Ramming Update #1

We have managed to ram a section of wall per day. Today, we rested the ramming crew and instead, started preparing all the waterproofing and concrete chamfers on the remaining stem walls. Tomorrow we will ram the last wall on the south side of the building. Johan being a traditional builder has calculated that our progress is equal to the build rate in brick. The difference is that we don’t have to plaster or paint so there is probably one day’s saving in that; however we have spent quite a bit of time manufacturing the formwork. By the end of the project, the build rate is probably equal to brick.

There have been some issues that have arisen. The major issue being the forces at play on compaction. Besides having to dramatically increase the number of walers we use and the huge increase on endboard support to prevent movement, we have since discovered a curing issue. We braced the endboards on our last attempt where we rammed an unsupported wall, with steel jacks. Despite this, there was still movement between the bracing points. Now we realise that we need to brace the endboards at around 300mm intervals. The traditional support of wood with wooden wedges has proved to be the simples and probably most effective. The curing issue is another story.

Our first attempt at a window opening was not great due to the significant movements in the VDB. We attempted a repair and it looks like a repair. It is no longer an option to attempt repairs of the rammed earth wall and we now realise that our preparation needs to be significantly better in order to prevent issues later. Also, we had a fairly slender section that was adjacent to a column. As this dried out, it curved away from the wall. The movement was around 10mm and I think it had to do with differential drying rates. The section of the wall next to the concrete column did not dry out, but it did on the opposite face. Due to the fairly high clay content, it shrinks as it dries. This would have caused the one face to shrink significantly more than the other face which resulted in the slender section bowing away from the concrete wall. When we pulled it back in line, it cracked. Since this all is around our repaired window, we will either cut out a large section and redo it or alternatively redo the whole wall. Now we have decided to brace all slender sections. Also, the moment we remove the formwork, we wrap the wall in cellophane or ‘cling film’. This is quite amazing stuff as it bonds with itself and creates a watertight plastic layer which is an ideal way to control the rates of evaporation and consequently the moisture content. The most important effect of wrapping the wall in cling film is that it stops us from attempting repairs on the wall. When the face is exposed, the inclination to fix little imperfections is overwhelming. Again, every repair looks like a repair and by wrapping it in cling film keeps our grubby hands off the slight imperfections until they’ve had time to cure.

I decided to add a little bit extra lime to the wall thinking it would be a good idea. However, I have just learned that the extra lime may result in hairline cracking. So this is another unintended consequence of erring on overdoing something. Another lesson is how to calculate the moisture content. We have been advised to purchase a scale that can weigh 500g and is accurate to 0.1gram. With this, we are supposed to weigh out 500grams of soil. Then we add some methylated spirits to the soil and set it alight. While it’s burning we are supposed to stir it and this burns off all the moisture – as alcohol would. We then weigh the dried soil and by doing this, we can calculate the moisture content of the soil. From this we can calculate precisely how much water we should add to get to our 9.4% moisture content. Apparently if the moisture content varies in our mixing, it may affect the colour of the cured wall. However, it must be said at this stage that I’m grateful to have a rammed earth wall of any colour and I’m sure a slight variation in colour will just add to the character.

So now we are going to leave the walls under plastic for a week and then we will remove the plastic for a day. By then we are hoping that the moisture content of the exposed surfaces will have reduced by around 50%. Then we will spray on a water repelling sealant. This will have two purposes, one to protect the wall from rain and other sources of moisture and the second is to prevent carbonation. Carbonation occurs where carbon dioxide in the air reacts with the bonding process of the lime. This results in the wall being much weaker and layers of the wall can literally be rubbed off. It comes off as a powder/dust. We discovered this occurring with one of our test walls before we sealed it. However, once it is properly sealed, the wall will cure to rock and look stunning to boot.