Wednesday, April 18, 2012

Gearing up to ram

I’ve been spending my idle moments (yeah, right) thinking about all the little things that could get in the way or go wrong this weekend with my test wall. So far there are two little gotcha’s:

  1. The footing for the test wall is not at the same height as the slab. The slab has a 75x50 rebate cast into its perimeter to accept the Hebel panels, and I poured the test footing to the level of the rebate and not the full height of the slab. I did this mainly so there will be no problem installing the Hebel later (trying to squeeze it into a gap which would inevitably be too narrow).
    This means that one formwork column will be positioned higher than the other, since it won’t fit in the 75mm space of the rebate and so I’ll have to work out an alternative means of securing it to the footing, as my 50x50 angle solution won’t work.

  2. When I cast the footing I didn’t provide a 400w raised section upon which the RE wall will sit. Usually this is done to ensure that the wall will not be damaged by either ground or rain water.

I’ve not really come up with a solution to problem #1, but when I assemble the forms on Friday I’ll probably just wing it and cobble something together. No biggie.

Number 2 is a little more concerning, but I’ll kill two birds with one stone with this one. The test wall is an external feature, so at some point it will need protection from the rain lest it saturate the wall and reverse the action of the cement, causing the wall to fail. Now, in its position I’m not really going to be able to completely protect it from the elements (this is the job of the wall as a heat shield, after all) so I have to take some alternative measures.

I had originally planned to seal the wall using a TechDry stabilised earth sealant, but when I went looking online for a retailer I realised that their head office is a stone’s throw from mine and so I paid them a visit instead. In the process I discovered they have an alternative product call Plasticure, an additive which is mixed in with the raw materials before the wall is rammed which makes the entire wall hydrophobic, inside and out.

This is what I’ll use to solve the water problem. Apparently this stuff is so good that once it reacts with the cement and activates, you can’t wet the mix any further - it will simply not accept any more water. So it’s important to get the consistency right before adding the Plasticure, otherwise the batch has to be discarded. I don’t have enough sand for this kind of mistake (since I’m using up the last of the concrete sand I have on site to test its colouring), so I’d better get it right the first time ;)

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