Do I need a pull-out test when fixing into concrete decks?
- Read time: 3 minutes
- Date: 05 Jun 2023
- Flat Roofing
Whether you need a pull-out test will depend on the type of concrete.
Pre-cast concrete decks: pull-out tests are not required for pre-cast concrete decks because the concrete ‘mix’ is standardised, and the slabs are already cured when delivered to site. As a result, fastener manufacturers' guidelines for fastener performance values will be accurate for this type of flat roof deck.
Poured/cast in situ concrete decks: The SPRA states that pull-out tests must be undertaken when fixing into poured/cast in situ concrete decks. That’s because minor differences in the mixing process or even weather conditions during pouring can result in variations in the concrete.
The SPRA states that pull-out tests must be undertaken after the concrete has cured. As a guide, it takes 28 days for poured/cast in situ concrete decks to cure.
Why can’t I fix into poured/cast in situ concrete decks before the concrete has cured?
We know that installers are under pressure to finish jobs quickly, but fixing into green or uncured poured/cast in situ concrete desks can introduce risk and could result in fixing or total system failure. The SPRA gives the following guidance:
It is important to be aware of the moisture content of a concrete roof slab or screed, as excessive moisture that is trapped within can cause a number of issues that are detrimental to the overall quality of the finished roofing system, which may not be immediately apparent until some time after installation is complete. These include the corrosion of metal products, degradation of materials, loss of adhesion of roofing layers, mould growth, or even total system failure in extreme cases.
Surface dryness of a concrete roof slab or screed can be misleading, as excessive moisture can still be retained within one that is apparently dry at the point of installing the roofing system above. Cast in situ concrete roof slabs typically require 28 days’ curing time before any roofing system can be installed. This is a general rule by which the concrete should have achieved a minimum of 80% of its full structural strength. Guidance may be found in BS EN 13670:2009 Execution of concrete structures, or through information provided by the manufacturer or installer of the concrete roof slab or screed.
