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Fabiano0129 Jun 2017 20:19Hello dear builders and experts,
My name is Fabian, and I am a trained roofer.
Since I now want to take care of some things in my home that have nothing to do with my roof, I need your advice or the correct approach from experts.
It concerns my basement. The floor slab is waterproof concrete with a gravel layer underneath. On top of the slab, there is 3.5 cm (1.4 inches) of insulation and 4 cm (1.6 inches) of screed. This has been in place since I was born, so about 30 years. Construction moisture is therefore not an issue. I am now planning to tile my basement. Recently, due to a clogged drain on the terrace, some water entered a basement room through an electrical outlet. The wall in question is located directly below the terrace. This has given me something to think about. To protect the screed and insulation from such incidents in the future, I wanted to create a waterproof layer between the screed and the tile covering using Schlüter uncoupling mats. However, my question is whether this is advisable at all. Waterproof concrete is water-resistant but not vapor-tight. This means that theoretically, water vapor can penetrate through the waterproof concrete to the insulation and into the screed. If a waterproofing layer is applied on the screed, the moisture could get trapped there and potentially cause damage. This is my conclusion. Since I am now completely unsure what to do, I turn to you and hope for helpful advice.
So, should I waterproof and protect the screed, etc., from water coming from above, or rather not, because there is a risk of trapped moisture from below?
Regards, Fabian
My name is Fabian, and I am a trained roofer.
Since I now want to take care of some things in my home that have nothing to do with my roof, I need your advice or the correct approach from experts.
It concerns my basement. The floor slab is waterproof concrete with a gravel layer underneath. On top of the slab, there is 3.5 cm (1.4 inches) of insulation and 4 cm (1.6 inches) of screed. This has been in place since I was born, so about 30 years. Construction moisture is therefore not an issue. I am now planning to tile my basement. Recently, due to a clogged drain on the terrace, some water entered a basement room through an electrical outlet. The wall in question is located directly below the terrace. This has given me something to think about. To protect the screed and insulation from such incidents in the future, I wanted to create a waterproof layer between the screed and the tile covering using Schlüter uncoupling mats. However, my question is whether this is advisable at all. Waterproof concrete is water-resistant but not vapor-tight. This means that theoretically, water vapor can penetrate through the waterproof concrete to the insulation and into the screed. If a waterproofing layer is applied on the screed, the moisture could get trapped there and potentially cause damage. This is my conclusion. Since I am now completely unsure what to do, I turn to you and hope for helpful advice.
So, should I waterproof and protect the screed, etc., from water coming from above, or rather not, because there is a risk of trapped moisture from below?
Regards, Fabian
Hello Fabian,
30 years ago, the topic of "calcium sulfate screed" (CA) was not nearly as well known as it is today. Back then, it was more of a rarity.
The screed in the basement (and CA screeds were never used there) will almost certainly be a cement screed.
This type of screed is completely moisture-resistant. So, if smaller amounts of water did indeed seep under the screed along with the insulation, well, that would just be how it is. It does not have any negative effects.
A DITRA uncoupling mat, however, serves a completely different purpose. Installing one in the situation you described would simply make no sense—it would be a case of "using a sledgehammer to crack a nut."
The cement screed actually benefits from the water, as it helps the "old gentleman" (like your 30-year-old cement screed) to cure further. That really is the case.
So, no need to panic: if only one or two liters of water penetrated the screed from the side, that is a small amount and not a reason to worry or to invest money in the wrong place.
---------------------------
Best regards, KlaRa
30 years ago, the topic of "calcium sulfate screed" (CA) was not nearly as well known as it is today. Back then, it was more of a rarity.
The screed in the basement (and CA screeds were never used there) will almost certainly be a cement screed.
This type of screed is completely moisture-resistant. So, if smaller amounts of water did indeed seep under the screed along with the insulation, well, that would just be how it is. It does not have any negative effects.
A DITRA uncoupling mat, however, serves a completely different purpose. Installing one in the situation you described would simply make no sense—it would be a case of "using a sledgehammer to crack a nut."
The cement screed actually benefits from the water, as it helps the "old gentleman" (like your 30-year-old cement screed) to cure further. That really is the case.
So, no need to panic: if only one or two liters of water penetrated the screed from the side, that is a small amount and not a reason to worry or to invest money in the wrong place.
---------------------------
Best regards, KlaRa
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Fabiano012 Jul 2017 12:07Good morning KlaRa,
first of all, thank you very much for your response!
It is true that the screed is not affected by water. However, the insulation or its insulating effect is. Of course, not with just a few liters. My luck was that I noticed the incoming water quickly and was able to fix the problem promptly. But if this had happened during a vacation trip, I would have had a lot more water trapped between the slab and the screed. Without drying the insulation layer, it would have remained there for a longer time. That is also why I am considering Ditra. I am aware that it serves other purposes as well, but it can also be installed to be waterproof.
So you are saying I should skip that and lay the tiles directly on the screed?
That would be about half the cost. However, if a large amount of water ever gets in, a professional drying process would be necessary. I am torn back and forth.
Best regards, Fabiano01
first of all, thank you very much for your response!
It is true that the screed is not affected by water. However, the insulation or its insulating effect is. Of course, not with just a few liters. My luck was that I noticed the incoming water quickly and was able to fix the problem promptly. But if this had happened during a vacation trip, I would have had a lot more water trapped between the slab and the screed. Without drying the insulation layer, it would have remained there for a longer time. That is also why I am considering Ditra. I am aware that it serves other purposes as well, but it can also be installed to be waterproof.
So you are saying I should skip that and lay the tiles directly on the screed?
That would be about half the cost. However, if a large amount of water ever gets in, a professional drying process would be necessary. I am torn back and forth.
Best regards, Fabiano01
Hello Fabian,
You need to decide:
a) Are you building a house for normal residential use, or
b) a building where you want to account for every possible damage scenario that might occur in the future, which definitely do not apply to typical residential living? This includes landslides, earthquakes, and lightning strikes.
A household water damage event, as the name suggests, is an incident that you generally do not expect. It is therefore outside regular use and represents an exceptional situation.
If water manages to get behind or underneath the insulation layer for any reason, what is the function of the DITRA membrane in that case?
Nothing. That’s correct!
The DITRA membrane is an excellent uncoupling system for unstable screed conditions.
If you are concerned that the thermal insulation layer loses its effectiveness due to minor water intrusion, then drying the area thoroughly and intensively will be necessary.
But neither you nor anyone else can prevent the entire construction from becoming damp or undermined in a damage event – especially one covered by appropriate insurance – simply by using DITRA!
Suggestion:
Close the windows and doors in the affected room for 48 hours.
Place a hygrometer on the surface of the screed right from the start.
If the hygrometer shows a relative humidity above 70% after 48 hours, consider the further drying process carefully.
If it is below that, proceed with tiling after the appropriate subfloor preparation and leave it at that.
Rule of thumb: Problems either exist – in which case you need to respond accordingly – or you create problems artificially and make life unnecessarily harder for yourself!
Kind regards, KlaRa
You need to decide:
a) Are you building a house for normal residential use, or
b) a building where you want to account for every possible damage scenario that might occur in the future, which definitely do not apply to typical residential living? This includes landslides, earthquakes, and lightning strikes.
A household water damage event, as the name suggests, is an incident that you generally do not expect. It is therefore outside regular use and represents an exceptional situation.
If water manages to get behind or underneath the insulation layer for any reason, what is the function of the DITRA membrane in that case?
Nothing. That’s correct!
The DITRA membrane is an excellent uncoupling system for unstable screed conditions.
If you are concerned that the thermal insulation layer loses its effectiveness due to minor water intrusion, then drying the area thoroughly and intensively will be necessary.
But neither you nor anyone else can prevent the entire construction from becoming damp or undermined in a damage event – especially one covered by appropriate insurance – simply by using DITRA!
Suggestion:
Close the windows and doors in the affected room for 48 hours.
Place a hygrometer on the surface of the screed right from the start.
If the hygrometer shows a relative humidity above 70% after 48 hours, consider the further drying process carefully.
If it is below that, proceed with tiling after the appropriate subfloor preparation and leave it at that.
Rule of thumb: Problems either exist – in which case you need to respond accordingly – or you create problems artificially and make life unnecessarily harder for yourself!
Kind regards, KlaRa
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Fabiano014 Jul 2017 06:22Good morning KlaRa,
that sounds reasonable to me so far. I’m probably overthinking it. When I get back from vacation, I’ll take another look at the situation regarding moisture. Then I will probably just go ahead and finally install the tiles.
Thank you!
Best regards, Fabiano01
that sounds reasonable to me so far. I’m probably overthinking it. When I get back from vacation, I’ll take another look at the situation regarding moisture. Then I will probably just go ahead and finally install the tiles.
Thank you!
Best regards, Fabiano01
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