Sand and cement screeds vary in proportions. The industry standard and the mix proportions that are generally specified are 1 part cement to 3- 4.5 parts sand. This is numerically expressed as 1:3-4.5.
It has been heavily debated over many years which method of supplying sand and cement screeds is most effective and reliable. The old age way of mixing screed by hand or the modern way of having the screed ready mixed by a mechanical batching plant and delivered to site.
It is true to say that the way in which the screed is laid is just as important if not more important than the mix proportions. This highlights the importance placed on your decision in choosing a floor screeding contractor.
However a major decision when screeding a floor and ultimately choosing a contractor lies in their screed mixing method. Are they ready mixed or site mixed in the material they lay.
Site mixed material
Site mixed sand/ cement screed has been used for generations on building sites as it supposedly the cheapest method to install a floor screed. It has stood the test of time and is still used in the industry today. However there are several drawbacks with this method. These are as follows:
- It incurs increased levels of manual handling.
- It gives rise to a problem with the inhalation of cement dust as bags of cement need to be split and mixed with sand.
- It increases the amount of packaging that is used and so a higher wastage on site. This is something that the industry has been actively seeking to reduce.
- The quality of the material as regards the mix proportion is determined by a man on a mixer. This could mean that the floor once laid has a higher cement to sand ratio on one half of the floor than the other increasing the likelihood of a screed failure.
- It needs to be delivered in two separate deliveries. One for the sand and one for the cement.
Readymixed sand and cement screed has become the most popular method of supplying and installing a sand and cement screed. There are many reasons for this.
- It reduces the level of manual handling and packaging associated with site mixing.
- The mix proportions are set by machine to all relevant British and European Standards and is guaranteed by the readymixed supplier. This is effect providing an insurance safety net in regard to material quality.
- It can be delivered in one load and is pre mixed reducing the health and safety implications of working with cement.
- A higher level of production is also achievable when using readymixed material as site mixing is a lot slower process. This means programme times can be shortened.
In short the site mixed sand and cement material is only as good as the person mixing it and current industry standards being as they are a guarantee that can only be provided with a ready-mixed material is a vital aspect of any contract where screeding a floor is concerned.