Be Aware of Water in Concrete

Wood Floors are Beautiful in the Bedroom TooWhen a client’s water heater flooded their Goodwin Heart Pine engineered wood floor the insurance company called in a restoration contractor. The contractor pulled up half the floor to the point where they said the water had gone in the concrete. After three days of dehumidification they declared the concrete dry.

Following the National Wood Floor Association’s procedure we used a concrete meter that requires drilling a small hole 40% of the depth of the slab. The meter readings were much higher than recommended to install a wood floor over concrete.

We pulled up the remainder of the floor so that the entire slab could be dried. And we provided the restoration contractor with the meter readings and a study on water movement through concrete. Fortunately, they agreed to bring back the dehumidification system and get the slab to the proper moisture content.

Wood floors are not rocket science; however, they do demand a scientific approach to water and subfloors of all types. Call if you would like us to send you the research paper on how to properly test concrete for moisture content.

Best wishes for great wood floors all the time for the longterm.

Antique Wood Flooring Myths

Download "Kiln Drying 101" by by Andrew St. James ARS PhD, COO Goodwin Heart Pine and Director of the company dry kiln.1) Some people think that antique wood does not shrink and swell anymore so it does not need to be brought to the proper moisture content on the jobsite.  On the contrary wood science and field experience both indicate antique wood shrinks or swells when the moisture content changes.  You need to install the wood at a moisture content that is close to the value that will be maintained while the building is in use.

2) We often hear the remark that old wood does not need to be kiln dried.  There are two issues here.  First, most air dried wood has a moisture content too high for interior use.  The second is the possible presence of living organisms such as powder post beetles, termites, or mold.  Kiln drying to 140 F for several hours eliminates live insect pests in the wood.  Proper kiln drying also eliminates living mold and brings the moisture content down to a level that wood will not support mold growth.  Click on the link to read more information about kiln drying in our article in WoodSource KilnDrying101 or click the thumbnail above.


How long should you acclimate wood flooring?

We are often asked How long it takes to acclimate wood flooring?  Many people have heard of bringing wood flooring to a jobsite in advance to let it acclimate, but still do not really understand the process in detail.  The goal should be to get the moisture content of the flooring close to what it will be when the space is occupied in the long term.  Additionally the moisture content of the subfloor and the rest of the jobsite should be near to the long term value before the flooring is delivered.  The HVAC should be operating.  Installing wood flooring in a wet building is an invitation to future problems.  Moisture meters are used to measure the moisture content of wood.

The next question that commonly comes up is How do I know what the moisture content should be when the floor is installed?  The answer depends on your location and possibly some of the details of the building.  One way to learn the desired moisture content is to consult an established wood flooring professional as they should know the long term moisture content values for their geographic area.  In existing buildings you can often measure other wood that has been in place for more than a year to get a number for the appropriate moisture content.

Getting back to the original question the correct answer is not given in terms of how long but in terms of achieving the correct moisture content.


Reclaimed Flooring Installation

ow that you have made the decision to install heart pine, you are ready to go. Some suggestions we feel might come in handy throughout the process are included in this section. Please click on any of the headings for useful information on everything from site preparation to sanding and finishing your new hardwood floor.

The subfloor: Your wood floor’s foundation

Nearly all squeaks and cracks can be directly traced to an inadequate subfloor. A sound subfloor is the crux of a sturdy floor. A plank subfloor should be at least 6″ wide boards installed diagonally to the joists. When installing a plywood subfloor, 3/4″ exterior grade is recommended if your finished flooring is 3/4″ thick. If wood flooring is installed over concrete, check for wetness by taping down a square yard of plastic for 72 hours to see if condensation forms. Once dry, you can install a joist system or just a grid of pressure-treated lumber (screed system) over the concrete. Align the edges with the joists for strength and stagger adjacent rows four feet. You can even cut the plywood into 4′ squares to create a smaller area over which each panel can move. Nail every six inches along each joist with 8D or larger nails. You can use adhesive before nailing to further reduce movement and possible squeaks.

If you choose to put in a sleeper (or screed) system over a concrete slab, dry pressure treated 2x4s are preferred. These should be 18″ to 4′ in length and staggered on centers with an air gap on all overlap joints. Lay them perpendicular to the direction of the finished flooring and secure them with T-nails staggered side-to-side 4” to 6” apart.

Leave expansion joints of at least 1/8 inch between each panel, section, or board of the subfloor. Research has shown that two or three years after the floor is installed the subfloor will measure 2-3% higher moisture content than the floor. The subfloor has less access to heating and air conditioning than the floor, and will expand slightly from the additional moisture.

Use a 6′ to 10′ straightedge to check the subfloor for high areas, and sand any high spot so the subfloor is as flat as possible. Next put down 30 pound felt paper carefully butt-edged, not overlapped. The felt reduces the chance of squeaks and helps circulation around the floorboards.


First of all, heart pine, like any wood, is a natural product. It is made up of tiny cells, which take on or give off water with moisture in the air, and will therefore shrink or expand somewhat with changes in relative humidity. The humidity levels inside a building will vary with heating or air conditioning seasons. As the humidity varies the dimensions of floorboards and any wood products will also change slightly.

Relative humidity in the dwelling should be stabilized at 40-60 percent. Be sure the drywall and sub-floor of the house are dry prior to installation. If the newly installed floor absorbs moisture from its surroundings it will expand and compress, but it will not decompress to the full dimension once the site dries.

Here’s how to best preserve your wood floor and all fine wood:

  • Turn the thermostat to your typical setting about three weeks before the flooring is due to arrive with all outside doors and windows in place. This will help to stabilize humidity levels between 40% and 60%, and establish an ambient temperature of between 50 degrees and 90 degrees Fahrenheit. It’s ideal to maintain these humidity and temperature conditions as much of the time as possible throughout the life of the building.
  • Some buildings may need a humidifier to maintain a healthy humidity level and prevent excess shrinking of the building materials.
  • Beware of leaving a house closed up with the air conditioning off during summer months when excess humidity may get trapped inside the house.
  • Season all concrete, mortar, and plaster areas a minimum of 60 days. You can check if concrete is dry by using a few drops of phenylthalene (available at most drugstores). Or you can use a vapor barrier test. Tape a 3’ x 3’ piece of 6 millimeter poly-film securely to the slab. Allow this barrier to remain secured for 72 hours, then remove and check for moisture under the film.
  • Check that crawl spaces are dry and well cross-ventilated. Even an old house can have moisture in the slab or water under the house. All that is required for these conditions to occur is for dirt to be piled up around the slab for landscaping or for the ground under the house to be lower than the ground around the house.
  • Direct rainfall or excessive moisture away from the structure with surface drainage. Good drainage is a 3″ or greater slope per every 10 feet. Build up the ground level under the house so that it is higher than ground level around the outside of the foundation of the foundation.
  • If you do have the potential for moisture intrusion from underneath the flooring, the treatment may be as simple as a layer of plastic taped under the building or between the slab and subfloor. Tape the plastic anywhere there are seams. Be sure not to pierce this vapor barrier with nails or staples when installing the floor.

There are many, many solutions to moisture intrusion depending on the type of construction and area of the country. For example, some of the oldest houses in southern Florida were built without any subfloor to provide maximum circulation for the floor. This is an extreme example and requires the best drainage and planning. We do not recommend it, but it serves to demonstrate the diversity of options that are available if you investigate the natural construction techniques for your location.


Ideal acclimation time is two to four weeks, with a seven to ten day minimum. Air temperature and humidity conditions that will exist throughout the life of the structure should be established well before the flooring arrives and left on during the entire acclimation time.

When delivering wood flooring to the site, do not unload in the rain, drizzle, snow, or extremely moist weather. While the wood is acclimating, it should be stacked so that air can circulate around each board. Use a good quality moisture meter to check your floor. Be sure the floor and subfloor are within 2% of each other’s moisture content at installation. The moisture content should be consistent board to board and section to section within 1-2%. If there is a variation of more than 2% in the moisture content of the more dense boards from the lighter boards, this is one sign that the floor may not be fully acclimated.


Check moisture content with a high quality, accurate moisture meter. The floor should measure 8 to 14 percent in most conditions and the floor and subfloor should be no more than 2 percent difference at installation. However, the moisture content of the floor should match the relative humidity of the environment in which it will be installed. If your indoor living areas are outside the range of 8 to 14 percent, you may want to consider special measures: additional acclimation time, a vapor barrier, or perhaps a humidifier or dehumidifier.

Site Preparation

All concrete, plaster and mortar projects should be seasoned at least 60 days before delivery of flooring materials. Always test concrete for moisture regardless of how long it has been poured. Check basements and crawl spaces to be sure they have good cross-ventilation. Wood floors require 1 1/2 square feet of ventilation per 100 square feet of floor. Surface drainage should direct rainfall or excessive moisture away from the structure. Keep sprinklers from spraying on the house around wood floors.

Plan the Layout

Take time to plan the layout of your wood floor so that the last few boards don’t have to accommodate all of the difference for an out-of-square room. Maintain a 3/4″ gap around the edge of the room. Never “zero-fit” the floorboards to the room. The floor must be able to expand in all directions without any pressure.

You can often hide any differences in dimensions around the room gaps around the edges of the room. Or you may be able to hide a tapered floorboard under a counter or along a wall that is not immediately noticeable when you first walk into the room.

Consider any special treatments such as “framing” doorways, fireplaces, masonry, or other protrusions into the room with wider boards and decorative effects. You can turn decorative boards perpendicular to the floor, screw and peg them, and join them at the corners with a 45-degree angle instead of a butt joint.

Board Selection

Select several straight boards for the first and last few rows. Some boards are naturally more crooked than others, and you can pull them into place easily when working in the middle of the room. The simplest way to get a crooked board into place before nailing is to drive a screwdriver into the subfloor for leverage. However, it’s easier to work with a straight board while you’re pulling up near the wall.

Laying the Floor

Lay the floor perpendicular to the joists if possible. If you decide to lay it parallel to the joists you’ll need an especially strong subfloor. Small marks at the base of the wall help locate the joists during installation. Stagger flooring during installation so that the end joints are at least 4″ to 6″, or farther, apart in any direction.

It is not necessary to end-match heart pine. Oak is often end-matched because the average board is only 2-4′ long. A heart pine floor usually averages 6-10′ boards. There will be some shorter pieces, but these can be mixed in or used at the walls.

Many professionals suggest that installation begin in the middle of the room. Flooring expands in the direction of the tongue, so any movement as humidity levels change will be from the center out instead of across the entire width of the floor. Use a center spline between the two facing grooves of the center boards. Others suggest that you install from one wall to the other, left to right if you are right handed. All agree that power nailers are faster and diminish the chance of hammer marks on the floor.

Always maintain a 1/2″ to 3/4″ air gap around all walls or protrusions. The floor must be allowed to expand without any pressure. You can cover the gaps easily with base and matching shoe moulding. Base and shoe moulding is usually nailed to the wall instead of the floor. Leave room for a business card (a very slight air gap) to slide on top of the floor and under the moulding. Undercut doorjambs for flooring to slide under.