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How thin can I lay concrete on a floor. Help please, urgent!

Postby goose » Thu Oct 23, 2008 7:16 pm

I'm doing work on my house and the top coating on the floor (floor has a concrete slab then a top 'smooth' layer about 12mm to 15mm thick ontop of it) it's this smooth layer which is cracking and loose.

The self leveling compounds I've seen only state 10mm as a maximum and these bags are very expensive.

Can I lay a concrete (or cement) layer with a waterproofer mix to a thickness of about 10-12mm ontop of the slab and then lay a layer of self-leveling ontop of this to level with the rest of the rooms/undamaged floor.
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Postby Tony Coward » Wed Dec 10, 2008 10:38 am

I have a very similar problem with an old concrete floor but the height variation is bigger up to 40mm starting from 0 at the walls - it dips towards the middle. I am using this forum for the first time so i do not know my way around it. There seemed to be no replies to your problem and I am wondering if you managed to solve it. I was thinking of doing exactly the same thing as you using sand to to provide a level base and pouring a thin self leveling compound on top. I shall be floating a laminate floor on top.
Another possibility I have read of is an old-fashioned technique for laying tiles using a base of sand "fixed" by a lime and water mixture - but I am hesitant to try it - but if it works for tiles should it not work for a laminate floor?
Hope to hear from you

Tony Coward

Can I lay a concrete (or cement) layer with a waterproofer mix to a thickness of about 10-12mm ontop of the slab and then lay a layer of self-leveling ontop of this to level with the rest of the rooms/undamaged floor.[/quote][quote][/quote]
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Postby GaryS » Wed Dec 31, 2008 12:35 am


you will first have to find out what is causing top layer to crack at the moment subsidence ect and also remove loose areas before proceeding.

for both questions yes you can float on new layer of sharp sand cement mix and then finish once this is dry with self level compound to smooth.

please note that cement depending on thickness can take weeks to dry and you must then use some form of vapour barrier between your nice new flat floor and laminate.
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Postby stoneyboy » Wed Dec 31, 2008 10:01 am

As you have found a thin layer of screed on concrete breaks up like toffee. If you can, remove the whole surface layer then use a latex self levelling compound to resurface the floor - make sure the surface is wet before you apply the compound.
If there are areas where the original screed is still OK, dig out the defective areas, wet the areas for repair and lay a sharp sand / OPC mix 4:1 don't bother with waterproofer, use a fine sharp sand (may be called rendering sand), and ordinary portland cement (not mastercrete which has additives for bricklaying). Once this has set wet the floor and apply the self levelling compound.
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