A new concrete slab is a huge consideration with regards installing a wood floor. Here I have compiled a simple guide for you to follow.
Before installing a wood floor over a concrete slab whether new or old, the slab must be adequately dry! A rule of thumb for new concrete is one month per inch or one day per one millimetre drying time. This rule of thumb should never be used as the single basis to start a wood floor installation. Wood floors can be expensive and it’s heart breaking when they go wrong.
The concrete slab, again new or old, should be tested using a surface relative humidity meter. A reading of less than 65% RH is required prior to installing a wood floor directly to a concrete sub-floor. Although adequate moisture protection layers such as a liquid moisture suppressant is well advised regardless. Some of these can be used to suppress moisture in concrete with readings of up to 98% RH.
Drying times can differ greatly, and are subject to many factors
- The type and mix of concrete used. For example a slab that has been made from a water dense mix may take several months extra to dry out compared to a drier mix.
- The depth of slab. Referring back to the rule of thumb, a thicker slab will take far longer to dry than a thinner slab.
- Rainy weather and inadequate protection of the slab can see the concrete soaked and hugely increase the drying time.
- Low temperatures can increase the drying time. If the slab has been installed at any point during winter, this should be considered when applying the rule of thumb guide.
- Poor ventilation can increase the drying time. As the slab releases moisture vapour, that vapour needs to be removed from the property. A fully sealed property will trap most of the moisture resulting in some of the vapour returning to the slab and also potentially preventing further vapour release until adequate air flow has been introduced. If this was the case at any point during the drying process, it is clear to see that the overall drying time could have been increased.
Many of the factors above are often subject to someone’s opinion or information. For instance a client may be told that their new concrete slab is five inches thick when it may be six inches thick or a client may have been away for some of the construction process and not fully know the weather conditions or how the slab was helped to cure etc.
The reasons above and more besides are why you should never guess at how dry the slab is. If a builder tells you the slab is dry by a simple knowing glance, do not take this as gospel. A concrete slab may look dry but can hold moisture deep within that WILL come out.
Even if the slab has been down for eight months and is perhaps five inches thick. In this circumstance you may believe that over exceeding the rule of thumb guide, you’ll be in the clear. It is well advised that you should not take this approach. Always have the slab tested as per the recommendations above.
There are ways to install a wood floor on a wet slab. These are classed as fast track methods such as liquid damp suppressors or even certain adhesives. However, to use any such products effectively, it is necessary to know the exact relative moisture content of the slab.
We can’t all know the complete technical in’s and out’s of the process of drying times in concrete. There are simply too many factor’s involved. As promised I wanted to give you a simplified approach to addressing this issue.
That approach is this.
- Step 1 : Use the rule of thumb drying guide at first to give a rough idea of drying times and take note of the day the slab was first installed and the conditions during the drying process.
- Step 2 : Hire a surface relative moisture meter or contact a company to assess the moisture content for you. The latter being the ideal as further advice from an experienced person can be very helpful.
- Step 3 : Use adequate moisture suppression that suits the moisture content of your slab and the time during the curing process that you wish to install the wood floor. However, if you wish to install the wood floor close to the installation of the slab, be very careful as other conditions can effect your new wood floor, such as other wet trades i.e. plasterers or plumbers, resulting in increases in relative air humidity. Do not attempt to install a wood floor before the windows and heating system have been installed and are working correctly.
My aim here was to break this process down for someone that is new to concrete drying times and to do it in a short simple way. I hope I’ve done that but should you have any questions or comments, please leave them below or drop me a line.© Copyright 2013 Wes, All rights Reserved. Written For: Fitmywoodfloor