Floor preparation

[fad]

I 've just looked at a potential job where the floor seems to get wet easily and has resulted in the tiles becoming loose. Apparently water has even penetrated to the next room. A plumber has been around and said that there isnt a leak.
I am told that there is plywood under the tiles which surprises me because this is a basement flat. If is plywood and i take it up what are my options ?
Cement board onto whatever is below the plywood ?

 

[david campbell]

if there is water getting beneath the tiles then there is no point in re-tiling this area,if the plumber claims there is no leak then is sounds like the damp proofing in the flat is damaged or non-existant,and would need to be sorted first

 

[Colour Republic]

I have had a similar problem with one of my jobs, I visited the job on 4 or 5 occasions as the damp would appear and disappear at will. I could not find any leaks despite looking extremely hard for them. In the end the only other option that I could think of was the flat above, it was running perfectly down the cavity before finding it's way into the flat at floor level, hence why there was no staining to the ceiling above. I'd get the flat above checked out, seems like this could be exactly same if not rising damp as David says

 

[brian c]

i am with Davy on this,furthermore it will need to be bone dry before any retiling is done.

 

[Ajax123]

In terms of damp which can appear and disappear without apparent source of moisture - I have seen this a few times and the only explanation I have been able to come up with is dew points which occur within laminated systems.
An obvious example of this is when the warm air inside a room is moist (people breathing etc etc) and the moisture hits the cold window pane it condenses at this dew point to form the moisture on the window.

If the underside of a screed on a polythene membrane is colder than the upper portion of the screed e.g. in a basement then any moisture in the system (and there will always some moisture) will condense at this point.

If there is an air gap allbeit a small one, between the major and minor substrates this phenomenon will be particularly pronounced because there will be moistur in the air gap.

I have seen this occur on poorly designed screeded floors over block and beam and on timber floors over concrete particularly in basements. Where thermal stability cannot be acheived ie. placing insulation on the cold side the key to preventing it is generally ventilation and vapour stabilisation.

I think my old Victorian suspended floors work on this principal. The air bricks allow air curculation under the floor to equalise the vapour pressures and to stop damp and thus mould and rot etc.

 

[Ajax123]

Having said that I'd check for the obvious sources of moisture first e.g. leaks, drainage, rising damp, changing water table, breaks in DPM leaks in other parts of the building sumping etc etc... Mainly because they are more easily explained and dealt with.

 

[fad]

Thanks for that information Ajax- I think that first post is going to take a bit of digesting. When I was in the bathroom it had a very wet feel to the place. I didnt notice any form of ventilation-I may have missed it. But that would contribute to anything else that was wrong I would think,but that alone couldnt cause it could it ?

 

[Ajax123]

Is this a basement flat in South London and is it an old house?

 

[fad]

Yes, it's actually a total of 8 flats in an old house. It's difficult to say how old because it' s been modernised.

 

[fad]

The flat in question is most definitely in the basement.

 

[Ajax123]

First thing I would be looking at in an older house in a basement would be penetrating or rising damp. Bear in mind many basements will be low relative to the surrounding water table. If the house is old and messed about (eg turned into flats) you will have no idea if the original tanking , if indeed it was ever there, has been compromised.

It might be worth checking to see if you got damp penetrating from outside.