The Plan
We had booked our concrete over three consecutive mornings. I went with the volumetric mixing trucks because they have up to 6m of reach from the back of the truck and because they can hold 9+ cubic m of materials, however the trucks are 8m long, much bigger than barrel mixers, so we had to do some rearranging on site to give them access. The first day we would fill the garage and master bedroom areas in the west wing, with one load, estimated 7.6 cu m. The following day we would use two loads to fill the north wing, estimated 14 cu m. Then on the third day, do the east wing, estimated 7.6 cu m.
The Reality
We used more concrete that I expected: My estimates were bad, I had assumed a dead-level blinded surface and exactly 125mm depth of concrete. There was a few cm variation within each discrete area (master bedroom & garage in the east wing, the north wing and the east wing) and some variation between them. So the garage area base was not exactly 15cm higher than any of the other areas. These differences were significant. If the north wing, for example, was just 1cm lower than it should be relative to the other areas, we would need almost one extra cubic metre of concrete. My other mistake was to assume that the extra volume to fill the troughs (along the sides of the east & west wings, to support structural timber) were to be spread evenly across all the floor area.They were not. So I particularly underestimated the amount of concrete for the east and west wings.
Both my brothers told me, after the event, that I should have added 10% to my estimate and ordered 33 cubic metres.
Day 1
Anyway, the truck turned up on the first day. We got him to pull up in next-door’s driveway and back up to the master bedroom area. We had parted our fence, so the truck could get as close as possible: We will patch it up once the job is done. It went very smoothly. The concrete was set up for a C35 mix and was fairly runny and well-mixed, so flowed easily. By adjusting the number of chutes on the end of the mixing auger and the direction of the auger, we really did not have much raking to do. My youngest brother, Geoff, did the skilled work. He had a laser level that stood at one end of the area and a receiver that he fixed at the right height on his tamping tool. If the tool was low, it made rapid beeps, when too high, it made slow beeps. When it was at the required level it made a continuous tone. So with a minimum of fuss we got the master-bedroom area filled.
It had used at least a cubic m more that I had estimated and the driver thought he did not have enough materials to fill the garage area, so we rescheduled for a separate job over a fourth day. This was annoying, but not disastrous. Geoff used his concrete roller to push the aggregate down, then his float at intervals to smooth out the surface. It rained, but we still got a good surface.
Day 2
The following day a different driver turned up with a smaller truck. he backed up to what will be our garage door and filled the garage area. We opted for a stiffer mix, which was bit more work, but should allow a better finish, since it is the final surface (no insulation or screed on top).
Annoyingly it rained more heavily than the previous day, but again Geoff got a good smooth finish. Ric spent part of the day clearing lintels and granite out of the way so the truck could back up next day to the north wing through two openings.
Day 3
We got the first truck load in the west half of the north wing and got the full 9 cubic m. We were a bit concerned about whether we had got the area more or less that half-filled. We also had to get the concrete spread over a longer distance. Ric constructed a separate chute from a sheet of galvanised steel on a wooden frame and, when the truck reappeared an hour and a half after leaving, it worked perfectly. As it happened, we used 6 cubic m from the second load – I think the floor must have been, on average, a bit higher here.
The galvanised sheet on the chute came out looking polished and shiny – just like new. Was this the abrasive action of the flowing concrete, or a chemical thing?
At one point the driver did say he would had enough concrete on the first day to finish the garage area, after all. Hey ho!
On the final day, the driver loaded a full 10 cubic m of material on the truck, got it backed up to the bathroom window area and, with Ric’s chute, got the whole area filled with one load. Just. There was about a bucket of mix left over. It rained again and Geoff worked a smooth surface under water.
We used 33 cubic m of concrete in total – my estimate of 30 illustrated exactly why I needed to have used the ‘add 10%’ convention. Laying concrete is stressful because of what can go wrong and the difficulties with correcting mistakes. Aberdeen Concrete ltd made it much easier than it could have been. They were helpful and we only paid for the concrete we needed. But we were all relieved once the last load went in. We did have to clear quite a lot of space to allow their trucks to get backed into the opening we wanted to use.
Having spent the last three years climbing about inside the steading, it is quite strange walking on a flat, hard, continuous surface. The drain pipes look much more professionally installed now they poke vertically out of the concrete and it is blessing not to be tripping over the external electrical cables and water supply. We know from the puddles on the concrete that the surface varies by less than 1cm over each area. It will be a good base for the insulation panels and screed.
East Byreleask Steading 