In my experience, more often than not, floors warp, bubble and "let go" due to the presence of moisture in the concrete from hydro-staic pressure or green concrete. Alot of people consider concrete to be dry as soon as it can be walked on, but this is not the case. A moisture barrier must be used to solve these problems.
Throughout my career as a flooring contractor, I have come across countless numbers of timber and vinyl floors that have failed due to one reason or another. After thorough investigations more than 80% of these floors have failed due to either wet concrete or hydro-static pressure. To my amazement most of these floors had never been moisture tested, (a very quick and easy test). Time and time again I hear builders saying "she'll be right mate the concrete's been down for weeks".
To conform to the Australian standard of flooring installations, concrete must have a reading of no greater than 5.5% moisture content. As a general rule of thumb, concrete dries at approximately 20-25mm per month.
If you take these figures into account, then a average slab of 100mm thick can take 4-5 months of drying time before it will conform to Australian standards. If, in this drying process, the concrete is exposed to rain or any water again, this will further increase the drying time. Concrete is like a sponge and will continue to absorb water if present. These times can vary due to surrounding conditions etc. It is generally a myth that concrete dries faster in hotter climates. In hotter climates you normally find that relative humidity is alot higher, meaning there is much more moisture in the air, which will slow the drying times even further.
The other concern for installers is hydro-static pressure. Hydro-static pressure comes from underneath the concrete and moves it's way through the capillary voids in the matrix of the concrete. Once a floor has been installed, it will draw any moisture present in the concrete to the surface and if there is no means of escape will react with, and break down glue's etc. Hydro-static pressure can come from a lack of plastic underneath the concrete or such things as a hidden spring running underground which is forcing the water up through the concrete. Water has only 2 objectives in it's life, to fall down and to evaporate back up into the atmosphere. Floors such as ceramic tiles generally do not suffer from this problem as they can breath through the grout, but vinyl and timber are very prone to hydro-static pressure. The glue underneath the vinyl will break down and timber floor boards will cup.
The most effective way to deal with both of these problems is to use a moisture barrier. Most people will shy away from this because of the costs involved. I can not understand this thinking considering the cost of the floor installation in the first place, and for a few more dollars they can ensure there floor will still be in tact many years down the track.
Moisture barriers have come a long way in recent years and have become very cost effective. Gone are the days of 2 part epoxy membranes that require3-4 days for installation and a topping over them to smooth the surface. This is a very costly exercise which can blow out costs to $50-$60 per m2. There are now moisture barriers that are sprayed directly on to the concrete and penetrate deeply into the matrix forming an internal barrier. These products are considerably cheaper and more time efficient in comparison to the old methods. One particular product that I have used is specifically designed for the flooring industry and if sprayed onto the concrete at time of pour will give a perfect cure as well as lock up excess moisture and allow you to lay floor coverings inside of a 14 day period, as opposed to 28 days with typical moisture barriers. These are a very cheap alternative and can be installed for $12-$15 m2, saving alot of time and money.
This product can be sprayed in a matter of hours (for a 200m2 floor) and has virtually no down time for other trades. The other great thing about this product is that it can be worked over by other trades almost immediately after installation without compromise to the product. The old system of epoxy membranes had to be well protected up until laying, as 1 pin hole in the barrier rendered it useless.
This particular product is a colloidal silicate and should not be confused with a much cheaper and inferior sodium silicate.
This moisture barrier can be directly installed over without the need for a self levelling compound and has no known adhesion problems with any of the leading brands of glue, polyurethane or self levelling compounds.
Colloidal silicates will remain in the concrete for the life of the concrete and this particular company gives a 20yr guarantee against any hydro-static pressure.
In conclusion, I would recommend a moisture barrier under any floor covering whether it has problems yet or not. These products are very cheap and give peace of mind that no further moisture related problems will occur down the track.
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