher than near the top.

Deciding which kind of moisture meter to buy is a matter of sorting through the features you think you will need, and how often you may use it, and then understanding the various features and benefits. It is important that the meter you choose offers the following:



  1. Hi Alfredo, yes you should do a moisture test. If the subfloor is not within the recommended percentages your floor could buckle. You could also void the warranty. I would check your installation instructions. Thanks for your inquiry and for choosing Lumber Liquidators!

  2. Alfredo Corral on

    Installing solid bamboo on second story on top of plywood. Should I worry about doing a moisture test?

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