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Renovation Finish or oil 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. Here are a few examples of what can go wrong. They emphasise 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. Use only sandpapers with high quality adhesives that hold the pieces of grit in position and minimise 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 colour. When a coat of finish or oil is applied, the colour 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 colour 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 fibres 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 colour no matter what was the colour of the original abrasive grit. The finish reacts with the metal present in the grit to form a dark substance. This substance also discolours 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 colour. 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.

Hardwood floors add beauty, charm and value to a home. They are easier to clean and with minimum care, can be kept looking like new and will outlast many other floor coverings.

To know when to completely refinish a wood floor or when to just lightly sand and apply a new topcoat is as follows:
If the finish is only scratched or slightly worn, it can be lightly sanded or screened without sanding the wood.

A floor buffer with a mesh screen, a square buff orbital sander with a screen or a random orbit sander can be used for this process.

First, remove all furniture and floor coverings and inspect the floor for any nails that need to be set or splinters that should be trimmed to avoid damaging the abrasive screen, sandpaper or equipment.

Remember, any sanding process will produce dust, so the room must be prepared properly. Screening with a floor buffer and using a drum sander creates the most dust because they don't have a dust-collection system. Some of the square pad machines can be used with an industrial vacuum. The random orbit sander has a built-in vacuum.

To lightly screen or buff the floor, start with 120-grit sandpaper or screen and go over the entire area. The way the machine is running will indicate when the paper, screen or buff pad is getting dull. As the paper or screen is less effective or has dulled, there will be less drag on the machine and the user will not feel as much torque as when the paper was first put on. The operator will see results much quicker with new sandpaper as opposed to sandpaper that has been used for 15 to 20 minutes. Change the sandpaper or flip the screen over for a new cutting surface.

Some small or tight areas may need to be sanded by hand. After using a scraper on these areas, lightly sand by hand with the grain of the wood to prevent cross-grained scratches.

Always vacuum the entire floor surface when switching sandpaper or screen grits to remove any abrasive grains. If a courser grain gets stuck on a finer paper, it will make deeper scratches.

After all sanding is complete, vacuum thoroughly and follow the manufacturer's instructions for applying stain and finish.

If you are changing the floor's stain color or are going with a natural color and a clear finish, the old finish and stain must be removed completely.

The first step is to sand the large areas with the drum sander. Sand the floor with each grit as recommended. Generally, start with the coarsest grit and proceed to the finest grit. Remember to keep the drum sander moving to reduce the risk of damaging the floor. Use an edger to sand the areas along the wall that cannot be reached with the drum sander.

Sand with the edger between the different grits of the drum sander or use the edger to blend in after the drum sanding is complete. Again, some areas such as corners, under radiators, along walls, cabinets and around door openings will need to be scraped and hand-sanded. Inspect the floor and determine if any gaps need to be filled with putty. This should be done prior to using the finest grit of sandpaper on the floor.

After all the work with the sander and edger is complete, screen or lightly sand with a buffing machine to produce a smoother finish. This is a very dusty process and this machine can be difficult to operate.

To finish the floor, vacuum it thoroughly, then apply stain and varnish according to the manufacturer's directions.

A square buff or orbital flat pad sander also can be used to refinish a floor. This machine is similar to a buffer and has a square pad that simply moves in a small circular motion rather than with the rotary motion of the buffer. This machine is easier to operate than a buffer, but is not aggressive enough to level the floor or remove imperfections or damage done by table or chair legs. New models are equipped with dust-collection systems that use a separate vacuum or have a small vacuum added onto the unit. Sandpaper grit and the sequence in which it is used is similar to that of the drum sander, but will vary depending on the floor.

First, start with the most coarse grit of sandpaper. Sand the entire floor surface. Then vacuum thoroughly before progressing to the next finer grit. Inspect the floor for areas that need additional sanding.

Then, inspect the floor and determine if any wood putty must be used to fill gaps that may exist. Hand scrape and sand any areas that the square buff cannot reach. Remember to go with the wood grain to blend into the larger floor areas and avoid cross grain scratches.

Finish sanding with the finest grit of sandpaper, vacuum thoroughly and apply a tack cloth.

Follow the manufacturer's instructions for staining and varnishing. Use the finest grit of sandpaper and lightly sand after applying the first coat of varnish. Vacuum thoroughly and apply a tack cloth.

Finally, apply the third and final coat of varnish.

The random-orbit sanding machine enables the user to sand, edge, buff and scuff between coats, all with one machine. It is equipped with an on-board vacuum system that virtually eliminates airborne dust. This machine doubles as an edger because of the pad location. The dust skirt acts as a seal for the vacuum to operate more efficiently.

After preparing the area to be sanded, attach the coarsest grit of sandpaper recommended. Begin sanding the floor, changing the sandpaper every 10 to 20 minutes depending on the type of finish you are trying to remove. After sanding the entire area with the coarsest grit, thoroughly inspect the floor for areas that are not level and concentrate on those areas to blend them with the remaining floor. Vacuum thoroughly prior to changing to a finer grit.

Continue sanding the entire floor with each grit, vacuuming in between, until the floor is smooth. Scraping should be done prior to the last grit used. These areas also should be hand-sanded with the wood grain to blend them into the larger floor surfaces. Prior to using the finest grit of sandpaper, determine if there are any gaps that must be filled with wood putty. Apply the putty and allow it to dry completely. Then sand with the finest grit of sandpaper.

Prior to staining or varnishing the floor, vacuum thoroughly and apply a tack cloth to remove any remaining sanding particles or dust.

Follow the manufacturer's instructions for applying stain and varnish.

Between the first and second coat of varnish, buff the finish lightly to ensure a smooth finish coat. After vacuuming thoroughly, use a tack cloth before applying the second coat. Then apply the third and final coat of varnish.

Protect your refinished wood floors by attaching felt or material pads to the bottom of furniture legs. With a little care and preventative maintenance, hardwood floors will last a lifetime.