Cement for concrete basics

Well soon enough im going to be writing about my favourite part of the build. I especially love the groundworks. Before then you need to know a bit about cement and concrete - so everything you will need to know about cement and concrete to prepare you for groundworks.

A brief history of cement;

In 1820 Joseph Aspdin discovered that when he ground up the limestone and clay and heated it, then added water to the resulting ground up powder, he found that it hardened. He decided to call it Portland Cement because he was a business minded guy and the majority of the building work at that time was done using a type of stone quarried on the Isle of Portland which is off the British coast. The accepted view is that his mix looked like portland stone but im doubtful.

Applications in order of importance as defined by me

To make a good general purpose concrete mix;
one shovel of cement to two shovels of sharp sand to three shovels of max 20mm aggregate.

To make a good paving concrete mix;
one shovel of cement to one and a half shovels of sharp sand to two and a half shovels of max 20mm aggregate.

To make a good foundation concrete mix;
one shovel of cement to two and half shovels of sharp sand to three and half shovels of max 20mm aggregate.

If your using ballast, its a different story. Ballast is an all in mix of sharp sand and aggregate. It is more common down south then it is up north. Im not that keen on ballast - its never the same, each ton bag is always different plus theres never enough 20mm aggregate. Rubbish because your never assured of a consistent strength of concrete, but used because its convenient - a factor which has an amazing ability to corrode good building practise, a factor which is driving most building innovation. . .Ask your project manager if he uses ballast. If he does think twice about hiring him. If he mentions ready mix...thats another blog.

In all of the mixes above, dont put too much water in the mix - water will reduce the strength, just use enough water to make it possible to place it and to compact it.

Since I'm writing of concrete its only fair to add a bit about admixes;

SBR: Has a lot of benefits main benefits are when doing a screed that's going to end up as a tiled floor - the SBR in the concrete that is the screed, will become a tiny bit flexible, so when the underfloorheating goes in under the tiles its just better because the screed will flex a tiny amount when the UFH is turned on and it wont breakup. I usually use SBR its inexpensive and has many benefits.

Dustproofer and Hardener: Not that important its basically used to seal a concrete floor, you end up with a hard wearing non dusty surface. I suppose it is cheaper than concrete paint, which costs a fortune. If you need to finish a floor where the visual aspect is not important use this instead of paint. Plus with concrete paint technically you shouldn't use it till the concrete floor has been down for 6 months minimum.

Waterproofer: I wouldnt leave it to an admix to waterproof concrete, if its going in a render its a different story.

So of the above which brands to buy, well they are all pretty much of the same, the main distinction being branded or undranded, I personally would go for the Sealocrete products and as far as PVA goes buy Unibond 10litre stuff then water it down - works out far less expensive thant the 2.5litre unbranded stuff. As far as the waterproofer, i will discuss below. The real major issue / screw up that will occur when on site, the absolute main reason why failure occurs is because some bright spark isn't putting the right amount of admix into the mix. That's the main reason why the admix will fail to do its magic not because of brand.

So which waterproofer? Sika is in a class of its own, far far far better than any other waterproofing product on the market. And its a lot more expensive, unless you know where to buy - If you need it for a big job, go Travis Perkins and buy the 25litre ones - will set you back about 100quid but well worth it.

I should mention that not all admixes work well together. For example, lime makes a render more workable, sika makes a render waterproof but if you are adding lime to a Sika render it will have a negative effect on the waterproofing abilities of the render. And sika at 100 quid/25 litres you dont want the waterproofing capabilities diminshed in any way. So dont get into the habit of throwing everything in to the mix - always check the data sheet. Or call the tech helpline.

Im gonna mention all the different types of cement; to be honest the important stuff is above but here we go

General purpose cement - Used for most applications
Premium cement - Lighter colour and has improved workability offers slight protection from freeze-thaw attack
Rapid cement - High strength NOT early setting!
Fastset cement - Sets hard within an hour, its suitable for fixing posts
White cement - Used for decorative purposes but also has high strenght
Sulfate cement - Use this below damp proof course where sulphates are present in the soil

Stick with general purpose cement.

This blog is getting really big and im probably at risk of losing your attention, thats why i wrote in order of importance but since we are talking of concrete i must put in a note about A142 mesh.

Its a mesh that reinforces foundations, ill post more on this when i discuss the foundations.