Let’s hope you lay the foundation for a good year

YOU are probably waiting to see if your builder is going to be back on Monday to complete what he did not finish last year. Meanwhile here in the country our builder returned last Monday as promised, completed the external plastering in a day, built a vegetable tunnel on Tuesday and has moved inside today to complete our ceilings – and all this in temperatures of over 40°C, so we are off to a good start.

As always, as we start a new year I ask that you let me know if you have topics that you would like me to cover in detail. We will continue to fill up your tool box; look at buying properties in a market that I believe is slowly improving for the seller, so we need to ensure that you will not be buying a dud.

I would also like to have another go at getting a more open dialogue with the City of Cape Town which, although it promised much when I went to see it, did not really deliver for us. Please let me know if you are having problems with having plans passed or with your building inspector.

I had some plumbing problems the other day, which meant the mains had to be turned off. Luckily my stop-cock is above ground and easily accessible, not like many of you in town whose tap is buried somewhere in the garden. The local plumber turned up and said to me: “Mr Mac, don’t you know there is an easy way to switch off ? There is a knob on your meter box. So please go outside and check your box with a small spanner and a screwdriver, and your water will be off in 10 seconds.

Tony has got my year up and running and although I will send him a specific answer his question is one that a lot of people battle with.

“Just a good old fashioned quantity surveying question needing your confirmation. At the immediate start of the new year upon contractor return, the plan is to cast a 9m by 6m concrete slab (standard 6-7cm max in thickness).

“Marginal over-procurement of building sand or cement (other than cement shelf life concerns) is never a problem as these extra amounts can always be utilised somewhere/ somehow. But additional quantities of building stone are something difficult to find a future use for.

“Utilising your experience and quantity formula knowledge, what is the cubic metre of building sand and building stone that will be needed? Also your suggested quantity of 50kg cement bags required? I understand it is always a good idea to add 10 percent to the number(s)?”

An engineer and not a quantity surveyor is actually the correct person to answer this question, but when pricing a bill of quantities a quantity surveyor does need to know on average what is included in a cubic metre of concrete or mortar. Obviously the ratio of sand, stone and cement depends on what strength the concrete needs to be when it has finally set and cured, a process that takes 28 days. Different strengths are needed for different building components, with the concrete in columns and beams needing to be stronger than that in surface-beds. I have for years tried to find two cement manufacturers that give you the same quantities for one cubic metre of concrete – there are always slight variances.

The best method of obtaining the right mix is to mix by weight, but unless you have a large batch plant, this is impossible, so the average builder will rely on mixing by volume and as long as you use the same size container this method is fairly accurate. Pop into you local hardware store – they always have pamphlets on how to mix concrete.

Personally, if I want to mix a good quality concrete 25mpa, I always stick to the following formula: 8 pockets of cement, 0.6m of sand and 0.7m of stone.

I am a little worried that you only want to cast a slab 60 to 70mm thick. Not sure what you are going to use it for, but I am always nervous of going under 100mm, and I also always like to put some weld-mesh into my surface beds.

So if you are going to cast 100mm thick you will need 44 pockets of cement, 3.25m3 of sand and 3.78m3 of stone – I would suggest that you order 4m3 of each.

I don’t believe that concrete stone is unsightly and often use it around the garden as decoration over sand patches, etc.

Hentey from Welkom in the Free State has sent me some photographs and asks:

“Hope the pictures tell you enough. Are the cracks serious and can they be fixed? Apparently houses routinely crack in Welkom. The cracks are vertical alongside three inside room door frames. There are no cracks on the outside walls.”

I have included this question as it is a problem we often see in the city, in houses were the floor level is well above ground level, which means there is a lot of filling under the floors. To save money, foundations under internal walls are often omitted. In my opinion this is a dangerous practice – the foundation is supposed to be replaced with a thickening in the surface bed under the wall, but this is often omitted as well or not constructed properly. To add to the problem, the “filling” under the floor is never properly laid and compacted and mesh is seldom used in the surface beds. So what happens is that the filling starts to collapse on itself, often assisted by underground water or leaks. The walls above put stress on the unsupported floor, which starts to sag, causing the walls to crack. The only permanent remedy is to open up through the floors and underpin the walls and slab. Please ensure that if you are building, that your internal walls have foundations. Please keep your questions or

comments coming to don@macalister.co.za or SMS only to 082 4463859