In a lot of circumstances a new floor can go on top of an old one. With the obvious benefits being it’s easier, less labour, no uncovering anything nasty, extra insulation. However, there’s a science to this that you should consider before doing so. In this article I’m NOT going to give blanket advice that any floor covering can go on top of anything because that simply is not true. I’m also NOT going to go through a multitude of floor covering options, both new or old, giving you a million combinations. I AM going to give you the critical information you need to decipher whether fitting your particular floor covering onto your particular old floor covering is going to work. So let’s get started…
The first tool in your box is to recognize if your new or old floor covering is sensitive to moisture like solid wood, engineered wood, or laminate flooring etc. If either your new flooring (the floor going on top) or old flooring (the floor being left beneath) is sensitive to moisture, then STOP and think!
What does moisture sensitive mean in this context? A material that will change dimensionally or structurally when exposed to certain levels of moisture.
A lot of properties in the UK have been built prior to 1965. Protection from rising moisture wasn’t on the priority list before 1965 and damp proof membranes (DPMs) were rarely used beneath solid sub-floors. What does this mean to the layman. Well, on solid sub-floors without a DPM, your concrete slab is continually wicking up moisture. This moisture often evaporates through the floor covering i.e. stone and ceramic (evaporation through grout), textiles (evaporation through fabric).
It’s helpful to note that different materials will allow moisture to pass through at different rates. Understanding this, now fit a moisture sensitive floor covering (that allows moisture to pass but at a slower rate and is effected greatly by high levels of moisture such as laminate or real wood) on top of a floor covering that is constantly allowing moisture to pass and you have a bottle neck. In other words a gradual build up of moisture that could eventually effect your new or old floor covering. Let’s also be clear, even in properties where there is a DPM beneath the original concrete or in the instance of a suspended timber floor, that doesn’t mean that a build up of moisture is not possible. There are many circumstances that can create a build up of moisture in properties both pre or post 1965 i.e. concrete slabs that have high levels of moisture within them prior to the installation of a floor covering thus slowing down the natural moisture evaporation rate, or a lack of ventilation (subsequently resulting in a rise in humidity/moisture levels) with a suspended timber floor, perhaps due to an extension to the property or a blockage of the ventilation due to building rumble or blocked air bricks etc.
There are ways to protect against such rising moisture, however, you must understand the right ways to do it. Here’s an article that will help. It’s also advised to read all manufacturers installation literature for guidance before you install your new floor covering.
Now let’s look at this from the opposite angle. What if you wanted to fit a none moisture sensitive floor covering i.e vinyl, on top of a moisture sensitive floor i.e. Wood or laminate. Now the bottle neck I mentioned above becomes more like a complete dead end, do not pass situation for any moisture! This can result in a build up of moisture to the underside of your new floor covering. If the new flooring has been bonded (adhered), you can expect de-bonding due to this build up and the breaking down of the adhesive used. If the new floor covering has been floated (installed without the use of adhesive) and you have even been diligent and used a 1000 gauge visqueen sheet, although the new floor covering will be well protected from moisture, you may experience a constant damp and musty smell through your property due to the build up of moisture stagnating.
The effects of trapped moisture can also directly affect the original flooring below! For instance, a classic method of installing solid wood parquet blocks was to use a bitumen resin (as the bonding method) directly to a concrete sub-floor. The bitumen also being used as a DPM. Wood IS a moisture sensitive material. Over time, bitumen can become brittle and crack, allowing moisture through. Bitumen can also crack due to the shear forces imposed on it by the natural seasonal expansion and contraction of a solid parquet floor. Certain lower levels of moisture will often pass through a parquet floor without any adverse effects being noted. However, increase the amount of moisture the wood blocks are subjected to by hindering the transmission of moisture by covering the blocks with a floor covering that does not allow or slows down the rate at which moisture can pass and the wood blocks will expand excessively, often resulting in ‘cupping‘ or ‘buckling‘. The obvious consequence of this being the potential failure of your new floor covering.
The second tool in your box is to understand how your new and old floor covering are going to react to each other in terms of movement. For instance, laminate flooring expands and contracts seasonally with changes in humidity. With this in mind you can see that installing a carpet directly to a laminate floor may result in the carpet becoming saggy when the laminate floor below contracts come the winter months.
Questions to ask.
What type of new and old floor coverings do I have? – Are either moisture sensitive?
What could happen if I install my new floor covering on top of the old one? – Could this create issues with moisture?
How is my new floor covering going to react to the old and vice versa? – Will my new or old floor covering move and how will either be effected by this?
Is my old floor covering an acceptable substrate for my new covering? – Is the old covering too spongy perhaps?
What other precautions can I take to facilitate and give greater guarantees to a long term and satisfactory outcome? – Would it be best to remove the old floor covering and essentially start from a fresh?
There are often consequences to cutting corners. In certain situations installing a new floor covering on top of an old one will be fine and on occasion may actually be beneficial. However, be sure to ask the right questions to yourself or your installer before you do so as a failed floor can be extremely expensive and inconvenient indeed! The path to knowledge isn’t always about knowing everything, it’s about knowing the right questions to ask!© Copyright 2015 Wes, All rights Reserved. Written For: Fitmywoodfloor