Concrete basements are one of the most popular home extensions nowadays in London and surrounding areas. As many people don’t want to sacrify part of their garden or are unable to undergo a loft conversion due to building permission. This option is even more popular for new build properties as is much cost effective as doing the similiar project to already standing ones. This can add up to 100% of ground floor area of existing property and not change the look of a house at all. In this blog post we will look at concrete basements and how to build them.
Cellars used to be used as a storage before. As these underground spaces were not supposed to be made for living no one really cared if they were wet. As basements are now created to be a living space, keeping it dry is a priority, and it is not as easy as it might seem.
Basements leaks are very hard to fix and are pretty common. Designers put their efforts to put as many layers of protection as possible (membranes, clay coverings, internal drainage etc.). Importance is to make a primary structural material waterproof so in case of leak in future it is easier to identify who and what caused the leak in the first place - this will save money and time.
It is important to build a concrete basement by following a specified methodology which when will be followed correctly there wont be any leaks in a future. It is advised to have an independent representative who will make sure the work is done as it should be. Doing it properly will mean that concreting will take longer than usual therefore it will be more expensive - but money will be saved overall.
Concrete should have a certificate to BS EN 12390-8:2009, which proves that the concrete is completely waterproof. This mix should be a min P350, CEM1 and over-sanded for pumping. As this concrete is a low water-cement ratio (WCR) of max 0.45l of water to 1kg of cement a PCE plasticiser has to be used.
Pretty common reasons for leaks are formations of voids, cracks and dirt during the concrete pour. It is therefore very important choosing a reliable concrete supplier and having a supervision when undergoing the pour. Few concrete additive suppliers offer monitoring in their pricing. It is a great choice having someone monitoring the pour and even creating a report after every pour is completed.
Do not use kickers at all as they are not suitable to use with a waterproof concrete. They will sink when used at the same time as the slab during compaction and when used with the concrete later the concrete will be too shallow to compact properly.
- Pour the concrete in frequent intervals
- Never allow for concrete to free-fall more than 1,250mm
- Never fill more than 500mm deep in a single pass
- Never held still a poker, always move slowly along 200mm
- Wait until the concrete have cooled before releasing all formwork
- Waterproof concrete will never self-level itself as it stiffens quickly (pokering will be enough to level it if a smoother finish is not required)
As pouring the waterproof concrete has to be highly monitored and the amounts of concrete poured in one go are important it is advised to use a volumetric truck which can create as much concrete on site as needed for the next pour. This will save money and time as it won't cause over ordering. In case you need some more information about waterproof concrete pour please contact Mister Concrete professionals who are really happy to help.