RAILWAY STRUCTURES MAINTENANCE

No. 5 In an occasional series - written by Dave Haynes

First published in FMRC Turntable Newsletter No 150 Nov/Dec 1998

also in NWMRCA The Signalmen newsletter Vol 3 issue 1 Spring 2000

Painting in the Park - A look at BR paint specification

The Model Engineering, section of the Furness MRC have a dual 3½ " – 5 " gauge railway in the public park at Barrow-In-Furness. Among other maintenance work this year, the section has painted the traverser and steaming bays for the first time and the steelwork looks much better for it. The paint used is the one coat variety made by Dulux and it is a full bodied paint with good ease of application and coverage. It is intended for wood or steel but I couldn’t help but wonder how it would compare with a BR steel bridge paint specification which was used both in bridge repainting contracts and by BR painters. This set me on a little bit of a investigation. Although the last time I looked, Railtrack were using a 3 coat chlorinated rubber system, I don’t know its long term record and have therefore used the old 'Br Specification No. 70 covering Paints for Civil Engineers', more often known as BR Spec 70.

In an effort to consolidate the acquired knowledge of the chief engineers of the pre-nationalisation companies, various industrywide guides were produced including a painting handbook in 1954. A later, if not the last, version of which was published in 1980, on which my experience has been based.

BR Handbook 10, Manual for the Cleaning, Surface Preparation and Decoration of Structures discusses its development as being partly due to the need for greater understanding of the new paint products by those who use them. As many people will recall, few things seemed as good at preserving steelwork as good old red lead. Unfortunately, this became no longer acceptable, thus prompting the introduction of the new products that although less robust in application were better in performance and safer. Furthermore, painting of buildings and structures suffered considerable deferment due to their future being uncertain or budget shortfalls; repainting items were first to be dropped from a tight budget. As a side note, this may be one advantage of the budget system that Railtrack have. Under the BR financial system, Area Civil Engineers, along with the various other bodies, would put forward proposals for expenditure several years in advance. The budget allowance for each financial year stood alone and it was an annual event towards the end of January to either axe schemes or quickly find mothballed ones to resurrect as a means of using up all the budget. Either way, the fear of not getting next years full allocation was always there. Not an efficient way of working. Railtrack is able to spread finance over several years, thus taking away some of these uncertainties.

The format of Handbook 10 considers the whole structural painting system, including, amongst other things, new and maintenance work, substrates, standard of work, supervision and defects in paint films. A choice set of monochrome plates is included showing in full detail different levels of paint deterioration in order that objective decisions could be made as to what treatment was required.

Painting of new work of course has many luxuries associated with it, not least because access and work environment are as best as they can be, with bridge components prepared and painted in a controlled factory environment. Some small amount of touching up is always required on site, but this is negligible. In the case of maintenance painting however, substrates can be very variable, sometimes even requiring steelwork repairs prior to painting. Furthermore, access can be difficult and weather conditions unpredictable at the best of times. Often best use has to be made of access platforms and their temporary existence during painting is sensibly used for other works when possible. Weather is a major constraint and a big irony often finds the only ROR* possession window occurring during the wetter times of the year. Temperature range for painting is between 5º and 27º C but a proviso that temperature is not less than dew point also exists. Often precipitation also prevents painting. Anticipating these problems, a set of possessions may well have to be doubled at the planning stage in order to allow for weather.

*Rules of the route, ROR, is the normal possession programme for a particular route. As can be imagined, some routes have a much tighter ROR availability as alternatives may be difficult to obtain. The Lancaster and Carlisle line, for example, has the Settle and Carlisle as an alternative however in other areas, a diversionary route may not be as simple. Some patterns may be almost impossible. The North Union 4 track sections south of Preston for example may only allow 2 to be blocked at one time, and this may be a pair together or 2 single lines trapped by the other two. This can make operations such as painting sporadic, not following a logical sequence across the structure.

Handbook 10 gives guidance based on existing paint conditions as to what surface preparation is required. Typically wire brushing or blast cleaning are specified, in various percentages of application depending on what the steelwork demands although a mature paint film as a base is preferred and where possible this would be just cleaned down. The Handbook 10 definition of mature is solid paint in the region of 300 microns (12 thou) thick and this can be measured with a non destructive Elcometer thickness gauge.

Once the surface has been prepared, it must quickly be sealed, using a quick drying undercoat which should be followed in the same possession by a priming undercoat. In the case of a 5 coat MIO scheme, the following 3 coats should follow shortly after with minimal time delay between each, however it is inevitable that due to possession constraints, a week lapses between each. One of the alternatives to the 5 coat MIO treatment is the gelled bitumen system which allows a thicker film to be built up in less coats, whilst also being well suited to marine environments. One disadvantage with the gelled bitumen system however, is not being able to apply a decorative finish, which may be required in certain situations.

The basic 5 coat MIO paint system to BR Handbook 10 is:-

DFT - Dry film thickness (microns) OT - Overcoating time (hours)

Finish colours for item 21-25 are limited but include steel grey and mid green although with MIO, a further decorative coat is possible, to one of many BS colours.

The 1998 cost is £1.68/m² compared to £0.88/m² for the one coat paint

(after 10% B&Q senior citizen discount!). Five time as many coats at twice the price makes this a paint system that the club is unlikely to go for even if it lasts 3 times as long. Not only that, we don’t have all the other add on costs such as scaffolding, possessions and isolations, which play an important part in reducing the time between painting. Anyway, it’s good for the moral fibre of the members to get covered in green paint every 5 years!

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Copyright D Haynes
Last revised: November 27, 2000.

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