Hardwood Flooring
Hardwood Flooring

How many times can you sand a wood floor?

This is a very common question I have heard over the years, “How many times can you sand my wood floor?” There are a number of variables that we can talk about for a little bit that should help you.

1) What type of flooring is in your home?

Wood flooring is milled in a variety of thicknesses. In order to make sure we just level the discussion between engineered flooring and solid wood flooring, the area that is capable of being sanded is the wear-layer. The wear layer for solid flooring tends to average about 5/16″ thickness. For engineered flooring, this can vary to as little as 1/32″ to 5/16″. This is why I encourage all of you to really evaluate your engineered wood floors at the time of purchase. We did a video on this a while ago that you can view here.

If you have flooring with a very minimal wear layer thickness 1/16″ or less (or a hand scraped engineered floor), then honestly your best option is total replacement in most cases. We have successfully refinished floors with no greater than 1/8″ wear layer, but this requires a cautious approach.



This can be done by either pulling a floor vent and looking at your floor from the side. All of the wood that is above the tongue of the board is yours to sand. If you have floors on concrete, then either try to pull a transition strip at a junction with carpet, linoleum, etc.. or look at a piece of the original flooring. Sometimes, you cannot determine the wear layer of a floor if you cannot determine the name of the manufacturer and the products specs. In these cases, I recommend you do a test sanding in somewhere like a small closet in a corner with an edger. Although this is risky, the affected area will be out of sight.

 2) Sanding skills and Approach are Essential

My industry is one that lacks an established set of benchmarks for knowledge before you can make it your career. Moreover, many contractors who have only been educated by the generations of contractors before them tend to stick to the same sanding procedures that worked in the 50’s. Guess what? In the 50’s virtually every wood floor in any home in America was solid floor with a thick wear-layer. Many of the old school sanders in this business believe in starting with extremely coarse grits (36grit or 40grit) and cutting floors 3 times or more with a belt machine in order to achieve a flat floor. With the luxury of a 5/16″ wear layer, this is an okay method because who cares if you remove 1/8″ of sanding life? You still have plenty left.


If you know that you have a thinner wear layer (such as 1/8″) then it is imperative that the floor be sanded only one time with a belt machine using no more than 80 grit paper on a lighter head pressure. Although this may not remove every little dent and ding in the floor, these can be filled with something like a Mohawk touch up filler. All you are trying to achieve is a complete removal of the old finish. Proper hard plating of the floor after the belt machine will give the floor the desired flatness. Preserving the look of your floor by not sanding through the veneer is more important that anything in this case. The cost of removing and replacing some wood floors is quite high in certain circumstances.

The National Wood Flooring Association specifically references the question in this blog post, and they default to the skill of the operator of the sander as being most pivotal. In addition, the NWFA generally does not recommend refinishing wood floors with a wear layer of less than 3/32″.


3) What About Sandless Refinishing?

I’m sure that the idea of refinishing wood flooring without sanding conjures up ideas with the public of being so clean and effective. This procedure has been implemented in a few different versions with franchises such as NHance, Wood Doctor, etc… and if you search online or talk to a neighbor, you will find that the promises outweigh the value. In sandless refinishing, the company will typically clean the floor and prepare it for chemically bonding a new finish layer. Afterwards, they apply a tinted finish coat that will obscure the look of the scratches and restore the color somewhat. This procedure can work with some success, just be aware that the procedure is not likely to flatten the floor at all, so your dents and dings will remain.

If you have talked to your friends or neighbors, then you’ll likely hear people talk about “buffing and coating” a floor, which is a very light sanding. This procedure is akin to sandless refinishing, but involves a very mild abrasion of the existing finish coat in order to remove cursory scratches and provide a “tooth” to which a new finish coat can adhere. Sandless refinishing relies more on chemical processes to create adhesion for a new finish coat instead of a mechanical bond. We have done lots of clean and coats to floors, some of which had a wear layer that was unable to be sanded. These procedures will work well.

In the end though, make sure that you prepare a list of questions and discuss all options. I’ve been told by many industry colleagues that many sandless franchises really push their system because they are highly profitable even though the results are not long lasting. An honorable contractor will help you determine which method is possible and provides the best value.



I really hope that you have learned something here, but if you are still confused, email me or call me. I am absolutely glad to help you in any way possible.

A great resource for homeowners in regions where we are unable to provide service (outside of Sacramento, CA) I encourage you to search for an NWFA certified professional with the “sand and finish” certification. These individuals are held to a standard and code of ethics as contractors and will help you make a good choice with integrity. Do not confuse an NWFACP contractor with a general NWFA member, which means they simply paid to be a member.

Acclimation versus flooring type

The last ten years in the wood flooring industry have seen an incredible growth in the diversity of wood species available for flooring. Because of this, consumers need to understand something important, flooring will behave (in terms of seasonal movement) many different ways depending on the specie you choose. It is also important that when making purchases, that the seller has a thorough understanding of the material and how it will behave in differing environments, such as radiant heating, concrete, or even different areas of the country.

Below I have placed a picture that diagrams what wood flooring cells look like up close. Wood is kind of like a sponge essentially and the area that gains and looses moisture is the lumen. Lumen thickness can vary quite a bit depending on the specie of wood. For example, many exotics have larger lumens than traditional domestic flooring like red oak. This means that exotics generally have more potential for shrinking and expanding in comparison.


So if you take an exotic wood such as Ipe (brazilian walnut) and assume that it’s acclimation will be as rapid as traditional rules for oak, then you are making a mistake. A wood like Ipe can take two to three times longer to acclimate than a domestic like red oak.

A second factor regarding wood floor stability is width. The formula for determining wood floor expansion or contraction for solid flooring is:

Percentage moisture change in flooring x dimensional change coefficient x width of board

Let’s do a problem for example. Let’s say that our 5″ wide hickory floor lost 3% moisture after installation. I chose hickory because it is generally less dimensionally stable than other flooring.

3 x .0041 x 5 = 0.0615 Doesn’t seem too bad, but in reality that’s about 1/16″ for each board. I can tell you reality is that the gaps may be even bigger depending on the other factors involved, that I will discuss in the next blog.

I have yet to meet anyone who pays for a 5″ hickory floor (or any wood floor) who will accept a uniform 1/16″ gapping across the whole floor. Looking at the example, you can see if we change certain variables, that we can improve things. There are only TWO variables in the equation that we can influence if you are set on a hickory floor: width of the board or the percentage in moisture change. Let’s investigate this further:

Width of the board– This is relatively simple because you can just order a narrower floor. However, the width of the boards in your floor has a big impact on the appearance and wider boards are in demand. To counteract the movement, a second option to consider is to buy an engineered floor in which the hickory is integrated with a cross-ply base layer. As you will see in the video I linked, it is certainly possible to buy a really high quality engineered floor that has a wear layer equivalent to traditional solid flooring.

Moisture change- If you have your heart set on a wide board and a solid flooring, then you need to understand proper acclimation is key as well as maintaining an optimal living condition for the floor. If you are installing a flooring with questionable stability that is solid and wider than 3″ I recommend that you allow closer to one month of proper acclimation. If you are remodeling or building a new house, the proper acclimation requires:

Fully operational heating or cooling system.

Windows installed, siding on and gutters operational

Insulation and drywall are completed and doors leading to the exterior are installed.

Once you have all of these factors, then the subfloor and the hardwood floor must be within 2% moisture content to one another for boards 3″ wide or wider. The rule of 4% difference only applies for narrow floors and this is often mis-referenced by those selling or installing wood floors.

After the floor is installed following proper acclimation then you should understand that maintaining a ideal interior heat and humidity balance will help prevent seasonal movement. The chart below shows what “ideal” is indicated by the yellow highlighting. On the chart you will see temperature and relative humidity (RH) are on each axis. Relative humidity is a very big deal for wider floors and I’ve written about it before. The chart below illustrates how the relationship works:


I realize that this post seems lengthy, but I felt it is important for consumers to understand that all the pretty samples on the rack at your local flooring retailer require a larger bank of knowledge than we tend to expect from sellers of flooring. Demanding knowledge from your wood floor provider means more than being upsold on warranties for finish. If you are about to embark on building a new house or doing a major remodel, then I urge you to possibly make sure that your well qualified flooring contractor, builder, and architect meet each other a whole lot earlier than you may have previously planned.

How long should I wait to move back in after refinishing my wood floors?

A frequent discussion I have during estimates is regarding when people can have their home back. When can they walk on the floor? When can they put back area rugs? I’ll dive into this as best as possible.

Cure time- A finish is technically cured when 100% of the solvents have left the coating. This is quite variable between the types of finishes. A general rule follows:

  • Waterborne finishes-(7-10 days)
  • Oil modified polyurethane- (30 days)
  • Conversion varnish-(30-60 days)

Keep in mind that the cure time is not a good measure for judging when the floor is durable enough to move back into the home. The cure time of a finish simply is a measure of when the floor will no longer emit a smell and will have achieved the best optical clarity.

Dry Time-This is a pretty simple term. When the finish no longer sticks to your feet when you walk across the floor, it is dry. Most finishes dry within 3-12 hours per coat.

Despite mass marketing by certain companies, I don’t encourage any homeowner to be present during the application of floor finish whether it is low VOC or solvent based. VOC(Volatile Organic Compund) is one way to measure the toxicity of a floor, but some components of toxicity may not be able to be measured using VOC because they may not be airborne (i.e. volatile)such as iso cyanate, the chemical hardener in waterborne finishes. In addition, Acetone (think nail polish remover) is one chemical with VOC that is exempt from measurement. In the end, don’t become a victim of marketing, all finishes have a degree of toxicity until they dry and the air in your house clears.

My general rules for returning to your house for most finishes:

  1. Allow 24 hours following the application of a final coat until you return and walk on the floor
  2. Allow one week until you put down area rugs.
  3. Replace the felt on your moving furniture and allow 2-3 days before using chairs that move or slide.

I hope that this helps explain the practical side of having your floors refinished.

What’s all that chattering about?

I’m not talking about the latest Justin Bieber album at the high school girls locker room.

This post is about something a majority of homeowners and surprisingly 8 out of 10 “floor guys” don’t see as a problem with floor sanding…. Chatter from the floor sander.


A contractor’s belt sander or drum sander is the cause of this problem. Typically it is because the machine has not been regularly maintained. It is possible to remove chatter, but this requires a methodical hardplating process with either a buffer or a three disc random orbit sander like the Lagler Trio.

The above photo is a before picture from a recent project we completed in the  Alameda neighborhood around Portland. We sanded the floor flat with our belt machine and did a final hardplating using the Lagler Trio.


The point of this post is simply to inform you that if you see this phenomenon in your hardwood floors that it is a real sanding error and you’re not being a picky homeowner. To hide chatter, a number of companies use very low sheen finishes, particularly waterborne finishes because the more plasticized resins do a great job of obscuring the clarity of the floor.

Be informed, be bold in demanding great service, and be a better consumer. You should love your floors, not think they’re just OK when you move back into your home.

Trust me, it’s not normal seasonal movement

The National Wood Flooring Association says that a gap of up to the thickness of a dime is acceptable for normal seasonal movement within a wood floor. The relative humidity in a home drops during winter because the air is dried out from a forced air heating system. One of the issues with seasonal movement is that it really tests how well the finish is adhered to the boards.

I have recently been talking with a homeowner in NC who is having problems with white lines syndrome and poor adhesion of oil based polyurethane to a walnut floor.


Looking at the pictures and having seen this problem firsthand, the floor is going to have serious issues with peeling finish. This is not a “normal seasonal movement” problem. It is an operator error issue regarding preparation and application of finish. The oil based polyurethane is not sticking to the boards.

Unfortunately, the only fix is to re-sand the entire wood floor. The floor is 3000 square feet and that will not be a quick problem to fix. The wood floor contractor tried to pass these problems off as normal seasonal movement, but that’s just a last ditch effort in hopes that the homeowner will buy that explanation and go away. These types of problems do not surface immediately, so sometimes choosing the wrong company can cause real issues with your time and countless headaches after you have “the keys” to your brand new floor.

The top 3 bait and switch selling points used by desperate wood floor refinishers

In the wake of a toughened economy, the number of desperate contractors has risen dramatically. The end result is that contractors are using very vague language to describe their process so that they appear to be offering more for less. Here are the top 3 red alerts for anyone considering a hardwood floor refinish:

“Oil finishes”– There are two common finishes that are lumped together as “oil” finishes, oil-modified polyurethane or conversion varnishes. Oil modified polyurethane (poly) typically costs 60% less than a conversion varnish or true “Swedish” finish (Made by Glitsa or Synteko). Polyurethane generally gets worn through about 2-3 times faster than a quality conversion varnish because it is considerably lower in solids (the stuff that provides durability). This price difference is how a company can refinish your floors for $1.00/sq foot less than other companies and say they’re doing an “oil” finish without distinguishing the type of finish.

“Waterbase”– Not all waterbased floor finishes are equal. As a general rule, if the finish isn’t a two component waterbased finish, then you’re pretty much getting a very inferior finish. I wrote a lot about that in a previous blog.

Two coats versus three coats– This is funny because it’s the wrong number to really consider. Film build thickness is the key to durability and three thin finish coats actually has less film build than a high build two coat system. Rollers and brushes apply finish much heavier than trim pads and T-bars.

PLEASE don’t get sold on the wrong buzz word phrases and not ask the appropriate questions. Unless you like moving your furniture every three years, I encourage you to become a more meticulous consumer.

I would love to hear from anyone about their stories or observations from the field.

Be afraid, very afraid

Currently, I am helping advise a homeowner in NC whose walnut floors have a severe adhesion/white lines syndrome issue. I’m glad to help her and email back and forth and not charge a fee because I feel that paying it forward is essential in my industry. I know my stomach would turn if I had just paid for 3000 square feet of walnut to be installed in a custom house and it had major issues, so being empathetic isn’t a problem.

During our discussions, she recently sent this link for a so called “online expert” who charges $70 to answer a question


This guy is scary to me for several reasons:

There is no indication he is or ever was a hardwood flooring contractor. Supposedly, he has been around since 1979 (well before the internet).

The advice he is giving is usually not accurate and just strikes me as someone who has read a few Fine Homebuilding magazines and watched a few wood floor sanding videos.

A majority of the products he is referencing and recommending no longer exist or comply with VOC standards in some states.

Nowhere on his website does it indicate that he is a member of the National Wood Flooring Association, the premier wood floor organization in the world.

There is NOWHERE to reply or comment to his “advice” on the website. This makes me really question things because he thinks his answer is perfect, without any input.

Homeowners, the internet is filled with so called experts in this industry. Be very careful of what you read because there are more charlatans than experts as a general rule.

What defines integrity in our industry?

Integrity is a commonly thrown around word by many contractors and some companies have it in their name. Let me just lay these items out:

Your reputation is being evaluated long after the final check is cashed. To the fairness of us contractors though, if you don’t point out something after we have gone, please contact us to deal with it. Contractors with integrity will be back to fix problems.

Time tells all-In an era of increasing pressure on pricepoint, the world of pre-finished wood flooring warranties has become ridiculous. If you’re worried about your dogs and children, then get customer lists of a product that is a few years old and pay them a visit. It will tell you more than a warranty paper.

A contractors house is where you will see the most high value products. They know what performs best for the money and put it into their house. That doesn’t mean expensive, just high performance level for the money. Whatever they’re selling you, ask if they would put it into their house if money wasn’t the only issue.

Everyone makes mistakes-end of story. It’s how you work with the buyers to deliver a resolution that makes them happy in the end. Attitude gets you nothing, but high stress and sometimes lawyer bills.

My good friend Jesse Pender of Portland Tradesman was the inspiration for this blog.

Temperature versus humidity

A majority of people in the construction industry will tell you that moisture is a huge problem for wood flooring and they are right. Excessive moisture is certainly an issue. The hidden factor most people often do not realize is massive temperature swings in a floor. This is most prevalent in remodeling projects. Here’s a sequential scenario of how a problem may arise:

  1. Flooring is installed at appropriate moisture content in relation to subfloor
  2. Remodeler and homeowner both agree to cut costs and maintain heat at 55 degrees F during that time the flooring is installed.
  3. Hardwood flooring is sanded and finished.
  4. Remodel is completed and homeowner moves in and turns up heat in the house to 70 degrees Fahrenheit.
  5. Newly finished floor cups from excessive moisture


Warmer air has a much greater potential for holding moisture (relative humidity). I won’t go into extreme detail other than to point to this article by Craig DeWitt Ph.D in Hardwood Floors magazine. I have observed this phenomenon personally on a couple of remodel projects done by other flooring contractors. Both installations were done in the middle of winter also.

If you are remodeling, please don’t skimp on the heating bill or you will have more costly issues later.