Sand and cement screed - how long to go off

[F]

I've got a small cloakroom floor consisting of concrete blocks with an up to 2" covering of sand and cement. How long do I have to wait before I can drill and plug it to install a studded partition?

TIA.

[Phil L]

You can fix to it after it's been down a week, although you should fix to the sides and top primarilly

[Andrew Gabriel]

It goes off in 2 stages. First takes 24-48 hours, when it will feel set, but doesn't have much strength. Second stage takes weeks. I would suggest that unless you are going to wait a few weeks, you drill right through into the concrete blocks. If you try to get any kind of grip with plugs in the sand and cement before then, it will likely crumble when the plug expands to grip it.

[The Natural Philosopher]

At least 24 hours, 60 preferably. depending on temperature

[F]

Room temperature...

[The Natural Philosopher]

Well 24 hours for it to be safe to walk on...BUT it may take a week or two to be full strength.

[Rick Hughes]

Screed is a surface leveller not a structural layer - don't fix to it ... fix through it to floor below.

Screed should have a week per inch of thickness .... if you want to go quicker give it a soaking with water (it sets by chemical action not drying)

You can sprinkle the surface with a concrete hardener (easy availability) give a very hard dust free surface if that is needed)

Rely on the vertical fixing of stud partition for fixing, and just count on anything to screed as a bonus - but don't rely on it for mechanical fixing.

[The Natural Philosopher]

Haha. That's like saying plasterboard isn't structural, or breeze block.

I can assure you that going through 4" of screed, 2 " of polystrene and into precast concrete beams is not an option here..

The screed is FAIRLY structural.

Its a cheap gap filler, as its mainly sand, with enough cement to render it fairly solid. How solid depends on how much cement of course.

Paint it with dilute PVA.

You can,. if its deep enough and has more than a whiff of cement.

>

[Osprey]

Screed is classed non- structural by building regs.

This will do very little other than seal it, it will not harden it.

The purpose of screed is to take the sub floor - concrete pour, beams etc. .... and top it off to provide a level firm surface for final finish, often to an exact DPM point, it has and provides no structural strength.

By all means use it as an additional fixing point to help restrain, but do not rely on it.

I have 230m2 of 75mm thick fibre reinforced screed on my ground floor, all treated with surface hardener - and not a single thing has been fixed to it other than tiles - all Wood floor is laid floating I would not put a nail or screw into the screed.

[The Natural Philosopher]

That is not the pint. The point is that screed has strength..and takes weight well.

It hardens the surface considerably. It even connects cracked slabs together..I've done it. PVA on screed will produce an almost completely dust free surface.

Firm=structural in ordinaryspeek.

Well I have the same, but I have mounted toilets and bits of studwork on it. Its OK if you accept that - like plasterboard - its got very low tensile strength, abut isn't bad in compression and shear.

[Osprey]

Well - we agree on this partly ... Screed is a levelling finish, and is good in compression ... however it is not good for any edge, shear, tensile etc. Don't believe me, pull back a carpet and look at screed around stairs for example - it will more than likely have large cracks in it.

As for PVA giving it hardness & increased strength ... hmmm ...if that was the case don't you think that this would be standard in the building trade ? rather than purpse designed hardeners .. and it is not just a selling ploy, they are a totally different formulation. PVA give a sealed finish ... not a hardened one.

Screed is certainly not good for holding screws ... hole edge easily crumbles, very low pull out strength. If I needed to fix a sole plate of a studded wall and couldn't screw through to concrete below - then I would glue the wood along it's length to the screed .. and then just put a few screws into screed act as location & reinforcing fixing pins.

I spent a long time working on sites - one of the easily damaged items was floor screed, nice flat finish easily ruined for example by a carpenter dragging a saw horse over it.

Anyway - advice given, ... the original poster can take their choice over whether to consider screed as a suitable medium for a secure mechanical fixing or not.

[Stuart Noble]

Might be helpful to establish what exactly you mean by "screed". The latex stuff?