Timber Floors / Wooden Floors

March 10, 2015

There are two main types of wooden flooring; 1) structural, where the boards rest over joist and are an integral part of the house and 2) decorative, which are laid over the structural floor and provide a finished surface to walk on. When people talk about wooden floors today they are generally referring to this second type of flooring. Although in recent years there has been a trend to finish structural floor to serve as a decorative finish in their own right.

Tip: If gaps between structural wooden floors make is unsuitable for use as a decorative floor you have two options. Firstly you can fill the gaps between the boards with a sawdust / wood glue mix. This filler will blend in well with the boards once you use clear varnish or paint as the final finish but if you use a stain the difference between the two materials will be marked. The second option is called ships lacking. It involves cutting a shallow 5mm slot between each board and filling it with a contrasting piece of timber.

Timber floors can be made up of blocks or boards. Boards can be made up of a single piece of timber or smaller strips of timber bonded together as is the case with composite boards. Boards of 100mm wide are referred to as ‘strips’, while boards greater than 100mm are called ‘wide boards’ or ‘planks’.

Boards can have straight or bevelled edges. Bevelled edges are typically angled at 45° and are between 0.5mm and 2mm deep. It can help to avoid damage caused by moisture-induced swelling at the edges of laminate boards. A floor made up of boards with beveled edges makes a feature of the joints between the individual boards.

Tip: The bevels between boards can act as a dirt trip.

Semi-Solid Floor / Engineered Flooring
Semi-Solid and Engineered Flooring are effectively the same thing but some manufacturers use the term ‘semi-solid’ for boards with a thin layer of wooden veneer on top and ‘engineered’ for boards with 5-6mm layer of wood on top. The benefit of having a substantially thick top layer of timber on top is that is allows the floor to be refinished a number of times. Semi-solid boards are typically 100, 150, 200mm wide and 6, 9, 12, 14 or 25mm deep. Engineered boards often come in wider planks than solid timber because it is less susceptible to shrinkage and expansion due to fluctuates in temperatures. It is also cheaper than comparable solid wood planks. Semi-Solid / Engineered Flooring can be laid as floating floors or if the flooring is thicker than 21mm, nailed directly to joists.

Solid Wood Flooring
Solid wooden floors are a desirable feature in any home and when chosen and installed correctly can add thousands to the value of a house. Solid wooden floors can be installed on a concrete slab as long as the floor is on or above ground level. They can be sanded and refinished over several generations and unlike semi-solid floors can be ‘aged’ with treatments. Wood is a dynamic material meaning it expands and contracts with extremes of temperature and moisture, to the extent that small gaps may appear in your wooden floor temporarily. Most solid timber floors are unsuitable for use over under-floor heating although some manufactures offer products that they claim are suitable. The dynamic nature of solid wood can make it unsuitable for south facing rooms, conservatories, bathrooms and kitchens.

Probably the most important strength property for wood used in flooring applications is its side hardness, also known as Janka hardness. Side hardness represents the resistance of wood to wear, denting and marring.

Tip: If you like the pristine look of a newly laid solid wooden floor you will need to stripping and re-finish every few years.

Tip: The relative amounts of heartwood and sapwood in a flooring batch may affect the way it accepts stain and finish and, therefore, the finished appearance of the floor. In general, quartersawn and riftsawn flooring will contain less sapwood than plainsawn flooring and will tend to have a straighter grain and more uniform appearance. Heartwood is also more dimensionally stable than sapwood, so flooring with a high percentage of heartwood will shrink and swell less than flooring that is mostly sapwood.

Parquet is a type of solid floor made up of blocks of hardwood, most typically oak, laid in a pattern and fixed in place. Traditionally the blocks were fixed with hot mastic or bitumen but now they are fixed with PVA or similar. Modern parquet comes in pre-made tongued and grooved panels that can be stuck in place.

Tip: Make sure the timber floor you order is certified as being from a sustainable source.

Types of Wood
Generally the denser the timber the more hardwearing it will be as a floor. Typically this means hardwoods will be better wearing than softwood and of all the hardwoods Jatoba is said to be the hardest wearing. Also the denser the timber the less it will fluctuate in size, which is why dense woods such as oak is so popular for wooden floors.

Tip: The paler a timber floor, the more light it will reflect back into a room but the more easily dark marks will show.

Visit our page on the different types of wood available

Bamboo is a relatively new on the flooring market and becoming increasingly popular. It is a renewable resource that grows more quickly than timber and has a high resistance to abrasion. It doesn’t react to water and so is stable under both humid and dry conditions. It is low allergenic and easy to repair. On the downside it fades in direct sunlight and it’s newness to the market means it’s long-term wearability hasn’t been tested.

There is no British Standards or industry standards for wood floor grades and any grades quoted are species specific, i.e. prime oak might not contain either knots or sapwood but prime walnut might allow for some of both. So you should always check what is included / excluded in the grade being proposed by your flooring supplier.

Air Dried timer is not usually sufficiently dry for hardwood flooring so kiln-drying is required to achieve a moisture content of 8 to 10% which conforms to BS8201. Before installation, solid wood flooring should be acclimated to the area in which it is to be used, then tested with a moisture meter to ensure the proper moisture content.

Installing Timber Floors
A minimum of 2 weeks should be left between the completion of all plastering and the introduction of wooden flooring to a place. If you can leave it longer, so much the better, especially as damp weather can prolong the drying time. It is also important to have the heating on in the building for 2 weeks prior to bringing the wooden floor to site. The heating will help to dry out the plaster on site, otherwise the moisture will sit in the plaster and only get released when the heating is switched on.

Before a wooden floor is laid the boards should be stored flat in the space to receive it for a 24 – 72 hours, away from radiators and fires, and if possible raised off the ground. The room should be dry and heated to normal room temperature and the moisture level of the subfloor should be less than 4%. A concrete subfloor needs to dry out completely before receiving a timber floor. As a guide allow a drying time of a month per inch of concrete. A damp proof membrane should be laid between a concrete sub-floor and timber floor. A good preliminary indicator of whether a concrete subfloor is ready to receive a wooden floor is to leave a rubber car mat on the floor overnight. If there is condensation on the underside of this in the morning, then the floor is probably still too wet.

When nailing some of the denser woods with hand or air nailers, installers may encounter splitting tongues, as well as failure to secure the fastener even after repeated attempts. This can sometimes be corrected by changing the angle of the nail’s point of entry, drilling pilot holes or blunting the ends of fasteners.

Tip: It is essential that wooden flooring is unloaded in dry weather as rain can cause planks to warp.

Decorative wooden floors can be installed as floating floors or nailed / stuck down to the subfloor. Floating floors are where planks/boards are connected together and ‘float’ above the subfloor. Floating floors ‘bounce’ a little when walked on. This is normal and can be useful for reducing leg fatigue. An underlay sits between the wooden floor and the subfloor to prevent the ‘tapping’ sound that can occur when a floating floor bounces. A ‘click’ jointing system is available with some laminate flooring brands. It is so named because the boards click into one another. Only laminate or semi-solid floors can be installed as floating floors.

Tip: Floating floors may not be suitable for well-traffic areas as the bounce created can be unsettling.

Floors can be nailed down in two ways; face fixing or secret nailing. Face fixing is when a screws or nails are fixed through the face of the floorboards into the sub-floor and is generally used in addition to secret nailing on boards wider than 150mm. Secret fixing is when nails are driven through the tongue of the floorboard into the sub-floor and is so called because the nails are hidden when the floor is complete. Glueing is only recommended for narrow boards and floors without underfloor heating.

Tip: Some modern adhesives for fixing solid floorboards to a subfloor expand as they dry, filling small voids under the boards and ensuring that they don’t sound hollow as you walk on them.

If you wish to nail fix your floor but currently have a concrete sub-floor, you will first need to fix softwood batons onto the concrete. Batons should be at least 20mm x 50mm in order to allow sufficient fixing for the nails and will need to be set at 400mm centres to prevent the floor ‘bouncing’. The batons should also be laid perpendicular to the direction of your wooden floor and the space between them can be filled with vermiculite to increase thermal and acoustic insulation. Remember installing batons will increase the overall depth of the finished floor.

Tip: If a screed has not been you can opt to lay batons instead reducing overall cost of installation and cutting down on drying time.

Semi-solid and solid wooden floors expand and contract with variations in temperature and moisture; therefore it is essential to leave an expansion gap around the perimeter of the room. There are three ways to deal with this expansion gap; firstly you install a base moulding at the base of the skirting boards to cover over the gap, secondly a strip of cork is fitted into the gap or thirdly the timber floor is fitted under the skirting boards so that the skirting board covers the gap. The last options will mean having to remove the skirting before the wooden floor is installed and fitted it back afterwards. This pushes up the cost of installing the wooden floor and may require patching-up of the plaster and paint along the bottom of the wall afterwards. It does however provide a much neater finish than the first two options.

Tip: One key problems caused by wooden floors in existing houses is the increase in finished floor levels. Installing a wooden floor can mean having to sand down the bottom of internal doors and junctions with adjoining floor finishes will have to be considered before installation. With really thick wooden floors you may find that the depth of the first step on a stairs is reduced so much as to make it a trip hazard.

Finishing Wooden Floors
Finishes protect and enhance the beauty of wooden floors. They can be applied before delivery (pre-finished) or upon installation in your home (site-finished). Pre-finished floors require virtually no maintenance, only the usual cleaning but purchasing an unfinished floor gives you the option of finishing the boards insitu making sure that the final colour is correct for the environment. The benefit of pr-finished floors is that they can be installed straight out of the box, which can make the job easier when you are replacing floors in a house you live in but the joins between individual boards can be more visible in prefinished floors.

Sealing is not a finish in its own right, just a requirement to treat the timber before a finish is applied. Depending on the type of timber, ‘sealing’ has one of two functions – to keep the oils of the timber in or to prevent the subsequent finish from soaking too far into the timber. Softwoods can generally be sealed by applying one or two coats of thinned varnish and this is suitable for both varnish and wax finishes. Hardwoods can be more difficult to seal as they must first be ‘cleaned’ with a recommended wood sealer.

Pre-finished wooden floors have typically been coated with at least four coats of ultraviolet-cured urethane resin although water- and oil-based urethane and wax are also available. Manufacturers say these finishes are more consistent and durable because they are applied under strict controls.

Acrylic impregnating is a form of pre-finishing. Through a high-pressure treatment, acrylic and color are forced into the pores of the wood, creating an extremely hard surface. These floors are highly resistant to abrasion and moisture and appeal most to customers who like a ‘perfect’ floor finish.

Options for site-finishing include lacquer, oil or wax and they fall into two main categories; penetrating finishes and surface finishes. Penetrating Finishes are absorbed into the wood fibers and typically have a matt or satin appearance. If you can feel the wood grain when you run your hand across the surface, it is most likely a penetrating finish. Surface Finishes shield floors by forming a protective layer that looks like clear plastic on top of the wood. Varnishes, lacquers and paints provide protective surface coatings. Oils provide penetrative finishes. Waxes can be either. If a wax is applied to a varnished/painted surface they provid a surface coating but if it is applied to bare wood it provides a penetrative finish.

Tip: Maple and cherry do not absorb stains as evenly as other hardwood species. If you prefer a penetrating finish for your maple or cherry floor, use the natural, non-coloring type.

Varnishes & Lacquers
Traditional varnishes and lacquers were based on resins and natural oils whereas modern types are usually based on synthetic resins. That said low-fume, water based acrylic varnishes are now available on the market. Varnishes are usually available in gloss, satin and matt finishes

Water-based finishes tend to adhere well to most woods, including exotics, whereas some solventbased finishes have adhesion, drying or color change problems with woods like African cherry, rosewoods, teak, Brazilian and African walnut, purpleheart, padauk and wenge.

Polyurethane is the most common base in modern varnishes. It provides a waterproof, hard-wearing and heat-resistant finish. White spirits is usually used as the solvent/thinner but once it has dried, the varnish is not affected by white spirit.

Catalysed varnishes provide a chemically cured surface which is harder than the normal polyurethane varnishes. Pre-Catalysed varnishes are applied directly from the can and left exposured to the air to cure. Two-part varnishes require the catalyst (or hardener) to be mixed with the basic varnish in the required proportions before it can be used. Once mixed, the varnish has to be used within a predefined time period.

Water-based acrylic varnishes give off less fumes during application and tend to have shorter dry times than solvent based varnishes. The finish look of water-based acrylic varnishes tends to be less natural-looking than solvent based varnishes, but their wearability is said to be the same. It does require waxing 2-4 times a year.

Tip: Water-based acrylic varnishes should not be used over a water-based stain as there will be a reaction between the two.

Tip: some species (hard maple, pine and fir, for example) do not accept stain as readily or as evenly as other species.

Tip: A grain filler is sometimes used for wood species with large pores, such as oak and walnut, if a smooth finish is desired.

All varnishes are available as clear or coloured. A coloured varnish tends to ‘subdue’ the grain of the wood and obviously change its colour as well. Sometimes it is better to first stain the timber to the desired shade and then use a clear varnish rather than using a coloured varnish.

Tip: Even clear varnish will tend to darken the natural colour of wood somewhat.

  • Alkyd Resin is a non-yellowing, non toxic and quick-drying sealant but also needs waxing 2-4 times a year.
  • Shellac is a traditional floor seal that is easily scratched and stained and becomes brittle with age.
  • Epoxy Resin is a rather yellow sealant and is slow to dry but is very hard wearing.
  • Urea Formaldehyde is a hard-wearing transparent lacquer that settles to provide a brush-free finish. They are however difficult to patch-repair.
  • Oil-based Urethane is the most common floor finish. It ambers with age and comes in gloss, satin and semi-gloss sheens. Two to three coats are typically called for. Each coat takes about eight hours to dry. A solvent like paint thinner must be used for clean up. This type of finish emits fumes as it dries so windows and doors should be left open to provide good ventilation. If it’s too cold outside for that, a water-based finish is best.
  • Water-based urethane gives off less fumes, dries in two to three hours and is crystal clear when dry. Some manufacturers sell “cross-linkers,” additives that can be mixed into water-based finishes to make them tougher. Non-ambering urethanes are often recommended for finishing white or pastel floors.
  • Moisture-cured urethane is a solvent-base polyurethane that is more durable and more moisture resistant than other surface finishes. It is mostly used in commercial, high-traffic settings like stores or offices. It can be clear or amber with age and is available in satin or gloss. This type of finish has a strong odour.

Oil finishes have become particularly popular in recent years. Oil finishes don’t interfere with the texture of wood and so an oiled floor looks and feels more natural. Some are simply oil by themselves while others come combined with a stain. Oiled floors need maintaining around once per year and although they need more maintenance than other floor seals but when properly maintained they can last longer. There are many different types of oil with varying wax (high-solid) content. One bonus of oiled floors is that if there is a particularly nasty stain in the floor, you can spot sand it out and re-oil There are two main types of oils used in finishing wooden floors;

  • Danish Oil is simply a mix of various oils such as Tung and Linseed Oil with some additives (usually phenolic resin) to aid drying. It has a slightly yellowish tinge and is slow-drying but simple to apply.
  • Contrary to its name Teak Oil has nothing to do with the wood Teak and is simply a mixture of various oils extracted from vegetables. It has a slightly yellowish tinge and is slow-drying but simple to apply.

Wax is another traditional finish for flooring and it both protects and enhances the appearance of the wood. Wax is durable, water resistant and anti-static but needs to be re-applied regularly. The most durable wax is carnauba wax. Wax is usually available as a paste or liquid – liquid wax is easier to apply and gives just as good results. However wooden floor finished with wax can easily become marked especially by water spills. Therefore it is recommended to use solvent-based waxes rather than water-based waxes on floors.

Tip: Wax can also be applied over a varnish finish to give added protection to the floor.

Tip: When applied to bare timber, the surface first needs to be sealed to prevent the wax from penetrating too far into the timber.

Tip: Sandpaper should always be used instead of steel wool when sanding water-based finishes because undetected steel fibers can cause rust marks.

Tip: Stains such as rust, water marks etc can become exaggerated when wooden floors are finished.

Tip: All surfaces, stains, fillers or finishes must be completely dry before you apply a finish.

Tip: All finishes apply and dry best when the finish, the room and the surface are all at the same optimum temperature.

Tip: Satin finishes may dry glossier in humid weather conditions.

Tip: Overworking sealants can cause air bubbles.

Tip: As a general rule less is more when it comes to coats of finish.

Tip: Flooring paint should ideally be protected with a coat of varnish or an application of wax.

Specialty Finishes for Hardwood Floors
Bleaching, pickling and antiquing are all popular treatments for hardwood flooring.

Bleaching. Most hardwood species can be bleached but darker hardwoods like red oak, hickory and ash are particularly suited for this application. The preferred method for bleaching hardwoods is a two-step process. Firstly the wood is brushed with caustic soda or ammonia and then hydrogen peroxide is applied. Bleached timber should not be dried in direct sunlight, since this will intensify the bleaching process and lead to uneven coloring. Uneven bleaching can also be caused by leaving the caustic soda on for too long. Bleached timber needs to be well rinsed before being left to dry or problems will occur when finishing. Bleaching causes the wood grain to rise and so the surface will need to be sanded down before being sealed.

Tip: Bleaching can weaken the wood and affect its ability to withstand every day wear.

Tip: White oak is not recommended for bleaching applications because it has a tendency to discolor

Antiquing makes hardwood look ‘aged’ by distressing the edges, cracks and crevices of the wood. Before antiquing, the surface of the wood should be sealed with a thin coat of white shellac to protect the bleached shade of the wood. Well antiqued wood will have less glazed applied to well trafficed areas and more in out-of-the-way crevices.

Pickling highlights the pores and crevices of wood by adding a stain that contrasts with the bleached finish.

Colouring involves applying varying degrees of pigmented stains to lighter-hued hardwoods to highlight the grain of the wood and add color. Oil-based stains and aniline dyes are most popular because of their workability, but a variety of stains and coloring mixtures are available today.

Tip: The normal gaps caused by expansion or contraction are more noticeable in chemically-lightened woods.

Caring for your Wooden Floor
To prevent solid timber floors from swelling or shrinking it is advisable to keep humidity levels and temperatures as constant as possible. A humidity level of 50-65% is preferable for solid timber. Crowning is the distortion of boards or blocks so that the surface is convex. It is usually caused by very damp atmospheric conditions above the wooden floor. Cupping is the opposite of crowning and is generally more common. It is generally caused by moisture in the subfloor.

Tip: You can use a humidifier as well as plants or flowers with watering troughs in order to retain the right amount of moisture in the air.

Tip: All timber darkens with age but most solid wood will darken most in the first 6 months, so for this period don’t use any other floor coverings, such as rugs, or the colour change may be more apparent.

A thin layer of wood is called a ‘veneer’.

‘To laminate’ is to glue two or more layers together but the term ‘laminate’ is commonly used to refer to products faced with decorative top layer of plastic.

‘Bird’s eye maple’ is a decorative form of maple with a pattern that resembles a bird’s eye.

Registered embossing is a manufacturing technique that creates laminate flooring planks that have the feel of a real wood plank.

Radiator pipe roses are ring-doughnut shaped pieces of wood / plastic or metal that cover the expansion gaps left around radiator pipes. Sometimes wood pipe roses ‘pop’ open when the heat is turned on.

Tongue-and-groove describes the way that planks fix together. A tongue that projects from the side of one plank fits into the groove of the adjacent plank.

Click-lock planks have shaped edges that require a certain sequence of actions to fit them together, but once they are in place they shouldn’t move apart but cheaper ranges have less robust edges and may open up over time.

Underlay is used to cushion the flooring boards, increasing their durability and providing sound insulation.  There are several different grades, which range from thin sheets of closed-cell polythene foam, to top-of-the range felt underlay with a silver foil layer. The thicker the underlay the better the noise and thermal insulation it will provide.

Leveller board is fixed to the floor with nails to create an even surface to lay the floor on. It provides sound insulation and increases the floor’s durability. It can either be a thick, recycled paper board or multipurpose wood boards, such as hardboard or plywood.

Screed is used to level uneven floors. It is often a liquid such as latex or fine concrete that is applied and spreads out to create a level surface.


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