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21(6)x189 Unfinished Oak Flooring (for finishing on site)

£38.96 ex VAT per m2(£46.75 inc VAT per m2)

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This unfinished engineered oak flooring is 21mm thick, made up with 15mm of Eucalyptus plywood underside that is bonded to a full 6mm French oak wear layer that is 189mm wide single strip oak; showing off the extra width that is available when ordering from our range of engineered oak flooring products.

Our unfinished mixed grade 21x189mm engineered oak flooring is suitable to be installed over under floor heating. The engineered boards do not have a softwood core and they are strong enough to be fitted using any of the three common methods of gluing down, nailing down or floating.

The unfinished engineered oak floor is sanded ready to receive the finish of your choice after installation. You can create whatever colour and style of finish you want for your room simply by finishing the floor with a product such as wax oil.

Unfinished mixed grade engineered oak flooring allows you to create a variety of looks; from a contemporary, modern look in your home or venue through to darker, deeper tones that can create a more antique or vintage appearance.

This flooring is particularly popular in rooms with large staircases and similar features because the floor can be easily finished to match up with the rest of the room. By finishing this flooring on site in your home or venue, a “seal” is achieved between each board, which is particularly useful for areas that might have spillages occur. Having said that, any spillages will need to be cleaned up quickly to avoid lasting damage to any timber flooring.

By choosing our unfinished 21x189mm engineered oak flooring, you are able to create a bespoke look to your floor that can be changed by simply adding more waxoil in the colour of your choice, giving you increased flexibility in changing the look of your room.

Additional information

Weight 30 kg

Unfinished and sanded for site finishing

Board Thickness

Board Width


Approx 85% @ 1830mm long, 15% shorter

Oak Wear Layer




Moisture Content

6-9% on arrival to site.


6mm Oak on 15mm Eucalyptus plywood: structural


TG4: T&G sides & ends, all micro bevelled

Length Tolerance

+/- 1.0mm

Width Tolerance

+/- 0.2mm

Thickness Tolerance

+/- 0.5mm

Carton Size and Weight

1860 x 195 x 130 weighing 30kg each

m2 Per Carton


m2 Per Pallet

72.8 (35 cartons)

Installation Method

Float, Glue Down, Nail/Screw Down

Suitable for UFH?


Can be floated, nailed down or glued down.

For more information on these fitting methods, please see our Fitting Guidelines guide.

Installation Above UFH Our 21mm Engineered Oak can also be fitted above underfloor heating when the correct installation guidelines are followed and the necessary levels of heat, humidity and moisture are maintained by the owner after installation. However it should not be used in this situation as your primary heat source because the 21mm thickness can 'hold' heat within its structure, so UFH systems can continue to 'dry out' the flooring further after installation, even when the correct acclimatisation process has been followed. This can cause dimensional movement within the floor and sometimes create a 'de-lamination' effect because the 6mm oak layer is so strong that when it wants to move, it actually 'pulls away' from the plywood base.

We recommend using our 15mm board with UFH because it has a lower thermal resistance than the 21mm board, thus allowing the transfer of heat more easily and quickly.

We can supply a Self-Regulating UFH System that's perfect for use with our Oak Flooring because it never overheats, making it safe and super energy efficient.


Sometimes the plywood backed engineered boards will seem as if they are ‘bowed’ from end to end when they are first removed from the packaging. This is very common with a plywood backed product because of the difference in molecular structure of the solid oak face and the plywood backing.

It is not a fault with the board and should be expected. It does not cause any problems during installation because of the required staggered joint fixing for an oak floor. Obviously as each board is ‘surrounded’ when fixed, by at least another 4 boards, it is straightened and aligned perfectly every time. In fact, some fitters claim this actually strengthens the floor further.

Although our engineered products have an underside of high quality plywood and are designed to provide extra stability after installation, they’re still constructed of all natural products.

After proper and sufficient acclimatisation, the conditions during installation should be maintained as consistently as possible thereafter for optimum performance and to avoid dimensional movement of each board within the finished floor.

For information on important, ongoing maintenance, please refer to our Care & Maintenance guide.

Weather, Humidity, Temperature and the Ongoing Maintenance Of Your Flooring

Because oak is a natural, hygroscopic (water absorbent) material, and its dimensions are directly relative to its moisture content, we must control and maintain the relative humidity within our homes to enable the moisture content of our oak flooring to remain constant. This will ensure stability of each board within the finished floor, because failure to do this may force these boards to change dimensionally and structurally. This is not at all a fault of the flooring itself but all to do with the conditions that it’s being forced to endure.

Here’s an example of what can happen when the outdoor temperature is 0°C

The maximum amount of water that a cubic metre of air can hold at this temperature is 5 grams, so when you bring this cubic metre of air inside and heat it to 25°C, the relative humidity drops to only 23%.

We actually recommend a minimum of 40% for optimum floor stability (incidentally, this is also the level that health experts recommend for our bodies too, so good for our floor and good for us).

But it gets worse as the temperature outside falls lower, and this is why the air inside any heated building in the winter can become too dry, which can obviously have an effect on our flooring (and our bodies).

When relative humidity is allowed to drop too low, our flooring is forced to lose moisture itself and will try to curl upwards towards the dry air (similar to a piece of bacon under a grill) in an effort to find moisture.

Any time the temperature outside is well below freezing, relative humidity inside will be below 20% unless you do something to increase it, and not increasing it can have a devastating effect on your oak floor.

Our 21mm Engineered Oak is constructed as a multilayer board, consisting of a Solid European Oak face or wear layer of 6mm, with a 15mm quality plywood backing that forms the T&G, and provides a good strong underside suitable for installation by nailing, gluing or floating. The underside is also ‘sealed’ with a final stabilising veneer.

Our Engineered Boards do not have a softwood core and because of this are strong enough to be fitted using any of the 3 common methods; Glue Down, Nail Down or Float.
  • 21mm Overall Thickness
  • 189mm Wide
  • Single Strip Oak Face
  • Mixed Grade, so will contain natural grain and colour variance, sapwood, and various size knots (some filled and sanded). Grade details are explained below
  • 15mm (9-Ply) Eucalyptus Plywood Backed
  • Full 6mm Wear Layer of European Oak
  • 75% Lengths of 1830mm
  • 25% Lengths of 610mm, 915mm or 1220mm
  • Moisture Content 6 – 9%
  • Micro Bevelled Sides & Ends
  • TG4 End Matched
  • 2.08m2 Per Carton
  • 72.8m2 Per Pallet
  • Extra Important Detail;
    • Extra Stabilising Veneer to Underside (extra stability after installation)
    • Very Accurate Machining Tolerances for Fast & Simple Fitting (saves on fitting costs)
    • Angled T&G Joint for Excess Adhesive (reduces risk of excess adhesive reaching the surface)
  • All our flooring products are machined to very accurate machining tolerances for fast and simple fitting.
  • Length Tolerance: +/- 1.0mm
  • Width tolerance: +/- 0.2mm
  • Thickness Tolerance: +/- 0.5mm

Grades Explained  Grade A
  • Very few knots if any and no sapwood allowed
  • Clear and consistent grain pattern
  • Very few natural features
  • Slight colour difference allowed
Grade B
  • Small, live knots allowed up to 15mm
  • More natural grain pattern and filled dead knots up to 15mm allowed
  • More natural features allowed
  • More natural colour difference allowed
  • Sapwood allowed up to 10% of face area
Grade C
  • Bigger knots allowed, some repaired with filler before being sanded
  • More natural grain pattern allowed
  • More natural features allowed
  • More natural colour difference allowed
  • Sapwood allowed up to 15% of face area
Grade D
  • Large knots allowed, some repaired with filler before being sanded
  • All natural grain pattern allowed
  • Most natural features allowed
  • Significant natural colour difference allowed
  • Sapwood allowed up to 30% of face area
Celtic Character Rustic
  • Contains all of the above grades and also some lower grades
  • Lower grades allow open natural defects that are repaired with dark filler before being sanded
  • All natural features allowed
  • All colour differences allowed
  • All sapwood variances allowed