Why screed cracks? New screeds commonly develop cracks because the excess water evaporates from the surface faster than it is replaced by the water still trapped in the concrete slab, alternatively, at pressure points like entrances and corners. This may be brought on by either adding too little or too much water during the mixing process or by poor mixing.
Water evaporates quickly with underfloor heating, which raises the possibility of cracking. Before looking at why screed cracks? Should note that cracking is typical and generally does not indicate that the screed’s integrity is compromised.
Why screed cracks? And what can you do?
Screed shrinks, and there may be a possibility of cracking due to shrinking, controlling the location of the cracking during shrinking. Is it okay to crack there? Anything that contains water will contract as it dries, and if the screed doesn’t have controls, it will naturally crack to alleviate the pressure.
The screed will only be as good as the substrate that it is laid on. If the substrate is not sound, dry, contaminated, or stable, if the insulation is rocking, or if you have gaps, there will be issues with the screed. Preparation is always essential when working with screed. Water content is important. Too much water means you will get excessive shrinkage and cracking. And if there’s too little water, all the cement particles won’t hydrate, and you’ll end up with a weaker screed.
Is the sand the proper grade and quality? Does it adhere to British regulations? Is it beginning to fail as a result of the bad grade? Even though it may have a lovely smooth surface finish, it won’t be as strong if there is no sand at the top of the grade. So perhaps the sand is the incorrect grade. For sand and cement, compaction is a significant element. Therefore, it must be compressed in layers.
Has the screed been trafficked too early? Is it why screed cracks?
Why screed cracks: Stress Relief Joints
Has there been any stress relief joints? As mentioned, this might be the most significant factor in your question: why does screed crack? 90% of the problem, in my opinion, will be caused by shrinkage cracking. I doubt you’d ever promise to eliminate shrinkage cracking completely, but if you wanted to manage it, you might consider cutting the material into little bays. We should also add Polypropylene fibres because both items will reduce shrinkage cracking. It ensures the stress relief joints are positioned correctly to consider the bay’s size, the space’s form, and any floor limitations.
But that’s an overview of Why screed cracks. As I mentioned, between 80 and 90 % of all cracks are most likely the result of shrinkage cracking, which doesn’t necessarily compromise the screed’s integrity and is a problem that frequently affects screeds and concretes. There is no guarantee that it will not crack, even though you try to reduce the shrinkage cracking with joints and fibres. I hope that was useful.