Neglect Proper Priming & Risk Failure
I HAVE previously focused on how to correctly prepare non-absorbent surfaces (see my column in the March issue of CFJ. This month I will provide advice and guidance on an essential part of subfloor preparation, priming. Perceived by some contractors as unnecessary, costly or time-consuming, primers can be the key to a successful flooring installation.
Priming can often be overlooked when preparing a subfloor for the installation of a floorcovering, yet its absence is a common cause of installation failure, along with the poor management of subfloor moisture. Primers are designed to improve the bond performance between the substrate and the subsequent material, for example a smoothing underlayment, and to reduce the incidence of surface defects. Although primers cannot be used to correct poor quality substrates, or as a stand-alone surface preparation system, they can reduce risk of surface imperfections known as ‘cratering’ and ‘pin holing’. In addition, primers also enhance the application characteristics of flooring installation products.
Sealing the porous surface of a subfloor reduces the surface tension and improves, for example, the flow properties of the subsequent materials being applied. Where cement-based smoothing underlayments are used, priming helps to reduce water loss into the substrate, retaining a wet edge longer for ease of installation, as well as adding to the strength and shrinkage characteristics of the underlayment material. Furthermore, reducing the amount of water lost through the use of a primer helps to maintain the open time of flooring adhesives when they are applied directly to porous screeds and concrete surfaces.
A prime selection: To select the most appropriate primer for a project, it is important to take into account the type of screed that will be applied, as well as the condition of the subfloor surface. Polymer emulsion primers, such as acrylic systems, are recommended for use with cementitious screeds. Specially developed neoprene primers can be used for a broader range of absorbent and non-absorbent applications. For resin-based screeds, two-pack epoxy, or polyurethane primers provide the best solution. Selecting an inappropriate primer, or failing to install it correctly, can lead to an installation failure.
Once the floor is in use, cracking or delamination of the underlayment material can occur due to insufficient or incorrect priming, which is likely to result in costly remedial work. n Effective preparation: To maximise the performance of primers, they must be applied correctly and in a suitable concentration. When it comes to applying the primer, the subfloor surface must be smooth, clean and dry as well as incorporating an effective damp proof membrane. It is also important that the temperature of the surface is assessed when the primer is applied to the subfloor, to ensure the product can be applied correctly.
When a project involves underfloor heating systems, those systems must be switched off 48 hours before, during and after an application of a compatible primer, to enable natural drying of the product. n Contaminated surfaces: As well as providing performance and installation benefits for absorbent and non-absorbent subfloors, priming can also enable a screed to be applied over some contaminated surfaces, such as minimal hard, stable adhesive residues.
However, contractors should be cautious when priming a surface that may contain silicone-based treatments as this can inhibit bond formation. For advice on selecting the most appropriate primer system for contaminated subfloors, contractors should contact the manufacturer. To ensure the longevity of a flooring installation, priming should form part of a contractor’s subfloor preparation work. Quick and easy to apply, primers improve bond strength and reduce the risk of surface imperfections.
Neil Sanders is the technical manager at F Ball and Co
T: 01538 361 633
This article has been reproduced from the Contract Flooring Journal website. You can find them online at www.contractflooringjournal.co.uk.