In addition to this there are also terms used that are specific to sanding imperfections. This information sheet will provide a glossary of the terms associated with the floor sanding process, equipment used and imperfections that may occur.
Terms relating to the sanding process In reference to sanded and coated floors the intention of the sanding process is to create a flat smooth floor surface suitable for accepting the chosen coating system. To a degree the processes are going to vary depending on the condition of the floor, the type of timber, whether it is a new floor that is to be sanded oran existing floor that is to be re-sanded and if the floor is to be clear coated or stained and coated.
Sanding abrades the board surface and by progressing through finer grades of paper the ‘scratches’ are also made finer to the point where the impact of the scratches, in the completed floor, are at an acceptable level.Each paper grade reduces the depth of the scratches made by the previous paper grade and therefore it is important not to ‘skip’ grades as a fine paper is not capable of fully removing deep scratches from a coarser paper.
Level or Basic Sand – This is undertaken with coarser grades (or grit) of sand paper with the purpose of ‘cutting’ the boards flat by removing unevenness (or mismatch) between board edges and any shape deformation (e.g. cupping) in the boards. Prior to the removal of cupping from a floor it is important to assess the cause of the cupping and if it is moisture gradient related the floor should not be sanded as crowning may result at a later date. The paper grade selected for the first cut will vary from one project to another and each project should be assessed on its merits to determine the starting paper to be used.
Generally, three passes are made over a new floor involving a large drum or belt sander, often referred to as the big machine (refer section below), with the initial passes over the main body of the floor at an angle to the boards and then in line with the boards. This equipment is unable to access areas close to walls, around doorways or in corners of rooms. Edging is the process of using a smaller sanding machine to bring the boards in these areas flat and also to provide a similarly smooth surface to the main body of the floor. In areas that are particularly difficult to access, a hand scraper is used and often a smaller sanding machine is used in conjunction with hand sanding. A ‘pass’ refers to sanding of the complete floor surface with a particular grade of sand paper.
Finish Sanding – This is the process of taking a floor that has been level sanded and bringing it further along the path to the coating stage. The purpose of this stage of the sanding process is to smooth off the coarser sanding marks left by the level or basic sand with finer grade/s of sand paper. The aim is to reduce the depth of scratching and ready the floor for the next stage of the process.
After the completion of the finish sanding the floor should be ‘hard plated’. Although this is not undertaken by all contractors it should be seriously considered by all floor sanders if the best possible result, in regards to the finished floor, is to be achieved. Hard plating is the process of utilising a rotary machine (refer section below) with the sand paper on an inflexible base plate, and it enables a flat floor surface to be achieved and if undertaken effectively will help eliminate minor sanding imperfections left from using the big machine and edger. After hard plating the perimeter of the floor would normally be sanded with a random orbital sander (refer section below). The importance of both hard plating and random orbital sanding cannot be overstated in order to obtain a flat floor surface with little or no variations in the appearance of the finished floor when the perimeter of the floor is compared to the body of the floor.
The final stage is the ‘buffing’ of the floor. This is usually carried out with the same rotary machine as used for the hard plating but with the sand paper attached to a more flexible pad on the base of the machine.This is the final process prior to coating the floor and is designed to produce a uniform scratch pattern across the entire floor and is also used as the last checking process, of the floor, prior to the application of the coating.
Each stage of the sanding process is designed to achieve a specific outcome with the end result a floor that is flat with a minimum amount of very fine sanding marks and little visible difference between any areas of the floor, when compared one to another.
Terms relating to the sanding equipment
The exact machines used to sand a floor vary to a degree from contractor to contractor as do the techniques used. Having said that, all floors are sanded in preparation for coating in a similar fashion, with similar machines. It is important to understand the characteristics of the machinery being used on the floor as they all have their own peculiarities and different machines will produce different results.
Drum sander – This is the traditional sander used on floors and consists of a drum (cylindrical wheel) with sandpaper fixed to the outer surface of the cylinder. Sanding is controlled by the operator who brings the sanding drum into contact with the floor, but only when moving the sander forwards or backwards, in order to avoid drum marks (refer section below). The machine is used throughout the main body of the floor to initially flatten the floor which as indicated above is usually done with passes at an angle to the boards and then in line with the boards. It is then also used with finish sanding. It is often referred to as the big machine. Common brands of machines or machine names include Hummel, Clark and Galaxy.
Belt sander – This also contains a drum similar to the drum sander but has a small cylinder above the drum which then allows a sanding belt to be used. It performs the same task to the drum sander, being used throughout the main body of the floor. Also often referred to as the big machine.
Edger – Due to the size of the drum or belt sander it is not possible to sand close up against walls and a smaller hand guided machine is used around the main perimeter of the floor.The edger has a rotating disc and is easy to manoeuvre.‘Clocking’ the edger is a technique of orientating the edger to the wall being sanded up to, so as to minimise the visual impact of the scratches left by this part of the sanding process.
Rotary machine – These machines have a rotating circular base plate and are used for hard plating and final sanding of the floor. A finer grade of paper is fixed to the plate for the sanding operation. Such machines are often referred to by the manufacturer’s name such as ‘Polyvac’ or ‘Canterbury’. With heavier machines such as the ‘Canterbury’ a less flexible or harder plate that supports the abrasive can be used with the machine to enable the floor to be ‘hard plated’. This type of machine is also used for ‘cutting back’ between coats (when used with a more flexible base plate or pad) where the coating is mildly abraded to remove roughness and provide a mechanical key for the next coat. Often a fine sand paper or mesh known as a screen back is used for this process. This type of machine may also be used in the application of some stains.
Trio – The Trio is a machine produced by Lagler and is a multi-head sanding machine that is ideally suited to hard plating. Where a rotary machine has a single rotating disc the Trio has three smaller rotating discs on the main rotating disc. Multi-headed base plates are now available for a variety of rotary machines including the ones mentioned above.
Random Orbital Sander – In sections of the floor that have been edged and areas that are difficult to access, this could include in cupboards, a very small hand held random orbital sanding machine is often used to ensure that these areas blend smoothly into the main body of the floor.
Corner sanding – In areas that are difficult to access, and have been hand scraped, this would include corners and sometimes along skirtings and joinery, a very small hand held corner sander is often used to ensure that these areas blend smoothly into the main body of the floor.
Terms relating to the sanding imperfections
It is evident that with the various types of sanding equipment used on timber floors that these can lead to a variety of sanding imperfection. Those relating to a rotating drum differing in nature to those from rotary disc equipment. Over the years various specific terms have been used that identify the types of these imperfections. Note that some sanding imperfections may be permitted in a floor and their acceptability depends on how pronounced their appearance is, their location and how often they occur.
Drum marks – These are depressions left from the big machine and are caused by the sand paper (over the drum) pausing on the floor. The principle of the big machine is that whilst the sand paper is touching the floor the machine must be moving either forwards or backwards. The marks can be seen in the body of a floor or close to the perimeter of a room.
Chatter marks – These are (often slight) indentations that run at right angles to the run of the flooring. The marks are regular and closely spaced. These are often caused by the drum or belt sander having something out of balance, worn or not adequately clean or the combination of a particular machine on a particular floor.
Wave and ripple marks – These are similar to chatter marks in that they are at right angles to the run of the flooring and they are spaced wider apart than chatter marks. Ripples can occur from debris on the wheels of the drum or belt sanders.
Scalloping – Generally this fault results from ineffective or poor technique when edging. With inattention to sanding up to the likes of patio doors it is possible to get a scalloped appearance across the floor.
Rotary scratch marks – Rotary sanding equipment does leave scratch marks in a floor. At times the appearance is exacerbated when floors are stained as the scratches provide greater absorbency to the stain and thereby highlighting them.It is important to understand what degree of scratching will be acceptable in the finished floor, this will vary depending on the coating selected and if the floor is to be stained.
Straightening scratches – These are scratches that run parallel with the direction of the flooring and are from the drum or belt sander.
Swirl marks (or cob-webbing) – Light abrasion between coats (screening) is usually carried out with rotary equipment and can result in swirl marks. Again understanding the coating you are using and drying characteristics of the coating is important to help minimise this occurrence.
Edger marks – Marks created by the edger which is the sander that is used to sand the perimeter of the room. These can be unsightly scratches or scallops in the floor.
Grain dish out – A soft pad on any rotary machine has the capacity to remove more of the softer grain timber than the harder grain timber and this can cause small variations in the board surface known as ‘dish out of grain’. This is most common when a floor is “over buffed” with a rotary machine and a soft pad combination.