Screed ordered but rework required

Too little water or too little cement or too much sand (depending on how you look at it). Or cement too old.

Questions to the expert: 1. What does a screed look like when too little mixing water is added? Correct, it is not workable. This answer can thus be excluded as accurate. 2. What does a cement screed look like when too little cement is added? Correct, it dusts heavily from the surface. Since this was not indicated by the questioner, this aspect can also be excluded as an answer. 3. What does a cement screed look like when sand is added? Answer: Sand is never added to a cement screed. Only washed gravel with a grain size of 1.2/5mm is added. This aspect of the answer can therefore also be deleted as incorrect. 4. What does an "overly old screed" look like? Correct, there are no professional indications of when a cement screed is "too old" nor whether it then breaks off at the edges. Since the screed was newly installed, the aspect "screed too old" can be put aside anyway. --------------- The question now is: what is usable for the questioner and interested forum participants in the statement by "Tolentino"? Nothing. Also correct! So if answers to requested topics are to be given as accurate hints (thus clearly not speculative), at least the professional basics (here: screed technology) should be known. My opinion! ------------ Greetings to the group: KlaRa

I am not an expert, nor have I claimed to be. They are probably in the minority here in the forum anyway. In this respect, we are very grateful for members like you .

1. Too little does not mean a reduction of 2 levels. It is quite conceivable to me that processing is just still possible, but an even setting is no longer possible and has not taken place sufficiently in parts, here specifically in edge areas.

2. Since omitting relevant information in this forum (and other lay forums dealing with construction and craftsmanship) is almost traditional, I would not rule out any possibility. It is in the nature of things that a layperson does not know what relevant and irrelevant information is.

3. Since sand is geologically considered to have grain sizes up to 2mm, there seem to be overlapping areas here and also various articles from reputable sources, which I am not allowed to cite here, write about sand or gravel in relation to cement screed. I meant the properly to be used aggregate grain size. What would be the consequence of using too little washed gravel with a grain size of 1.2-5mm?

4. I wrote about too old cement, meaning aged cement that has already absorbed too much moisture and formed lumps. The consequence, in my opinion, would be an insufficient distribution of cement in the mix, thus too little binding, which could lead to the screed breaking.

(My numbering:)
5. These were a few suggestions, to which the questioner as well as other participants could respond again, or which could be paid attention to on the second attempt.

6. What reasons could still apply in your opinion under the above-mentioned information? So far, you have only recommended a repair of the existing screed and pointed out incorrect terminology. You have not addressed the risk that the entire screed could be defective, or have implicitly already ruled it out. My suggested questions addressed this.

@ "Tolentino"
* If too little water is added to a cement mortar, this has only and exclusively an impact on workability!
Let’s assume a w/c ratio of 0.45 (which would be a WU concrete in concrete technology), then it is almost no longer possible to smooth or work with it manually.
The cement mortar itself and its hardening are not "disturbed" by this. It only has to release (dry) less water to the ambient air, but the chemistry remains unaffected due to the relatively low necessary amount of water.

* An unwashed sand and/or too fine aggregate grading is associated with a higher water demand. This results in a larger pore distribution and volume, leading to lower ultimate strength of the structure and high risk of cracking.

* A mortar that has already taken up too much water can only mean: the mortar had already set, was in an advanced stage of hardening. Such a mortar cannot be spread and compacted manually. It is also only possible to a limited extent by machine, since the hardened mortar lumps repeatedly tear open the surface during mechanical smoothing. A corner area of a hardened screed can break off due to higher stress.
I personally know construction sites where corner areas were chipped away. Not a defect, just a side note, but a material-specific characteristic for cement-bound building material systems. When the architect jumped on the corners, they broke off. As an argument, this "jump test" was completely unsuitable.
My remark that this was arbitrary vandalism was well received; the architect had to bear the consequential costs of his jumping experiments.
Remote diagnoses regarding the causes for structural fractures are no more than coffee grounds reading. A factual visual inspection of the fracture zone and the screed structure is required, possibly even a confirmation test according to DIN 18560 Part 2.
This would be the case if further aspects were found across the surface indicating a deficiency in load-bearing capacity.
But corner areas are special cases in the evaluation, since here the bending tensile forces under load have to be set significantly higher than on the surface, where the occurring point load is carried (supported) by the adjacent screed mortar.
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In the hope of having brought a little clarity to the situation: KlaRa