grinding. pt2

Concrete grinding took a bit longer than I originally thought. I don’t know what I thought actually, maybe it was wishful thinking that it would be all done & dusted in a weekend, but in the end it took 88 man hours to get the 100m2 slab to a finish I’m finally happy with. It’s not perfect, but the irregularities in the extent of revealed aggregate and areas where the float created some surface streaks add to the character. In terms of the concrete mix, we’ve used a small local concrete supplier who was flexible enough to allow us to choose a nice warm coloured aggregate mix (as opposed to standard mid grey used in Herefordshire), the rest is 100% cement, red sand and water.  We would have liked to use some recycled content (GGBS) and plasticisers to make the concrete ‘greener’ and slow down the drying times, but unfortunately the small supplier wasn’t geared up for this. It did mean we had to work fast during the slab pour, and as a result some areas had gone off before they were floated, so ended up a bit ‘rough’ which, in turn, made the grinding a bit trickier. All in all, pretty happy with the results and hope the effort will be worth it.

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grinding. pt2

grinding

So after the concrete slab was poured, rollered and tamped, we covered it up for a few days and started with grinding. The idea is that the slab will be the final internal finish. A day and a bit into grinding the machine had a bit of a fit and stopped working, later we found out one one of its gearboxes gave up. Replacement grinder turned up this week, so I can carry on. It’s quite satisfying to reveal what’s just a few milimeters under the surface…

grinding

slab pour

Monday was a big day. After last week’s installation of Isoquick insulated raft system and necessary steel reinforcement, it was time to pour the concrete slab. We have chosen concrete slab as a base for our house for couple of reasons: it would provide useful thermal mass in an otherwise medium density construction and once ground down, it would provide a durable finished floor surface. Due to tricky site access we had to use a concrete pump and direct the pipes over our neighbour’s garden. Six mini mix lorries supplied 24 cubic meters of concrete with specially selected aggregate. Unfortunately this meant that we had to use 100% cement in the mix, which in turn made the mix go off really quickly – it certainly kept the team working hard until it was all poured, rollered with a giant steel roller and finally tamped with a big float and hand trowels. Can’t wait to start grinding the slab to reveal the aggregate…

slab pour

warm foot

AKA insulated raft foundation. Fundamental part of passivhaus design is eliminating thermal bridging and keeping the insulation layer around the house as continuous as possible. We have chosen Isoquick insulated raft system as it is pre-cut to the right shape and individual pieces interlock for greater stability, like giant lego blocks. Local legendary AECB builder Mike Whitfield and his team started on site on Monday 1st August. First they accurately set out the footprint of the house and laid drainage in the 150mm Type 1 stone, and followed by 40mm of gritty sand, which formed the base for the Isoquick system. We started the Isoquick with perimeter L-shaped pieces and finished off with central base, which was made up of two separate 125mm layers, laid in staggered directions. Special Compacfoam high density EPS pieces were installed to support door thresholds. All floor penetrations were meticulously sealed before the waterproof membrane was laid down. Two layers of steel mesh followed on top, providing reinforcement for 225mm concrete slab. There were some tricky details around recessed matwell and shower room – hopefully it will all be worth it in the end!

warm foot