I’m Andy Parkin, Managing Director of the Multi Award-Winning Speed Screed. I’m here today to talk about “screed how much water” you need.
Screed How Much Water?
When we are talking about the addition of water, it could be for a flowing screed or smoothing compound, however I would like to cover sand and cement screed.
Sand and cements screeds cover a few different variants such as traditional sand and cement 1:3 or 1:4 ratios, modified sand and cements (fast drying, rapid strength gain), and hydraulic binders.
Water needs to be present in screed for two reasons:
- To react with the cement particles, this process is know as hydration. If there is not enough water, then not all the cement particles hydrate and thus overall strength is reduced.
- Placement of the screed, this allows the screed to be shaped and levelled. Workability of the screed is directly effected by water content.
When considering workability of the screed you are looking for the snowball test. Take a handful of freshly mixed screed, and cup and form the screed into a “snowball” shape. Just like a snowball, you don’t want it to be too wet or too dry. The snowball needs to retain shape and firmness.
Too Much Water
As the screed is laid, compacting and trowel finishing, the finish needs to be to standard. Too much water, and it will be sloppy and hard to finish. When you form the snowball, if you get water dripping, then there is too much water in the mix. Too much water in a screed mix will mean that you are going to get increased shrinkage, and with it more risk of cracking, and you could be left with a weaker screed. A wet screed is going to make it hard to achieve a good finish, and you may end up with surface dusting due to high water contents.
The water content is going to vary from mix to mix, this is due to the moisture content of the sand, and that content can change throughout the day as it dries, or perhaps get’s rained on. Most screeding sand passes through the washing plant, and starts out very wet.
A sand with a high moisture content is going to generally dry as time goes by (unless it gets wet again). The top of the pile tends to be the driest part, with the central bottom of the pile being it’s wettest. The water demand is going to change throughout the day, and so it is important just to make sure that you are monitoring the water content and not just blindly putting the same amount of water in constantly, because the mix more than likely will change throughout the day.
Monitor Sand Moisture Throughout The Day
Monitor the sand throughout is the only way to ensure mix consistency. The sand may have been rained on (if not covered), just been delivered from the plant having just been washed it will have a high moisture content.
In summer it could be very dry and you will have to add more water into the mix.
Effectively the acid test, is forming a snowball. That will give you the indication of where you need to be and how much water needs adding.
Too little water
- Struggle to finish
- Weak and friable surface
- Poor compaction
- Not all cement will hydrate
Too Much Water
Too much or too little water = screed problems
I hope that has been helpful. If you have any further “screed how much water?” questions please get in touch.