Cementless screed Bioterra

What is cementless screed?

Wouter Vermin: "As the name suggests, this screed (covering floor) contains no cement.

The sand, which is 100% recycled material, is bonded with a lime-based 'new binder'. Apart from lime, this binder contains hydrating residues and a natural starter.

The recipe was developed by Greenager +; Bioterra NV is the producer of the high-quality recycled granulate 0-4 mm."

What makes the screed circular and why did you choose to use it in 't Centrum?

Wouter Vermin: "The sand is 100% circular, recovered from construction and demolition waste, street sweepings and sand from sewers. So at least this sand has already had its first life. This is in contrast to traditional screeds, which today consist of 100% virgin materials, materials that have never been used or processed before. Primary raw materials are coming under more pressure every day and this unique screed is therefore a perfect alternative based on 100% recycled materials.

- The binder is partly composed of residual streams, supplemented with natural lime.

The big difference between lime and cement is that lime, at the end of its useful life, can be reused again and several times.

Additional lime has to be added if it is ground up or will be used again to have a full, high-quality product again. So 100 per cent circular is not yet but work continues on that."

How is this screed applied? Which substrate is suitable for it?

Wouter Vermin: "This screed is applied in exactly the same way as a traditional sand/cement screed.

Because the specific gravity of lime and hydrating fines is lower than that of cement, more paste can be made with the same amount of binder. The end product is therefore slightly greasier, making the surface more closed and more wear-resistant.

For this reason, we recommend light polishing of this screed, further improving its quality. The latter also has the advantage that the installer of the floor has to use less force when finishing it; thus, working comfort can also be improved.

In terms of substrate, there is no difference compared to traditional screed. However, it should be taken into account that the drying time is slower. The latter can also be considered an advantage because it also reduces the risk of cracking."

Did the preparation (composition) and installation in 't Centrum go as smoothly as it would have with a traditional cement-bonded screed? What are the areas of concern?

Wouter Vermin: "It can be assumed that there is no difference for processors. However, unknown is unloved. The first time it takes a while to find the right amount of water and additive. The latter is also the case when a processor switches to different sand or cement. In the face of new sand, this sand is specially constructed from several types of recycled sand in order to achieve a suitable and constant grain distribution.

However, there are some points of interest:

- For the processor: this binder (lime) has a greater water requirement.

- For the recycler: make sure no coarse materials (e.g. stones) that are on the site get into the sand because otherwise you can get pummelled in the yard (this has already happened at 't Centrum)."

What is the end-of-life scenario of this screed?

Wouter Vermin: "Recycled materials are recycled and reused again. Unlike cement, you can also reuse lime. The second and possibly even third life of the materials used has already been studied and found to be positive."

What (circular) benefits does cementless screed offer?

Wouter Vermin: "The base consists of several types of recycled sand as filler. In addition, a binder is used that also comes from residual streams that hydrate throughout the mixture. We then supplement that further with natural lime. At the end of its lifetime, everything becomes raw material again."

Does this screed have the same technical properties and are the execution thicknesses the same as classic screeds?

Wouter Vermin: "Currently, this screed is still in the pilot and testing phase; everything is not yet known.

For now, we assume that there are only advantages:

- For instance, the risk of cracking is lower because of the slower curing.

- What is certain is that in combination with underfloor heating, this screed will heat up faster and retain heat longer. After all, this sand is up to 15% heavier and therefore contains more mass. Studies on this are due to start soon.

For the time being, we assume that the execution thicknesses are the same as those of traditional screed. What the minimum thickness is still needs to be investigated. For the sake of completeness, we also mention that for the time being we always reinforce this screed as standard. For this purpose, a natural vegetable fibre (CO²-neutral) is made from the plant Kenaf.

Currently, there is still a small price difference compared to traditional screed, but this is only temporary given the rising cement prices. You also have to factor the residual value into the economic picture here. In an end-of-life situation, i.e. when demolition takes place, this screed can be recycled for the same application. A classic cement screed that is broken up usually ends up between the bricks at a crushing plant and is used in a lower-value application."