Backfilling, at last…

27 06 2020

After waiting weeks for my neighbour Matt to find time to bring his digger over to move all the mounds of dirt behind the house that were left there after the site excavation, he cancelled because really wet weather was forecast. Saturday morning, no rain, and still no rain by 11am…. so Matt decided to come over after all, until the rain starts. Which it didn’t.

Last year, our wwoofer Charles and I coated the block wall with very expensive bituminous paint. Two coats to ensure waterproofing, even though the blocks themselves are waterproof, and the mortar had waterproofing added as well. I’ve had personal experience with retaining walls leaking, it wasn’t going to happen here….

Then, coreflute had to be fitted over the black goo, to protect it from all the rubble that had to be piled up over the original drain Nico and I built all those years ago, right at the start of this project…. Over the years, I’d accumulated scrap concrete from overestimated pours, old bricks, lots of rocks, you name it….. So much work, and it all disappears just like all the work in and under the slab…

Then came the job of insulating the block work with all that polystyrene I bought just before the virus hit the fan. Many tubes of builder’s glue, some 200 concrete fasteners, and a completely worn out masonry drill bit later, the deed was done.

Matt started backfilling the tank area he dug out last year, while Glenda and I fitted the geotechnical cloth that prevents all that dirt from filling the gaps in the rubble and disallowing water from flowing down the drain.

The 25mm conduit that contains the heavy duty cable emanating from the power station up the hill was carefully buried by putting fill on both sides until fully supported underneath. We didn’t want to break it, after waiting for years to make it disappear once and for all…. It all went well. By dark, which now is 4:30pm, Matt called it a day. Next morning, it was still not raining, and he came back to scrape the high points and fill the low points to avoid the house acting like a dam, and boy, was it a good idea, because no sooner had he finished, an eastern low off the coast of Tasmania dumped some 100mm of rain over three days, turning the whole area into a gigantic quagmire.

Now the rain has finally stopped, we’re facing a huge landscaping job. We’ve decided to build a swale there to assist controlling runoff, and a food forest based on fruit trees will be planted there before Christmas. Watch this space; literally. The biggest surprise arising from this exercise is just how spacious the whole area feels. We’ve put electric meshing around the house to stop the chooks eating the green board foam until it’s finally rendered, not to mention keeping escapee goats off the roof, weather permitting. Any progress is good progress.

Interestingly, all this backfilling has cooled the wall down internally. I suspect this is caused by the fact all the dirt that went into the trenches was very cold after several frosty morning and temperatures struggling to reach double digits. The bottom course of blocks went up 2° while the higher courses that had been hovering around the 20° mark since the insulation went in dropped to 16°…… I’m expecting this to eventually stabilise around the 20° mark once the thermal mass reaches the temperature of the deeper earth behind the wall. Wait and see, proof of concept will be nice when it happens.


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