Building the Six Sisters Viaduct

Clive Tucker

Note: This article first appeared in the autumn 2004 edition of the G-Scale Journal

In building my own garden railway I have always sought ideas and inspiration from the efforts of others; through the pages of the G-Scale Journal, the G Scale Mad web-site, and indeed from the several garden open days to which I have been very kindly invited. Inspiration, however, comes in many forms, and often from the unlikeliest of places: a tile shop, for example. For just such a place was where I found the small yet significant item that was the key to completing the viaduct project on which I had embarked back in November 2003. More of this later; first I must provide some background.

Firstly, why a viaduct? Well, my railway, the Scampington and Chipside Garden Railway, is built almost completely on a raised bed, some 18 inches off the ground. Along its length, various obstacles to progress are overcome mostly by bridges. No less than 3 exist already, with the prospect of building a trestle bridge still to be contemplated. With the end of the line in sight (at the Scampington terminus) I felt there was an opportunity, nay an obligation, to do something different to span the last gap; and if it was to be different, then it may as well be very different.

As a youngster, I read of, and became fascinated by the achievements of Roman civil and for that matter military engineering (don’t ask me why – I would probably be depriving some psychiatrist somewhere of a tidy living if I were to try and analyse it). Spending a number of my post-16 college years in the beautiful city of Bath did little to diminish that. Now, all these –hem-hem-ty years later, the needs of the Scampington and Chipside rekindled that interest. I would build a viaduct.

Easy to say, of course, but… how to go about it? There are of course pre-cast bridges and tunnel portals one may buy, but the individualist in me, rarely given a voice, was not to be silenced this time. It had to be hand made. I did some research, based mainly on the internet (as is so often the case these days, how did I ever survive before it came along?), and came up with a few options. Casting my own concrete sections was considered, but discounted on the basis that I would have to make at least one mould first, and I didn’t really fancy my chances with that. Then I heard mention of autoclaved aerated concrete, or AAC. This material is most commonly to be found at builders’ merchants, DIY stores and other such places, in the form of building blocks – often sold under several trade names, most notably ‘Thermolite’, and ‘Celcon’. These are light yet strong, can be cut with a (preferably old!) saw, and shaped by all manner of tools. Instantly I had a vision of a succession of arches each carved from a small section of AAC block. We were in business!

I figured that as even though AAC blocks in themselves are strong, cutting arch-shaped lumps out of them was likely to compromise that strength. I made a guess that as long as the block was never narrower than 1.5 inches, that would minimise the chances of breaking the block during cutting and shaping the arch. I also figured that the fewer cuts I had to make, the less chance there was of damage ensuing. I adopted a simple cardboard template for the arch shape, so as to allow me to draw on the block where material was to be removed. The template also ensured a consistent shape to all the arches I would have to make.

Once the lines had been drawn, a single cut was made from the base of the block to within 1.5 inches from the top, followed by 2 diagonal cuts from the foot of the arch, down to the end of the first cut (Diagram 1). With those 3 cuts, most of the waste was removed. The remaining arch curve was achieved by lots of miniature saw cuts (Diagrams 2,3), and the careful use of an old chisel. To make the first arch took just over 90 minutes. I freely admit to taking things particularly carefully with that first attempt, concerned as I was about the possibility of the thing disintegrating in a hail of AAC fragments without warning. With each successive arch confidence grew however, and by the time I had completed the sixth, only 45 minutes had elapsed from first cut to last.

The blocks were cemented into place and left for a week, whilst more mundane tasks, such as earning a living, intervened. With the arches firmly in place, I was then able to apply a mortar render to the overall structure, so as to build it up to something approaching the required width. At this point, I hesitated – I had invested a considerable amount of time and effort already, now I was unsure as to how I was going to get the final ‘Romanesque’ look. Just scribing lines in wet mortar just didn’t appeal; cladding it with moulded plastic ‘stone’ sheet seemed to me to be defeating the object of building my own structure. It was at this point that I had the inspiration I needed. I had been browsing a local tile shop in connection with one of those little ‘indoor’ projects one faces from time to time (in my case: tiling our kitchen), wherein I discovered some rustic looking kitchen tiles, made from natural stone apparently from Turkey. They certainly looked the right colour, being not too dissimilar from Bath Stone. The only problem as I saw it was that each tile was 10cm square, and about 8mm thick. Scribing and cutting these would be impossible. The solution? An electric tile-cutting table saw, on sale in the very same outlet (how very convenient!) for the princely sum of £30. So I had my answer: one electric tile-cutting table saw and 20 Turkish kitchen tiles later, I was ready for action!

It took a little while, but eventually, armed with a box full of miniature Bath Stone look-alike blocks freshly cut using my new tile cutter, some leftover waterproof tile adhesive, a file and a pair of tile nibblers, the final phase of the Six Sisters Viaduct could begin. Starting with the edge of the arch, some small pieces were stuck on and allowed to set. Then the larger blocks were used to clad the rest of the structure, cut and shaped to fit as appropriate. Even allowing for the abysmal weather over the Easter period, cladding the structure took about a week.

I suppose the acid test in all of this is: was the effort worth it? Though I feel the S&CGR is some way away from an inaugural Open Day, I hope that one day soon, others will get the chance to judge for themselves the success or otherwise of what I had set out to do. For myself, however, the results far outstripped even my fevered imagination. The viaduct is now, at the time of writing, a few weeks old, but has the look of something that has been there for hundreds of years. With time, it is hoped that Mother Nature will take the hint and encourage the growth of moss or similar in between the blocks. The technique of cladding structures with miniature tile blocks is one that I believe could find a use elsewhere – I have an idea for a goods shed clad in the same material.

I mentioned earlier my evident dependence on the power of the internet – I took quite a few photographs of progress along the way (of the railway generally as well as the viaduct in particular), and have arranged them on a web page of my own. The address, for those of you who have internet access, is:

http://homepage.ntlworld.com/cetucker/gardenrail/viaduct.htm

Post script: July 2005. Having endured a fairly run-of-the mill winter, the viaduct has survived with the loss of only a handful of blocks from the top course. Not from wind damage directly, but from the netting that had been put up to act as a privacy screen! Repairs have been completed however, and aside from some minor weathering all is well with the Six Sisters of Scampington!