Timber floor preparation

There are three common sub-floors that you will encounter when preparing to lay down a timber floor. We'll tell you what they are and how to deal with each.

Timber floors
ARTICLE Nicol Botha

There are three common sub-floors that you will encounter; these include joists, particle board or plywood, and lastly concrete. All three sub-floors require different preparation before the timber can be laid.


It is important that all nails, staples, glue residue or anything that is fixed to the top of the joists is removed and the surface is smooth and clean. If any of these are not removed you will find the new floor won’t be level and there will be movement between the board and the top of the joist. This can cause creaking when walking across the floor or the movement could work the adjacent boards loose over time.
joist diagram
Depending on the direction that the new boards are running, you need to ensure there are nogs installed between the joists. Nogs are additional supports which run perpendicular to the joists. If your new floorboards are spaced parallel to the joists then nogs are required, however if the boards run perpendicular to the joists then you don’t need to worry about installing nogs. The above diagram shows a floor with no nogs where the floorboards run perpendicular to the joists.
Lastly, it is important to ensure that there are joists or nogs around the edges of the room to support the ends of the boards. Leaving the ends of the boards floating without supporting them will result in a “spongy” feel underfoot and will cause the boards to crack over time.

Particle board/plywood

Particle board or plywood follow similar lines to joists in terms of preparation; it is important to ensure that any nails, staples or old floor coverings are removed. The adhesive used between the sub-floor and the bottom of the boards requires a clean surface to ensure proper adhesion. If there is any residue present, a drum floor sander will be required to sand the residue off.
Particle board can show signs of water damage if it has gotten wet in the past; signs to look for include swellings or the particle board crumbling. If the damage is minor, a sander can be used to level these areas, however if the damage is severe and the integrity of the particle board has been compromised then these areas will require replacing.
plywood floor
Whether your subfloor is particle board or plywood, it is important to check the seams where the sheets meet; these need to be flat and level. If you have any unevenness or a ridge where the sheets meet, a drum sander can be used to sand these flat.


Concrete requires a bit more care and preparation than the previous. If the slab has recently been poured then generally it will be fairly flat and clean, however older slabs might have signs of damage or aren’t flat.
The first issue is to ensure the slab is level. If there are high points, a concrete grinder will be required to remove these. A general rule of thumb is that the tolerance will need to be within 2 to 3mm across a 1m area.
Secondly check for any damage; if there are holes present these will need filling in the floor leveling compound to create a flat surface.
The overall condition of the slab will need to be clean and free from paint, glue or any other residue that might be present.
Once the slab is level and clean a moisture barrier will be required to stop any moisture raising up through the slab and condensing between the board and slab.
If this occurs the adhesive can be affected, causing boards to lift off the concrete. Moisture barriers are generally a 2-pot mixture and vary from single coat systems to multiple coats being required. (Check the application instructions for your chosen brand).
A moisture barrier is only required if the concrete slab is in contact with soil. Second storey slabs do not require moisture barriers.

A few tips to make your life easier when installing your new timber floor:

Remove your skirting boards before you lay the timber, trying to undercut skirting boards is a very time consuming task or if you lay timber up against the skirting you will need to fill the expansion gap with coloured chalk which never matches the timber perfectly.
Use plenty of adhesive when laying your flooring on concrete, particle board or plywood. Rectifying boards that have lifted due to insufficient adhesive at a later stage is a major.
Use weight - if laying on concrete buy some cheap 99c buckets from a hardware store and fill them with sand to weigh the floor down while the adhesive sets.
For more information, visit the Endless Flooring website.

You might be interested in reading: Replacing carpet with wooden flooring.

This article by Nicol Botha featured on page 37 of Issue 013 of Renovate Magazine. Renovate Magazine is an easy to use resource providing fresh inspiration and motivation at every turn of the page.

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*All information is believed to be true at time of publishing and is subject to change.

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