The quality of the finished wearing surface is very much dependent upon the quality and preparation of the sub floor and foundations.  Any shortcut in these areas has the potential for failure of the building and floor system.

Poor quality workmanship in floor screeds can have issues for the thinner-wearing surfaces such as vinyl.  The thinner the wearing surface, the more noticeable any defects and variations will be.

Foundations
Any building requires foundations that are adequate to ensure its stability.  Without suitable foundations, any building is liable to move over a period of time.  It is essential for any permanent brick/block or concrete constructed building to have foundations suitable for the size and weight of the building and local ground conditions.  It is important to take into account the vegetation around the building, the proximity and type of trees, the type of soil and other issues such as old mine workings etc.  Also the removal of large tress has a noticeable, long-term effect on local ground conditions.

On sites that have firm, shrinkable clay soil, it is not uncommon to find that foundations have to go down to a depth of 1metre.  A local structural engineer is the best person to advise on the suitability of foundation types and depths.  Any concrete slab base should have a well-consolidated base, and allowance made for expansion and contraction.

New Concrete and Screed Bases
One of the main reasons for the failure of wearing finishes is moisture in the substrate.  In order to prevent failure of the screed and wearing surface, it is essential that the substrate be allowed to dry out properly prior to the wearing surface being laid.  The timescale required to reduce the level of humidity in the substrate will vary depending on the building design, the thickness of the slab, the ambient temperature, special concrete mixes, etc.

Then general guide time for drying is 2 day per millimetre of thickness of substrate.  On this basis, a concrete slab of 150mm/6" thickness with a 75mm/3" sand/cement screed could take 225 days.

Obviously, this is not practical for most construction projects.  In extreme cases, the use of suppressants can be used.  The general guide for the laying of finished products to ensure that the substrate has a moisture level not exceeding 75% Relative Humidity.  To ensure the RH levels, a Hygrometer should be used.  The readings need to be taken over a 72 hour period to give an accurate result.

Damp proof membranes
All concrete bases should have an effective damp-proof membrane (DPM).

If you are carrying out remedial works to an older building, particularly one that has an agricultural history, check to see if it has a DPM.  If in doubt, ask a local builder to carry out some investigative work to establish if one has been installed.

Movement
Any flooring product should allow for any flex or movement.  A rigid screed won't allow for flex and will crack.  Any limitations of a floor finish should be discussed with the manufacturer.

Contaminants
Any contamination in the substrate (this relates particularly to buildings that are being converted and adapted from previous uses) could affect the finished product.  This needs to be checked with the contractor before any works commence, and the necessary corrective works undertaken.

Movement Joints
Any movement in a building will cause the wearing finish to crack.  In order to help combat this, movement joints need to be installed.  The guideline is for a movement joint around the perimeter of the building and at 4.5m centres.  This should be 6mm wide, and run through the depth of the concrete slab, screed and wearing surface.

Screed Thickness
The sub-screed needs to have an adequate depth and strength to support the imposed loads, and provide a suitable surface on which to lay the wearing surface.

Product not correctly specified
The correct specification for the environment in which the product is to be used in is essential.  This becomes critical if you need to use power washers and steam cleaning machines.

Temperature
Most of the resin-based systems require an environment that is dry, with a temperature of 15⁰ C or above.  A reputable company will not lay these products if the environmental conditions are unsuitable.

Work Quality
All of the above products require good quality workmanship to succeed.  It is essential that before the final wearing course is installed, you determine the quality of the concrete or screed sub-base.  As previously mentioned, for the installation of vinyl finishes and thinner resin-based systems (up to 6mm) any undulations in the floor surface will show, or could affect, the quality or thickness of the final wearing surface.  Obviously with a thicker wearing surface finish of 12mm any undulations can be disguised in the final finish.

FAILURES IN THE FOUNDATION AND FLOORS ARE GENERALLY THE MOST DIFFICULT AND COSTLY TO REMEDY

Source: Kennel Design by David Key