Hemp Lime Rendering Commenced and Nelligen Studio Revisited

A busy long weekend was spent,  finishing the wardrobe in the front room and putting on the door jamb and inbuilt pelmet for the curtain that will be the wardrobe door. I used Tasmanian Oak timber, as I had for the other door jambs on the house, cut to size to provide a render stop for the 10mm of render on each side of the wall. The ceiling and door jamb was then covered in plastic, reusing the plastic bags the insulation came in, to protect them from the render.

Our friends Martin and Nerida stopped in on an unwintery warm sunny Saturday with their chainsaw  and we cut up some very sizable tree branches that had fallen onto the block over the previous 12 months, most significantly the branch that dented the fence and the other that cut a hole in the back gate. They left with a trailer load of firewood , but not before I had roped Martin in to help me with the battens and valley boards for the awning over the front door. The tricky part with this was that the section of the awning over the front door only has two rafters, one of which is the valley rafter. Because we needed to put the valley boards in next to this rafter we could not attach the battens to it. Instead, we used left over material from the awning rafters to create perpendicular rafters that ran between the two rafters and on top of which we attached the battens. Over the rest of the weekend we finished the battens, valley boards and hip battens for the whole front section of the house. 

Valley boards and battens with extra support installed

Battens and hip batten installed

Being a long weekend we took a trip down to Nelligen to help our friend Nicole with her hemp walled studio. She had made good progress since we had last been on site. We spent the day helping her build the hemp walls along he south wall and above the stone foundation wall. The east wall above the stone foundation was originally to be made of stone but a change of plans after the frame was made meant that adaptations had to be made to change the originally 500mm walls to be partly 300mm and 500mm. The thicker walls used up the hemp very quickly.

Stone foundation wall and formwork for hemping

The west and part of the south wall are completed up to door height.

West wall

West and south walls

With all the different spacer sizes she was using, Nicole abandoned the use of spacers and instead used a level to ensure the formwork went up vertical from the lower measured section of the wall.

Formwork being filled with hemp

Sheet bracing filled on both sides

Permanent formwork around windows

Nicole's hemp came from two different sources. The first sections of wall used hemp from Ashford and the current sections she is making use hemp from the Hunter Valley. Although I also sourced my hemp from Ecofibre in the Hunter Valley it was very different from the hemp Nicole was now using. Her hemp came in compressed bales and was much finer than the hemp I got from the Hunter Valley and was even finer that the hemp from Ashford. Having worked with all three different chops of hemp, my current preference is for the chop from Ashford. The larger pieces of hemp from the Hunter Valley did not interlock as well as the finer chop, but the very fine chop from the Hunter Valley appeared to compress so much together that the walls seemed quite dense. The Ashford hemp seemed to be a balance between the two. However, I will reserve my final judgement until Nicole's walls are thoroughly dry and the properties of the walls using the different hemp can be better observed.

Compressed bale of Hunter Valley hemp

Wall using Ashford hemp

Wall using Hunter Valley hemp

Hunter Valley finer chop of hemp

Nicole loaned us he old cement mixer for our rendering and John the renderer came around to try out the hemp lime mix. John made up the mix a bit runnier that I had done the test samples, but that may explain why I had some difficulty applying the render on my test samples.

Hemp lime render being mixed

Render ready to go on the wall

Self adhesive fibreglass mesh was applied to the joints between the hemp and MgO boards.
 John first tried out the render on the inside of one of the wardrobes, the top section of which was a very awkward area to access. Perhaps this was not the best place to start, but it was an easy place to hide any mistakes that were made. John found the hemp lime render different to any other product he had used. He found that it was best to put the render on at as closest to the final thickness as possible, float it and them leave it. Floating the render again later, as is done with cement render just brought up the grains of sand and made the finish less smooth. Unexpectedly the render did not cover anywhere near the 5sqm advised by the manufacturer. When we next do a larger section of wall we will more accurately measure the square meterage covered by each bag of render. John was able to get the finish we wanted to achieve, a consistent but not completely flat finish, just like a traditional lime rendered building.

Render mesh applied to joints

Rendering the inside of the wardrobe

Awkward top section of the wardrobe

We need to get the inverter for our solar panels installed by 30 June, to take advantage of the government rebates that were in palace when the panels were first installed. So, John did a patch of render where the inverter will be placed. John was unsure of the best way to render the MgO boards and whether the render worked better with or without render mesh so he did some tests, doing a 10mm coat of render mesh, a skim coat on render mesh and the same again 10mm coat and skim coat without render mesh. The skim coat is a thin coat that is later covered with the finish coat of render. When dry we will be able to see which method provides the best adhesion.

Render patch for solar inverter

Skim coat and 10mm coat on render mesh

Top to bottom; skim coat no mesh, 10mm coat, skim coat with mesh, 10mm coat with mesh all on MgO board

Nelligen Hemp Studio

The ANZAC day public holiday meant there was an extra day to build, so what else do you do when you are half way through building a house, we went and helped a friend build her studio. Nicole is building a hemp walled studio at Nelligen on the NSW South Coast. Approved by Council it is the first hemp build in the Eurobodalla Council area.

Nicole helped us out with building our hemp walls, so we wanted to repay the favour and I was keen to see how the studio was going. Her studio is being built in a beautiful location in a hill in Nelligen, with swamp and river views to the east and mountain views to the west.

View of the swamp

View out western window to the mountains

Nicole's build is different to ours in many ways and it shows that hemp walls can adapt to different styles. Nicole is building on a half suspended concrete slab, with a beautiful stone wall on the lower side. Her hemp walls are 300mm thick, to provide extra insulation in the cooler climate. To achieve deep window reveals on the inside she offset her frame toward the outside. The frame uses 90 x 35mm studs set at 450mm centres combined with large section recycled wharf timbers around the glass on the north side and as exposed beams supporting the first floor.

North and East side of the studio

Recycled wharf timbers

Nicole put up large sections of form work on the outside, avoiding the need to regularly move the form work up in the steeper sides of the studio. 600mm sections of form work were put up on the inside.

Form work on the steeper Western side

The use of 300mm thick walls was both easier and more difficult. It was definitely easier to place and tamp the hemp as there was no difficulty getting your arms and tampers around noggins and window sills. Nicole requested that her framing company put the noggins all in the same line, unlike my offset noggins. Noggins all in one row was definitely easier so that rises of hemp could be finished at the same point.

The smaller 45mm gap between the form work and studs was not a problem and plastic pipe spacers were cut to fit and she attached the form work with bugle-head batten screws. On the inside however, the larger gap between the studs and the form work meant that Nicole could not get bugle batten screws long enough to cover this distance and had to attach blocks of wood to her studs to be able to use the bugle batten screws to attach the form work. To complicate matters further the frame for her window openings were not the same distance from the form work as the frame and required different spacers.

Spacers with extra blocks of wood

Different sized spacers with window frame in background

Nicole used fibro as permanent shuttering around her window openings. If I build again I would do this, but would use something breathable like magnesium oxide board. I chose not to use this method, although it was recommended, as I wanted to curve the edge of my window openings. Nicole found a better way to do this by stopping the permanent shuttering a little bit short  of the edge, still allowing the edge of the window openings to be curved.

Permanent shuttering around window

Unfortunately Nicole has had to use sheet bracing, due to the high wind rating of the site and the second storey. Concerned about how the hemp will key into this she has attached some axe shaped blocks of wood to the sheets to give the hemp something to key into.

Sheet bracing

Nicole used Alcor as her damp proof course and I think this was a better choice than the embossed polyethylene I used. The Alcor keeps its shape when bent and was easier to turn down and hold in place.

Alcor flashing neatly turned down

Nicole is mostly using hemp that has come from the Ashford and and is a finer chop than the hemp sourced from Ecofibre in the Hunter Valley. The more finely chopped hemp seems to mix easier and tamp down more evenly. The pieces in the Ashford hemp were also more consistent in size. Given the choice I would use the more finely chopped Ashford hemp. Nicole also had her hemp in pre measured bags which made mixing much quicker. Nicole used the same Australian Hemp masonry Company binder we did. One bag of hemp was used with one bag of binder. This was a real advantage in her build since the thicker walls used up the hemp mix much quicker and the person mixing had a hard time keeping up with those filling and tamping. Nicole borrowed our pan mixer and this works well for a small crew of workers but with the thicker walls and easier placement of the hemp a large crew of workers would need a bigger mixer to work efficiently.

Finer chop of hemp

Hemp and binder mix

Pre measured bags of hemp

The sand Nicole used was a brownish yellow, rather than the grey Shoalhaven river sand we used. This meant that her walls were a warmer sandy colour when wet, but they look like they will still be a grayish white when dry, albeit with a brownish yellow tinge.

Hemp wall a few days old

Placing hemp walls

Nicole made a chook house with hemp over 12 months ago. It has been left unrendered since this time. The wall is only showing a very small amount of weathering on the bottom of the wall. This is very good as although the wall does not face the prevailing weather it only has small eaves.

Hemp walled chook house

Small amount of weathering on exposed hemp wall

I am looking forward to helping Nicole again and seeing how her studio progresses.

Western walls

Hemp walls in the afternoon sun