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Wood Floor Restoration, Refinishing, Cleaning and Maintenance
This overview of wood floor coating is intended to help you broaden your knowledge of the steps in finishing newly installed wood floors, refinishing and restoring wood floors, and cleaning and maintaining wood floors. This information is applicatble to both hardwood floors, such as oak or maple floors and softer wood floors, like pine.
The key factor in selecting a wood floor coating is to determine what your specific performance needs are, and what kind of results you expect to achieve from your application. Different types of sealers and finishes present different performance characteristics and often present a trade-off of some kind.
A point of information which can be helpful in selecting the best material to finish a floor involves the sometimes misunderstood relationship between solids content and the ingredients used in a coatings manufacture. A materials solids content is not necessarily an indicator of a products quality. Wood floor coatings are generally composed of a solvent or aqueous carrier, into which a resin or polymer is dissolved, or dispersed; and a leveling agent, drying enhancer and/or a catalyst that prompts a chemical reaction, which forms the coatings film. The ratio of solvent to resin is the solids content. As an example, in a 50% solids wood finish, half of the finish will evaporate and the other half remains to form the film.
The quality of a finish is entirely dependent on the quality of the combination of raw materials used to make it. Manufacturers attempt to balance cost and quality of raw materials, and film formation characteristics to produce the best product possible for a particular range of applications. Materials which carry the same generic product name such as "polyurethane floor finish", and the same solids content, often contain different resins or combinations, and produce different film characteristics.
Both solvent- and water-based materials generally form a film in one of two ways; drying through evaporation of the carrier material, or curing through a combination of evaporation and chemical reaction induced by a catalyst, or cross-linking initiator. These two categories present some different considerations in both performance and application.
In the instance of single component materials that dry by evaporation, floor temperature and humidity are a primary consideration. These factors must be considered during the application of any product that forms a film through evaporation, to avoid problems that are annoying and sometimes costly to correct. First, floor and air temperatures are often different. In application sites such as gymnasiums which have high ceilings, forced hot air heat, and may be laid directly on a concrete slab or have an unheated sub-basement underneath them, the floor temperature can be a number of degrees lower than the air temperature. We recommend that wood floor finishes not be applied if the "floor" temperature falls below 60o - 65o Fahrenheit. If materials are applied to floors at lower temperatures, various problems can result including significantly extended drying times, peeling and lack of gloss. Also, high humidity conditions inhibit the evaporation of water or solvent carriers from a finish, and can result in similar problems as those encountered with a cold floor. One notable exception to the problem of humidity-related extended drying times are moisture curing urethanes. As the name suggests, these materials cure in the presence of moisture; and high humidity conditions can cause these materials to cure so quickly that there is insufficient time to blend parallel applications of sealer, allow the coating to level properly, or allow for sufficient penetration to achieve adequate adhesion.
Catalyzed or two-part materials as this name implies consist of a base material that provides the primary ingredient for film formation, and an additive that initiates a chemical reaction and causes the material to cure. These materials tend to be more durable and chemical resistant, particularly in the case of water-based materials, than are their single component counterparts. Once catalyzed, they all have a limited application time, and some may only be catalyzed once, after which they are rendered unusable so it is best to mix only what is immediately required. These materials can also be effected by low floor temperature that can slow down, or even stop the curing process. The floor preparation procedures are generally the same as the procedures for single part materials and may be applied using basically the same types of applicators and techniques.
Oil-Modified or Polyurethane Finishes are one of the most commonly used materials offering a wide range of applications on both new and in service wood flooring. Polyurethanes offer an excellent combination of high gloss, depth of appearance, durability and reasonable cost. They are offered in a wide range of solids contents for different applications and effects with 40% materials generally being used as penetrating-type sealers, and 50% polyurethanes used as finish coats. With correct floor preparation, polyurethanes are relatively easy to apply, have positive adhesion characteristics; and with some variations among different manufacturers materials, are generally easy to recoat. Polyurethane finishes usually dry within 4 to 6 hours depending on prevailing environmental conditions. This can be a consideration if a floor must be taken out of and put back into service quickly. Additional considerations are that polyurethanes are inclined to darken somewhat over time, are degraded by constant exposure to ultraviolet light, and are most effectively removed either mechanically by sanding or grinding, or chemically using a methylene chloride-based stripper or a solvent. Although the odor associated with polyurethane is not overly unpleasant, they do have a noticeable solvent odor and are generally combustible. Clean up must be accomplished with a compatible solvent such as mineral spirits, napthol spirits, or waterless cleaner; and waste must be disposed of under EPA and state guidelines.
Moisture-Curing Urethanes represent another coating for wood. This material is only available in very strong smelling, highly flammable solvents, or hazardous acetates which requires the use of respiration equipment. The adhesion characteristics of moisture-curing urethanes also require meticulous floor preparation or they are prone to peeling. These materials also do not adhere well to themselves, and because they form such a hard surface are difficult to roughen up via sanding or disking, making them more difficult to recoat than other materials. Due to their high degree of durability and hardness they can even be a challenge to remove by sanding. Clean up must be performed with a solvent such as toluene, again requiring disposal in compliance with government regulations. Exacting preparation, application and handling properties, higher prices, coupled with environmental regulations and health considerations, have led to a decline in their use as an everyday coating material.
Solvent-based epoxies are another product which provide excellent performance from an appearance and durability standpoint, but present many of the same considerations as moisture curing urethanes, require meticulous floor preparation and are more difficult to recoat than polyurethanes or solvent-based acrylics.
Water-based coatings for wood flooring are gaining increasing popularity primarily due to environmental and health concerns. Increasingly stringent VOC (volatile organic compound) emissions regulations, disposal concerns, and health concerns over exposure to some of the solvents used as carriers for the resins are turning more attention to water-based coatings.
The advantages of water-based coatings are that they generally have a lower level of odor than solvent-based coatings, are less or non-flammable, and easier to clean up without presenting the disposal problems associated with solvent-based sealers. The drawbacks to water-based products are that they are usually not as durable, and are often much more expensive than many solvent-based materials. Water-based coatings involve similar procedures for floor preparation as those required for solvent-based systems. As with solvent-based coatings, there are two general groups of water-based materials; single component and two component coatings. Again, the single component materials dry by evaporation of the water used as a carrier, while the two component materials cure through a combination of evaporation and chemical reaction. In most cases, the two-component materials are the more durable and chemical resistant of the two products.
There are currently two materials that are most often being used as base materials for water-based products; urethanes and epoxies. Both materials performance characteristics are dependent on the specific base urethane, or epoxy, used in their manufacture. Water miscible-urethanes or epoxies, are rarely used in their pure forms in floor coatings. Both materials are usually modified with some form of acrylic polymer. This also applies to the water-based epoxy coatings currently available. The higher the proportion of urethane, or epoxy, the more durable the coating is.
Due to their beauty, durability, and relative ease of maintenance, wood floors have historically dominated the sport flooring market and, after a downturn due to the extensive use of carpet, are regaining their level of popularity in both commercial and home floor applications. Many wood floor manufacturers have reduced the initial need for additional preparation or sealing by applying some type of factory finish. There are several types of materials that may be used. Seal-and-wax and urethane factory coated floors are the most common.
Seal-and-wax floors are usually first coated with some type of penetrating, or surface sealer, which could include polyurethane, alkyd resin-based, or lacquer-based and then finished with an application of hot melt carnauba, or synthetic-based wax. Urethane finishes are applied with rollers, or squeegees, and then dried by infrared lamps, hot air, or ultraviolet curing depending on the type of urethane applied.
Unlike the aforementioned coatings which are principally surface-coating procedures, a method which is becoming more common is acrylic impregnation. This is a procedure by which liquid acrylic, is forced, under pressure, through the entire thickness of the wood. Proponents state that this procedure increases the woods resistance to water absorption and swelling, denting and other damage, and improves its fire-resistance rating. Most of these finishing procedures will give the floor a reasonable appearance and level of protection, but many wood floor owners, especially in commercial applications such as gym flooring, find that factory finishes can fall short of their requirements and desire a more attractive and durable finish.
As is generally the case with any floor finishing procedure, correct and thorough preparation is the initial key to obtaining optimum results from any type of wood floor sealer or finish.
Floors are sanded for several reasons; to bring an newly installed floor to a uniform grade, to remove existing finishes, or to smooth and open the pores in a floor surface to provide a smoother appearance and proper adhesion of finishes. The grit or coarseness of the sandpaper used depends on what is being accomplished. Coarser grades (40-80 grit) are used for leveling floors or removing finishes, while finer grades (100-120 grit) are used to finish sand.
Sanding of wood floors is a procedure that borders on being an art form, and is best done by experienced professionals. High-speed drum and belt sanders can severely damage a wood floor literally in the blink of an eye, if used incorrectly. Even the briefest pauses while sanding can leave gouges, or valleys, in a floor, some of which will not be seen until finish is applied, but will then stand out like a neon sign. Although it is possible to repair this type of damage, it involves sanding the rest of the floor to the grade of the valley, a tricky and expensive proposition that reduces the overall lifespan of the floor.
If it is necessary that someone sand the floor other than a professional, it is strongly recommended that the procedure be performed with a random orbital or rotary buffing type machine. Although the procedure will take longer and require more labor, use of this type of machine is much less likely to result in damage to a floor and ultimately will yield the same results as a high-speed drum sander. These types of machines are also commonly used to prepare existing finishes for recoating.
Following sanding, the floor should be swept, or vacuumed, to remove large quantities of wood dust and dirt. Next, tack rag the floor with a turkish towel or other tack rag treated only with Perma #250 Waterless Cleaner or pure mineral spirits to remove fine dust or dirt and any oily residue. Avoid tacking with rags treated with a less refined oil-based material such as kerosene or a wax-based treatment that could leave a residue and cause poor adhesion and peeling.
Depending on the condition of the existing floor, there are two ways previously coated floors are prepared. If the floor is severely worn, gouged, or otherwise damaged, it may need to be sanded back to bare wood. The floor would be treated as a new wood floor and sanded with a drum or belt type sander as previously described.
Most wood existing floors do not need such aggressive preparation. If the floor is mildly scratched and worn, it can usually be lightly sanded using a screen disk. Screening disks are open mesh abrasive screens that are used on rotary 300-rpm rotary buffing machines. Often, floors in good condition are screened with 120 grit screens. If the floor is in tougher shape, 100 or even 80 grit screens can be used. If a more aggressive screen is used, it is advisable to rescreen the floor using a 120 grit screen to remove some of the swirl marks.
Again the floor should be swept or vacuumed and tack ragged as indicated in the previous section to remove wood dust and dirt.
When recoating an existing floor, consideration must be given to product compatibility. If an existing coating is not compatible with the new coating, problems such as peeling can occur. Assuring compatibility can be accomplished in one of several ways. The most obvious is to recoat with the same product that is already on the floor provided the material originally used lends itself readily to recoating. Moisture-cured urethanes and epoxies, for instance, are very tricky to recoat and often exhibit poor adhesion even when recoated with the same material. Most coatings generally must be roughened up by sanding or disking to achieve adequate adhesion. If the nature of the existing material is known and the desire is to recoat with a different material most manufacturers of wood floor finishes can generally give advise regarding whether or not a new material will be compatible with their existing finish. The safest method of determining compatibility, especially if the composition of an existing material is unknown, is to select a small unobtrusive area and apply a small test patch. If, after a couple of days, the material does not exhibit any signs of bubbling, peeling, or reduction in film integrity then it should be safe, following appropriate preparation, to seal the entire floor.
No wood floor sealer or finish is indestructible. Although they are formulated to provide the most attractive appearance and maximum durability possible, they are all subject to wear due to the harsh, high traffic conditions that are encountered in gymnasiums, manufacturing and business locations and, to a lesser extent, in residential applications. An inadequate maintenance program can significantly aggravate these wear conditions. The greatest contributing factor to the premature demise of any wood floor finish is the belief that once they are put down, they are so tough that you dont have to do anything to take care of them.
Maintenance procedures should be tailored to the specific traffic conditions and obviously must take into account the availability of labor and resources at a particular location. The more severe the traffic conditions the greater the degree of maintenance necessary to get the maximum life expectancy from a finish.
Wood floors should be dry mopped, or swept, as often as needed to keep abrasive sand and soil off of the floor. The continued presence of abrasives will act like sand paper and degrade a wood floor finish faster than any other single factor.
In many cases, dry mops will be treated with some type of mop treatment to improve the mops ability to pick up and hold soil. Correct use of oil-based mop treatments requires that mops be treated 24 hours before they are to be used. This allows the oil to be absorbed into the mop and the solvent carrier to evaporate completely. If used incorrectly this type of treatment can create safety and sealer, or finish, application problems. Sometimes maintenance personnel are inclined to apply the oil-based treatment and then almost immediately use the treated mop to sweep the floor. This usually results in an oily residue being left on the floor which can, with routine use, cause the floor to become slippery, retain dirt and if not removed completely prior to recoating, cause adhesion problems.
Perma recommends the use of a water-based mop treatment such as Perma #135 Aqua Treat. Water-based mop treatments, which are comprised primarily of surfactants and acrylic resins, are less likely to cause the same type of problems that are associated with oil-based treatments. Use of #135 Aqua Treat or other water-based treatments minimize the buildup of treatment on the floor as it is readily removed by damp mopping with either water-or-solvent-based cleaners. It is also easily removed from dry mops by washing with detergent and water, making them easier to maintain and consequently more effective. Although it is advisable to treat mops the night before when using water-based treatments, particularly if used at full strength, they can be used within hours after treatment without causing any significant problems. Any residue left by their use usually dries without leaving a sticky or slippery residue and can be removed with routine washing. The dry mops themselves should be washed routinely to avoid a buildup of dirt and soil that, if not removed from the mop, will ultimately be redeposited onto the wood floor with subsequent sweepings.
In addition to routine sweeping, sealed floors should be washed daily if possible and a minimum of once per week.. Washing removes the fine dirt and dust that is not picked up by dry mopping. This fine dirt and dust can create very slippery conditions if it is allowed to accumulate over time. Washing also removes residues left from oil-based or water-based mop treatments or the oily residue from human perspiration often encountered on gymnasium floors. Well-sealed floors can be washed with a good neutral cleaner such as Perma #127 Synthetic Neutral Cleaner or #70 Stand Up if increased slip resistance is desired. More highly alkaline cleaners such as #129 Super Blue or #100 Traction Clean can be used particularly if there is a heavy soil problem which needs to be addressed. Constant use of alkaline cleaners, however, can prematurely dull down the gloss of the finish. A good Waterless Floor Cleaner such as Perma #250 or pure mineral spirits, can also be used to maintain wood floors, particularly if there is any indication that there are bare spots where the sealer has been worn away. The use of water-based cleaners on an unsealed wood floor can cause blackening and raising of the grain.
Appearance of urethane beads between boards - Almost every wood floor has some separation between boards. When the air is cold and dry, and homes are being heated, wood floors lose some of their moisture and shrink. As a result of the shrinkage cracks appear between the boards. These cracks may be the thickness of a dime for solid 2-1/4" wide strip oak floors. Once the humidity increases and the heat is turned off in the spring, wood floors will begin to reabsorb moisture and cracks will close up.
If floors are sanded and resealed during a period of very low humidity (like winter) the sealer will flow into the cracks between the boards. This can produce a thick column of urethane between the boards. Where urethanes are air dry materials, the solvent evaporates at the surface and dries, but traps the remaining solvent in the column leaving the urethane uncured. When the humidity increases and the openings between the boards begin to close due to expansion, the undried sealer will be forced to the surface and form wet or tacky beads between the edges of the boards. If this situation occurs, allow the beads of sealer to cure completely, and remove them with a putty knife or scraper.
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