Do I need a pull-out test when fixing into a concrete deck on a flat roof?
- Read time: 3 minutes
- Date: 05 Jun 2023
- Flat Roofing
These can be broken down into main groups: cast-in-situ & pre-cast. Cast-in-situ is where the concrete is poured on-site, and pre-cast is where the product is manufactured in a factory.
A pull-out test must be carried out into all types of concrete decks on both new build and refurbishment projects.
Some concrete decks are covered with a screed to provide a smooth surface. This screed is sometimes what is known as a 'laid to falls' screed. This is to provide a fall to direct rainwater to the roof outlets. Screeds are not normally structural so cannot be fixed into - you must fix through the screed to the structural concrete below. This will require different length fasteners depending on the thickness of the screed.
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. 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.
