Surface Moisture Test

One area of concern when using moisture meters is surface moisture. It’s a common problem for many meters used today, especially pin meters. While the user wants to determine the moisture content within the wood’s core, surface moisture – which can be caused by high humidity, rain, or even a liquid spill – can give a false reading. So it’s critical, particularly for wood flooring installers, makers of fine furniture, and people in the construction and inspection industries, to know which meters provide accurate readings when surface moisture is on wood, and which ones do not. This test will help determine that. NOTE: This test was discontinued in 2020.

Real-World Scenarios

Let’s look at a couple of real-world scenarios involving surface moisture. If a wood flooring installer stacks wood flooring in an air conditioned or heated building for any length of time before installation, most likely there will be no problems with surface moisture. But unexpected things can happen in the real world to change that. For instance, a liquid might be spilled on the wood flooring prior to installation. Or, the HVAC system could shut down because of a power outage, exposing the flooring to higher humidity. Humid air causes wood to expand, and this could lead to serious problems after installation.

If a floor installer is not aware of anything like this happening to the wood flooring, and then uses a meter that is extremely sensitive to surface moisture, it’s possible to get inaccurate readings and then end up with an unpleasant surprise after installation—such as warped or split flooring.

Alternatively, consider the woodworker who leaves wood out in a shed or garage or has it stacked outside overnight. That wood may end up with condensation. Even if the condensation is wiped by hand or with a cloth, the moisture is being spread along the board. If sufficient time is not allowed for that surface moisture to dry, it may dramatically decrease the accuracy of the readings when using any meter that is sensitive to surface moisture.

These are just two possible scenarios involving surface moisture that can happen in the real world. Our Surface Moisture Test will help identify those moisture meters prone to giving inaccurate readings due to surface moisture – readings that could result in a costly mistake.

This test requires a few basic tools (all dimensions are in inches unless otherwise indicated):

• 6x4x7/8 sponge cut in half (3x4x7/8)
• PLA plastic enclosure – 3x4x0.78
• Measuring beaker – graduated in milliliters (ml), 50 ml capacity

Testing Procedure

1. Take the 3 x 4 x 7/8 sponge and soak in water.
2. Place the sponge in a vice to squeeze the water out so that the sponge is almost dry to touch.
3. Place the sponge into the enclosure, or holder.
4. Add 30.0 ml of water measured in graduated cylinder and let sit for two minutes to absorb into the sponge.
5. Ensure that the wood being tested is elevated.
6. Record a dry reading of the wood in the measurement area.
7. Place the sponge and enclosure face down onto the wood measurement area.
8. While pressing down on the enclosure so that the plastic is touching the wood, swipe the sponge fully across the measurement area and back across to the starting position. There should be a sheen of water left on the board.
9. Immediately place the meter onto the surface in the measurement area and record reading.
10. Repeat all steps for each meter being tested (maximum of two meters for each board).

For three-dimensional (3D) printing of the sponge enclosure used in the surface moisture test, you can download the Spongeholder STL here. This file will need to be opened with either your 3D printer or computer-aided design (CAD) software.