Foundation blockwork

We had to go back down south, leaving Ric to work on blockwork for the foundations. As a parting present we had lugged the blocks to where he would need them, we also bought a number of 100mm x 75mm concrete lintels that will cover the openings in the blockwork, for drains to leave the building.

He started on the gable-end foundation because it was the most complex. He sculpted enough blocks to lay either side of the field drain, removed the temporary guttering, laid a modern 110mm clay drain pipe and caulked it in place. He put gravel over the pipe, set lintels over the whole lot and then proceeded to lay outer & inner leaves of blockwork around the structure, along the trench, round the corner and to the other end of the trench. He left holes in the blockwork, with lintels at the base,  to make a channel to run two drain pipes through from what would be a bathroom. The upper surface of the opening had to wait until we started filling the gap between the blocks with the weak concrete.

He moved on to the front door foundation, drained the trench and laid a single leaf of blocks, again leaving a hole, with a single lintel above, where the drain from one of the upstairs en-suites would run out of the building. Then the foundation to what would be the main bathroom window, with a pipe running from the bathroom and the other upstairs en-suite. Being a window foundation, this was again two leaves of blockwork.

He worked on some of the smaller, simpler, trenches before he ran out of time and had to head back to Cornwall.

Laying Foundations

We got all our foundation trenches dug out then moved on to pouring the concrete.

Cutting the mesh & setting depth markers: Ric cut up the rebar mesh ahead of time. He then cut lengths of rebar rod into c. 30cm lengths, to use as pins to mark the levels of the tops of each foundation. The short trenches needed a single pin, knocked in leave just 200mm exposed.

In the longer trenches we used the level & staff to find the highest point and knocked in a pin with 200mm exposed. We used the level to set the other pins along the trench at the same level. There was  no more than 5cm or so of variation in the base of the trench, not bad considering the rough going.

Mixing concrete: We worked out that C35 concrete required one bag of cement to 4.75 builders buckets of block mix, yielding two barrows of concrete. We spent several solid days mixing concrete: Jill filling the buckets; me/Ric chucking them into the mixer with the cement & water (some water, two buckets blockmix, the bag of cement, the remaining block mix, more water); me running the barrows to the trenches. Access to the maze of trenches was indeed a problem, we bought some long scaffolding boards to set up runs over trenches and obstacles.

Pouring concrete: We did the short trenches first, barrowing c. 75mm of concrete into each trench, used our patented wooden tamper to get air bubbles out and to level the tops and dropped the rebar mesh on top. Then more concrete on top until level with the rebar pins and using the tamper to level it off nicely. We ran out of blockmix, ordered more and carried on.

The gable-end trench: We did the gable-end trench next. We had temporarily diverted the water in the damaged clay pipes onto some guttering, caulked with clay, to allow us to finish the trench. We ran concrete under and up the sides of it, dropped in the mesh, then used rather stiffer concrete to build up either side without collapsing into the gutter and blocking it. The rest of the trench was as normal. The end result was 8m of foundation all within a cm or so of horizontal.

We filled the internal foundations just about in time for myself & Jill to head back down south.

Digging foundations

About our foundations: The tops of the foundations are to be at least 45cm below finished ground level, to allow for frost heave. They are to use 200mm thick C35 concrete using 20mm max aggregate and with A393 bottom rebar mesh. They need to be c. 70cm wide and to extend 100mm below any adjoining structures. The blockwork (10 Newton concrete blocks) above is to be in three configurations:

1. For doorways, these are to be built up to 150mm above finished ground level or the finished slab level, whichever is the higher, with a single 100mm leaf of concrete blocks.
2. For the window openings and the gable-end foundation we are to build a double leaf of 100mm blockwork with a 30cm gap. The outer leaf to be 150mm above finished ground level and the inner leaf round about the finished slab level. The gap to be filled with weak concrete.
3. The internal foundations are to be very similar to the door foundations, but using a single 150mm leaf of blockwork, roughly up to the level of the floor slab.

I am struck by the irony that the present structure has been in place for at least 120 years, with virtually no foundations – a single course of granite blocks below ground level. Anywhere we are to do any new building has to have ‘proper’ foundations. This includes all doorways, with negligible loading, and windows that are to be built up to 800mm above finished floor level. The gable-end is, I guess, more understandable.

Hand-digging the short bits: We agreed at the outset that I would dig out the dozen or so short stretches of foundation, in the old doorways, by hand, whilst Ric did the longer runs with the digger. When I say, by hand, I found out quickly that I was not strong enough to dig with the shovel. The ground was an ever-changing mix of pure clay, boulder clay and compacted grits. Interestingly, for me, the latter were really porous – after heavy showers they wept water for the next hour or so. Thinking it over, it made sense. The water table is variably a metre or so below ground level, we do get water off the ground uphill from us, but it does soak away quite quickly. We have some waterlogged patches, but these are man-made and we expect to sort those out with a couple of French drains. It also made me more confident that our surface water soakaway would work as planned – the water level may be high, but it flows quite quickly down-hill.

Anyway it was tough going and I ended up using Ric’s medium-weight concrete breaker to break the ground up and shovelling that out. It felt a bit wussy, however later on Ric had to do a bit by hand and decided to do the same, so I felt better. What also made me feel better was that I checked the structural engineers report and he had said that foundations were to be laid in ground that was too stiff to dig without mechanical means. I got about two sections dug per day i.e. a week of work. I dug the foundation holes 10cm longer at each end than the opening width and 70cm wide. Most were 65 cm below finished ground level (20cm for concrete, 45cm for frost heave). Two openings needed drain pipes running through the blockwork, so I went 15cm deeper.

I had problems in two openings. One had an enormous boulder at about 50cm. I did what I could to clear either end of it to 65cm and stopped there. The other was where our front door is to be. It was one that needed to be deeper, unfortunately it filled up with water and because unworkable at around 80cm, so I gave up on it.

On the north side of the steading, where the silage pit had been, I encountered several bits of clay field drain. Some ran parallel to the wall and had pools of foul black gunk around them. Another ran into the floor of the steading and went out the other side.

Anyway, after a week we had all the short stretches ready to go…

The gable-end foundation: Ric meanwhile had got going with the digger. He went for the big one first, the gable-end. This was to have drain pipes running through, so needed to be deeper anyway. Halfway down, the ground got bouldery, he had to widen the trench a bit to get them out and as he went down it got even rougher. Anyway, it ended up being quite a bit wider and deeper than necessary.

Land drain discovered: Which turned out to be OK because he uncovered a clay land drain at around 110cm, right in one corner, which was running a significant amount of water. Significant, because our architect knew that there was a land drain running under the steading and our warrant says we need to do something about it. We investigated (by pushing blue water pipe up the drain) and concluded that it ran northwards under the west edge of the steading and beyond for at least 30m. We could see it did a right-angle turn to the left and followed the edge of the foundation for a couple of metres, then a right-angle turn. It headed south and became the drain we already knew about. It more or less follows our boundary with our neighbour and it is the one that his sewage treatment plant discharges into.

We got the architect on site and agreed that we would 1) temporarily run the drain under the foundation, through a lintelled clay pipe, then 2) dig down on the north side of the steading, intercept it and divert the pipe into our surface water drain – when we have one.

More machine digging

Anyway, Ric carried on, finished the gable-end foundation, then moved on to digging out either end of the single-storey north stretch. Having pulled down the internal rubble walls that supported the roof timbers, we will need to build timber structures in their place, so they need foundations. The foundations weave around a bit to also support the staircases to the upper storey at both ends of the building. At the west end, the foundation then runs along to support the wall that separates the garage from the rest of the steading. Some tricky digging in a confined space. It took several days to sort out and cost us a broken window in the digger.

Our boggy bits

The drop from our track onto our hardstanding was clearly a problem for the truck that delivered the caravan, back in May. It did not stand up well to the blockmix being delivered, and the Ellon Timber trucks also had trouble getting out. Ric used the digger to scoop out the worst of the soil/mud and we put a couple of barrows of blockmix down, to see if it helped.

It did not, I went to Ellon Timber and ordered 6 tonnes of 40mm gravel and Ric dug out a lot more soft ground. Once the gravel arrived, we spread it in quite a wide arc, it made a lot of difference. I used a few barrows of the gravel to fill some of the potholes at our end of the track – it did a good job.

It looks like at least a temporary solution.

Getting settled in

Our caravan was as we had left it and we quickly found the value in being able to shelter from rain showers. We assembled the cement mixer and got the level set up & calibrated.

Levelling up for drains: Before Ric arrived, we did an exercise checking levels in the steading itself. It is indeed very level, we will not have any steps up or down within the steading, despite the existing flooring being quite irregular. We checked the amount of slope down to the bottom of our plot, this is of particular interest to whether our plans for drains were going to work. We thought they would, just about. Once Ric was on site, we did it properly. We set up a datum point, with a stainless steel screw, in a corner of the bothy, near ground level. We established secondary datum points within the bothy, then levelled up the paths of the drainage. This confirmed that we could get away with 110mm pipe at 1/40 slope, keeping our inspections chambers at acceptable depths and allowing us a standard septic tank, but with an extension neck.

Checking the warrant plans: We spent most of a day going though the plans in great detail. We had a lot of questions we needed answers for. We drew up a list and agreed we would see if the architect could run through them with us.

Grounds: We had arranged delivery of  a second load of woodchip a couple of weeks beforehand and spent a happy day barrowing it round to the exposed weed membrane in our runs of hedging. Once again it ran out before we got everything covered over, we will need another load at some point. It is wonderful stuff, I recommend it to anyone. It keeps weeds down, it keeps the ground at a more even temperature and it looks presentable. It does not blow away even with gales. A quick inspection of the hedging revealed quite a low failure rate from all three of our plantings – less than 5%. Most of the plants which had put growing tips above the tops of the tree guards had been nibbled off by bunnies/hares, some were clearly less palatable and were growing happily.

Our areas of grass, nettles and other perennial weeds were rampant. The Japanese Knotweed was greatly reduced in area again and was at an early stage of growth. We planned to leave it until September to spray again, when it as full growth and is flowering.

Setting up the caravan: Ric was keen to get the caravan set up, so I acquired a 19kg bottle of propane gas and a variety of fittings to run a temporary water supply using 25mm blue pipe from our standpipe. Once he arrived, he spent a couple of evenings getting the water and a temporary electricity supply connected. He checked out the gas system and got the Morco gas water heater running. The only thing missing being the plumbed in toilet and water waste – these will wait on getting our foul drainage installed, a job for September.

Tools & equipment: A cursory inspection of the areas we need to dig foundations convinced us that we either hire a concrete breaker, or buy one. We hired one the previous year and it worked out about £70 for two weeks. We clearly had a lot of use for one and I had had an eye on the cheap Titan breaker that Screwfix sell. I knew someone who had bought it and swore by it. I bought it, for a penny under £150. We treated ourselves to another wheelbarrow, more shovels, a pickaxe, a fork and plenty of builders buckets.

Working with Aberdeenshire Building Standards: There are a limited number of points at which Building Standards need to inspect our work, the first being the drains. However, our architect advised us to keep records of everything we do, to demonstrate that we are following best practice and standards. So we will take loads of photos of our building activities and have them available if there is a dispute about what we have done.

Before the main event: The grand plan for July is foundations, for September it is drains. Once we had the digger, however, we wanted to open up some of the new doors/windows in our north wall – ‘slapping’ them, as they say…

So Ric pulled rubble out of the wall where our front door needs to be. We quickly twigged that it is immediately where our new water supply comes to the surface. We took care, but suspected that once we dig the foundation out, our water supply will fall into the trench.

We needed another new opening, for a window, where an old doorway had been blocked up. In true Aberdeenshire fashion, the mortar and blocks were just about indestructible. After a lot of trying, the entire column of blocks parted company with the granite either side and came out in one piece.

The third opening was another old door, that we had opened up last year, but it needed widening to break off the cement and brickwork that would otherwise be visible once it is converted to a window.

All an essential step on the way to re-building, but it once again made the steading look even more like a ruin!