Lino over concrete - damp

14 Jun 2007
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United Kingdom

I am decorating a rear lobby area of an old victorian terrace house, which has a concrete floor.
It had lino down, which I lifted up last night and it was very damp and a bit mouldy underneath.
I'm not sure if the damp has risen through the concrete, or just moisture that has got trapped underneath.

If I want to lay new lino, should I seal the concrete somehow first? Even then, won't I still get condensation/ moisture trapped under the lino again.

I was thinking I might be better with tiles laid directly onto the concrete?

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many thanks

we had a builder measure damp in walls a while ago, presume its the same tool. I'm sure I can get him back to measure the floor.

How long should I leave it to dry out? just until I cant see or feel any more dampness?
Firstly air everything out and dry the floor naturally.

If the damp issue is residual and not linked to anything like a leaking pipe for example, provided you can clean the surface well, and it's not too uneven, you can use something like F-Ball's isolator sheeting (and tape to seal the joints) This allows the floor underneath to breath and also smooth's the floor layer out allowing the fitment of vinyl or linoleum style products with the minimum of floor preperation.

In our domestic flooring business we find this product very useful on installations where there is either a questionable history to the damp course (old cottages etc) or where customers require the minimum of disruption to their installation i.e. are unable to accomodate the drying time of screed.
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thanks I will take a look

It's only a fairly small rear lobby and toilet, I am not too worried about it looking 'perfect'

I believe the concrete was laid about 6-8 years ago, so I would have hope that a DPM would have been installed then. I can see a small piece of plastic rising out from the edge of the concrete where it meets the wall, so assume this could be the DPM?

If I just want to install slate tiles rather than lino, would I still need to do all this preparation first?

If the DPM was not installed correctly or was damaged when put in, only moisture testing will lead you to where the issue lies.

I would'nt suggest installing screeds and tiles etc without the floor being dry, excessive moisture will simply blow the new floor. The Isolator and Vinyl route is likely to be the quickest and less expensive option, but then depends on the overall look and finish you wish to achieve.
With this isolator it says it allows water vapour into a drywall or ventilated skirting, but I don't have these - where would the moisture go?

My wife is quite keen on tiles now I have mentioned it, do I still need to do the method above if laying tiles?
the product mentioned above can be used in a normal area, but make sure the fitter does not seal the edges. The moister will escape from the edges.

There is a down side to the isolator membrane tho. That is that it can cause you to leave dents in the flooring if you have table and chairs, other than that its a very good product.

If its a newish base etc it stands a chance the last vinyl was fitted while the subfloor was still wet, but slim chance.

Also the meter that they test walls with is different to a flooring hygrometer.

To british standards the floor should have a working DPM. However, if you installing tiles and use exterior grade adhesive, compounds and grout then you will be o.k. (this is not the correct method tho)
still don't really understand, surely the linoleum would go up to skirting board and trap any moisture underneath?
its only a v small area so could tile cheaply I think, might be easier if I could get away with no additional dpm then..
Hi agh100

Your old vinyl would have restricted the evaporation of moisture from your sub-floor and made things look worse than they realy are.

There is oviously moisture coming from your concrete but that plastic you have seen is the DPM underneath the slab.
it's probably safe to install ceramic tiles without a DPM.. Liquid DPM's are relatively new and recommended theses days but we got away with laying tiles directly onto concrete in 60's 70's 80's etc without these and without any problems. A small risk of them blowing if moisture is excessive though.

You can pay to have the readings done by a pro or take your chances. With ceramic tiles, small amounts of moisture will escape naturally through the grout, so you should e fine.

If i were to install them i would take the readings to be sure but for your diy purpose i'd say it should be fine although there is no guarantee. The concrete floor might only be 6 years old but theres no way of knowing if the DPM underneath was punctured or damaged at some stage.

The moisture meter your builder used for damp in the walls is not the same as a hygrometer (used for measuring relative humidy) so don't ask him to measure your floor.
thanks for the info.
so would exterior grade grouting allow some moisture to escape or am I trying to stop it escaping?
would there be any point putting any type of sealent on the concrete before laying the tiles or would the tile mortar take care of that ?

not an expert on floor tiles ( can you tell?) , are most ceramic? not looking for anything to expensive..
You want any moisture in the concrete to escape so use ordinary floor grout.

To be safe you could apply a liquid DPM (damp proof membrane) you will need f ball F75 or F76. It will stop any moisture but it's not cheap and you will have to lay a screed over the top unless your tile adhesive is compliant with the DPM.

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