House slab update

3 05 2017

Nico has left. Boy, I will miss him…..  Since pouring the footing for the retaining wall, he and I quickly laid out the drainage behind the footing, and not a moment too early, because over the past couple of days, we’ve had 15mm of rain, turning the

20170427_120114

Sloping gravel ramp

entire site into a quagmire which will put an end to more work for at least two days. Or however long it takes to dry out. I was hoping to cut the last lot of trenches this coming weekend, but that simply won’t happen now……

The drain has to have a 1 in 100 fall to work effectively, so the first thing we did was, after removing the formwork, mark out this slope on the new concrete…. which was smoother than the proverbial baby’s bum, a testament to the effectiveness of the concrete vibrator. It looked like polished concrete!

The drain being 300mm deep, and the pipe 100mm in diameter, I decided to install the top of the pipe at the pointy end of the back of the building at basically footing level, while having it at the bottom of the drain at the other end, 20m away…. an exact 1:100 slope.

The way the drain works is that as water falls into it, the water level rises up through the gravel until it reaches the perforated pipe, filling it up. The water then follows the path of least resistance, which is down the pipe. The ‘sock’ around the pipe filters out any silt that may dissolve from the clay, stopping it from entering the pipe and clogging it. In theory it works, and I have to say I have seen it work in real life in Cooran where I did something similar, though not as high……

20170427_153827

Nico backfilling the drain

The drain was then filled at that slope with 20mm gravel to the marks laid on the concrete every 2.5m, and voila, one accurate slope all made ready for the drain pipes.

The engineer’s drawings call for one pipe, but having seen how much water can come down that slope, I went for two. $200 is cheap insurance, the last thing I want is water in the house!

Once the pipes were laid out, the rest of the trench was backfilled with more gravel – 5 tons of it, all unloaded from the utes by hand -, entirely covering the pipes. More hard work and expense that will totally disappear, never to be seen ever again…. and speaking of utes, they have really been earning their keep lately, with both of them simultaneously loaded with one and a quarter tons of gravel…

Having done this, we then went about on the following day – when the darn rain started – leveling the corner cleanout blocks that will be the formwork for the rear of the slab. This is critical work to ensure the slab turns out dead level. It took us half a day with rain interruptions to lay just six blocks (with waterproofing added to the mortar), but I now have cemented in starter blocks that I can use to string out the rest of them, and that shouldn’t take me more than a day if I can get Caleb back to help me mix mud. The levels were achieved using age old technology in the form of a water level, the design of which I got from Geoff Capper, an old peaknik friend who lives in Northern Tassie. It worked a treat, and even Nico who had never seen one before was impressed.

20170501_143310
20170501_122536

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

At left, Nico leveling what is literally the foundation stone, the highest point on the footing. At right using the water level to ensure that block at the opposite end of the 20170501_143507house is at exactly the same height as the first. The front of the house will be on the visible stringline, and 200mm higher than the footing lifting the whole house about ground level.

We would have laid more blocks, but the rain renders that Dolerite clay into gloop that persistently sticks to your boots making just walking around really unpleasant and even difficult….. in any case, it’s not recommended to either mix or lay mortar in the rain.

We did however spend time between showers cleaning up left over concrete and gravel off the mud in an attempt to alleviate the piercing of the plastic membrane that will be eventually laid down under the slab, weather permitting. And I really want to get this done before the real rainy season starts in the next couple of weeks or so……. I just hope I’m not too late already!

Glenda also wants to rearrange the bathroom layout, and that has to be all finalised so we can pour over the underslab plumbing, which once done cannot be undone!