Cracking up?
It is really a case of when, not if, a paint will fail in a coastal environment.
It's a pay off between maintenance and robustness when it comes to paint choice. Stevie Knight reports
Dave Herrod, one of Associated British Port's engineering project managers, bears this out, saying that for quayside structures, "we try to avoid painted steelwork and specify galvanised steelwork and plastic coated cladding for buildings".
But, as Mr Herrod notes, there are a wide range of different environments in any port, and there are some things you can't get around. "Unfortunately there is still generally little substitute for steel in terms of cost versus strength," he says. "Stainless steel might be used for small components and fixings. Galvanised steel doesn't last in the splash or tidal zone, and plastics are usually not strong enough."
Given this, there seems to be two main approaches to coatings says Mr Clarke: "maintenance" or "robustness", adding, "There is a big difference between maintainable coatings and ones that are robust in the first place but can't be effectively maintained on site.
"Some recommend you put in a high-quality system in the beginning," he explains. "The problem with this however, is that sometimes significant damage can happen during construction, let alone during its working life, so you can get a big scratch in the paintwork even before the client takes it over." Then you have the job of either taking it away again or trying to patch it up, on site - and many coatings happily applied and cured in a paint shop, simply do not take kindly to being applied in a port's damper, less regulated environment.
The other train of thought is to commit yourself to a long system of maintenance.
Nick Clarke adds that this approach too can be problematic, "because although paint says it has a 10 or 15 year life on the tin, it often only lasts two or three years if not applied correctly. This isn't because of the paint formulation - it comes down to surface application preparation and curing. In fairness, this is something you don't often get the chance to do properly - for example, I have heard of maintenance crews having to go out there and paint in November." Such an operation causes difficulties because even with two part epoxy paints, damp causes amine 'bloom' and problems in getting one coat to stick to another.
"This is a problematic area of engineering" points out Mr Clarke, needing a clear strategy before you begin.
However, it also makes good sense to know your schedule - the real one, with the 'is likely to overrun' margins in place. For example, sometimes extended schedules mean long periods of exposure before recoating, so a structure has to stand shivering in its shift while the maintenance round comes back along the line. The application of a good-enough first coat or primer that can weather well by itself is a necessity in this case - or have a rethink about the schedule.
Mike Taylor of PPG adds, most two pack epoxy paints have a maximum over-coating time, after which you need to put more work into keying the surface before you can apply another coat. It is as well to be realistic on this too, since some paints don't have a time-limit, and it would save you time and effort if you make your choice before you start.
On top of this comes the problem with incompatible treatments. Mr Taylor says: "These do turn up occasionally, especially when no one knows what was put on last time. However, taking the precaution of doing a solvent test will usually show up what type of resin system the paint is based on, if not the specifics, which should be good enough." What you want to avoid, says Mr Taylor, is, for example, "putting a modern, hard epoxy coat on top of a physically drying paint, which is softer, because this means you could get cracking as the base coat moves". So if in doubt - check and get the paint manufacturers help to specify a compatible system.
Environmental concerns are not far away from everyones' thoughts these days, and finding ways to reduce the solvents in paints is a hot topic. One development that helps this along is the advance of high-volume solids, which means a paint has a high percentage of solids compared with solvent in its formulation, resulting in both better durability and less solvent emissions per coat.
Another eco-friendly development is water-based epoxy: however, here Mr Taylor says: "At present the water-based technology is not as durable as the tried and tested solvent based technology in the harsh environments right next to the coast." But he is sure that, given time, "the technology will be comparable".
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