Despite using 32MPa concrete, we have cracks. So far it looks like there are cracks in the larger sections of concrete approximately every metre. We can only see the edge of the slab and where there are door openings because we have covered the floor with plastic and boards to protect it while we build, our walls also cover most of the top edge of the slab. So far we cannot tell how far across the slab the cracks go, but the cracks go right through the outer edge of the slab. We were warned from several sources that it is in the nature of concrete that “it cracks”, but I hope that the cracks are not too obvious in the final finish of our polished slab.
|Crack down the outer edge of the slab
|Crack on the top of the slab
We have joined the owner builder sharing merry go round. On the take side, Tony and his owner builder mates have kindly lent us a couple of pieces of scaffolding. Now that we are building walls over 2.7m high the scaffolding is immensely helpful. With no noggins in the way, working on the scaffolding was almost as easy as working on the ground again, with the exception of having to climb up and lift buckets of hemp onto the scaffolding. On the give side, we have passed some excess OSB boards on to owner builder Nicole for her to use as form work for her hemp building project.
|Bathroom window openings finished
|The very useful scaffolding
|Finished to ceiling height under 150mm rafters
Hemping around the parapet wall where the lower front pavilion roof meets the vertical wall of the main pavilion was tricky, mostly because there was a a section that will be in the ceiling space of the front pavilion, but is the back of the wall of the main pavilion that we could not get any form work into and ended up stuffing the space with a piece of Formex left over from the concrete joint.
|Parapet wall with black Formex filling gaps between the pieces of form work
I found a good price through an on-line building supplier, but the insulation was coming down from Queensland and the cost of freight was almost as much as the cost of the insulation. So, I contacted the manufacturer, Higgins Insulation, whose website indicated that they sold the same insulation at an only slightly higher price than the on-line seller and the insulation could be picked up from their Sydney warehouse. It turns out that the Sydney warehouse did not have enough in the R-value and size I needed, so with the offer to get 3.5 for the same price as 3.0 I now have a mix of each and in 580mm wide and 430mm (which cut in half will make 580).
I will use the 3.0 in the main pavilion as it has higher ceilings and the best ventilation, to make use of cooling breezes in summer, and the most amount of north facing glass, so I hope it will warm up well in winter. The rest of the house will have 3.5 except the hallway which has 90mm rafters. I am yet to work out the best form of insulation for the hallway but suspect it may have to be some sort of expanded polystyrene, in order to get the same R-value in a thinner material.
I will be using Magnesium Oxide (MgO) board on my internal cavity walls and then rendering this with the same 10mm of lime based render as the inside of the external walls, to give the walls a consistent finish. The MgO Board will be coming down from Quantum X in Queensland as a distributor in Sydney from another company could only supply 10mm or 12mm boards. MgO Board is not manufactured in Australia, but in my view is a greener option than fibre cement or plasterboard and I will render it with the same lime based render I am using on the external walls so you will not be able to tell the difference between the external walls and the cavity walls.