Why It Pays To Have The Inspector Call

Terry Wain, technical secretary at the Liquid Roofing and Waterproofing Association (LRWA), discusses the importance of regular site inspections on flat roofing projects, and what they should include.

The completion of site inspection on any roofing project means all parties involved – from specifiers to contractors – have traceable paperwork of every stage of the process. Not only is it best practice for field service personnel to visit a project and examine the works, but provides continuity and a paper trail to document all stages of the works from start to finish.
As part of the stringent LRWA membership criteria, all manufacturer members are expected to carry out this inspection procedure as a matter of course, and every inspection should include the following considerations.

Peace of Mind
The number of site inspections depends on the size and longevity of the project. The contractor – employing operatives who should have been trained on the correct application procedure of that particular liquid waterproofing system by the manufacturer – can walk away from the project knowing it has been completed to the standard requested in the manufacturer’s specification.
A site inspection has a positive knock-on effect on everyone within the building supply chain, and the manufacturer can also rest assured that the project has been carried out all in accordance with their specification and the project will last at least the term of the guarantee.

Sound Reporting
Before the project begins, an initial site meeting should take place and include the specifer, roofing contractor and the liquid manufacturer. Areas such as site storage, access requirements (including scaffolding) and health and safety procedures should be discussed at length.

During the project, the reporting system of site inspections is extremely important and can prove invaluable if, at worst, a system does fail. If field services staff inspect a project and find a fault, or an area not complying with the specification, details have to be stated within the report.
A copy of such a report should be left with the operative, or sent direct to the roofing contractor – ideally both. This should then trigger rectification of the areas raised, which should have been dealt with in time for the next visit from the field services staff. This provides a full, ongoing working report of the project and ultimately ensures a sound, waterproofing system by the completion of the project.

Inspecting Substrates
Main substrate inspection would include concrete, timber and metal decks, and there are different aspects to consider during such checks.
When inspecting a concrete deck for example, it is important to ensure the moisture content of the concrete is within the boundaries set by the manufacturer’s specification. The surface needs to be smooth enough to either take the liquid waterproofing, or the adhesive if it is a warm roof structure.

In some instances, a concrete ‘crust’ known as laitance can form on top of a slab or cement screed, which indicates a weak area and needs to be removed. During a site inspection, weak spots such as this should be picked up, whereby cement deck expertise is required to Identify and rectify the problem.
Timber decks for example mainly comprise of plywood and stirling board, which should be Type 3. Both of these types of timber decks should be fixed in accordance with British standards, meaning allowance for movement is designed into the laying of the boards – 3mm between each board.

Within the liquid roofing discipline, metal decks are generally fixed by other parties, but the waterproofing contractor should check all main fixings and side seams are secured in accordance with the specification. This will ensure stability of the deck prior to laying the vapour control layer and insulation.
When it comes to the refurbishment of existing substrates the main popular waterproofing materials in need of refurbishment are Mineral surfaced roofing felt, bituminous roofing felt with a chipping surface, asphalt roofing and single ply plastic surfaces. These are probably the most common types of existing waterproofing systems that are refurbished using liquid applied waterproofing systems.

All the above substrates may need to be primed depending on the manufacturer’s specification and the single ply plastic may need adhesion test to test for suitability of the Liquid waterproofing system.

Sequence Of Works
The inspection procedure should also cover sequence of works. Prior to any cleaning of the existing substrate for example, it is important that all steel work penetrations are cleaned and primed. It is also important that all chases are cut and cleaned prior to the laying of any liquid applied waterproofing. No matter what kind of waterproofing products are used, termination of the product is essential and liquid applied waterproofing is no different to other membranes.

Detail works upon the roof should be completed before the full application of the flat surface area. There are several items that need to be inspected on the roof area post-application, and the most important of these is to establish that the correct film thickness has been achieved by the operative. This is done by the use of a wet film thickness gauge, dry film thickness test or by electronic testing methods. Other items that need to be inspected are the inclusion of reinforcement, are there any pinholes, has the top coat been applied within the time period allowed.

A Sound System
The LRWA places great importance in promoting regular site inspections by its manufacturer members. Not only does it ensure a sound, waterproofing system for the client and end user, but provides peace of mind for the specifer and contractor, as by following every step of the process can avoid unnecessary, costly rectification work.