Re: How soon can I tile a new concrete floor?

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On 17 Aug 2003 04:05:15 -0700, snipped-for-privacy@alcatel.co.uk (Jon Weaver) wrote:

I had a very similar scenario of timescales and was told to leave the screed for 3 weeks before laying tiles. This was done and it has been fine.

Yes. One thing that you may well find useful is to wash over the floor with a 1:5 solution of PVA adhesive to water. This will provide a light seal and stop the release of dust.

It isn't a drying issue, but a chemical curing one. The screed should be allowed to do that naturally.

The tiles may well lift.
You should wait......
.andy
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Is there any insulation in this floor? There should be large chunks of Jablite or similar going down, as well as the plastic sheet (DPM). Although not compulsory in many conservatories, it should still be done for your own comfort.

Concrete doesn't "dry". It sets. It actually needs water to set properly. Removing the water by overdrying will actually slow down the setting process (sometimes so much that it never completes) and damage the floor.
Basically, you should wait the recommended time scales. How does the phrase go? Bodge in haste, repent as leisure. Or something like that. ;-)
Your floor will take much longer to complete if you disturb it too soon, cause gaping cracks and need the whole lot ripping up again.
Christian.
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There is going to be a DPM, but I must admit, I don't think that the builder will be putting any insulation down! How thick would a layer of Jablite be? Its not too late for me to get some myself and insist on it being put under the screed.
Where would the insulation layer go, ontop, or under the DPM?

I think that you are right.. However, I spoke to the 'tiler' who lives opposite, and he said "nahh.. I have been tiling for 20 years and I always lay straight onto the concrete.. As long as you give it a few days to set, you will be fine".. This is the same attitude as my builder who is doing the floor work for me. However, this is directly against the advice that I seem to be getting from EVERYONE, including the supplier of my tiles and manufacturer of the 'adhesive' (Dunlop) who quotes 6 weeks for concrete and 3 weeks for screed!
Its amazing what 'tradesmen' get up to, and people questioned why I wanted to keep an eye on my builder, to make sure he did things correctly!
As always, a huge thanks for your advice
Jon
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AIUI, on top of the DPM. Someone more knowledgable than me will suggest the exact ordering and thicknesses. However, I suspect 50mm of Jablite would make a real difference, and 30mm of screed might work on top to make the original thickness.
Christian.
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Christian McArdle wrote:

Actually it makes sod all difference where the DPM goes. Above or below the insulation. I asked teh architecet, and he just shrugged.
I put mine ABOVE for the imple practical reason that it wouldnt get puntured on teh rather rough surface underneath - the insulation is very good as covering sharp lumps :)
50mm blue/pink foam is excellent. 75mm is even better. At LEAST 75mm screed, and more if you can fit it in.
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My problem is that the current 'slab' height means that it will be impossible to raise the floor by any more than 100mm.. So, If I have to add 50mm of insulation and 75mm of screed, the only physically way possible would be to lower the slab by 25mm, and as you will imagine, this impossible.
A colleague of mine (who is building his own house) has suggested that I go for 50mm of insulation and 50mm of screed, but use a steel mesh to re-enforce the screed.
My other option of course is to forget ever having asked the question, and go along with the plan WITHOUT insulation.
If I can get away with 50mm of each and a steel mesh, I might be tempted to get the bits that I need and ask the builder to do this when he lays the screed at the weekend.
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Well, 25mm of insulation would be infinitely better than none. That would allow 75mm of screed.
Christian.
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Jon Weaver wrote:

Make sure you are gettng polystrne foam - blue or pink generally - not Cleotex. That price sounds about right for a 5 pack of 4x2 shhets.
Just slap it down, and you may, if its a huge area, want to lay some up the sides of the screed as well to allow for expansion, but it shouldn't be necessary on normal installations.

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What I was quoted for was 40mm 'Polyurathane'. They quoted me 16+vat for a 1.2 x 2.4 Mtr sheet, which seemed excessive.
However, I am starting to think that this might be a bad idea.. One thing which has bothered me from the start of this discussion is strength.. A 50mm sand/cement screed ontop a soft (foam) base, doesn't sound like it will have much local strength. I am worried that a few months down the road, the screed could end up cracking, and it will all be ruined.. Even if I added some re-enforcement in the screed, its fact is that its on a soft, flexible foam base which worries me.
I guess that I should have got the insulation put it weeks ago, when the slab was being laid, but its too late to worry about that now.
I am not sure how much difference the lack of insulation will make, but for peace of mind, I am thinking that it might be better to have a cold but solid floor then a slightly warmer, but weaker one!
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Jon Weaver wrote:

Sounds like they are trying to sell you polyisocyanurate - Celotex.
The best value for money for screeds is blue or pink polystyrene. Its hugely more dnes than teh whites tuff and is rally very strong - won't compress as long as you wire the screed.

It may well crack a little as it shrinks anyway. I poured gallons of thinned PVA down my cracks and they all shrank and glueed themsleves back togeher. It wasnpt the fom so much as inconsistent mixes in teh screed and doing it a little at a time.

Put in teh insulation. Its gione with 75mm screed, Hobenets.
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would
Not correct ..... you want floor grade polyuretane not polystyrene ... it has about twice the insulant value of polystyrene.
Jon has limited depth - and therfore to get max insulation with minium depth he should most defionietly go for Poyurethane.
I buy mine from Seconds & Co. http://www.secondsandco.co.uk /
Recently bought 140 m2 of 50mm polyurethane ... and 124m2 of foil faced 100mm polyurethane. Most of what they supplied was Kingspan product.

Vertical insulation is important if heating the floor - but if no floor heating agree you can leave it out - and on your size slab it is not really needed for expansion.
Rick
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Jon Weaver wrote:

Mmm. Actually for reason I'll explain, I'd use chicken wire.
The problem with thin scred over insulation, is that heavy pinted object - chair leg etc - over a small area could compress the insulation and crack teh screed. So you want a lot of local reniforcement rather than overall reinforcement. Chicken wire or the sort of mesh that used to render over on walls etc would I think be better able to do this.
Try and use the insulation if you can. If you slate or laminate the floor afterwards that will also help load spereading.

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Good point.. I suppose I could, however, I have already installed the metal capping.. It would mean ripping it all up and messinging about with it, whilst the builder is trying to work.
Thinking about it, I don't think that it would do any harm, to leave the cable un-covered.. The area in question would only be 100x400mm and I don't really think that this would affect the efficiency of the insulation.
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According to table 3A in the On Site Guide, PVC cable is "unsuitable for embedding directly in concrete".
However, I will re-state my previous advice. In the situation described above, 2.5mm cable *is* suitable for carrying the current of a 32A ring main. It may be "covered" with insulation, but it is "in contact with a [thermally] conductive surface on one side" (method 15) and is therefore capable of carrying up to 21A (table 6F, OSG). There *may* be a grouping issue, but I don't think so over this short distance with FTE.
Hwyl!
M.
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snipped-for-privacy@alcatel.co.uk (Jon Weaver) wrote:

Didn't realise you'd already decided not to lay it under the insulation :-)
I'd say that what you describe sounds fair enough. Let us know in ten years if it fails ;-)
Hwyl!
M.
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Don't fight technology, live with it: http://www.livtech.co.uk /
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so I guess, during the pour, some amount of

The screed will be laid semi-dry ... not a poured liquid, so leave it as you have it.
Rick
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It would, it would make a real difference.

Not enough, it will crack, You need much more than that over Jablite - I think 75mm minimum.
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Although
own
phrase
Jon, first off you don't want it to dry straight away. Screed sets by chemical reaction not by drying out ... screed can be walked on after 24Hrs .... give it a soaking with a fine spray (or watering can) and cover with plastic sheet. Re-soak if it looks likes it's drying out .... keep doing this for first 3 days.
After which no more water .... then let it 'dry out' , it will take around a week per 1" of thickness.
Your better half advises you are tiling on floor - then 3 weeks can be shortened, to 2 weeks ... slight moisture will not be a problem, but would be a big no-no if laying wooden flooring.
If it were me - I would still leave it 3 weeks.
Rick
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Cheers Rick.. I think I will be leaving it for a few weeks, but probably won't have the patience for 3 weeks (or the capacity for a daily ear bending from Helen :) )
I am glad that I can walk on it after 24 hours, as I have loads of things I need to do (specifically the electrics) and want to get started on SOMETHING. This whole project has takens 3 times longer than I planned, mainly due to the planning permission that I found I needed at the start. I am now just anxious to get busy on the things that I can do. The builders have taken weeks to do things that should have taken days. They were ment to be coming on Saturday to 'finish off', but now its been postponed (again) to Monday.. But the end is in sight and hopefully, this time next week, I will be able to get going...
Thanks for the advice from everyone.. All the best
Jon
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Hence there are circumstances where it is advisable to "water" new concrete. e.g. using a sprinkler on a concrete drive in hot weather. (after it has initially set hard enough not to wash away of course.)
One early form of cement was known as "hydrolic lime" because it would set underwater.
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