Water Damaged Hardwood Floor Drying
Water damaged hardwood flooring can be indentified by cupping, warping, discoloration and flaking of the surface. Water damaged wood floors are one of the most difficult materials we dry. Besides being dense and coated with vapor barriers, they can also reach a “point of no return” if the water damage is not promptly addressed. In the water damage restoration industry, damaged wood flooring is one of the most challenging materials to dry. DryHero has the experience, training and moisture testing instrumentation to inspect, evaluate and recommend the best restoration options for your wood flooring system.
Time is Not on Your Side
When it comes to water damage and wood flooring, time is definitley NOT on your side. Wood plank flooring can sustain permanent structural damage as well as mold growth between the finish floor and subfloor. Mitigation decisions should be made promptly. I urge people to do their best to prequalify the wood flooring “expert” that will help them determine what actions, if any, should be taken. This point can’t be stressed enough. You don’t want to needlessly tear out a perfectly good wood floor. However, the more floors I dry, the more careful I am to identify all the potential challenges. In the end, I want what is best for my client, even if that means I have to pass on a job.
Moisture and Wood Floors
There are numerous factors that affect how a wood floor will react to moisture. No wood flooring system will tolerate high levels of moisture over an extended period of time, but some do better than others when it comes to surviving water damage.
Solid wood floors have the highest salvage potential because you’re dealing with 100% real, solid wood planks. There are no resins, veneers or composite materials to deal with. In general, a solid wood floor can be sanded and refinished several times in its lifetime. So if you can control the moisture and stabilize the flooring system, refinishing can restore even badly damaged floors.
The harder the wood, the more slowly it will react to moisture. Oak flooring will react to moisture within a day or two whereas a hard maple floor may not cup for three, four or more days. The harder the material, the slower it absorbs moisture and the slower it will release it. Some softer wood floors (such as southern yellow pine) can be exposed to significant moisture yet only slightly cup, increasing the potential to underestimate the damage.
Another variable to how water damage affects solid wood flooring is whether it was finished on-site or pre-finished. Floors that are sanded in-place usually have a fairly continuous finish on them, reducing the rate at which they can absorb (and release) moisture. Pre-finished, solid wood flooring has the finish applied at the factory. To account for slight variances in the product thickness, manufacturers bevel (or “kiss”) the edges for a uniform look. Factory finishing produces a high quality finish, but the bevels will allow surface moisture to absorb into the wood at a higher rate. As a result, prefinished wood floors tend to suffer more from flood damage than traditional hardwood flooring.
Parquet flooring, although solid wood, has a much lower salvage potential. High quality parquet will be more forgiving than low-cost varieties, which are seldom worth saving. Since it’s glued and not nailed to the substrate, excessive exposure to moisture causes the adhesive to release, even before the wood cups.
Engineered wood, although more stable when exposed to minor moisture, has a major disadvantage. It has a veneer wear layer anywhere from 1/32” to 5/16”so it often can’t be refinished. Refinishing a floor removes 1/32” - 1/16” of material so you have to do your homework researching the material prior to evaluating the floor drying project. When the property owner has saved a sample wood plank or has any leftover flooring it will help identify the wood. Engineered wood floors always have beveled edges and you can also identify them by removing a floor vent and inspecting the plank’s cross section for laminated layers.
Laminate floors have a low tolerance for moisture. The high-density fiber core permanently swells when it absorbs water and cannot be saved. You can identify water damage to a laminate floor by inspecting the edges of the planks for swelling. Like solid wood flooring, it is possible to spot repair laminate floors but it’s often difficult, even with spare material. Since water can remain trapped beneath the laminate floor padding, it’s important to thoroughly test for moisture at the substrate level. Laminate floors are not restorable after swelling from moisture. If the laminate floor has a significant amount of water beneath the padding but the flooring has not yet swollen, drying may be possible but is unlikely.
Never Sand a Wet or Cupped Hardwood Floor
This is Wood Floor Refinishing 101. You never sand a wood floor until it’s completely dry. As elementary as this is, it can easily happen. Several years ago, the company I was working for had a flood restoration project that had cupped oak flooring. About a month after we refinished the floor we received a call from the client where he stated that the floor looked like a “washboard”.
Upon closer inspection, the floor was indeed “crowned”. After auditing the job file I found the wood floor contractor’s invoice. The oak floor had been sanded exactly five weeks from the date of the original water damage event. As the restoration professionals, we should have known better. We had to refinish the floors for the second time in two months. Needless to say, this was costly if not embarrassing for the company and a major inconvenience for the client. Although this is a rare mistake, I think it’s of value to know that it can happen and it validates the argument of completely drying a flooded floor before refinishing it.
Wood floor drying, like the rest of the structural drying industry, has greatly improved in the last few years. Specialty drying systems make it possible to successfully restore wood floors to pre-loss condition in about one week. Furthermore, the majority salvageable floors will not even require refinishing after being dried down properly.
Keep in mind that floor drying is a challenge for even the most experienced water restoration and drying professionals. Simply installing a wood floor drying device will NOT produce results. It is only part of a larger drying system. So property owners should ask water damage restoration contractors a lot of questions and have them explain to you how their drying processes work. You’ll both benefit from it.
Drying wood floors is labor intensive, but compared to the cost of replacement, it makes a lot of sense. Now take into account intangibles such as air quality, project duration, collateral damage and client satisfaction. Drying wood floors really is a “no brainer”.
WOOD FLOOR RENOVATION PROBLEMS
Finish or oil will bring out the best in a wood floor. They can also highlight marks and mistakes. Sometimes a problem only becomes evident after the finish has been applied. After applying finish, you can’t just sand away an ugly mark in a small area and put a dab of finish on top. The area of new finish will show up and be clearly visible. Unfortunately, you may have to start the whole floor all over again. On the next few pages, we show a few examples of what can go wrong. They emphasize the importance of not only choosing the right products but of using them in the right way.
Score marks all over the floor:
Sanding a wood floor is a gradual step-by-step process. If you go straight from a coarse to a fine sanding, for example, the result could look like the floor in the photo. We recommend three steps or more as shown below.
1. Coarse sanding. The purpose here is to remove dirt, old finish and marks on the wood. The most common practice is to start with grit 36 or 40. In exceptional cases, with very uneven floors or pine floors coated in old finish, you may decide to start with grit 24 or even grit 16.
2. Medium sanding. Next we recommend medium sanding with grit number 50 to 80, which will remove traces of coarse sanding and starting marks.
3. Fine sanding. The fine sanding is usually done with grit 120. If you use solvent-based finishes, you can use grit 100 for the final sanding and still obtain a well-bodied surface. However, with a water-borne finish, the final sanding should be done with grit 120 or finer.
After fine abrasion, deep grooves remain if you miss out the medium sanding. To obtain a good result, never jump from a coarse to a fine grit size.
Long scratches:
Unless you are really observant, it is easy to miss scratches on the surface of the wood after it has been sanded. But once the finish or oil has been applied, these scratches become painfully visible for everyone to see.
The problem may be due to a poor abrasive with pieces of grit that become easily detached. Even if you vacuum clean the floor after each sanding step, you do not always remove loose pieces of grit. Some of them remain in cracks in the floor.
The vibrations of the machine as it passes over can make them bounce up again and they could fasten under the back wheels or in the abrasive itself. The sharp pieces of grit can fall off the surface of a poor quality abrasive. Good abrasives are made with high quality adhesives to hold the pieces of grit in position and minimize the risk of scratching.
Tip: After every change of grit number, vacuum clean the floor because any coarse grit lying around can damage the finer abrasive that follows.
Chatter Marks:
This is one of the most common problems flooring contractors encounter and the cause of many complaints from customers. The chatter marks only become visible after the finish has been applied.
There are several possible causes:
• Parts of the floor flex up and down as a heavy sanding machine passes over.
• The abrasive is not tightly fitted on the belt or drum sander.
• A badly balanced drum.
• A shuddering movement in the sanding machine.
• The abrasive is not clamped in properly around the drum and protrudes slightly.
• An overlapping seam on the belt rubs against the floor.
Regarding the last of these causes, the problem is easy to avoid by using a belt with a flat butt joint.
The wood is darker around the edges:
Wood has its own natural color. When a coat of finish or oil is applied, the color will change. The way the floor is sanded influences the final shade. A coarse abrasive makes the surface rougher. The finish or oil will tend to penetrate deeper into the wood than when using a fine abrasive and the color becomes darker. That’s why it is important to use the same grit size for the main areas of the floor as for the edges and corners.
Tip: Whatever grit you use for the main part of the floor, use the same grit for the edge of the room and corners.
Nibs - Abnormal grain-raising:
If you sand properly and use grit 120 or finer for the final sanding, there usually aren’t any problems. However, if a coarser abrasive than grit 120 is used, the finish tends to penetrate deeper into the pores of the wood and gives more grain-raising. This is just one possible reason why abnormal grain-raising occurs. Another is the amount of finish you use. If too much finish is applied on the sanded wood, more water comes into contact with the wood fibers and more grain-raising occurs. Follow the recommendations given by the manufacturer.
If the first coat of finish hasn’t been given enough time to dry, this can also cause grain-raising. Suppose abrading is performed as soon as possible after applying the finish and then another coat of finish is applied immediately after. As the underlying finish hasn’t had time to dry properly, the new coat can penetrate through to the wood and more grain-raising occurs. Naturally, some species of wood are more vulnerable to grain-raising than others. Pine is particularly problematic.
Tip: Remember that proper sanding is very important when abrading between coats. Do not use a disc sander to abrade a water-borne finish as it creates too much friction and can cause swirl marks.
Swirl marks in the finish:
The commonest reason for these scratches is if the contractor has started to abrade too soon. At this stage, the surface of the finish is still slightly sticky. Most of the water has evaporated but the coalescing agents are still evaporating. These evaporate quite slowly. If you start to abrade the floor now, there’s a good chance that the finish will fasten on the abrasive and scratch the surface.
A good way to check if the finish is dry enough to abrade is to touch the finish with the back of your hand. If it feels cold on the surface, then drying is still in progress and you will have to wait a little longer. If you open a window to create better air circulation, you will speed up the drying process.
Tip: Let the finish dry properly before abrading.
Poor adhesion:
Most types of pre-finished wood floors are suitable for over-coating but not all. With a few of them, the finish just won’t adhere no matter how carefully you abrade. If you want to recoat a pre-finished wood floor, you must check that the finish will actually adhere. Do a test on a small area. If the test is successful, you should abrade the floor very carefully preferably using the Scrad system.
Alternatively, use a grit 150 abrasive disc with a sanding machine to avoid marking the finish applied at the factory. A new coat of finish will not adhere to a floor that has been waxed or polished. In that case, you have no choice but to sand back to the bare wood.
Tip: A coin is a way to test the adhesion of the finish to the underlying surface. If the finish starts to flake off when rubbed, adhesion is poor.
Black dots:
These dots are due to metal shavings or loose grit from the abrasive reacting with the finish. That’s why it is very important to vacuum clean carefully. The dots are actually larger than a piece of grit and are almost black in color no matter what was the color of the original abrasive grit. The finish reacts with the metal present in the grit to form a dark substance. This substance also discolors part of the wood immediately around the piece of grit.
If you look at the spot through a magnifying glass, you may be able to see the piece of grit sticking up in the middle surrounded by a ring of color.
Tip: To avoid black dots, vacuum clean carefully. Don’t sharpen scrapers in a room where you are going to apply finish. Check regularly that the drum of your belt or drum sander is properly adjusted.
The Seasoning of Lumber
Freshly sawn lumber begins to lose moisture immediately. Its color will darken and small splits or checks may occur. Movement of moisture continues at a rate determined by many factors, including temperature, humidity and air flow, until a point of equilibrium is reached with the surrounding air. The shrinking and swelling of wood are dimensional changes caused by loss or gain of water.
In Practical Terms, the Process Works Like This:
1.) A standing oak tree is felled and sawed into a board 1-inch thick, 10 inches wide and 8-feet long. Placed on a scale, the board weighs, say, 36 pounds.
2.) The board is placed in a stack of boards separated from the next by stacking strips of uniform size to keep the board straight. The stack is aimed at the prevailing breezes to accelerate drying. After two or three months of air drying, the board now weighs 25 pounds. It is also 31/32-inch thick, 9 3/4 inches wide and 8 feet long, with 25 percent moisture content.
3.) This 25-pound board is trucked to the flooring mill and loaded into a dry kiln, a building large enough to hold three or four railcar-loads of lumber. After six or seven days, this same board is now 5~inch thick, 9.2 inches wide, 8 feet long. It weighs 21.6 pounds with an 8 percent moisture content. If aH the moisture were removed, the board would weigh 20 pounds.
The Milling of Lumber
Most hardwood lumber is dried to an average of 6 to 9 percent moisture content before milling is begun. Mill inspections conducted by the National Oak Flooring Manufacturers Association, allow 5 percent of the wood outside this range, to a maximum moisture content of 12 percent. The 6 to 9 percent range is likely to be the average of all types of wood products used in a normal household environment, assuming usual heating and cooling equipment is used to ensure human comfort.
Wood Flooring Has A Comfort Level
Wood flooring will perform best when the interior environment is controlled to stay within a relative humidity range of 30 to 50 percent and a temperature range 60 to 80 degrees Fahrenheit. Fortunately that’s about the same comfort range most humans enjoy. The chart below indicates the moisture content wood will likely have at any given combination of temperature and humidity. Note that equilibrium moisture contents in the recommended temperature/humidity range (shaded area) coincide with the 6 to 9 percent range within which most hardwood flooring is manufactured. Although some movement can be expected even between 6 and 9 percent, wood can expand and shrink dramatically outside that range.
All The Way to The Floor
Flooring is usually dried to the national average moisture content expected in use so that shrinkage and swelling are minimized and buckling or large gaps between boards does not occur. However, the careful drying and manufacturing of wood flooring cannot entirely prevent an unsuccessful installation.
Manufacturers who have controlled storage may control the moisture content of the wood up until the point it is placed on the truck for delivery. Various parts of the country have EMCs that range from the dry, desert areas of the Southwest (under 5 percent EMC) to the moist areas along the Gulf of Mexico (over 10 percent EMC). Additionally, a wide range of relative humilities can be experienced between individual job sites in the same locale, such as an ocean-front or lakeside home versus one that’s a few miles inland.
Many manufacturers record moisture-meter readings before the flooring leaves the facilities, and such readings are attached to invoice and packing lists. The use of moisture meters, from manufacturing to distribution to installation, is discussed further on.
Dimensional Stability
When flooring manufacturers and distributors talk about relative stability of various wood flooring species, they are referring to how a floor “moves” once it is put down.
The numbers in the accompanying chart were developed by the Forest Products Laboratory of the U.S. Department of Agriculture. They reflect the dimensional change coefficient for the various species, measured as tangential shrinkage or swelling within normal moisture content limits of 614 percent. Quartersawn wood will usually be more dimensionally stable than plainsawn.
The dimensional change coefficient can be used to calculate expected shrinkage or swelling. Simply multiply the change in moisture content by the change coefficient, then multiply by the width of the board.
Example: A red oak (change coefficient = .00369) board 5 inches wide experiences a moisture content change from 6 to 9 percent—a change of 3 percentage points.
Calculation:
3 x .00369 = .01107 x 5 = .055 inches.
In actual practice, however, change would be diminished in a complete floor, as the boards’ proximity to each other tends to restrain movement.
Growing Boards
How much can temperature and humidity affect the dimensions of a hardwood floor? Take a look at one 5-inch red oak plank board:
1) Within “normal living conditions” (say, an interior temperature of 70 degrees and a relative humidity of 40 percent), the board has a moisture content of 7.7 percent and is 5 inches wide.
2) If the relative humidity falls to 20 percent, the moisture content of the board will be 4.5 percent, and the same 5 inch board will shrink by .059 inches. Across 10 feet of flooring that could translate to as much as 1.4 inches of shrinkage.
3) If the humidity rises to 65 percent, the board’s moisture content would be 12 percent and the same 5-inch board would expand by .O79 inches. Across 10 feet of flooring, this could translate to 1.9 inches of expansion.