Saturday, February 15, 2020

How I widened the raised bed at Bulkeley

Having recently revised the layout of the trackwork at Bulkeley Station, I realised that the siding which I had moved closer to the front of the raised bed was now looking somewhat precarious.

Rather than trying to revise the track layout again, I decided a better approach was to widen the raised bed. This would not only provide more support for the siding, there would also be potential for development of infrastructure alongside the siding.

The first job was to remove the sandstone cladding from the retaining wall of the raised bed. This was achieved with the energetic application of a hammer and brick bolster.

I decided that, rather than removing the existing retaining wall, I would simply build another alongside it.

A shallow trench (approx. 6-8" (15-20cm) deep) was dug into the lawn along the line of the new retaining wall. To keep things simple, its width was dictated by the width of the spade blade.

I placed a layer of rubble, approximately two inches (5cm) deep into the bottom of the trench ......

.... and then bashed it into submission with a sledge hammer.

I then put together 3 measures of gravel, 3 measures of builders' sand and one measure of cement ......

...... and mixed them thoroughly with a shovel. Shovelfuls of the mix was turned over repeatedly to ensure the components were fully integrated.

Water was put into a hollow in the middle of the mix ......

.... and folded in. This process was repeated a couple more times until a stiff mix of concrete was achieved. NOTE: Only small amounts of water were added at intervals as it is quite easy to accidentally make the mix too sloppy. Too much water weakens the mix.

The mix was then shovelled into the trench, bringing it level with the top of the trench.

A mortar mix was then prepared - 3 parts builders' sand to 1 part cement.

Once mixed dry, water was added as previously .......

...... in equal proportions to concrete plasticiser. The plasticiser is not essential, but it does help improve the creaminess of the mortar and helps it to stay workable for longer.

A concrete breeze block was then squidged into the concrete foundation, using a spirit level to ensure it was horizontal. It was then removed and a layer of mortar placed in the depression it had made before the block was replaced and its horizontality checked again.

Further blocks were laid alongside it .........

..... with a layer of mortar slapped on to the intermediate edge ......

...... before the new block was pushed against its neighbour. The excess mortar was then removed with the point of a trowel.

This process was repeated, including the addition of a course or two of bricks to bring the retaining wall roughly to the height of the original.

 The wall was then covered with fabric and and a layer of plastic to protect it from frost and rain, both of which had been forecast over the ensuing few days.

 The wall was left for four days (maybe half that time if it had been in summer), before the coverings were removed and a row of sandstone chunks concreted to the upper edge of the wall.

Soil was then shovelled into the gap between the old and new walls ......

 ..... to bring it up to level.

Another mix of mortar was prepared, 3:1 sand and cement.

A sprinkling of red and brown cement dyes were added to the mix.

Equal quantities of water and PVA were added to the mix .......
 

...... before being mixed into a stiff mortar.

 Diluted PVA was then painted on to the wall ..........

.... before dollops of mortar were thrown on to the wall with a large trowel.

Irregular slabs of sandstone were then pushed into the mortar and wiggled to help ensure they made a good bond.

Once a few blocks had been put into place, the excess mortar ......

..... was then tidied up with a stiff paintbrush using a combination of stippling and wiping to ensure the gaps were filled and smoothed off.

The wall was then covered and left for three or four days for the mortar to reach its 'green' state - half way towards fully hardening.

Any excess mortar which had attached itself to the faces of the sandstone blocks .......

..... was removed with ......

 .... a wire brush.

 Before .........

..... and after.

More stubborn patches of mortar were removed with a wire brush attachment on an electric drill.

The next stage in the process is to plant out the new bed and to think of how the new area of real estate will be developed. There might even be room for a goods shed or a coal storage shed similar to those found on the Southwold Railway.

2 comments:

Fairywood Light Railway said...

I really do think you explain how to do a proper job on building retaining walls Rik. It's the same principle I would imagine to build any wall. Get the foundation right and you are half way there.

Thanks Rik for another build, brilliantly explained in your excellent Blog

Rod

GE Rik said...

Thanks Rod
If the wall was taller then I would have put drainage holes in it and dug the foundations deeper, but apart from that I think the principles are sound for most retaining walls likely to be used for garden railways. My dad taught me how to mix concrete and lay bricks. I always think of him when doing jobs like this and hear his voice telling me to go easy with the water.....

Rik