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Renovation
If you already have a wooden floor which has seen better days or you just want to restore its natural beauty then at pure wood floors we have the expertise to help. Our renovation team can restore all types of wood floor and can carry out specialist repairs in even the worst of cases.
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. On the next few pages, we show 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 |
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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. |
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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.
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| Long scratches |
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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. Our abrasives, on the other hand, are made with high quality adhesives to 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 |
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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 |
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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 |
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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 |
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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 |
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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
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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 |
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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.
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