Help!: Tiling on concrete with/without damp course?

[Ryan Powder]

Hello is there anyone out there that can me?!

I am fitting a new kitchen in my house. I removed the old floor tiles and underneath was a plastic damp proof membrane. I removed this and there is bare concrete. My house is victorian and i cant tell if there is a main damp course or not further under the floor, i suspect not.

I want to lay slate tiles. Can i tile directly onto the concrete with say a waterpoof adhesive, or do i need to put down another damp proof membrane? if i must put down some membrane, can i tile directly on this? im concerned nothing will stick to it and i will get movement. or alternatively should i be using a liquid damp proof and then tiling on to this?

ive been looking on the net for ages, and even been to four local tiling stores but i havent managed to find an answer, hopefully someone out there can help me!

[diamondtiling]

Hello and welcome, What were the tiles fixed to? was it concrete and you removed it to find a membrane?
Lots of victorian houses did not have concrete floors, they were quarrys laid on ash,test the concrete with a damp guage to get a true reading before you proceed

[Ryan Powder]

Hi! the previous owners had put concrete garden pavng slabs down in the kitchen. these were cemented onto a blue damp proof membrane, however they were easy to lift up because the cement hadnt stuck tp the membrane. when i lifted the membrane i was left with bare concrete.

good idea about the damp gauge. are you thinking that if the reading is low, i can then just tile straight onto the concrete?

[diamondtiling]

Hayden
this floor sounds all mixed up, the correct way is for mot (hardcore) to be laid first, about 100 to 150mm deep then it will have a thin layer of sand , this protects the membrane which is laid over the sand, then concrete is laid to a specified depth, you floor description goes against all this, do you have pictures?

[Ryan Powder]

here are some pictures of the floor after i have pulled up the original slabs and the damp membrane. (hopefully i have up loaded the pics ok!)

looks pretty dry there. i did find a couple of old vinyl tiles stuck there too but have removed them as well.

i dont know what i can do to see if it has a damp course 100-150mm below the surface

[diamondtiling]

sometimes you can see a membrane where the floor meets the wall , it will be black or blue, I would have thought you would have a dpm, your inner walls would show damp problems if you did not have one, try the damp test and see what reading you get.

[Ryan Powder]

i have just looked all around the room and theres no visible signs of a black or blue membrane.

Just one last question, how do i do the damp test? and what result is acceptable or unacceptable? if i get an acceptable result, i take it this means i can tile directly onto the concrete?

thanks for all your help i really appreciate it

[diamondtiling]

meters are different, some have a scale and others have a series of lights, the scale is usually between 0 and 5% for concrete, are those black patches on the floor damp to the touch? its difficult to help without seeing it.

[Dave]

Hello ryan...

A quick damp test to do...

Cover a 2 foot square with clingfilm and tape it down so no air gets in...leave for 48hrs and then check for condensation....if not then no damp in the floor...

But that doesn't tell you if a DPM is installed...just if the floor has any damp..

[doug boardley]

those pics don't look like a floor from victorian era imo, I think it's been laid later,either with or without dpm tho'

[Ryan Powder]

hello all,
the dark bits in the pictures are left over bits of black stuff which i uncovered when i removed the handful of vinyl tiles i found. to look at and touch the floor seems dry. the concrete surface is very uneven and not smooth.

when i do this damp test, i will find i either have damp or i dont. the next question is what do i do next. if theres no damp can i just tile with a waterproof adhesive? and if there is damp, do you have any recommendations?

[Ajax123]

They rarely laid concrete floors in Victorian houses unless they were extremely well to do. They mostly used timber suspended floors or lime mortar with quarry tiles and the like. The concrete would be much lighter in colour and less grey if it were Victorian. It looks to me like relatively modern concrete - probably a refurb by a previous owner. If it has been laid properly it will have a DPM under it which will show at the extreme edges usually. A Damp test at this stage is likely to be un representative of wether there is a DPM under it or not because the slabs on top will have trapped any moisture in the concrete previous to your lifting them - The Cling Film idea is a variation on the test I use all the time and is a great idea.

If you decide the concrete is too damp for you to tile straight onto you could speak to one of the Epoxy DPM manufacturers - there are lots of them - PM me if you want some specific contacts. These Membranes simply trowel/roller onto the surface of the concrete and trap the moisture in so it does not cause a problem with the tiles.

They are not used commonly as far as I can tell by tilers but are used routinely for soft flooring onto concrete.

[Ajax123]

hello all,
the dark bits in the pictures are left over bits of black stuff which i uncovered when i removed the handful of vinyl tiles i found. to look at and touch the floor seems dry. the concrete surface is very uneven and not smooth.

when i do this damp test, i will find i either have damp or i dont. the next question is what do i do next. if theres no damp can i just tile with a waterproof adhesive? and if there is damp, do you have any recommendations?

Whether damp or not I would recomend running a floor sander over the concrete prior to putting anything down onto it because there will be residues from the various materials which have been left behind by previous coverings.

[Ryan Powder]

yes i looked all round the edges and no sign of a DPM. I'll buy some cling film and do the test.

do tilers ever tile directly onto a blue/black plastic DPM? i am a bit worried if i did that then the adhesive will not stick to the membrane and the there will therefore be movement. or is this normal practise with special adhesives etc?

[Dave]

do tilers ever tile directly onto a blue/black plastic DPM?

Nope....only type we tile too is an uncoupling membrane , which is another option for you to conscider...if you have damp..

do the test first and then come back to this thread so we can continue..

[Ajax123]

yes i looked all round the edges and no sign of a DPM. I'll buy some cling film and do the test.

do tilers ever tile directly onto a blue/black plastic DPM? i am a bit worried if i did that then the adhesive will not stick to the membrane and the there will therefore be movement. or is this normal practise with special adhesives etc?

There are membranes for soft flooring but not for tiles as far as I know. There are Decoupling Mats such as Ditra and Durabase. I think that these would probably be very suitable in this instance. The problem with Tiles is that they need a rigid adhesive and of course as you say the level of movement likely to be experienced with a polythene membrane would cause the adhesive to break up and so fail. As I said you could use an Epoxy DPM but thinking about it you would probably be better served by using a Decoupling Mat. This will lift your finished floor height by a few mm but long term is probably a better option to maintain the stability of the tiles. I am sure the tilers on here will be able to confirm whether this is right or not. It might be worth you talking to Schluter Systems about the decoupling mats.

[Dave]

Other membranes are available....we will discuss these once you do the test....or you can just go ahead and use a membrane anyway...