As an independent flooring inspector, I have repeatedly stated how important it is to check the subfloor to gauge its moisture content. If you do not check it at the onset it may very well come back to haunt you.
Even floating floors:
Builders have a habit of underestimating moisture contents in floors, suggesting that a subfloor is dry enough to lay a wooden floor on with a simple vapour barrier because there is a damp proof membrane installed under the screed. However, as a flooring contractor, you must be strong and insist on carrying out a moisture test. If the RH reading is above the magical 75% then it is vital that an appropriate liquid damp proof membrane (See image below) is installed.
A sandwich damp proof membrane can also be used (See image no.3)
All too often, as a flooring inspector, I am called to look at failed or discolouring flooring (See image below).
99% of the time the failure of the floor is a result of high moisture content and usually coupled with an inadequate damp proof membrane.
As a professional independent flooring inspector, I urge all you contractors to be stronger and insist on installing a suitable D.P.M. Because, if you do not, the floor WILL fail and it will not only come back to haunt you but hurt your pocket.
As my role as a flooring expert I come across floors that have been fitted on top of Asphelt.
Asphelt is a coating that was used frequently up until the mid-1970’s.
It usually has a dual purpose.
Acts as a damp-proof membrane
Is a surface that could be lived on and used as a finished floor.
Usually 19mm approximately thick, it was applied as a liquid that is applied over tar paper. It sets and goes hard.
Like glass, despite appearing to be solid, it remains a liquid.
The problems occur usually when something that is not dimensionally stable is adhered to it.
As a wood flooring inspector or wood flooring expert witness, it is not surprising that the floor covering is often wood.
The symptom is that the once flat wooden floor, has swollen up and now resembles an alpine mogul field.
I usually cut a test hole to reveal that the wood is bonded well to the asphalt, but the asphalt has lifted off the cementitious base.
Wood when exposed to changes in the environment that it has or is living in will either shrink when its moisture content diminishes or will expand as it increases.
The asphalt being bonded to the floor expands with it. The asphalt being laid with no expansion space at the perimeter has nowhere to expand into, pushes up.
If requested as a wood flooring expert to write a specification, I recommend that it is lifted, and the sub-floor then prepared with modern liquid damp proof membranes and smoothing compounds before the acclimatised flooring of choice is laid.
My advice if you are considering covering your asphalt floor is to contact a wood floor expert or wood floor inspector who will I am sure, be only to pleased to recommend a course of action to avoid a costly mistake being made.
As an independent flooring consultant, I regularly get asked to inspect and report on oak wooden floors that have cracked, warped, lifted, or delaminated.
Inevitably the floor failure has something to do with moisture.
Usually, due the moisture content being too high
Less frequent but becoming more common, due to the moisture content becoming too low.
This blog focuses on the latter “ to low”
The dimension of a piece of wood, even if engineered does have a relationship with the amount water that is held within it.
The moisture content goes up = The wood gets bigger
The moisture content goes down = The wood gets smaller
The wood will absorb moisture from above and from below.
For now, I going to assume that you have prepared the floor properly and that there is no risk of moisture ingress from below and have concentrated on from above “ Relative humidity” (this is the water that is carried in the air) and underfloor heating.
I will make one thing clear, engineered boards are not a magic way of eliminating risk from fitting oak floors in areas with under floor heating. An engineered board is usually constructed of a thin layer of solid oak ( Lamella) adhered to plywood.
This piece of solid oak will try to behave exactly the same as a piece that is not adhered to plywood.
This oak layer will get wetter when exposed to high levels of humidity and will try to expand (remember I have assumed that you have prepared the sub floor correctly so that there is no risk of moisture from below).
This same piece of oak will also shrink when it dries out with lower levels of humidity.
You may ask yourself what is all this to do with underfloor heating ?
The underfloor heating also dries the oak out, to an incredibly low moisture content level. This may result in movement “shrinkage” resulting in gaps or splits. Combine the underfloor heating with a low level of relative humidity and the oak will shrink further often resulting in greater splits, cracks, warping.
Turning the underfloor heating on full from being off may also result in your floor splitting, gapping, warping, or delaminating. Can you imagine your cold self jumping into a hot bath . No, you lower yourself in gently so that you gradually get used to the hotter temperature.
The same should apply to the oak floor, you do not want to shock it.
Instead measure the ambient temperature of the room and set the thermostat one degree Celsius higher and then increase this another one degree per day until the desired room temperature is achieved.
I have not mentioned this so far, but it is very important. “ The floor temperature”.
Most manufacturers insist that the floor temperature at the point it is glued to your correctly prepared subfloor is not above 27°C.
Why you ask yourself ?
Remember what an engineered oak floor is made from ? an oak lamella (top layer) adhered to plywood, the key word here is adhered. The whole lot is glued together with glue ! not surprisingly if the glue gets too hot it will melt, soften, and result in a raft of nasty symptoms such as delamination, wrapping, and splitting.
I can not count the number of times that the homeowner has stated that they never have the thermostat set at 27°C. “ it would be far too hot”
I then have to explain that the floor temperature is different to the room temperature and that in order to achieve a comfortable 21°C room temperature, that the floor temperature needs to be higher but this should be regulated.
There is another gremlin lurking in the background “Thermal block” as a flooring consultant I sometimes get asked to look at floors that have failed and the manufacturer is being blamed for the failure as the homeowner has followed all of the rules, so there can only be one culprit faulty flooring.
Wrong ! Beanbags, low level furniture, rugs, packed cardboard boxes sitting on top of under floor heating will allow the heat to build up in the floor allowing it to get too hot.
Like me under my double duvet but with my head sticking out, my head is cool, and my body is roasting and all of a sudden, I wake up in a sweat.
It is the same with the floor 90% of the floor is running at a nice 25 degrees on the surface as the excess heat energy is rightly lost into the room, but under the bean bag , it just builds up and up and up it is not unusual to record 36- 39 degrees where thermal block has been allowed to occur. The result being delamination, warping and lifting.
So here it is in a nutshell
Control the relative humidity, ideally between 40 and 60% RH
Do not turn the underfloor heating on full when it is new or after it has been turned off. Remember measure the ambient room temperature and then turn it up 1 degree per day until you reach your comfy 21 degrees.
Measure the floor surface temperature and never let it exceed 27 degrees at the glue point.
(or whatever your manufacturer stipulates)
Do not sit items on the floor that will allow the heat energy escape into the room.
Please remember to check the manufactures instructions as they may vary from the above.
