How to Properly Prepare Concrete Sub-Flooring

Vinyl flooring has become one of the most popular flooring solutions due to its durability, affordability and most of all, its range of colours and designs. But just like any construction material, vinyl must be carefully installed for it to perform at its best potential. Although it’s generally a straight-forward experience, the preparation of the subfloor has great bearing not only on the finished installation but on the life of the floor covering. An improper job can lead to severe and expensive repercussions. In this article we’ll cover how to prepare concrete subflooring, and the most common mistakes made, the consequences and ways to avoid a disaster in your next project.

Mitigating Moisture

As everyone struggles to meet tight deadlines, often inadequate time is given to allow for concrete to fully dry. Excess moisture can occur during or immediately following the laying of the slab or can linger due to ground moisture entering the slab. Planning and preparation is essential to ensure that the subfloor is ready for the addition of another surface. The quality of the concrete and its water to cement ratio is one of the key factors affecting the drying process.

The lower the water to cement ratio, the fewer pathways that allow water to move through the slab to the surface, and the shorter the drying time required. A ratio of 0.5 or less is recommended. The general rule-of-thumb is to allow one month of drying time for every 25mm of concrete thickness. So for a 100mm thick subfloor, four months would be required to ensure sufficient dryness. Once the allotted time for drying has been allowed, it is necessary to test the relative humidity (RH) which should be under 70% before floor coverings are laid.

Another factor to consider is the alkalinity. When this level is too high, it can stop the floor covering adhesive from bonding properly to the concrete. Australian Standards practice dictates that a pH test must be carried out on all concrete subfloors as part of the pre-installation process. Freshly mixed concrete is extremely alkaline, with a pH level well above 10. The pH levels will drop as the concrete cures and should be within the 9-10 range before proceeding. Last but not least, concrete subfloors that come into direct contact with earth require a vapour barrier or damp proof membrane to prevent the entry of moisture.

Consequences of poorly prepared concrete floors

The consequences can have tremendous adverse affects on the health and wellbeing of occupants and could cause the builder or architect a lot of money and their reputation. When moisture builds up from the concrete subfloor under non-porous vinyl flooring and comes into contact with flooring adhesives, a chemical breakdown can occur which releases volatile organic compounds (VOCs) into the air, often rendering a room uninhabitable until rectified.

Additionally, if moisture rises from the slab to the flooring, the dampness and high alkalinity can lead to mould growth, which if not picked up early can quickly spread, creating not just an unpleasant odour, but potentially harmful health issues including allergic reactions such as sore eyes and runny nose, and more serious respiratory tract symptoms.

Dampness rising from the subfloor can cause the glue used to lose its adhesion, causing the flooring to bubble or warp. As the issue generally won’t occur until many months after a project has been completed, the costly exercise of replacing or repairing the floor can often lead to lengthy unwanted disputes between builders, designers, developers and occupants.

Polyflor is here for you

The cornerstone of the Polyflor philosophy is an assurance of product superiority, customer service and technical support. Polyflor provides full technical support along with screeds, adhesives and moisture barriers to ensure a smooth installation. Don’t hesitate to get in touch if you need assistance any step along the way!