Hello everyone,
I have little experience with screed myself, so a quick question for the experts.
I had screed installed in a 36sqm (387 sqft) extension. Concrete screed was used, and the surface is not completely smooth. Apparently, an additional smoothing layer is needed, which I would have to pay for separately.
In my opinion, when I order screed, it should be suitable to apply a floor covering of my choice directly on top without requiring any further work.
Who is right in this case?
Thank you
I have little experience with screed myself, so a quick question for the experts.
I had screed installed in a 36sqm (387 sqft) extension. Concrete screed was used, and the surface is not completely smooth. Apparently, an additional smoothing layer is needed, which I would have to pay for separately.
In my opinion, when I order screed, it should be suitable to apply a floor covering of my choice directly on top without requiring any further work.
Who is right in this case?
Thank you
Tolentino schrieb:
Too little water or too little cement, or too much sand (depending on how you look at it). Or cement that is too old. Questions for the expert:
1. What does a screed look like when too little mixing water was added?
Correct, it is not workable. This answer can therefore be ruled out as valid.
2. What does a cement screed look like when too little cement was added?
Correct, it produces strong surface dust. Since this was not mentioned 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 (0.05/0.2 inches) is used. This aspect of the answer can therefore be dismissed as incorrect.
4. What does an "overaged screed" look like?
Correct, there are no technical indications as to when a cement screed is considered "too old," nor whether it then breaks at the edges. Since the screed was newly installed, the aspect of "overaged screed" can be set aside.
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The question now is: what in Tolentino’s statement is useful for the questioner and interested forum members?
Nothing. Also correct!
If answers are to provide valid technical guidance on requested topics (and not be speculative), at least the basic technical knowledge (here: screed technology) should be known.
My opinion!
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Best regards to all: KlaRa
I am not an expert and never claimed to be. Experts are probably in the minority here in the forum anyway.
Therefore, we are very grateful for members like you @KlaRa.
1. "Too little" does not have a resolution of two levels. It is quite conceivable to me that while processing was still just possible, uniform curing was no longer achievable and in some areas insufficient—specifically along the edges.
2. Since omitting relevant information is almost a tradition in this forum (and other amateur forums dealing with construction and craftsmanship), I would not rule out any possibilities. It is inherent in the nature of the matter that a layperson does not know what information is relevant and what is not.
3. Since sand is geologically defined by grain sizes up to 2 millimeters (0.08 inches), there seem to be overlapping areas here. Also, various articles from reputable sources—which I am not allowed to cite here—mention sand or gravel in relation to cement screed. What I mean is the properly used aggregate. What would be the consequence of using insufficiently washed gravel with a grain size of 1.2–5 millimeters (0.05–0.2 inches)?
4. I mentioned old cement, meaning aged cement that has absorbed too much moisture and formed lumps. In my opinion, the result would be uneven distribution of cement in the mix, thus insufficient bonding, which could lead to screed cracking.
(My numbering 🙂
5. These were a few suggestions, on which the questioner and other participants could respond further, or which could be considered in a second attempt.
6. What reasons could you still see under the given information? So far, you have only recommended repairing the existing screed and pointed out incorrect terminology. You did not address the risk that the entire screed could be defective or have implicitly ruled it out. That was the subject of my suggested questions.
Therefore, we are very grateful for members like you @KlaRa.
1. "Too little" does not have a resolution of two levels. It is quite conceivable to me that while processing was still just possible, uniform curing was no longer achievable and in some areas insufficient—specifically along the edges.
2. Since omitting relevant information is almost a tradition in this forum (and other amateur forums dealing with construction and craftsmanship), I would not rule out any possibilities. It is inherent in the nature of the matter that a layperson does not know what information is relevant and what is not.
3. Since sand is geologically defined by grain sizes up to 2 millimeters (0.08 inches), there seem to be overlapping areas here. Also, various articles from reputable sources—which I am not allowed to cite here—mention sand or gravel in relation to cement screed. What I mean is the properly used aggregate. What would be the consequence of using insufficiently washed gravel with a grain size of 1.2–5 millimeters (0.05–0.2 inches)?
4. I mentioned old cement, meaning aged cement that has absorbed too much moisture and formed lumps. In my opinion, the result would be uneven distribution of cement in the mix, thus insufficient bonding, which could lead to screed cracking.
(My numbering 🙂
5. These were a few suggestions, on which the questioner and other participants could respond further, or which could be considered in a second attempt.
6. What reasons could you still see under the given information? So far, you have only recommended repairing the existing screed and pointed out incorrect terminology. You did not address the risk that the entire screed could be defective or have implicitly ruled it out. That was the subject of my suggested questions.
@ "Tolentino"
* If too little water is added to a cement mortar, this affects only and exclusively its workability!
Let’s consider a water-to-cement ratio of 0.45 (this would be a waterproof concrete). At this ratio, the mortar is almost impossible to smooth or work with manually.
However, this does not affect the cement mortar itself or its hardening. It simply needs to release less water into the surrounding air (dry), but the chemistry remains unchanged due to the relatively small amount of water required.
* Unwashed sand and/or too fine aggregate is associated with a higher water demand. This results in greater pore distribution and volume, which leads to lower final strength of the structure and a high risk of cracking.
* A mortar that has already absorbed too much water can only mean one thing: the mortar had already started to set and was in an advanced stage of curing. Such a mortar cannot be spread or compacted manually. Even machine application is limited because hardened mortar lumps will repeatedly tear the surface when smoothing mechanically. A corner area of a hardened screed can break off under higher stress.
I personally know construction sites where corners were chipped out. This is not a defect but a material-specific property of cement-bound building systems. When the architect jumped on these corners, they broke. This “jump test” was totally inappropriate as an argument.
My comment that this was intentional damage was accepted, and the architect had to cover the follow-up costs for these jump tests.
Remote diagnoses of the causes of structural failures are nothing more than guesswork. A factual onsite inspection of the fracture area and the screed structure is required, possibly including a confirmation test according to DIN 18560 part 2.
This would be necessary if other aspects appeared over the surface that indicated a lack of load-bearing capacity.
However, corner areas must be considered special cases, as the bending tensile forces under loading here are significantly higher than on flat surfaces, where the applied point load is supported by the adjacent screed mortar.
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Hoping to have brought some clarity to the situation: KlaRa
* If too little water is added to a cement mortar, this affects only and exclusively its workability!
Let’s consider a water-to-cement ratio of 0.45 (this would be a waterproof concrete). At this ratio, the mortar is almost impossible to smooth or work with manually.
However, this does not affect the cement mortar itself or its hardening. It simply needs to release less water into the surrounding air (dry), but the chemistry remains unchanged due to the relatively small amount of water required.
* Unwashed sand and/or too fine aggregate is associated with a higher water demand. This results in greater pore distribution and volume, which leads to lower final strength of the structure and a high risk of cracking.
* A mortar that has already absorbed too much water can only mean one thing: the mortar had already started to set and was in an advanced stage of curing. Such a mortar cannot be spread or compacted manually. Even machine application is limited because hardened mortar lumps will repeatedly tear the surface when smoothing mechanically. A corner area of a hardened screed can break off under higher stress.
I personally know construction sites where corners were chipped out. This is not a defect but a material-specific property of cement-bound building systems. When the architect jumped on these corners, they broke. This “jump test” was totally inappropriate as an argument.
My comment that this was intentional damage was accepted, and the architect had to cover the follow-up costs for these jump tests.
Remote diagnoses of the causes of structural failures are nothing more than guesswork. A factual onsite inspection of the fracture area and the screed structure is required, possibly including a confirmation test according to DIN 18560 part 2.
This would be necessary if other aspects appeared over the surface that indicated a lack of load-bearing capacity.
However, corner areas must be considered special cases, as the bending tensile forces under loading here are significantly higher than on flat surfaces, where the applied point load is supported by the adjacent screed mortar.
----------------------------------
Hoping to have brought some clarity to the situation: KlaRa
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