Monday 25 March 2013

First Hemp Render Test

We did a test patch of render so that it will have plenty of time to dry, before we have to choose the sand we use for the render and whether we need to add any coloured oxide. For our first test we used the Australian Hemp Masonry Company bagged lime based render mix, we chose this for the ease of using a bagged product which would be consistent through each mix and because we like the fine hemp fibres in the render, so you can still see that it is a hemp house. To this we added  water and sand. Made up 1/20th of a 9kg bag, so ended up adding just over a kilo of sand. We used Sydney sand. AHMC recommended the use of river sand, however the locally available river sand in the Shoalhaven area is a dark grey. This was all right for the wall mix but is not what we want for the colour of our render. I was told by the landscaping and hardware store that the Sydney sand was what was used for rendering, that of course referred to cement rendering. The bulk Sydney sand I had seen was a light yellow, but when a bag of sand was purchased it was browner than expected.

Mixing the render in a bucket
Because we were mixing a small amount we just mixed it by hand in a bucket. We chose to do a test patch behind where the kitchen cupboards will go. The hemp fibre made the mix stiffer and less plastic than a cement render. Using a hawk and float it seemed to stick to the wall quite well, although pressing the render into the wall gave that arm muscles a good work out. The wall had to be damped down before the render went on. This was a bit tricky without a sprayer and we have subsequently bought form Aldi an 8L pressure sprayer, hopefully we can damp down the internal walls with this, so we do not have to use a hose inside the house.

I have read elsewhere hemp lime render being described as like "tuna and mayonnaise", the fibres in the render certainly made it different to work with than I had expected. With cement render, it is usually put on and left for about two hours before it is floated again. We did this with the hemp render, but two hours was probably too long. The stiffer mix was too hard to push out anything but the smallest lumps. At Steve Allan's workshop he had suggested rubbing the hemp plaster mix back with a rubber glove, when it was partially set to bring the hemp fibres to the surface. He was using a different render mix, that had large hemp fibres and no sand. We tried this out, but using the AHMC render mix this brought out too much of the fibre and I prefer just a floated finish.

Test patch of render
Render rubbed more at top of the patch than bottom
 Our rendering was a bit lumpy, but with some depth guides and a bit more practise I think we can get an acceptable finish. I would still like to get some lime rendering lessons if I can find someone willing and able to teach us. We will not be able to tell the colour until it is dry, but I have sourced some yellow river sand a bit further away, but if it gives us a better colour without having to add oxide it will be worth a couple of trips with the trailer. We will try this sand next time we are on site.

Meanwhile work on the ceiling continued. We returned the broken panel lifter, the problem was very obvious and they exchanged it for a new one. The paint job on the new panel lifter is a bit patchy but the mechanics seem fine. We put ti to use finishing the second bedroom in which the last ceiling panel had to fit into a recessed section over the door that had walls on three sides. This was tricky, but after cutting a little off two of the edges it fitted acceptably well.

Ceiling in second bedroom
Work then progressed to the last of the bedroom ceilings. Following the line of the eave rafters a ceiling board would have ended just short of the built in robe. The robe was also 10cm narrower than it should have been, another mistake by the framing company, but too difficult to fix now that the frame is all up. The solution was to add some extra blocking behind the ply ceiling boards so that the end board lines up with where the ceiling abuts the robe wall. The brick pattern was continued for the ceiling in the largest bedroom even though this meant that every second row had two small boards on each end. The alternative of one big straight line down the middle of the room would have looked odd and shown up any slight difference in the spacing of the boards.

Ceiling in largest bedroom

1 comment:

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