Ask Denver: Screed preparation – Who is responsible?

by Tania Wannenburg

Denver Coleman, Chairman of Polyflor SA, answers a question on screed preparation and who remains responsible.

With more than 50 years’ experience in the local and international flooring industry, Denver Coleman, Chairman of Polyflor SA, answers questions posed by installers, architects and readers. In this issue, he discusses screed preparation and where the responsibility lies in this regard.

“As a flooring contractor, I often get to sites where the screed is not of a suitable condition to fit vinyl flooring. As a result, the client is often faced with additional expenses for me to get the subfloor into an acceptable condition. Where does the responsibility lie with regard to screed preparation?” – Martin van Rooyen, Midrand

According to the official guidelines for “The installation of resilient thermoplastic and similar flexible floor covering materials”, covered in SANS 10070:2012, the division of responsibilities is as follows:
•    The specifier and main contractor shall ensure that the substrate is acceptable in respect of levelness, smoothness, soundness and cleanness and can receive the resilient flooring specified.
•    The flooring contractor shall ensure that the substrate is sufficiently dry before installation of the flooring material. If the substrate is not acceptable, he shall not proceed with the installation and shall in writing inform the main contractor accordingly.
Although this is the official statement, it is often the case that substrates are not acceptable and that flooring contractors are required to assist, especially in this age of fast-track building.

As a flooring contractor, your responsibilities include:
1.    Conducting a moisture test according to the flooring material manufacturer’s requirement.  The moisture content of the substrate is critical, and a record indicating the test method and result should be kept.
2.    Applying a suitable moisture barrier before installing the floor is essential if any reading above 75% RH (relative humidity) is recorded. There are several available on the market, but the flooring manufacturer’s choice should be recommended and suitably supported by technical documentation and results from tests conducted which indicate the suitability of the product.
3.    Correcting any minor deviations in the screed levelness with a self-levelling screed.
4.    Storing flooring materials in a warm, dry and well-ventilated area for a minimum of 24 hours before installation. If the area to be installed is air-conditioned, it is important that the air conditioner runs for approximately 72 hours before installation of the flooring. Alternatively, it should not be turned on for at least 10 days after installation in order to give the adhesive time to fully cure.
5.    Ensuring the temperature of your substrate is 12oC or above, and that there is good lighting. Discuss these and other requirements with the main contractor.
6.    Switching on any underfloor heating 72 hours before flooring is installed and allowing the screed to cool to room temperature before installation.
7.    Obtaining a certificate of completion once the installation is completed, after which the main contractor will then be responsible for suitably protecting the flooring product from damage.
8.    The SANS spec states that floor covering should not be installed if the ambient temp is below 12oC.
9.    Ensuring that batch numbers are checked and correctly allocated to areas. Any concerns with regard to material faults should be reported to the manufacturer prior to installing the product.

The responsibilities of the main contractor include:
1.    Providing the flooring contractor with a Class 1 screed, the definition of which includes “the permissible deviation of a maximum of 3mm under a 3m straight edge in any direction” in order to avoid abrupt level changes. Any major deviations should be corrected by the main contractor prior to the start of the flooring installation.
2.    Ensuring that all building operations that may cause damage to floor coverings are complete, and that the area is free of other trades before fitting commences.
3.    Arranging the necessary heating if the substrate is below 12oC in order to raise the temperature to acceptable levels. This is particularly important in winter in order to ensure efficient functioning of adhesive and self-levelling products.

The above theory, however, is not always carried out on sites and responsibilities become interchangeable depending on the project. It is therefore advisable to have a 100m² sample installation done by the flooring contractor. This test area should be cleaned and sealed to highlight levelness and the final appearance. The mock-up area can then be assessed by the specifying architect and principal client. If the installation is found to be unsuitable, it can be determined who will be responsible for correcting the situation, and who will cover the cost of such rectification. Not only will this avoid costly errors, but also assist with defining responsibilities.

Finally, remember to always refer any queries to the manufacturer of the flooring product ahead of installation, not after completion when it is often too late to efficiently rectify the situation.

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