A hygiene-critical project unravels after a coating failure reveals costly
errors in preparation and specification, writes Richard
THE building was going to be used for food preparation and hygiene was of paramount importance.
The main contractor was briefed by the client and was asked to ensure that twice every day each of the two new mezzanine floors could be hosed down to flush away all the waste food debris into channels in the screed where it could then be filtered out for ‘recycling’.
A specialist waterproofing company was engaged to specify the floor treatments and then the contractor wanted resin to be applied to give a pleasant looking and durable finish that would endure the harshness of the environment.
All appeared to be going well until the waterproof coating had been applied to the screed. Soon afterwards it was discovered the coating hadn’t bonded. It was no exaggeration to say you could pick it up at the edge and peel it up in a continuous sheet with next to no resistance.
Some tests of the adhesion had been commissioned and the results were extremely poor. Test results don’t, however, help you understand why, or what you must do to improve the situation.
A director of the main contractor met me at the site and showed me round. I had certain expectations about what I’d find – a screed overlaid with a smoothing compound and then a typical surface-applied DPM coating which could be peeled up and I needed to discover why it hadn’t bonded. The reality was very different.
The main contractor had very detailed records of all the work done onsite complete with product specifications, dates of every stage and all moisture readings and other testing that had been carried out. The floors were steel decks with a minimum depth of 100mm concrete screed. This had been power floated.
The DPM contractors had then ground the surface and applied a hot polyurea membrane at seventy degrees centigrade. I’d never seen this material used indoors as it was the same material used on some flat roofs.
As well as looking at the floor surface where the DPM was peeling, I looked at an area which had been prepared but where the DPM had not yet been applied. There were a few light grinding marks, but these were scratches and the surface hadn’t been ground away as the product technical data specified.
Power floated concrete has a surface which doesn’t hold adhesives, paints or other surface finishes. Any glimpse into a warehouse will show how easily painted lines and signage flakes off in weeks if not days. What’s more, this surface is naturally waterproof, and I explained to the director it could’ve been used without any floor finish to achieve what the client wanted.
Of course, I pointed out, the bare concrete might not have looked so good after a time, but the resin installers could easily have ground back the surface and applied their floor finish without the intermediate layer.
The director’s response is one of the most memorable of my career: ‘I wish I’d spoken to you months ago, what you just said would’ve saved me more than £260,000!’
Further investigation into the materials used also revealed the surface had been primed with a primer from the same system as the membrane, but this was not the right one because it was only suitable for applications involving temperatures up to 60deg C centigrade, so the hotter membrane would have broken down the primer. This also explained some of the scorch marks and blistering in the membrane.
The solution was surprisingly easy. The membrane would peel up with very little resistance and the floor would then be ready for the resin installers to grind the surface properly and proceed from there.
The reclaiming of the wasted expenditure would be rather more difficult.
www.richard-renouf.com
Richard Renouf is an independent flooring consultant
