Refinishing a Wood Floor
by Charles Peterson

Find out what you have to work with.

Examine the flooring to determine whether it's solid wood or a veneer engineered woo floor. You can get a peek at the bottom of the floor by removing floor registers if present. Otherwise you’ll have to remove a thresh hold or trim piece. Many times on an existing floor there will be separations between some of the flooring strips. This allows you easy way to measure the thickness of the hardwood above the tongue of the boards.

If the floor is solid, and you have access points (such as floor registers) the condition of the floor should be accessed to determine if it is possible at all to sand the floor. The wear layer thickness of the flooring should be measured in a few different spots. The floor should also be checked for flatness. There should beat least 1/8 in. of stock above the tongue on a solid thick floor, or the flooring may splinter when you sand it. There will not be much structural left above the hardwood groove locking the floor together.

If there’s less than one-eighth inch left of the wear layer, you should you should not sand the floor. It is also not recommended to use a chemical stripper. It is difficult to neutralize the stripper and clean it from in between the separation of the flooring strips. The striper will most likely cause problems with the finish.

Engineered floors and thin flooring (5/16", 3/8", ) will have different criteria for how deep you can sand. Many engineered product have their grooves actually in the plywood part. So you can sand as much as the top wear veneer will allow. Most thin solid floors allow you sand one to two times before you compromise the integrity of the floor.

After we have determined what type of floor we have, we must identify the existing floor finish. Floors that have been waxed will be impossible to coat with a non-wax finish. How do we check for wax? Water will make white marks on waxed floors. When you scrape a wax floor with a coin or your fingernail a waxy residue will come off. A drop of paint remover will make a urethane finish bubble. A rag with mineral spirits will generally remove some of the wax on the floor and leave the residue on your rag.

It may be difficult to sand below the wax because it may have penetrated into the sides of the wood through the any separations between the flooring boards. Trowel filling the entire floor with wood filler will help to seal the impurities and will aid in the chances of the new finish adhering. The only sure bet for a wax floor would be to reapply a wax finish.

Some floors may have hazardous materials on them. Some paints are lead base and some flooring adhesives contain asbestos. Do not sand these floors. The local authorities should be consulted on the proper abatement procedures. It is not worth taking the chance of sanding any finish you are not sure of because of it could contaminate the house with lead dust or asbestos dust. Just one person getting ill is enough to end your career.

Have someone remove all the furniture from the room. This includes paintings and other items hanging on the wall. It will be just your luck that the one nail holding it lets go after thirty years of the item hanging there. Remove the base ray heating or heating vent cover. There you will most likely find things that are fossilized (lost French fry, dust, dirt, toys and dead bugs) from being there over the past decades. All this contamination will find its way into your wet floor finish.

Prior to sanding the floor should be swept clean and a thorough inspection performed. Inspect the floor for damaged and loose boards. Repair or replace damaged boards prior to sanding. Inspect and countersink exposed nails to a depth lower than the amount of wood that will be sanded off. Remove any tacks or staples in the floor. One missed nail can destroy the drum on the sanding machine. Sparks from nails, tacks and staples can easily ignite the old finish laden sawdust on fire. When you slightly run over a nail with the sanding machine it cuts a flat spot in the abrasive. Now with each sanding pass an imperfection will be left in the floor.

Make sure there’s sufficient power to handle the sanding equipment. Professional 220-volt sander generally requires no less than a thirty-amp breaker. The sander running voltage should be checked with a voltage meter. When more than 75 feet of cord is required a piece of equipment called a power booster may be required. The power booster will raise the voltage up so the sander motor does not get damaged. Rental units are generally 110 volts and require at least a 20-amp circuit. The unit sand slower than the professional unit but that will not matter to the consumer.

If the above conditions have been met, proceed with the prep work. Remove anything from the room that may be damaged from dust or vibration. Protect heating, ventilation and air-conditioning openings. If the systems cannot be shut down use protective filters over the ducts. If possible use a fan to remove dust from the room. Protect smoke alarms and carbon-monoxide detectors from dust. Do not forget to protective coverings before leaving the job. Seal doorways with plastic.

Another way to minimize dust is to empty the sander’s dust bag often because it also acts as a filter. If the bag gets more than one third full, surface area is reduced; this reduces its filtering ability. Never leave the sawdust-filled bag in the house or truck for reasons of fire safety. It is not a matter of if the old finish sawdust will catch on fire but when the spontaneous combustion will happen.


It is imperative to remember to use personal protective equipment. Earplugs, safety glasses and a respirator are a must. Many of the dust particles are so small that they find their way into the deepest recess of your lungs. Also if you breathe the vapors from the floor finish for enough years, you will get cancer of some sort. When you try to have a conversation with many wood floor people, their hearing is gone from not wearing hearing protection.

The small wheels on the big sander should be inspected to ensure they are round and clean otherwise it will cause imperfections. Prior to leaving the rental shop find out how the machine is set up to run. My machines start on the left wall and work towards the right. This ensures my wheels are always running on new sanded flat floor. Each cutting pass will make the floor flatter. Make sure you have an adequate electrical circuit at home. Low voltage will damage the machine also cause imperfections in the floor.

The machines I have never touch the ground unless they are actually sanding. This protects the drum and wheels from damage. Sanding machines are very sensitive and just about anything can correspond to an imperfection in the floor. When not in use for ten minutes the drive belts are loosened. Imperfections in the belts will correspond to imperfections in the floor. Always start the machine and let it warm up prior to sanding for this reason. Prior to actually using the machine on your floor, practice raising and lowering the drum on a piece of plywood (or practice with a worn out 100 grit belt on the floor). The machine MUST be MOVING across the floor when the sanding drum is contacting the floor. It is similar to learning to drive a manual transmission car. Except each time you forgot to let out the clutch and the car lurched foreword; the sander you will leave a large deep sand mark in the floor that might not come out.

Sanding a floor should always start with the least aggressive sand paper grit that will best sand the floor. Sanding a floor is accomplished using a sequence of grits. Each step reduces the size of the scratch from the previous larger grit paper. No more than one grit size should be skipped per sequence step or it will be difficult to remove the scratch left by the previous step.

Wax and other old finish coating will have a tendency to gum up sand paper and may require open coat paper. Open coat paper has large course particles that are spread out on the paper so they have less of a tendency to gum up. Try the first sanding pass with a medium grit sand paper and adjust with the result.

Most of the sanding is done by a large drum driven sanding machine. The two types are belt and drum machines. I prefer a belt machine to a drum sander. On a drum machine the sanding paper is wrapped around the drum and inserted in a slot. The slot on the drum can have the tendency to cause imperfections on the floor. Belt machines have their sandpaper wrapped around a drive drum and also a tensioning roller. The belt machine runs cooler than the drum design. The sandpaper is more expensive for the belt machine but easier for the novice to install. This becomes more of a factor on worn rental shop equipment. When renting a drum or belt machine you should inspect the drum for damage. Any damage will cause imperfections in the floor.

Floors that are cupped or damage should first be cut at a 15 to 20 degrees to flatten the floor. Cutting at a slight angle will also remove old finish coatings more aggressively. The floor should be cut parallel to the boards with the same grit size prior to changing to the next sandpaper grit size in order to remove the cross grain scratches.

Using the proper abrasive sequence is one of the most critical factors to a successful job. The initial sandpaper grit will be determined by the new finish manufactures recommendation for the final grit and the types of old finish already on the floor (along with damage and stains that need to be removed). The sanding sequence should always be adhered to and never skip more than one grade of paper per step. Skipping more than one grade of sandpaper will leave the floor with scratches. This is due to only the very top on the peaks of the scratches would be removed. The deep valley of the scratch would remain. The wood floor finish would not fill these valleys and the floor will wear prematurely. Always start with the least coarse grit possible needed to efficiently sand the floor. The courser the starting grit means the more steps needed to remove the scratches. On a typical oak strip floor the finish manufacture might recommend ending the sanding sequence with a 100 grit screen. The sanding sequence might start with 36 grit sandpaper proceed to 50 grit then 80 grit sandpaper and finished with a 100 grit screen.

Between each sanding sequence the floor should be swept clean otherwise the sawdust on the floor will hinder the sandpaper from working. Sometimes you can make the sanding belt perform longer if the belt is removed and turned around after about 60 % of the life of the belt is used in that direction. During sanding the grit on the paper becomes dull on one side. By reversing the belt the sharp side of the grit will allow you to get another 50% of wear. Belts that have arrows on the inside of the belt from the manufacture cannot be turned around.

After the first sanding grit step of field with the big sander, areas that could not be reached will be sanded with the edger. The edger machine spins a round disk and is used to sand where the big machine can not reach. Edger’s have small wheels in the back, which help the unit glide over the floor. Do not press down on the front of the machine or the sanding disk will gouge the floor. It is important to understand where the on the disk the unit is sanding the floor. My edger’s cut on the edge of the sanding disk from the one to two o’clock positions. The edger is positioned such that this area will contact and sand the floor with the direction of the wood grain. An edger should easily glide across the floor. If it does not check to see if the unit is not set right or the rubber disk is distorted.

Normally you start with a disk that has a grit size from the next belt sequence size. This generally cannot be done on waxed floors because the paper will most likely gum up. The sanding sequences are repeated until the grit size recommended by the finish manufacture is reached.

Turn the power switch on with the sanding disk not in contact with the floor. Start the edger on the left side of the wall and work towards the right. Start with the edger against the wall with the machine turned as much as possible so as the disk is cutting in line with the direction of the grain of the wood. Move the edger back and forth a comfortable distance for across the wall for you, say twenty inches. Move the edger away from the wall a little after each pass. After the first pass the edger can be rotated slightly more in the clockwise to position the cutting area of the disk with the direction of the grain of the wood.

A hand scraper is used to reach areas in the corners of the room where the edger can not reach. Care should be taken to work in the direction of the wood grain. Going against the grain will cause deep gouges. Areas hand scraped should be blended in by hand sanding or an oscillating sander. A sander called a duck bill is used to get under base ray heating or into other low tight areas. The sander is like an edger with a thin long nose.

Sweep the floor clean. Load the buffing machine with a driving pad and 80 to 120-grit screen (depending on the finish manufacture recommendations). The buffing machine is used to blend the different types of sanding performed on the floor. Start by screening the outer perimeter of the room. Now, screen with the length of the room working towards the middle of the room. When you have reached the middle of the room stop and then start screening from the opposite wall towards the middle. As the screen is use the abrasive is worn down and abrades less, by starting on opposite walls and meeting in the middle of the room the floor will blend better. Verify which section of the buffer screen is abrading the floor. The buffer you are using probable turns counter clockwise and abrades the floor from the one o’clock to five o’clock position. Turn your buffer forty-five degrees in the clockwise direction to the floor so as the buffer will abrade the floor with the direction of the wood grain. At the end of the pass turn and return through the same area so as to abrade the other half other buffer swath. The areas where the buffer could not reach will have to be hand worked with a piece of screen.

A typical sanding sequence on a well worn and slightly stained oak floor might start with a 36 grit belt on the big sander. We would first cut the floor first at 15 degrees, followed by cutting it straight with the same belt. The beginning sequence with the edger might start with a 50 grit disk. The next grit for the big machine would jump over 40 grit to 50 grit. This time the floor is just cut straight with the big machine. The next grit used on the edger would jump to 80 grit. The big machine would finish after the edger using a 80 grit belt. All the hand scraping and hand sanding would be completed, followed by buffing the floor with a 100 grit abrasive screen.

What to look for when renting a sander.

When renting a drum or belt machine you should inspect the drum for damage. Any damage will cause imperfections in the floor. The small wheels should be inspected to ensure they are round and clean otherwise it will cause imperfections. Prior to leaving the rental shop find out how the machine is set up to run. My machines start on the left wall and work towards the right. This ensures my wheels are always running on new sanded flat floor. Each cutting pass will make the floor flatter.

Make sure you have an adequate electrical circuit at home. Low voltage will damage the machine also cause imperfections in the floor. The machines I have never touch the ground unless they are actually sanding. This protects the drum and wheels from damage. Sanding machines are very sensitive and just about anything can correspond to an imperfection in the floor. When not in use for ten minutes the drive belts are loosened. Imperfections in the belts will correspond to imperfections in the floor. Always start the machine and let it warm up prior to sanding for this reason. I get a cold chill thinking of having to use a rental machine or the quality of abrasives generally sold with them.

Never change the sandpaper with the machine plugged in. It is too easy to hit the power switch. Never leave the machine standing when not in use or while plugging the unit in. The edger can make a mess when it runs away by itself.


Vacuum ever inch of the room after time has been given for any dust to settle. Dust from windowsills will fall on your wet finish you are about to apply. Tack the room with a clean lint free rag. Lightly dampen the rag with the solvent used in the finish. Oil based polyurethane would use mineral spirits on the tack rag. Water based polyurethane would use water on the tack rag. Move the tack rag only in one direction while cleaning the floor so the dust stays on the rag. A dry micro fiber tack cloth also may be used. You can never clean too much. Every spec of dirt, dust, grit, hair and fuzz shows up after the polyurethane is applied.

Measure and record the moisture content of the floor. Read and follow the manufactures directions on the finish can. Not following the directions will probable lead to sanding the floor again. Sealers are generally used on the first coat and reduce the absorption of subsequent coats so that a layer of finish is built up on the surface of the wood. It can also help some finish adhere to the floor.


Oil base finishes seem to be easier for the novice to apply. Professional water base finishes especially two-part type take practice to develop the knack of applying it. Oil based finishes are applied with a lambs wool applicator and a brush. The water base finishes are applied a snow plowing type method use an applicator bar outfitted a tube with a synthetic type fur on it. The corners are done use a pad type applicator made of the same material. The finish manufacture Basic Coating does make a water base finish called Emulsion that applies likes oil. It is a one part and has the amber look of oil.

Stir the contents of the oil base finish container. Pour the finish through a strainer into a dish wash pan lined with a clean garbage bag. The garbage bag makes a great sterile container ever time and aids in clean up. Allow the finish to sit to allow the bubbles to escape. Areas that require more than one can of finish should have the cans mixed together so as to ensure a uniform gloss level. Use the original can container for the brushwork around the room. Remove the excess finish from the brush. Nail holes in the lip of the can will help drain the off finish instead of it running down the side of the can. Hand brush with the direction of the wood grain the area next to the wall using even brush strokes. Over brushing can cause bubbles in the finish. Remove excess finish from the lamb’s wool applicator. The sealer coat is applied using short cross stokes which change to long straight even strokes. At the end of the stroke the applicator is gently lifted of the floor in one graceful motion. Care must be taken not to overwork the finish so as to avoid imperfections in the floor.

The floor is abraded between coats of finish per the manufacture recommendations. The abrading promotes intercoat adhesion and helps removes grain raise and small imperfections. Finish coats are applied with the direction of the wood grain. The knack of gilding the applicator off the floor can be practiced on the first couple of coats. Vacuum and tack the floor like you are working in a hospital. A dry micro fiber tack cloth works well. If you wet tack the floor, it has become common practice to use water for both types of finish. Use a damp tack cloth, not wet. Do not use tack cloths that are contaminated with silicone or wax.

I do not prefer to intercoat abrade with screens, it can leave scratches that seem magically appear at the end of the job (I have inspected many floors that the contractor said the "Scratch Fairy" put them there). I prefer sanding strips under a buffer-driving pad. This seems to produces a higher quality finishes. I generally use 180 grit strips for oil based finishes and 240 grit strip for water based strips.

Water base finishes use different applicators than oil base products. Also make sure to the water base applicator recommended by the manufacture. The weight of the specific applicator helps meter the correct film thickness of the finish. Apply the correct thickness is crucial in a water base application.

The wall area is hand worked as per oil base finish except a pad applicator is used. The majority of the room is done using a snow plow method with a bar applicator. A line of finish is poured down the length of the room. The applicator moves this puddle in a snow plowing motion. A plastic garden watering can help meter the puddle line. The finish is pulled around the room. At the end of the room the applicator does an one hundred and eighty-degree turn and prepares for the next pass. The curved turn area must be straightened and blended otherwise the curved lap marks will be present when the finish dries.