14 May. 1981|
Moisture meter for wood flooring,wood finishes for outdoor use,fine woodworking miter saw stand plans - Test Out
To ensure quality, from the mill and dry kiln to the finishing floor, Delmhorst moisture meters help minimize defects such as shrinkage, cracks, and splits.
There are two types of moisture meters commonly used in lumber and woodworking applications. Pinless moisture meters read moisture closest to the source of the magnetic field, in this case, at the surface.
Please refer to the diagram below for a basic look at the difference between readings obtained from a pin-type meter compared to a surface meter.
This diagram illustrates that pin-type meters and surface meters provide different information about the moisture content in a board. Using the principle of electrical resistance, pin-type meters use the board as an element in a circuit by driving two pins or electrodes into it.
Most pinless meters use the capacitance method, which uses the relationship between the moisture content and the dielectric properties of the wood. Both the resistance and the dielectric properties of wood change in direct proportion to its moisture content, within a specific range. Resistance-type meters express moisture content as a percentage of the oven-dry weight of the wood. First, to determine how the moisture is moving through a board, make a series of shell readings in the layer just below the surface; then make a series of core readings, closer to the center of the board thickness. Pin-less meters scan through the cross section of a board taking into account the moisture in the entire penetrated area. Moisture caused by exposure to rain, fog or high relative humidity is easily and accurately detected with insulated pins. As described in the answer to the question above, readings taken with a surface meter are affected by surface moisture, making it difficult to determine if the surface moisture is a result of standing water caused by rain, or if it is representative of the moisture content throughout the board. The Delmhorst RDM series moisture meters with data collection and statistical analysis capabilities are ideal for simplifying the entire sampling procedure and providing backup documentation.
After moisture content and a moisture gradient, if one exists, wood temperature is the most important factor affecting the accuracy of your readings.
The temperature of the wood does not affect pin-less type meters, unless the lumber is frozen.
As long as the wood is not frozen solid and remains conductive, a pin-type meter will give reliable readings. When using a pin-type meter, all species yield different readings at the same moisture content. When using a Delmhorst meter on other species, either refer to the species correction chart, or key in your species into one of our microprocessor-based meters for an automatic correction. A good moisture meter is still valuable, even without a correction factor because you can use it to determine the equilibrium moisture content (EMC). For accurate results with a pinless meter, the material you're testing must be at least the width of the scanning area on the bottom of the meter. While Delmhorst meters are built for the harsh mill environment, continued exposure to high heat and humidity will invite corrosion and shorten the life of a meter's keypad, display and PC board components. Use the Delmhorst Kil-Mo-Trol, a remote probe system that measures the moisture content of lumber during the drying process. Drive the electrode pins into the wood with the meter turned off, and then turn the meter on when you are ready to take the reading. If two meters are not of the same manufacturer, readings will likely not correspond, because of the different calibrations used. Delmhorst moisture meters are well known for their ruggedness and ability to withstand years of rough handling.
Keep the meter and electrode clean by using any biodegradable cleanser sparingly on external parts only. If you have any doubt about the working condition of your meter, send it to Delmhorst. Given the challenging conditions, it pays to have an easy-to-use moisture meter that you can depend on.
AccessoiresMCS-1Moisture content standards are great for verifying that your Delmhorst moisture meter is in calibration.
Years of experience, high-tech tools and controls, and premium grade lumber cannot make a difference if moisture content goes unchecked. Pin-type meters are the only instruments that indicate the moisture conditions inside a board or a piece of wood.
For quickly scanning finished product, a pin-less meter is a convenient way to identify a problem area. This method works because moisture conducts electricity well and dry wood is an effective insulator.
These meters work best from the range of fiber saturation point (25 to 30 percent) down to around 6 percent.
You can check accuracy either through the internal check or with a Moisture Content Standard.
Wood for fine furniture should be dried to 6 to 8 percent in most areas of the country, with very little variation among pieces and between the shell and core.
To determine the attainable moisture content - or equilibrium moisture content (EMC) - in your part of the country, hang small, thin samples of a wood species in your shop or plant and taking daily readings. The Delmhorst 26-ES electrode with insulated pins is the easiest and surest way to detect a moisture gradient. For kiln-dried stock, the final reading should be between 6 and 12 percent; with your first reading about 1 percent lower.
If there is a high concentration of moisture at the surface, the reading will be skewed to reflect this surface moisture. In an ideal situation, when all the boards in a load have the same moisture content, and the distribution in each board is uniform, only a few readings are needed.
However, at moisture levels below 10%, it is usually sufficient to make good, positive contact with the wood. For greatest accuracy, a small correction is necessary when using electrodes with two insulated pins.
As wood temperature increases its electrical resistance decreases and indicated moisture content rises. However, most instrumentation, unless specifically designed for extreme weather conditions, will not work well in constant sub-freezing temperatures.
This is due to the fact that the electrical characteristics of different wood species vary. However, instead of electrical characteristics affecting the readings, wood density affects the readings. While not as accurate as individual corrections, the group correction is adequate for practical purposes, as long as the correction is close to the individual factor for the species.
A meter reading by itself is not always as important as allowing the wood to attain its EMC level where it won't change dimension, crack, or split.
Our experience has shown that at higher moisture content levels (above 20 percent), chemically treated lumber tends to yield somewhat erratic readings.
As long as the pins make good contact, the meter can be used on anything from small dowels to wide planks. Made in the USA, Delmhorst meters are calibrated on the USDA standard, while foreign made meters use other standards and often have different species and temperature correction factors.
Assuming both meters are electrically correct, the difference usually can be attributed to use of different electrodes, pin penetration, and species and temperature corrections.
Using insulated pins, only the uncoated tips are exposed to the wood fiber, providing more accurate readings of moisture content at various levels of penetration.
However, a pinless meter cannot differentiate between shell and core moisture content and will not detect a moisture gradient.
Before choosing a meter, it is important to understand these differences in readings and choose the type of meter best suited for your particular application.
Below 6 percent, it's tough to make accurate, repeatable readings because of the high electrical resistance in really dry wood. When the samples' moisture content remains constant, they have reached the equilibrium level. Even non-insulated pins, which measure the wettest fibers, will provide a good indication of how the wood is drying. For air-dried stock, the final reading is typically between 12 and 19 percent, with the first reading between 2 and 3 percent lower. If the surface is dry and core moisture exists, the readings will be lower than the representative moisture levels throughout the board. For critical use, check 5 or 10 percent of the load, and be sure to look at boards from all parts of the load.
At higher levels of moisture and especially if you have a steep gradient, full penetration is a must. The latest Delmhorst models available are calibrated either for the 2-pin electrode only, or are programmable for both 2-pin and 4-pin electrodes. If the temperature correction is not built in the meter, use the slide rule or chart we supply with each meter. Refer to the species correction chart enclosed with your meter to adjust the readings accordingly.
Pin-less meters, however, need full exposure to a flat surface so their readings on some uneven surfaces may be unreliable. This technique is proven for both hardwood and softwood drying, and can be used in any type of dry kiln, pre-dryer, or air-drying operation. When meters are used for lumber inspections by vendors and buyers, the two parties should have a basis for comparing readings obtained with the instruments they are using. With two electrical resistance values (12% and 22%) to test your meter against, you can be sure that your readings will stand up to the strictest standards of accuracy. It only makes sense, then, that you should carry the one essential tool that allows you to detect and battle moisture problems—the moisture meter. Using a pin type meter with insulated pins is still the most effective method to determine moisture gradient, which is the difference between shell and core moisture content. Otherwise you can have discrepancies between meter readings and actual moisture content of as much as 5 or 6 points, especially in the range above 20 percent.
If you must, take a few minutes to warm up the meter and electrode to a maximum 100°F, so that the higher temperature and moisture levels in the kiln will not affect the meter for a few minutes. For more information about Kil-Mo-Trol, please close this window and click on the Kil-Mo-Trol Moisture Monitor button. Although it is a relatively simple tool to use, one mistake made using a moisture meter can prove to be a costly one. If there is no increase, or the increase is less than 1 percent, the wood is wet on the surface and the readings are unreliable. Here are seven common moisture meter mistakes and how to avoid them.1) Using the Wrong MeterDifferent meters are calibrated to test the moisture content of different materials.
Carry two meters to the job site if you know you will be working with both types of materials, and learn how to properly use each meter. For added convenience, some manufacturers offer models with both wood and concrete moisture meters combined into one. Generally, both pin and pinless concrete meters qualitatively measure the relative moisture content of the slab, meaning they indicate which areas are dry and which are still wet. Know their limitations, one being that concrete meter signals can only penetrate—at the most—an inch into the material, failing to reveal moisture problems deeper in the slab that can migrate up into your flooring after it's installed. Also, any fast-cure additives or vapor retardants added to the concrete may give your meter a false reading. Consult the manufacturer to determine if further tests are needed, such as the ASTM F 2170 test of drilling a hole into the concrete, waiting 72 hours and then measuring the moisture content with an in-situ probe or using a relative-humidity meter.Using the right meter for wood can pose a different set of challenges from concrete. Evaluate which meter best serves your needs for the type of work you do.Pin meters feature two pins protruding from the end of the meter, between which an electric current travels and measures the moisture resistance in the wood. The pins can either be hammered or stuck into the flooring, and they must be placed in the direction of the grain for the best reading.
The pins can be driven into the flooring at varying depths to determine the moisture content of each section of a particular board, making it easier to find the exact source of the moisture. Some meters feature pins insulated with latex or rubber to give a precise measurement in a specific location, which is ideal for gradient testing (measuring the moisture content of the wood at different depths of the board after installation) because the readings come only from the exact area between the ends of the pins. It transmits low-frequency signals down into the flooring, which travel back up to register the average moisture content of the entire plank.
But for any flooring with thicknesses less than what the meter is designed to measure, the meter may measure the subfloor underneath and give an inaccurate reading. The pinless meters are considered more convenient because they don't require hammering or insertion of pins and are preferable to the pin meters for prefinished flooring because they don't leave any holes. For materials made of multiple species, such as engineered flooring or plywood, testing methods vary, so consult the flooring and moisture meter manufacturers on the proper way to test for moisture content.2) Not Properly Maintaining the MeterIt doesn't take much to ensure your moisture meter gives accurate readings, but there are a few things to keep in mind for maintenance.
Occasionally, the meter's calibration can be lost, in which case you should send it back to the manufacturer for recalibration. If you use insulated-pin meters, be sure to change the pins frequently, since every time the pins are stuck in the floor, some of the insulation is scraped off, eventually making the meter more susceptible to inaccurate readings.
The pins should be changed depending on how often they are used and for which types of species.
If they measure the acclimated flooring, the middle of the subfloor and once under the window, they think they have covered all their bases. Test the areas most conducive to moisture—along the exterior walls, under windows, around fireplaces, in exterior doorways, anywhere plumbing comes up through the floor and anywhere there may be discoloration. Testing the flooring before installation gives you a good idea of what happened to it since it left the warehouse. The more measurements you take, the better you'll be able to determine the overall moisture content of the flooring.
Record the readings from the subfloor and the flooring with either a spreadsheet or with photos of the meter on the flooring with the reading prominently displayed.
This shows you properly measured the moisture content on the job site in the event any moisture-related difficulties arise later.5) Not Interpreting Data CorrectlyOf course, all these measurements are meaningless unless you know what to do with them. Many wood moisture meters aren't calibrated to a particular species or, if they are calibrated, it's to a generic specific gravity such as that of Douglas fir. You need to adjust the readings to the flooring you're working with to determine if the moisture content is acceptable for that particular species.Consult a chart or do a calculation provided by the manufacturer to get the correct moisture reading. Some meters on the market can calculate this information internally—all you have to do is punch in a certain code.6) Not Knowing the Area's MCTo interpret the moisture meter's data, you need to know the acceptable moisture content for the area of the country you're in. For example, the meter may read 12 percent moisture content, which is within the normal range for some regions but which is too high in drier, lower-humidity areas. See the "Moisture Content of Wood" chart on page 66, which lists acceptable moisture contents for wood at certain temperatures and relative humidities. Some contractors try to rely on old-fashioned methods of feeling the wood or trusting that the acclimation time was enough.They may not want to invest in a good meter, or they may be under pressure from the general contractor to get their work done faster. Whatever the reason, with the great potential for problems and the myriad meters available in different price ranges, styles and functions, there's no excuse for installing flooring without a moisture meter.By learning from the mistakes of others, you can effectively use this tool to protect your floor from the disastrous effects of moisture—and therefore from costly callbacks.