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Fitting a Karndean floor

Subfloor Preparation

It’s well-documented that the longevity of a flooring installation - particularly when it comes to luxury vinyl flooring like Karndean - is dependent on the quality of the subfloor. Sometimes we find ourselves more concerned with the final result, and so may spend less time ensuring the subfloor preparation is perfect.


To ensure your designflooring installation looks perfect, here’s a few vital subfloor checks…

Remove and smooth

If you're not laying Karndean over your existing flooring, be sure to check that there are no traces of adhesive residues. It’s important that before you apply an ounce of smoothing compound or begin screeding, there are no obvious lumps and bumps in the subfloor, simply to ensure a smooth as possible finish.


Check the moisture level

LVT products must only be installed on subfloors with moisture levels below 75% relative humidity (RH). If your hydrometer reading is above 75% RH, regardless of whether the floor is old or new, it’s imperative that you install a surface damp proof membrane (DPM).


Wooden subfloors – Karndean do not endorse/approve any plywood product and so take no responsibility for the performance of any plywood selected. However, we recommend the use of a minimum 6 mm flooring grade plywood meeting the requirements of the CFA Guidance Note:-Plywood for Overlaying Suspended Floors, (soon to be included as Annex C in BS 8203)  as acceptable for use with Karndean products. It is incumbent upon the installer to verify this compliance through either independent certification or other means. It’s important to remember that plywood joints should be smoothed over using skim coat or a full coat of fibre reinforced smoothing compound.


Concrete subfloors

If you’re installing our designflooring on either a new or old concrete subfloor, as mentioned, it’s essential to conduct a moisture test to ensure the levels are no higher than 75%RH. If moisture levels are too high and you don’t have sufficient time to allow the area to dry out naturally, then be sure to install a surface damp-proof membrane. If RH readings are suitable for installation and the surface has been primed, apply a compatible smoothing compound to a minimum of 3mm.


Get screeding

Choosing the right smoothing compound is very much dependent on the kind of project (residential, commercial, retail etc), its size and timescale. If prepared and installed correctly, this thin cementitious top layer will ensure that your floor copes easily with the hardships it's put it through. As such, it's important to consider ambient conditions (ventilation, humidity etc), installation specifications, as well as the curing times.  


For further information on subfloor preparation, download our installation guidelines.