In this article, we will look at why MDF is not a suitable material for any type of sub floor. This includes small patch jobs and replacing individual boards. As well as jobs where larger areas are being covered.
The sub floor is a material that is fixed on top of the structural joists in a property. Its main function is to provide a flat, level, and stable surface for the finished floor to be laid on. In most properties the sub floor would be some form of timber floorboards, or an engineered sheet such as chipboard.
Other materials can be used, such as plywood and OSB. However, these are generally more expensive. In most older properties you will find standard timber floorboards. Whereas, in more modern and new build properties, chipboard flooring is more common.
All of the above options, provide a relatively strong level surface that distributes weight across the joists evenly.
Why MDF floorboards don’t exist
Unlike the materials we have mentioned previously, MDF isn’t a good option for this job. Below are 5 of the main reasons it shouldn’t be used in place of floorboards, or other engineered flooring sheets.
MDF does not have the load bearing capacity of other materials commonly used for floorboards. Solid wood takes its strength from the long fibres that run along the length of the board. These fibres result in high tensile strength and create a stable and durable surface.
Engineered woods that are commonly used in place of floorboards, also have good load bearing capacity. This is due to the way they are made, and the type of materials used to form the sheet. For example, plywood combines multiple layers of solid wood. Each layer runs at a right angle to the next. This cross lamination creates a strong, high load-bearing material.
Something more common like chipboard isn’t as strong as solid wood or plywood. However, it is still considerably stronger than MDF. This is due to larger particles of wood, combined with strong resin adhesives. It also benefits from interlocking t&g joints.
In comparison, MDF is much weaker under heavy loads. The material is essentially made from wood dust and adhesive. This does result in a versatile material that can be used for a wide variety of jobs. However, it also means it can’t support heavy loads without bending or breaking.
All floors will have some level of flexibility. This usually allows them to expand and contract slightly with changes to temperature and humidity.
MDF on the other hand, tends to be very flexible. This can result in bounce as foot traffic moves across it. As well as more pronounced bending and sagging over time.
Long term resilience
Due to its poor load bearing capacity, and its high flexibility, MDF is far less resilient. With increased foot fall and additional weight over time, it is likely to deteriorate and result in an uneven surface.
Also, as the material becomes weaker due to wear and tear it becomes far more likely that it will break.
Poor moisture resistance
One of the secondary functions of a sub floor, is it protects from moisture. The floorboards act as a barrier that stops moisture from reaching the finished flooring above.
This is a common complaint with cheaper flooring options like chipboard, as this material does absorb moisture and can swell. However, MDF is far worse in this regard. MDF is highly absorbent, and it can swell and become weaker when exposed to moisture. As a result it is more susceptible to damage and sagging.
No tongue and groove
Due to MDF being such a bad material for floorboards, there are no companies that make a specific flooring product with interlocking tongue and groove joints.
And why would they?
We have already established this is a very poor material choice for flooring, hence no one makes an MDF floorboard product.
The fact that MDF isn’t made with a tongue and groove joint just adds to its unsuitability. Due to this, it is more prone to movement. For example, because MDF is prone to sagging, swelling, and even breaking, the chance of an uneven surface is far more likely without interlocking joints.
Using MDF as a sub floor, or even to replace individual floorboards is generally a bad idea. It is not designed for this type of installation and can result in a whole host of problems.
There may be some unique circumstances where you could get away with using MDF, but these will be extremely rare.
For example, if you had a very small patch job in an area with no footfall, it might be acceptable, if it is all you have access too. However, in my opinion, this would be rare. In 99% of cases, choosing a more suitable material would be the correct choice.