Floor screed

[RMS]

Hi all,

I recently posted about the thickness of my new floor screed. The builders applied a depth of 35-40mm max and it cracked and started lifting.

They returned and started again the same thickness and used lots of SBR glue. The builder assured me that this would adequate. The new floor has had time to dry, there is heating in the room. i've noticed lots of hairline cracks. The floor feels soild when I knock it.

Is this normal?

Ps. I am having an oak floor glued to the floor screed tomorrow.

Any help appreciated.

 

[roughcaster]

You'll often get hairline surface cracks in a screed, concrete, plaster, or any other surface if it dries out too quick.
With regards to your floor screed,, as long as it sounds solid, and the actual surface is sound, (not sandy), there shouldn't be a problem gluing down your oak floor onto it.

 

[Chukka63]

make sure the screed is dry enough before installing your new wood floor.

 

[Blagard]

make sure the screed is dry enough before installing your new wood floor.

Chukka63
Yesterday his new floor should have gone down so I suspect you missed the boat!

RMS
The comment about being dry enough should extend to the screed having throughly dried out, not just appearing to be dry. Hopefully you will not have any problems, but be aware, I have known numerous cases of a floor finish debonding due to the adhesive being unsuitable for the conditions. Special primers may have to be used before the gluing if your works are being fast tracked.

I suggest you just check the specification for the new floor to ensure that the timing of the works was OK in relation to screed dryness. Also if the floor fitter is a separate contractor, they should not fit to an unsuitable surface. So if they know when the screed went down they are at least working in that knowledge.

 

[haveagosteve]

make sure the screed is dry enough before installing your new wood floor.

is it true if your floor screed is 35mm thick it will take 35 days to cure?
1 day per mm thick

 

[jeds]

make sure the screed is dry enough before installing your new wood floor.

is it true if your floor screed is 35mm thick it will take 35 days to cure?
1 day per mm thick

Do you mean cure or dry?

Technically any cement product will continue curing for as long as it's damp. The Hoover dam is still curing.

Screed should really be kept damp for as long as possible to allow it to gain maximum strength and also to prevent cracking.

You have to be careful of rules of thumb like the 1mm per day thing. If you are judging it for the fixing of floor finishes then it isn't accurate enough. You need to measure the moisture content properly and to the right standard. If not then what's the rule of thumb for - what does it tell you? Nothing. So I would file it and forget it if I were you.

 

[Blagard]

is it true if your floor screed is 35mm thick it will take 35 days to cure?
1 day per mm thick

A rule of thumb is to allow 1 day per mm thickness for a screed to dry out. This is a very safe allowance.

Curing time (not drying time) is often referred to in concrete mixes to ensure it reaches a particular strengh in a particular timescale for follow on work to be carried out. For a screed a similar strengh increase over time will occur but this is not usually an issue so you should not worry about this. Dryness is the key issue for you.

The floor laying contractor must be told when a screed was laid and must satisfy themselves it is OK to put their finish onto it. It is vitally important that the adhesive used by a floor laying contractor is not compromised. In some cases a special primer may need to be applied if a floor finish is laid on a screed that may otherwise be too damp.

Edit, Jeds is right about accurate moisture measurement. your flooring contractor should have the equipment to check this, that is why you need to make sure that they are happy before they do the work.

 

[haveagosteve]

Do you mean cure or dry?

Im glad you asked that question, i didnt know there was a difference between cure and dry, the hoover dam was a good example
cheers John