Floor Screed Thickness Over Insulation?

I’m Andy Parkin. Managing Director of the Multi Award-Winning Speed Screed.

Floor Screed Thickness Over Insulation

What does the thickness of screed need to be when you are putting it on top of insulation?  When we talk about insulation that can be either acoustic or thermal insulation.

Acoustic Insulation

If you are looking to sound proof an area, such as a multi occupancy building where there is a building regulation requirement. Or it might just be that you are wanting to make sure that you retain as much of the noise in the room as possible.

Thermal Insulation

With thermal insulation you are trying to keep as much of the heat in this time as opposed to generally keeping the noise in the room.

When we talk about floating if will generally mean one of the two options above.

If the insulation is foil backed a slip membrane over the top would be a must (even without foil it would be best practice to allow for a slip membrane).

Insulation Strength

When we talk about how thin a screed will go you have to look at the different construction types, and floating needs to have thicker screeds.  There is a certain amount of give in the insulation, and it has a particular strength rating.  Strength is measure as a KPA value (kilopascal), and the minimum requirement for domestic is 70 KPA, and 100 KPA for commercial.  The higher the KPA the stronger the insulation.

Depending what the loadings are within the building, and the floor has to withstand those loadings, then you may need a higher KPA. For example, a car showroom with large 4×4’s  the point loading is going to be quite significant. You may want to increase the actual KPA value of the insulation to withstand the loadings.

If we can now look at the floor screed thickness over insulation for different types of screed.

Flowing Screed

Calcium sulphate flowing screed (some people call it liquid screed, or flow screed).

  •  Domestic 35mm minimum
  • Commercial 40mm maximum
  • Maximum thickness would be 80mm, anything thicker and there is a high probability with more bleed water you will end up with a weak and friable surface that will need grinding down.

Modified Sand and Cement

A modified sand and cement screed has admixtures to make the screed perform differently. Rapid strength is often a feature of admixtures.  If you are wanting to traffic and load the screed quickly, rapid strength would be something that would allow you to do this.  Saving time and money by completing the program earlier, by not waiting for a traditional screed to gain strength.

  • Domestic/Commercial 35mm
  • No real upper limits on there providing that the screed is well compact. You may look at the other options at putting a void fill to replace some of the screed if it starts to get too thick.

Fast Drying Screed

Keracem Eco is a fast drying sand and cement screed, with hydraulic binders.

  • Domestic/Commercial 40mm
  • No real upper limits on there providing that the screed is well compact. You may look at the other options at putting a void fill to replace some of the screed if it starts to get too thick.

Traditional Sand And Cement Screed

Last but not least is traditional sand and cement screed. This is your 1:3 or 1:4 cement to sand ratios.

  • Domestic minimum is 65 mm and 75mm commercially. There are no upper limits for this product per say.

That gives you a broad idea of the floor screed thickness over insulation, both minimum, and maximum depths.

If you need any further information just please let us know.

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