Wooden Flooring

How to complete this course

The course is open access and the content is available to anyone with internet access. This course should be completed in the sequence of the numbered sections. We make use of four components in our course (a) sections with text and illustrations, (b) video clips to explain some of the concepts, (c) a short online quiz after each section to test your acquired knowledge and (d) a test, available to learners who wish to obtain a certificate of completion. Please contact us at info@thewoodapp.com with the short course name to complete this test.

To make the course accessible to most people, we’ve tried to limit the time needed to complete it (an estimated 2.5 hours). This course will give you an overview of selected building materials impact and the environment, and design strategies to incorporate timber in a sustainable way. For in-depth knowledge on some topics you might require input from other sources such as national standards, material suppliers, selected textbooks, articles, etc.
If you have any questions or suggestions, please contact us at
info@thewoodapp.com.

5. Traffic and hardness class

6. Preservation of timber flooring

7. Wooden floor material conditioning

7.1 Quiz 3

8. Laying of different types of wooden floors

8.1 Laying wood strip/board floor on timber substrate

8.2 Fixing wooden floor on concrete bed

8.3 Floating floors

8.4 Quiz 4

9. Finishing of wooden flooring

9.1 Patching

9.2 Sanding

9.3 Sealing

10. Maintenance of wooden floors

10.1 Quiz 5

11. Conclusion

Disclaimer
In the compilation of this module, free use was made of published information such as text, figures, drawings, tables, graphs, etc. As the use of such material is subject to copyright considerations, and the suitability and relevance of this content is in the process of being assessed, the content of this module is only reserved for personal use and the purpose intended. To adhere to copyright regulations, any publication of the module or parts thereof considered, is subject to obtaining the necessary copyright agreement from the publishers by the author. Photographs taken and figures, drawings, tables and graphs generated by the author, are subject to copyright as well.

Whilst all and the utmost care has been taken to ensure the accuracy of the information contained in this module, no warranty can be given regarding the use, suitability, validity, accuracy, completeness or reliability of the information, including any opinion or advice.

Wooden Flooring Video 1

1. Overview

Wooden floors are one of the oldest floor systems available. However, it is still a popular choice today due to some major advantages of this timeless material.

The advantage of wooden floors compared to other common floor surfaces:

Wood is a natural renewable resource and a carbon sequestrator. Using wood is good.

Wood is a good natural thermal insulator unlike ceramic tiles that are cold, especially during winter months.

Wooden floors are easily cleaned compared to carpets.

Wood is more shock resistant compared to tile floors which crack easily if heavy and/or hard objects are dropped onto it.

If looked after, wooden floors will outlast carpets.

Wood is available in a variety of colours, styles and patterns, creating a natural and unique timeless look that stays in fashion. According to estate agents, hardwood floors increase the value of a house.

 2. Suspended Floors

The term “wooden floor” refers mostly to the use of wood as floor finish. However, the structure of the floor platform itself may also be constructed from wood. “Suspended floor” refers to this type of floor construction. Both these topics will be dealt with in this course.

This floor construction is elevated above ground level and can be applied to timber frame and other building systems. The members of a suspended floor create a level frame on which a floor covering can be fixed. Understanding the structural application of timber will be important to design to deflection and sound insulation specifications.

Suspended floors can be used as a ground floor level but should be designed carefully to deal with soil moisture ingress that can influence the durability of the structure. It can also be applied to create upper levels and mezzanines successfully – keeping in mind sound design principles.

2.1 Design process of suspended floor construction

A detailed design process from the Timber Deck and Timber Frame Course can be used for a suspended floor design. See the following link.

A top-down design process is suggested, as the floor finish is mostly the determining factor for structural timber member sizes.  The finished floor height is also an important reference level to work from. Timber floorboards span typically between consecutive joists.

The relevant SANS standard 100082 which gives 20x thickness as a requirement and as a rule of thumb, the maximum span of the boards is: thickness (mm) x 20. For example, 20 mm thick boards could typically span maximum 400 mm. This would thus be the spacing between two consecutive joists. Thicker floorboards can thus result in larger joist spacing and lowering the number of joists used in the design.

The span of the structural graded pine joists can be extracted from the table given in SANS 10082. Note that increased commercial design loads influence the allowable joist span considerately as compared to domestic application loads. Also note that all structural timber elements must be of the correct grade and treated to applicable hazard class (see marking on timber elements).

Generally, S5 grading is more available than S7, and some dimensions are not produced on a commercial basis (76 x 114 and 76 x 152). Laminated beams can be specified should designs call for larger spans than tabulated in the solid wood joist span tables. See SANS 10082.

2.2 Ensuring squareness

Once the design is accepted, the layout and construction can start – this time from bottom upwards. Layout of any building is crucial as it will influence all the following alignments.

Most floor spaces are rectangular and attention to square layout will prevent many problems especially in the laying of the finished floor. Use the diagonal method to check for squareness.

To ensure that a square or rectangular building is accurately square, the diagonal measurements should be equal length. This is a quick and practical method to use and only requires a long length measuring tape.

2.3 Pole foundation

Treated timber poles are widely used for suspended floor construction. See link to deck building that covers the different pole planting techniques.

After plotting, the planting holes are dug and the poles are planted. Bearers/beams are fixed to the poles and joists are fixed to the bearers, either running over or between them. Over joist fixing is simpler, however, between bearer is often used when height is a limiting factor.

2.4 Bearer post connection

The most popular method of fixing a bearer to a post is bolting on a seated post. The post is notched 10 mm deep to seat part of the bearer. Hot creosote brush-on treatment is applied to the notched area. Two 10 or 12  mm bolts with oversized washers are used to clamp the two members together. Coach screws (lag screws) may also be used instead of bolts. A bearer is fixed to each post making sure it is level. Lengthening of bearers is done close to the post but not on the post using a scarf joint and fixing gang nail plates both sides of the joint.

2.5 Brick foundation walls

Should a timber post foundation not be suitable, a brick wall can be used instead. This is a popular system for a standard brick and mortar building with a suspended floor system. Pier walls are built on concrete strip foundations. Timber sole plates are fixed to these walls as a fixing base for the timber joists. DPC is used to protect the sole plate from rising damp. Sleeper or internal walls are used to support joists and decreasing spans.

2.6 Joists

These are members that span between bearers and provide fixing for the subfloor or the finished floorboards. See tables previously listed for typical joist sizes as well as spans.

Although 38 mm thickness joists are available, a 50 mm thickness joist will provide a wider butt join surface for the floorboards, if strip floor system is installed directly onto a joist with no end matching. Some joists are more readily available in H2 preservation classification than others.

Joists can either be fixed on top of or inside the bearer. Fixing on top is simple and effective using skew nailing technique. Joists can be joined by overlapping and nailing on a bearer and should not be butt jointed on a bearer.

To limit floor depth, the joists can be connected inside the bearer with a truss hanger (Figure 5). This galvanised steel bracket is available in 38 mm, 50 mm and 76 mm widths and various depths. Levelling a floor can be done on the bearers as well as on the joist, making it possible to result in a well levelled platform.

Note – All crosscut ends and notched areas must be remedially treated with a suitable brush-on preservative to ensure that any exposed untreated core is protected.

2.7 Under floor ventilation

Crawling space under the suspended floor should be high enough to allow a person to move to service the structure. This space is often used for building services and entrance is thus crucial.

Ventilation of the crawl space to extract high moisture air is necessary if walls enclose the area. Cross ventilation openings at regular intervals positioned as high as possible seems to be effective. Openings can be covered with fine mesh to deter unwanted pest entering. Note that repeated painting over the mesh and block opening can prevent moisture extraction. Covering soil with DPC and fixing with 50 mm concrete can also reduce soil moisture escaping into the crawl space.

2.8 Subfloor

Creating a working platform on a suspended floor frame that is only finished with a second layer at a later stage, is highly recommended. The working platform is not only practical and safer for operations but also stiffens the floor system and may assist in sound and thermal insulation. Board products are successfully used as subfloors, e.g. plywood, OSB, blockboard and fibreboards. Note that blockboard should be applied in the correct orientation while OSB, fibre boards and plywood can be applied in any direction. Timber boards can also be used and act as a ceiling for the level below.

2.9 Acoustic insulation

One of the major challenges of a suspended timber frame floor system is the transferal of impact sound vibration to the level below. The issue of squeaking boards will be dealt with, however footsteps can cause a thumping noise. There are some techniques that can reduce this noise.

The simplest method to reduce the impact on the floor surface is by using a shock absorber, e.g. a rug or carpet. Another method is the addition of mass that uses more energy to vibrate.

Concrete screeds can be poured on a subfloor. Typically, screeds are poured at about 36 mm thick, the same thickness than a batten that is spaced on the subfloor acting as a fixing member for a strip floor. Make sure to design the floor system so that it will be able to accommodate the mass of the concrete (+/- 100kg/m²).

Another option is a floating floor system on a synthetic buffer sheet which interrupts the vibration pathway and so reducing the impact noise significantly.

Ceiling sound absorption batting can be installed to muffle some of the impact sound and most of the air borne sound.

2.10 Quiz 1

3. Concrete slab floor

One of the most popular floor construction systems in South Africa is the concrete floor slab that is cast within the foundations walls. Wooden floor covering can be successfully installed on such slabs.

A batten that is used as fixing for the floorboard is fixed to the slab at set spacing, depending on the span of the floorboard. The space between the batten can be filled with concrete to prevent unwanted cavities.

Some wooden floor systems can be fixed directly onto the floor slab. Block and mosaic floor systems are examples of such systems.

4. Wood flooring types

There are several wooden floor coverings that will be discussed in the following section. Specifications also guide the industry regarding quality and installation aspects. The following SANS codes deal with wooden floor systems:

SANS 10281 Hardwood block and strip flooring (out of print)

SANS 10629 Softwood flooring boards (out of print)

SANS 10043 The installation of wood and laminate flooring

SANS 10929 Plywood and composite board

SANS 10400 -Building regulation J Floor

4.1 Strip/board flooring

Solid wooden boards varying in size are one of the most common wooden floor systems used. Board width dimensions vary from 50 mm to 300 mm. Common thickness is 22 mm, however thinner hardwoods of 19 mm are popular and thicker softwood of 32 mm can also be found. Available lengths are around 3 m while more scarce hardwoods might only be available in shorter lengths up to 600 mm.

Usually the boards are moulded into “tongue and groove” profiles that consist of a groove running along the length of the board on one side and a lip on the opposite side. This helps to align the boards creating a continuous flat surface and acts as a fixing place for nails that would not deter the surface. Additionally, should the boards shrink, the gap should not create an unsightly separation split, especially when no subfloor is used. Certain shorter length boards are “end matched” to ensure a strong and level butt joint. This is a lip on the front and a groove on the end of the board. See section later on advantages of installation of this system.

4.2 Panel flooring

The standard shutter ply panel size in RSA is 1220 mm x 2440 mm x 18 mm or 21 mm. This is a popular choice for subfloor because of the ease and speed of installation, and is sometimes left and used as finished floor, especially in industrial application where appearance is not so important. Panels should be nailed every 150 mm to the joists. Another important advantage is the strength and stability of this sheet. Shrinkage is limited due to cross-grain design and strength is uniform due to multiple thin veneer layers overlapping and spreading weak areas.

In the RSA, panels are square edged and joints between panels can become an issue. Panels in certain countries can be ordered with a tongue and groove to assist in installation accuracy and speed.

4.3 Laminate flooring

This product consists of medium density fibreboard (MDF), cardboard and melamine glue impregnated paper film as with a e.g. wood print pattern. The sizes vary slightly and are normally found in 1500 mm x 150 mm x 6-12 mm. The shorter lengths support transport and installation, especially for the DIY market. Clip in type “lip and shelf” edges allow for final finished level surfaces. A large choice of wood prints is available.

4.4 Engineered wood laminates

A 4-6 mm thick wood veneer of solid wood is laminated on a tongue and groove plywood board. This stable board product gives a solid strip floor look with plywood panel stability. The board lengths vary between 1800 and 2800 mm and are wider than solid wood flooring ranging between 190 and 260 mm. The boards can be laid on suspended or concrete slab floors. They are relatively easy to install and available in a wide range of species and looks. The most popular is oak. This is also currently one of the most expensive wood floor products.

4.5 Wood mosaic flooring

These are wood tiles comprising of a material backing with about 8 mm x 20 mm x 80 mm wooden pieces arranged in basket weave or herringbone pattern that glues on. This floor tile is glued onto a level subfloor. The installation is relatively simple but needs sanding and sealing. This system was popular some years ago and is not so readily available in RSA currently.

4.6 Parquet / Block flooring

This is a hardwood wooden block of about 22 mm x 70 mm x 150 mm that is glued onto a level substrate in various patterns. The wood block normally has a bevel machined on the sides, so the face edges fit tightly against each other. Some blocks have a tongue and groove type edge to assist in alignment.  This system also needs sanding and sealing. As with wood mosaic tiles this system is not readily available in RSA currently.

4.7 Quiz 2

5. Traffic and hardness class

The nature of use of the floor will guide the construction and the floor covering. There are 6 traffic classes: three in domestic and three in commercial buildings; 3 subgroups of moderate, general and heavy traffic, e.g. the floor covering in a domestic bedroom does not need to be as resistant to wear as in a school.

Different wood species exhibit different hardness and resistance to indentations. Correct application is important to extend the service life of the floor.

6. Preservation of Timber Flooring

There are a few factors that can cause a timber floor to deteriorate which needs to be addressed for increased service life.

Fungal attack is caused when the moisture content of the wood rises to above 20% moisture content. The highest equilibrium moisture content (EMC) in South Africa is 15% which is well below the limit of 20%. This is the expected moisture of the timber in the specific region after it has reached equilibrium state. Thus, in general timber should not rot if kept dry. Leaking water pipes, unvented soil moisture and areas where water collects continuously on wood, are areas where wood is expected to rot.

Insect attacks occur in timber with a high sugar content and in timber that does not have a natural durability. This occurs in regional areas, mainly around the coastal strips of South Africa. Termite attack can be severe thus precautions should be taken. Removing termite colonies around buildings and treatment of the wood with preservatives are some of the more effective methods. Permethrin chemical can be used successfully to treat wooden floors as it is effective and does not influence the colour of the wood.

7. Wooden Floor Material Conditioning

Before installing wood as a finished floor, it must be at the equilibrium moisture content (EMC) of the area to reduce shrinkage and swelling once installed. It is good practice to store the wood in the building for a few weeks before installation. Elevate the wood from the floor on dunnage and cover top surface tarping to reduce dust and excess moisture. The wood would naturally dry and shrink or moisten and swell to the ambient moisture of the area. For example, in Upington, the wood will dry up to 6% moisture content, and should it have been sourced from George (15% EMC), it is expected to lose 9% moisture and shrink significantly. Should the boards not have been conditioned before installation, unsightly gaps will form over time. If the scenario was to be reversed, boards will expand and could lift from level and cause ridges.

Generally, hardwoods take longer than softwoods to adjust to EMC. However, hardwoods generally show larger dimensional changes due to moisture changes. See table 5 for example of average linear shrinkages.

7.1 Quiz 3

8. Laying of different types of floors

8.1 Laying wood strip / board floor in timber substrate

The laying of a strip floor can be done successfully if basic principles are adhered to. Planning of board alignment needs to be considered when joists are installed as strip floorboards run perpendicular to joists. Should a subfloor be installed, then the floorboards can run in any direction.

Normally the boards will be aligned parallel to the longest length of the area/room/hallway. This not only seems aesthetically more appealing but has a very important stability effect. Timber shrinks and swells as the ambient moisture content changes. This effect can only be noticed over time (weeks) and is species dependant. Wood is anisotropic, shrinking and swelling differently in different directions. Basically, the length shrinkage is much less than the width shrinkage in a floorboard. Accumulative width shrinkage must be limited to the narrow part of the area. This technique will cause less opportunity for floor defects. It is extremely important that an expansion gap of about 12 mm is left open on longitudinal sides (width side) of the floor and 6 mm on the ends (see Figure 29). This allows for shrinking and swelling of the floorboards. This gap can be covered by a skirting board.

The first board is laid groove side to the wall, tongue inward. This board is nailed from the top wall edge and secret nailed in the tongue corner at about 40° to the surface. A punch can be used to drive the head into the board without damaging the tongue with a hammer blow. 63 mm oval nails are used for this application. Predrilling a 4 mm hole in hard timber of easy splitting timber can greatly improve fixing. Pneumatic floor nail guns have reset angles that speed up installation significantly.

Once the first line of board has been installed, the next line is slipped and tapped into position with a hammer and a board off-cut as protection, not to damage the tongue.  A builder’s line can be used on regular intervals to make sure laying is straight and parallel, especially in long rooms. It might be necessary to rip the last line of boards to width and drive a nail through the top surface to fix. Both the first and last boards’ nail heads can be conceived by a skirting that should also hide the expansion gaps.

Floorboards are seldom long enough to cover the length of the rooms and need to be butt jointed. If no subfloor is installed, then the joints must be on the joists. End-jointing boards do not have to be joined on the joist. This is a board-end tongue and groove system that greatly assists with joining and optimization of boards that do not have to be cut back to the previous joist. A staggering of butt joints will increase floor stability and aesthetic value.

If the boards have some deformation, e.g. spring (side curvature over the length), then large side pressure is used to close the gaps between boards. Specialised floor clamps and jacks work well for this. A large flat screwdriver that is knocked into the joist can be successfully used as a prying/pressure lever as well. The gap between boards should be 0 mm on all sides.

Wooden floorboards squeak because of differential movement of adjacent board parts, sliding over each other causing vibration noise. This phenomenon is also linked to seasonal changes in ambient moisture. During dry months, the individual floorboards shrink slightly creating small openings between joints. Foot pressure on the boards cause deviation within this joint area resulting in differential board movement. During the wetter months, this process happens in reverse. This is a very common occurrence in wooden floorboards in a suspended floor, and prevention should be considered during the design and construction of the floor. Use the following guides to prevent squeaking boards:

• Fix each board properly to the substructure (joist). Use longer nails for twisted boards.
• Reduce the span of the board by decreasing joist spacing.
• Reduce joist load deviation by using deeper dimension joists or decrease joist span.
• Use talc as lubrication between boards.

8.2 Fixing wooden floor on concrete bed

Block and mosaic flooring are fixed directly onto the floor slab with glues or bitumen. The quality and levelness of the substrate is very important. Weak concrete will cause ineffective adhesive joints. Slight humps and bumps will not only show on the thin mosaic floor tile but will also cause misalignment.

The laying technique of parquet/mosaic wood floor tiles is much like that of ceramic tiles except that there is no spacing between the tiles to assist with adjustment during installation. Pack out a set of tiles along the length and width of the room to optimize full tile placement. Draw lines on the floor and/or mark references on wall ends. Clean the substrate with a vacuum cleaner and wipe with a wet cloth to remove dust. Use a toothed trowel with 3-4mm indentation to spread adhesive for 1-3 floor tiles at correct volumes evenly. Use manufacturing specification.  Place and press the tile in position. Lay the rest of the tiles in such orientation to repeat the pattern, also making sure that the reference line is adhered to with zero gaps between tiles. Wipe excess adhesive with a wet cloth immediately. Start at blind corner and work way to exit. Tiles can easily be cut with a carpet knife should it be necessary.

Wood block floors are more challenging to install as the wood blocks are relatively small individual members that are laid in several repeating patterns. A bitumen adhesive has proven to work best. Certain block shapes have a tongue and groove like system that assist greatly with block alignment and surface evenness.

8.3 Floating floors

This is a floor system that is not fixed to the subfloor. Laminate flooring is becoming a popular floor system that is developed for the DIY market with easy installation. A thin insulation matt is laid, on which the laminates are simply placed. The system uses a tongue and groove adapted system that clips into each other ensuring a continuous flat surface with no gaps.

Tongue and groove strip floorboards can be glued together on edges, instead of nailed, also acting as a floating floor. If wood with a high shrinkage value is used (e.g. oak or eucalyptus ) it is better to leave the edges without glue to ensure that shrinkage is evenly spread over individual boards.

 8.4 Quiz 4

9. Finishing of wooden flooring

Most newly installed wooden floors need to be finished by patching, sanding, and sealing. Laminate flooring is the exception that does not need either of these two operations, making it the easiest and cheapest wooden floor system to install. However, the other systems do need finishing to a greater or lesser extent. For example, engineered flooring needs much less sanding as board flooring because of its dimensional stability and accurate manufacturing system.

9.1 Patching

Before sanding the floor, it needs to be inspected and repaired if necessary. Filling in knot holes, board defects, installation damage or machine damage with either glueing slithers back or using epoxy resin that does not shrink for filling large holes. Small holes can be patched with a mix of sanding dust and PVA glue.

9.2 Sanding

Sanding is necessary for most wooden floors, except subfloors (that are being covered by finished floors) and laminate flooring (that has a near perfect surface). Floor sanding machines are used to do the major areas and hand belt sanders for the corners and sides. Most common sanders for rent are drum sanders that are robust and easy to maintain, but it needs some skill to produce an acceptable finish. Platen sanders are better as they have a larger contact area and are less prone to grooving. Disc sanders are difficult to operate and cannot control the angle of sanding but should work well on mosaic flooring.

With belt or drum sanding, board floors receive a 45° angle, to grain sand in both directions with a rougher paper (60 grid). This is followed by a fine sanding repeat of direction and final finishing is with the grain direction. Sanding across grain is aggressive and uncontrolled leaving unsightly grooves. Using a sanding machine needs some skill, especially when changing direction from forward to backward movement. At the point of turn the floor will experience more sanding and can lead to deep grooves. Also take care when using hand belt sander in corners as it is not always possible to not sand across grain. Vacuum systems that effectively collect the dust greatly extend the sander belt life and reduce dust inhalation. Clean the floor regularly to inspect the floor condition and to look out for missed spots. Some boards need more sanding than others.

9.3 Sealing

Clean the floor properly with a vacuum cleaner and mop repeatedly until there is no sign of dust. Remember to clean the walls and ceiling as well, as the dust accumulated on these surfaces can contaminate the floor sealant later, spoiling the smooth finish.

There are various types of floor sealers on the market which are grouped in either solvent or water-based products. Some are in gloss finishes and other in matt, with no difference to quality. The water-based sealers are becoming more popular due to reduced health risk during application, and due to the application and cleaning of brushes. It’s always important to adhere to the manufacturer’s instruction. Apply the correct quantity of product on the specified floor area in prescribed layers. Too thin sealer layer may not live up to expectation. Note that high traffic areas will need more layers, e.g. entrances, foyers, and passages. Some sealers can be tinted for colour effects that can be used to create a more even colour effect, should you wish to do so.

There are also several wax finishes that can be applied should sealing be undesirable. Note that waxing a floor can create a health risk due to slipperiness.

10. Maintenance of Wooden Floors

Sand and soil can be very abrasive and quickly scratches the floor sealant away, leaving unsightly patches. Take care to sweep/vacuum regularly. Use felt pad under furniture that is moved regularly, e.g. chairs. Clean these pads routinely as well. A moist cloth (not wet) can be used to mop the floor and caution should be taken not to spill water puddles. Absorb liquid from the floor as soon as possible should there be a spill incident. Remember wood reacts to changing moisture. Under normal wear and tear conditions, the floor should be resealed every 5 years. Some products do not require a complete sand down to the wood surface, but only a light “key” sanding with a fine grid.

10.1 Quiz 5

11. Conclusion

This course should have given you an overview of wooden floors in a South African context and some practical guidelines on design, installation and care of these beautiful and useful wooden floor products.