Anhydrite Screed – Is it right for you?
I’m Andy Parkin, Managing Director of the Multi-Award Winning Speed Screed. Anhydrite Screed, exactly what is it?
We are used to cement being a part of screed mixes, however in this case, it is an anhydrite binder, and so there is no cement whatsoever.
Where does anhydrite screed binder come from?
In the UK, it is mainly from the chemical industry. From the production of acid, it is a waste product that would normally go to the landfill, but in this case, it is milled, and it is actually used in the screed.
Does that mean that there’s any detriment to the product? Does it mean that it’s weaker? It is not as durable?
No, none of those things. It is equally as strong. It works to its designed strength, and so whether your project is a 50-year life or 100-year life, it will be suitable to meet those requirements.
What are the benefits of using an anhydrite screed?
It is a recycled product, it has eco-credibility, and has a far less carbon footprint than a traditional cement-based product.
Any product with water will shrink. however, with an anhydrite screed, the shrinkage is by far less than we would normally see in a cement-based product. This means we can lay in a larger base because there is less risk of shrinkage cracking.
The bay size with traditional sand cement should be no more than 40 m2 when you’re working with an aspect ratio of 2:1. With the anhydrite screed, for a screed with underfloor heating in it, you are looking at 300 m2. And without underfloor heating, 1,000 m2.
You can see the difference. Bear in mind the aspect ratios, and if there are any restraints within the screed, as they will reduce the bay size.
How quickly can you traffic the anhydrite screed? Typically it is 24 hours, but you have really got to monitor the conditions. If the area where the screed is being laid is suffering from poor conditions, it could be 48 hours. On rare occasions, it can be a little bit longer than that. However, typically, 24 hours is normally the time when you will be able to light foot traffic the screed.
One of the things that you notice in sand cement, from time to time, if it’s laid on a membrane or onto insulation, is that it will sometimes curl. You get just a little bit of curling at the ends. I liken it to putting a slice of bread on the side, in the kitchen, and then coming back to it after a couple of days, and it’s all curled at the edges. Literally, that’s what it is doing. The screed is drying quicker on one side, and it is curling up at the edges.
Anhydrite screed does not curl.
Do you need to have reinforcement with an anhydrite screed? Generally, when we put reinforcement into a screed, it is not to make it stronger per say, but it is to reduce the potential for shrinkage cracking. So because the shrinkage is very minimal in this particular product, we do not need fibres added.
How Far Can It Be Pumped?
It can be pumped 200 metres. The screed is delivered in a truck mixer, and it is then discharged directly into the hopper of the screed pump. The pump is a worm-fed system, and a screw turns and pushes the screed through the pipe. The screed can be actually delivered 200 metres away from the point where the truck mixers come in. That gives you great flexibility. There is even an opportunity to piggyback with pumps if a greater length is required.
How quickly does it actually pump through? Typically a machine can discharge something like 20 cubic metres of screed per hour. Just to put that into some kind of context, 6 m3 at 50 mm depth will actually cover an area of 120 m2. You can see that you could actually lay something like 360 m2 of screed within an hour.
The productivity is tremendous. It of course all depends on good preparation, everything being lasered and ready, and then you are just able to work straight through. There is a finishing process with the screed, everything needs to be controlled and done correctly. With this great productivity, you could end up laying anything up to 1,500 m2, and possibly even more, if the conditions on site are right.
One of the big benefits when laying underfloor heating with this system is that it is almost twice the thermal conductivity of traditional sand and cement. Over a period of time, just think of the cost savings of that screed that will heat and cool quicker.
The product in itself is very controllable, very clean from the perspective of the site. You are not having materials delivered to site, having to store them, being left with big piles of materials. The pipes would have to be cleaned and would need an area for waste, where the pipes can be flushed out.
The material goes into the hopper, it is pumped through to the area where the screed is being laid, nice and simple.
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