Fresh concrete screed - what's the truth?!

[Grace'sDad]

I've a customer and she is desperatly trying to get me to lay some tiles in her new conservatory as soon as possible....

The concrete screed has been put down 3 days ago - normal concrete mix 75mm over polypipe underfloor heating. Approx 30sqm.

I have heard two extremes of opinion today - One friend who has been a builder for 15 years claims that once dried enough to walk on, the heating can be switched on and the floor can be quickly dried. He reckons that any cracks appearing will not impact the life of the floor or the tiling (using Ditra).

The other opinion, from the builder who put the screed in was allow at least a month of natural drying and ideally 2 months.

Does anyone know the truth about this, and why??? Who says so???

Thanks!

 

[wetdec]

If you can walk on it then after 24hrs you can use Bal Green Screed on it HERE

and fix Durabase CI matting before tiling over using a flexible adhesive

HERE

The green screed adhesive will give you the fix and the Durabase CI will protect your work by absorbing any latteral movement due to expansion/contraction.


As for heating 2 degrees per day until optimum is reached then reverse, to prevent cracks is the norm I believe....


The absolute truth screeds should dry 1 day per mm of screed while covered with polythene untill the Techi guys got at adhesives and Durabase 😉


Tiler


mm

 

[pjtiler]

if you tile it before the adhesive manufactures recommendations you,ll loose the guarantee you have with them

3 weeks is the norm

concrete doesn't dry it cures its a chemical reaction

 

[sWe]

If you chose an adhesive classed as C2/S2 (improved cementious highly deformable), you could possibly get away with tiling it after a month of natural curing, but make sure it says so in the product specs first. Ardex has atleast one adhesive that can handle it, and I believe MAPEI has a two-component adhesive that can handle it as well. Can't remember the names at this late hour though. I know that atleast the Ardex one is DAMN expensive.

I would not crank up the heating. I'd rather wait a month and then tile it using the most deformable adhesive I could lay my hands on.
Cranking up the heat can result in cracks and other nastiness, and I'm not just talking surface cracks here.

I have little experience with decoupling membranes, but they might be worth looking into...

Most adhesives require regular concrete to be in the region of 3-6 months old before tiling should be even considered.
Why the hell didn't the builder chose ultra rapid curing concrete for that screed, such as ardex eb2? It's guaranteed to be tileable after 24h, and it's not THAT much more expensive than the regular stuff, and it's certainly ALOT cheaper than the super modified stuff you need to tile concrete less than a month old if you want to be able to leave a guarantee...

 

[Dan]

Never turn the heating on TO dry the floor. The products used (especially 'flexible' ones) require the correct amount of 'curing' time (as they appear dry but haven't actually finished their chemical processes yet) for the floor to be solid long-term.

Heating systems both wet and electric require the floor to be complete and cured / set / fully 'dry' and then you switch them on a low temperature (often a degree or two above the floors current temperature) and wait a period of time (depending on the system / setup would depend on how long that is - most electric it's simply 24 hours) and then you turn the heating up a degree or two every 24 hours or so until it's at its max. You can then use it as you want to and it's conditioned the floor. Some systems may require you to also cool the floor in a similar way the first time its reached max temperature.

On another level (perdon the pun) some products that have been used may allow the floor to be tiled early, though the heating will still need to be treated the same with few exceptions.

 

[DHTiling]

BAls recommendations to tiling onto a fresh screed/concrete are to leave it for about 5 days then tile with green screed adhesive...if you are using an un-coupling membrane for the tiles..they recommend 2 adhesives for this purpose on fresh screed...

The top recommend is green screed adhesive and the 2nd recommend is Single part flexible.....the adhesive has to be a highly flexible slow setting adhesive.......

hope this helps...and always contact which ever manufacture you use to confirm what they recommend......

 

[wetdec]

This is taken fron the Bal green screed data sheet in case there is any confusion :

CEMENT: SAND SCREEDS:
Lay screed to the required thickness in accordance with BS
8204:1999 using appropriate cement and fine aggregate sand
(BS 882:1983 Grade C or M) in the proportions 1:3 to 1:4.5 parts
by weight. Cement: sand screeds, including BAL Quickset
Cement screeds, must be at least 24 hours old prior to tiling.

tiler


..

 

[DHTiling]

Yes wetdec that is true-ish , but i just put up data for times if using uncoupling membranes and bal adhesives on fresh concrete/screed......and this is from BAL......

 

[wetdec]

Hey Dave

I am just quoting their data sheet m8, am not a bal person just going on what they have said in the circulated data sheet.

Bit of a catch 22 I think on their part.


tiler

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[DHTiling]

I know.........but concrete screeding is slightly different from sand screeding..don't you agree mate.........but green screed is great for both......and if using Ditra or durabase , then SPF will cope as well.........I agree some manufactures are a bit shy at there guarantees when tiling onto new concrete/screeds...

 

[wetdec]

Ye ye see its these bloody manufacturers they give you all the info but wont answer a question straight.

Me personally I would just use a decent flex after about 10 days and I think that just about keeps them all happy :yes:




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