As stated in the name, this is when flooring experiences horizontal or vertical movement. It may be more appropriate to call this problem failure of bonded floors, as the problem is not always caused by poor adhesion.
Failure of adhesion can come about in many ways, each of which is avoidable if good practice is followed. The failure of adhesive bonded floors can be categorised in four basic ways.
Because bonded floors can fail due to exposure of wood to excessive moisture without any other contributing problem, when trying to identify the cause of failure of bonded floors the problem of excessive moisture should first be investigated.
Where individual flooring elements have cupped there will invariably be a problem with moisture. Flooring elements can be uplifted and moisture readings taken to check for abnormally high results, or abnormal variation between the upper and under sides of the product. Moisture readings of the sub-floor itself can also be checked.
Where no moisture problem is found, adhesive bonded floors may still fail because inadequate or complete lack of space for expansion has been provided in the installation. Factors which affect the amount of expansion a floor will include timber species, size of the floor and the moisture content of wood / RH of environment.
Where floors expand and meet an obstruction such as a wall, structural support, or hearth, horizontal pressure builds up on the obstruction and horizontal and vertical pressure builds up on the floor. Eventually the vertical pressure exceeds the adhesion strength resulting in the failure of adhesion, the floors lifting or buckling, or flooring elements simply becoming loose.
Failure can come about where the moisture content of the flooring and the ambient conditions (temperature / Humidity) are incorrectly matched. BS8201: 1987 recommends a 15-19% mc for wood flooring used in unheated environments and 10-14% moisture content for intermittently heated environments, 9-11% for continuous heating, (e.g. Typical domestic)
Where excessive environmental moisture or inadequate provision for expansion are not at fault for contributing to this problem, poor adhesion will be found somewhere within the floor
In order to identify the problem more specifically, a loose flooring element can be taken up and the point of the failure identified. It is important to note that any of the following points of failure can occur in combination with the previously mentioned causes. It is therefore necessary to assess these factors first before identifying poor adhesion as a cause.
Concrete hardens not by drying but by a process known as hydration. During the chemical reaction, calcium silicates form two new compounds. The principle new compound is Calcium Silicate Hydrate Gel (C-S-H). This compound results in the engineering properties of concrete including its strength. The cohesion of concrete and sand-cement sub-floors develops over a period of time whilst simultaneously moisture-curing. Once the RH is below 80%, the hydration process of the floor virtually stops and strength development stops with it. Trying to accelerate the drying of the mineral base by heat and / or dehumidification can lead to a reduction in the development of cohesion and can contribute to floor failure, especially in thin screeds. Inadequate cement used in making screeds can also result in poor cohesion Where direct bonding to mineral bases, a flexible adhesive may reduce the transfer of stress to the sub-floor from movement of wood floor covering.Shows how the strength development of concrete depends on the length of moisture-curing period.