A stream for the Elderbury & District Light Railway - FINISHED

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philipy
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Re: A stream for the Elderbury & District Light Railway

Post by philipy » Fri Nov 09, 2018 3:04 pm

Well, I ve been a busy bunny for the last couple of weeks. Having got the basics of the stream sorted I decided it was time to get serious about the railway bridge over it. My initial thoughts were to make a mould and pour it in solid concrete, in situ. As I've posted before, I have previously made a bridge support using a plywood mould with the mortar courses applied to the inside with hot melt glue, but that was a simple slightly tapered box. This bridge is much more complicated, being on a skew for starters, plus needing the arch of course, plus I really wanted to cast the parapets as an integral part, plus I would need to cast it with the stream liner already in place. I started by making a kind of 3D template out of some foamboard, on the basis that its easy to cut and I could replace bits if the geometry came out wrong. It wasn't as bad as I feared so started to apply the mortar courses as well, thinking that perhaps I could reinforce it and actually use it as the mould itself rather than using ply.
DSC_0004 (2).JPG

At this point Greg was posting his Bridges of The Sandstone & Termite, thread, with a link to his web page on using Hebel blocks. I had seen this before but forgotten about it but the picture of his huge viaduct got me thinking. Why couldn't I carve a bridge from Thermalite blocks ( the UK version of Hebel)? It also jogged my memory that Rik used similar methods for Beeston Castle. So last weekend I made a trip to Wickes and bought a couple of blocks for a whole £1-60 each! They aren't actually Thermalite, Wickes sell them as "Aerated blocks" but they seem to be much the same. Although in theory 200mm thick Thermalite/Celcon blocks are available, as far as I can see you have to order a pallet load, individual blocks are only easily available in the 100mm thick version so I needed two and would have to 'glue' them together. They have rather rough faces which are bit difficult to smooth but I got rid of most of the roughness by laying the two blocks together and simply rotating one on the other like a pair of millstones. The one on the left is smoothed and the RH one is as they come.
DSC_0001.JPG

I made a template for the shape of the arch which was copied onto one face. Then the two blocks were clamped rough sides togther and angled parallel lines drawn across the bottom to match the angle cut through the track base. The template was then used again to mark the opposite arch. Finally the two blocks were separated and the template used again to draw arches on the inner faces. I then used an old panel saw to cut the vertical faces of the arches and a masonry bit in an electric drill to chain drill the curves. The curves were then approximately smoothed to the required shape, although final shaping would have to wait until the two halves were fixed together.
Next I used the saw again to cut out the track bed from the top of each block, leaving a side piece sticking up to become the parapet wall in due course.

DSC_0012.JPG

To fix the two pieces together I used Stixall, as recommended by Phil ( Lonsdaler) and it seems to have worked well. To hide the join on the inside of the arch, I made up a slurry of waterproof PVA with some of the sawn block dust, and used it as a grout. It dries slightly darker but is approximately the right colour - a grey line can just be made out in the picture below.
Next I cut the spare out of the blocks at each end by sawing down parallet to the arch sides and then sawing horizontally to meet them. This allows the bridge to drop into the hole in the trackbed with ( hopefully) enough play to allow for the stream liner and underlay.
I then cut the parapets down to the right height and had a minor disaster, one of the overhanging parapet ends broke off. It turned out that there was an internal airhole right at the junction with the main block which made it very weak. I tried using Stixall to glue it back together, and although it did stick, it left the joint rubbery and flexible, so I made another slurry, this time using SBR and block dust, and grouted the gaps all round. Again there is a darker shade but I think it will be ok once everything is finished.
At this point I started scribing the blockwork onto the faces.

DSC_0015.JPG

The off-cuts from the top of the parapet walls were using to form coping stones which were glued on by liberally damping both faces and then painting with SBR. Once rigid I again grouted the gaps with SBR and dust.
The join in the broken parapet can be seen as a pale grey diagonal line towards the LH end of the rear parapet
In this picture I had started colouring one face before I remembered to take a photo!

DSC_0020.JPG

This is the bridge with a first thin coat of Everbuild mortar colour (Buff plus a touch of Brown). It actually looks better, less blotchy, in reality than the photo, but I'm wary of putting on too much colour since I'm trying to get close to a pale Cotswold colour. I can always go over it with more, but I can't take it off!

DSC_0002 (2).JPG

Finally I took it outside and placed it loosely into position to get a feel for the eventual look - clearly it does need more colour, but I'm very wary of it going too yellow, like the top shows, and adding a little more brown tends to make it go a reddish shade.

DSC_0001 (1).JPG
DSC_0002 (1).JPG

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Re: A stream for the Elderbury & District Light Railway

Post by IrishPeter » Fri Nov 09, 2018 3:17 pm

That's looking raight grand already!

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Re: A stream for the Elderbury & District Light Railway

Post by SimonWood » Fri Nov 09, 2018 3:21 pm

It would never have occurred to me to carve a bridge from aerated block but that looks very effective. I know it'll weather even more naturally, but it's already looking the part. Brilliant.

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Re: A stream for the Elderbury & District Light Railway

Post by Andrew » Fri Nov 09, 2018 3:55 pm

That really, looks the part, love the skew design too... If you build the colour up gradually I reckon you'll get it spot on. It might be a candidate for the "only in natural light" rule I apply when I'm weathering rolling stock etc, I find it very hard to judge colour accurately in artificial light...

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Re: A stream for the Elderbury & District Light Railway

Post by Dwayne » Fri Nov 09, 2018 4:42 pm

Very nice. :thumbright:

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Re: A stream for the Elderbury & District Light Railway

Post by Peter Butler » Fri Nov 09, 2018 5:59 pm

Wonderful work and great result. once sited it will naturally weather and darken, so colouring is probably not crucial at this stage.
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Re: A stream for the Elderbury & District Light Railway

Post by ge_rik » Fri Nov 09, 2018 7:07 pm

That looks great. Not yet had the courage to make something regular and geometric, so this will act as a spur for me to have a go.Thanks. :thumbright:

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Re: A stream for the Elderbury & District Light Railway

Post by FWLR » Sat Nov 10, 2018 8:17 am

Superb Phillip. It looks so real.

How did you scribe the blocks please Phillip. They do look very natural.
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Re: A stream for the Elderbury & District Light Railway

Post by philipy » Sat Nov 10, 2018 8:39 am

Thanks chaps.
With regard to colour and weathering, yes obviously it will weather but I'm not sure what that will do to a bare, almost white/very pale grey concrete. I'm fairly sure it won't end up looking like Cotswold stone without some help though, so I need to get some approximate colour on. I may have the answer but need to experiment. The mortar colour tub says that pastel shades of the colour can be achieved by mixing in white cement. I have looked previously and could only find 25kg bags at around £20, which is a bit OTT when I only need a couple of teaspoons full! However yesterday evening I found somebody flogging 250g bags for £4 which is more realistic. I'm hoping that mixing it with the buff colour will give me something like the shade I'm after and with some density of colour to avoid the streaking. I also had a flash of perspiration in bed this morning and remembered that I have some cream coloured grout lerft over from a tiling job. I haven't looked at it yet but that may also be a possibility.

Rod, the stones were scribed with a hacksaw balde. The method is described in some detail on Greg's website which I mentioned above.

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Re: A stream for the Elderbury & District Light Railway

Post by FWLR » Sat Nov 10, 2018 8:53 am

Thanks Phillip, completely forgot about Greg’s website and his method… :roll: :roll:
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Re: A stream for the Elderbury & District Light Railway

Post by Lonsdaler » Sat Nov 10, 2018 9:00 am

Well done Philip, your description has made the construction sound simple, but I know from experience that carving aerated blocks is a real chore. The original tunnel mouths on my line were made that way, but nowhere near as well as your bridge came out.
With regard to colour, I think the problem you have is that the 'base colour' (the block) is too light. I would go for a dark grey or even black base coat, and then colour from there. it will tone down the yellow you are trying to achieve, IMHO. But excellent work, and well done for having only the one breakage 8)

Edited to add: this is one of the two tunnel portals that I 'carved'. I cheated and used aluminium angle to support the cross piece. Also the colour of the stonework is very different now it has weathered, with greys and greens mellowing the yellow. They've now been replaced by portals from Brunel Models, heavily modified.
2014-09-18 19.02.24_zps2ad84dul.jpg
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Re: A stream for the Elderbury & District Light Railway

Post by philipy » Sat Nov 10, 2018 1:47 pm

Phil, your stone colour in those pictures is exactly what I'm trying to match!
You may very well be right about the base colour. I did a couple of trials a few weeks ago by casting a simple length of wall using a 1:4 cement/sand mortar, with various quantities of buff colour added. I was really quite pleased with one of them being a close match to some of the stones laying around in the pictures. However, those trials were of course on a grey mortar not the almost white block, plus the colour was uniform through the mix not just painted on the surface, which will affect the apparent depth of colour.
Anyway, I'm hopeful that I may be on the way to solving things after some experiments this morning. The cream grout powder mixed with a lot of water and painted on to a piece of scrap block, did give a surprising depth of colour as the very fine particles settled into the pores of the block. The dried finish was very similar to some of the real stones I have. I then raked out the mortar gaps because more of the grout had settled in them, and the pale grey block colour then showed through as a quite convincing mortar colour. Adding a small amount of the buff dye to a section of it has darkened it slightly to a deeper cream colour.

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Re: A stream for the Elderbury & District Light Railway

Post by IanC » Sat Nov 10, 2018 3:00 pm

The bridge is an excellent build. The detailed write up too deserves a mention. Well done. I'm sure when it's in place and the stream is in full flow both will form a wonderful scenic feature.
Ian

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Re: A stream for the Elderbury & District Light Railway

Post by Soar Valley Light » Tue Nov 13, 2018 7:32 pm

Cracking job Phillip! I'm thoroughly impressed.

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Re: A stream for the Elderbury & District Light Railway

Post by Lonsdaler » Wed Nov 14, 2018 9:47 am

philipy wrote:
Sat Nov 10, 2018 1:47 pm
Phil, your stone colour in those pictures is exactly what I'm trying to match!
You may very well be right about the base colour. I did a couple of trials a few weeks ago by casting a simple length of wall using a 1:4 cement/sand mortar, with various quantities of buff colour added. I was really quite pleased with one of them being a close match to some of the stones laying around in the pictures. However, those trials were of course on a grey mortar not the almost white block, plus the colour was uniform through the mix not just painted on the surface, which will affect the apparent depth of colour.
Anyway, I'm hopeful that I may be on the way to solving things after some experiments this morning. The cream grout powder mixed with a lot of water and painted on to a piece of scrap block, did give a surprising depth of colour as the very fine particles settled into the pores of the block. The dried finish was very similar to some of the real stones I have. I then raked out the mortar gaps because more of the grout had settled in them, and the pale grey block colour then showed through as a quite convincing mortar colour. Adding a small amount of the buff dye to a section of it has darkened it slightly to a deeper cream colour.
Good luck anyway. Certainly up here in the damp Northwest, those stones are no longer that colour! This is what they had 'mellowed' to last year. In fact, the green of algae or whatever is getting more prominent as time goes by.
IMG_1340_crop.jpg
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