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sand layer under surface beds? recommended?

sand layer under surface beds? recommended?

sand layer under surface beds? recommended?

(OP)
Hallo Engineers

I just wanted to find out if it necessary to provide a sand layer under the concrete surface bed.
Very often you see this detail in books. I guess it is there to level the natural ground

Section would be then (from top to bottom):

1.    tiles
2.    surface bed 100 mm
3.    plastic sheet
4.    sand layer 40 mm
5.    natural ground


BauTomTom

 

RE: sand layer under surface beds? recommended?

BTT...it is there for several reasons.  First it compacts well. Next, if sufficiently coarse, it provides a capillary barrier to bulk water rising to the slab, while conversely, it provides adequate drainage beneath the slab.  It also provides a less restrictive friction surface when used with plastic as compared to a gravel layer (less restraint for the slab, thus reduced cracking potential)

RE: sand layer under surface beds? recommended?

(OP)
--to Ron--

thanks for the comment

compact well: this makes also sense, right

capillary barrier: by normal sand? gravel I would understand but by sand?

less restrictive friction surface: this didn't come in my mind but you right.

so in the end you would definately say it should be provided, right? and how thick should the layer be?

BauTomTom

RE: sand layer under surface beds? recommended?

For the sand to work as a capillary barrier, the fineness modulus should be more than about 2.75.

The sand layer should be 6 to 8 inches thick.

RE: sand layer under surface beds? recommended?

(OP)
200mm sandlayer ??? this is to much for my case. This would mean further excavations and costs

higher then 2.75mm sand this makes sensse

BauTomTom
 

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