Significant Progress

Bathroom external wall rendered

Rain chain and more finished walls

Having a renderer that has been able to give some full time attention to the house has led to significant progress being made over the last few weeks. The internal walls are finished and there are only three external walls, three upper walls and a small section around the front door to go.

Freshly rendered back wall

Front of house freshly rendered

The hemp lime rendering  has not been easy. The window headers have been particularly difficult as the render is not very sticky and so tends to fall off the window headers, the render also does not spread very well and so cannot be moved around on the wall, it also tends to get rougher if you go back and try to touch it up.  But Brett, the renderer, persevered and has managed to do the window headers by filling any gaps or holes first (particularly any patches where chunks of the hemp wall have broken away or crumbled), then when this is dry he has attached a straight edge to the window and finished the underside of the window header, then when this has gone off a bit he has gone back and done around the face of the window header. The window headers have been done the day before the wall has been rendered. Then when the wall is done the sides of the windows or doors have been done first followed by the face of the wall. 

Patching the worst of the holes in the window header

Window header rendered

 The walls were wetted down before being rendered, then sprayed with a light mist of water on the evening after the wall was done on warmer days or the next day, to slow the drying down.

The hemp render was not suitable for use on the Magnesium Oxide (MgO) board at all. It had to be done in two coats, increasing the cost. The MgO wall could not be wet down first otherwise the render just slid off. Even then the render had great trouble sticking to the wall and if done too thickly would bubble and fall off or crack and just slide. The last MgO walls were done by splattering the first coat on which seemed to work better, but it was a bit late in the project to worth this out.  The second coat of render on the MgO was very difficult to work and on most walls the finish was very patchy both in texture and colour.

Left - Hemp render on MgO Board and right- hemp wall

Hemp render on MgO Board

With only a few walls left to do the render will be finished in a few weeks after Brett takes a break from the hemp walls, with a few more conventional jobs. The completion of the internal walls and the external walls, that have lights on them (thank you Brett for doing those walls at short notice), meant that the electrics in the house could be finished. Paul and Luke from Solar Connections came down and fitted all the internal and external wall lights and got all the power points working. A small problem arose when the back circuit and stove circuit would not work. I panicked that there may be a problem with the wiring in the wall or roof and I would have to start pulling the ceiling down to find it. Thankfully this was not required, but a mix up of the stove and dishwasher power points will hopefully be resolved by long cords on these appliances or a short extension cord hidden under the cupboards.

External light installed

Front of house with external lights installed

 I had forgotten about the LED lights under the overhead kitchen cupboards and so spent much of the day putting up the cupboards so the electricians could install the lights. The LED lights were made up to fit the length of the cupboards, leaving a gap for the range hood over the stove.  

Kitchen cupboards and LED lights underneath

Everything happened at once as on the same day the electrics went in, Brett was rendering the external walls and Greg from Alpine Glass put the semi frame less shower screen in the front bathroom. Plus he helped me out by drilling the holes in the tiles for my toilet roll holder, I had been scared to do these for fear of cracking the tiles. With the right drill bit and experience it was no problem.

Semi frame less shower screen

Toilet roll holder

The completion of the internal rendering meant that the final finish on the floor could be done. Before this could be done I had to remove all the boards and plastic protecting the floor and remove the tape and clean the excess render from around the edges of the walls. I used vinegar and hard work to clean up the render from the edge of the floors and had to vacuum and mop the floor several times with multiple changes of water to get rid of all the fine dust. 

Floor in need of more mopping

Cleaned concrete floor

 The first coat of finish on the polished concrete had what looked like crazy paving type pattern cracked in the top of it. This was only visible when light hit the floor at an angle but was much more obvious under artificial light. There were also a few patches of white spots and some rough sections where things had fallen on the floor when the first coat was drying as this was done before the windows had been put in.  

Crazy paving cracks in sealer

White dots on concrete

Henry and Adrian from Dayman Group returned to fix up the floor. It had been two years since they did the first cut on the polished concrete and almost a year since the first sealer went on. The floor was given a light sand which will hopefully resolve the crazy paving cracking and remove the rough sections. A bit more of a sand was required to get out the white spots, which I was told were caused by the floor being covered before the first lot of sealer had fully dried. They also fixed up some patches which would have been covered by the kitchen cupboards, except that the cupboards we are installing are about 30cm off the ground. 

I left while the final coat of floor sealer was still wet and so am keen to get back down there and see what the final finish is like.

How to Hemp Lime Render

With well over half of the internal walls rendered, John our renderer has mastered the application of the Australian Hemp Masonry Company hemp lime render. We have put together a little video on the rendering process.

The first room to be completely rendered was the bathroom. In the bathroom the render produced a very nice finish that ended flush with the tiles, each being about 10mm thick. The main kitchen living area was the second room to be completed. Two of the bedrooms are not far off completion with only the second coat on the Magnesium Oxide board to go. Even the third bedroom now has one wall rendered. All the hemp walls have been rendered in a single 10mm coat. The MgO board walls have been rendered in two approximately 5mm coats.

Last wall in the main room freshly rendered

Main room rendered

First wall started in the last room to be rendered

Progress Made on Hemp Lime Rendering

We bought our pre mixed bags of render at the same time we bought the binder for the house. The lime render came with just a list ingredients to add and instructions to wet down the wall before applying the render. I had never used the AHMC render before I bought a pallet load of it for my house. I had done a brief bit of hemp lime rendering with Steve Allin at his workshop in St Ives in January 2012, but they used a different binder, very large hemp fibre and put on a layer almost 1 inch thick. This process was so different to that done at the St Ives workshop that it was of no use when it came to the hemp lime render we were using. My experiments to get the right colour and sand only gave me experience in doing 300mm square patches and even then the render sometimes went on really well and other times was really difficult.

Thankfully we had John our renderer to help us out, so these issues of getting the right mix and consistency were placed in his experienced hands. The first test wall John did, inside the wardrobe just in case things did not go well, was slow going but worked out fine. The next wall was faster but still quite slow. He quickly learnt that the hemp lime render does not spread easily across the wall, whether it is the hemp fines or some other reason, it is best to apply the render as close as possible to the location you want it and as close as possible to the finished thickness, then just use the float to smooth and even it out. The steel float gives a nice smooth finish, but the pieces of hemp and some of the large pieces of river sand ensure that the render maintains some texture.

The order of mixing using a standard cement mixer was ¼ bucket of water, ¼ of the 22.35kg bucket of river sand, ½ a bag of AHMC render mix, 80g of yellow oxide, the rest of the water and the rest of the sand and the rest of render mix. Mixing was a bit dusty but the holding of an empty bag over the mouth of the mixer after the render mix was added kept a little bit of the dust down. Later we changed this to using a bit less water and then adding a spray of water from the hose after the render mix went in and this kept the dust down.

The first part of the third wall went well then a slightly stiffer mix slowed John down substantially. He was not able to achieve the same finish as the first half of the wall, so he had to damp down the stiffer render, use a sponge float to work this water into the render then steel float it all again. Lesson learnt that there needs to be consistency in the amount of water in the mixes and the slightly sloppier mixes go on better. Achieving consistency in the wetness of the mixes is not as simple as using the same amount of water, as some buckets of river sand contain more or less water this needs to be adjusted for. So, like cooking it is about getting the look and feel of the mix right.

Front pavilion one day after rendering

Left wall fully dry and right wall 12 days after rendering

3 weeks after rendering

Wall freshly rendered

12 days after rendering

3 weeks after rendering

The weekend John worked on the third part of wall, my mate Tony was on site and having been to two hemp building workshops himself, he was keen to give hemp rendering a go. Tony and I got to work on one of the small MgO Board walls on the inside of the wardrobe. I used the stiffer mix and it was very slow going, in the confined space of the upper wardrobe it was awkward to trowel the render on, so I rubbed handfuls on the wall pushing them on until they were the right thickness then giving it a trowelled  finish. Given that John was at that time rectifying the effect of the stiffer mix Tony experimented with using a much wetter mix. The much wetter mix went on faster and could be put on with a trowel, however in parts it had difficult adhering to the wall. Going back several hours later to fix a patch where the wetter render had slumped a bit, a whole patch fell out. It appears that you need the “just right” mix, not too sloppy and not too stiff.  

The skinny wall done and patched by the non professionals

The following day John only had a couple of hours to spare and finished one of the walls with lots of windows. I used the “just right” render left over from John to patch the hole in the render on the side of the wardrobe. I had sloped the edges of the patch that had fallen out so there was less of a line where the join would be. Wetting down the edges of the patch and working the new render into the old, by making circles on the wall with my rubber gloved hand, the patch was filled and while it was not prefect  it was acceptable. John had also left a small join next to one of the doors and when he finished it the following day had to feather in the new mix.

With still more render mix left over I worked on the upper inside section of the wardrobe. A ridiculous section to render as no none will ever see it, but a good place to practise. I was painfully slow at rendering and it was very hard work on my arms, but the finished render was acceptable and was sticking to the MgO Board walls. Given the snail like speed of my progress I am glad to have outsourced the rendering.

We have applied self adhesive render mesh diagonally across the corners of the windows and along the joints between the hemp walls and the MgO walls as well as along the joins in the MgO Boards. I am using a 5mm mesh that comes in 200mm wide rolls from Foamex. The render mesh is to try to restrain any movement within and between walls to prevent cracking. Despite using the render mesh we did get some hairline cracks at the corners of the first window we did. Later window corners had either no cracks or only very small cracks.

Only a very fine crack at the corner of the window

No crack on the other corner of the window

We used 200mm x 300mm strips of render mesh across the corners of the windows, however had some adhesion problems and these sections of render had a tendency to pull away from the wall while they were still wet. These patches were identified and fixed while the render was still wet. The cause of the problem was hypothesised to be the hemp fibres in the render preventing the render from pushing through the 5mm grid in the render mesh and coming into contact with the wall. For further corners we tried halving the width of the render mesh to 100mm x 300mm across the corners of the windows and doors. This resolved the adhesion problem and when fully dry after about 4 weeks we will see if there is any cracking. The adhesion problem was not such a big issue at the corners where 200mm wide render mesh was run along the joints between the hemp and MgO walls, but here only 100mm wide on each wall was being rendered at each time. 

I had originally thought that we would need render mesh to cover the whole of the MgO Boards so that the render would adhere to it so I bought from Foamex (manufacturers of polystyrene walling and insulation systems) two rolls of 200mm wide mesh and two rolls of 1200mm wide mesh. I had believed that both widths were self adhesive, I checked the small rolls when i purchased them but the larger rolls were wrapped up and I just assumed they were the same. But, when I got them to site I found that the 1200mm rolls were not self adhesive. Going back and checking my original quote I found that the mistake was mine and the 200mm rolls were listed as self adhesive and the 1200mm were not. I confessed to my mistake and e-mailed Foamex asking if I could return or exchange the 1200mm rolls. As they were unopened and unused this was not a problem. I went back to their warehouse where I had originally picked up the mesh from and had no problems at all returning the 1200mm rolls, getting three more 200mm rolls and getting a refund for the difference. The fabulous service I received from Foamex could not be in more contrast to the problems I have had with the plywood. 

While I was off site John continued rendering, as rendering is his second job it had to fit in around work and family commitments. John did three walls of western bedroom in the back pavilion and a section of the external wall, before he was struck down by illness and forced to take a break. It was interesting to watch the process of the internal walls drying. For the first three days after they are done it is hard to see much visual evidence of drying, although you can feel the render firming up. After about a week the walls look unpleasantly patchy as different parts of the wall dry unevenly. Two weeks later the wall looks much more even and after three or four weeks the render is all dry and stops changing.

Back pavilion a few days after rendering

About a week after rendering

Right wall done later than left

Rendering our first external wall was good and bad. Without the ceiling and floor detail to worry about the rendering went quickly and we chose to have a slightly rougher texture on the outside. Problems arose when a chunk of hemp wall next to the window fell out. I had taken an angle grinder with a masonry blade on it to the walls and taken off the sharp corners around the corners and around the windows, so that I could get a nice curve around the window frames. However, I believe that this cutting off of the corner may have cracked a weak section and we will not have to try and patch the section with render. Next time we will try rendering around the window without cutting the corners off the hemp walls.

Detailing around the window

Rendering the external wall

Where a piece of the wall fell out

Window detail

External wall a week after rendering