floor slab with damp proof membrane on surface?

[browfish]

Having taken up some of my carpets, the whole ground floor of my bungalow is tiles in what i suspect may be asbestos vinyl tiles. Alot of these are loose and come up very easliy. The floor screed underneath is black with what looks like a bitumeny type material. Could this be the damp proof membrane or just the adhesive let go of the tiles. What made me really think this could be a membrane is that i knocked down a couple fo internal block work walls today and although they go through the screed they have slate DPC at the top of the screed height.

Having removed these walls, i need to infill the screed. If the DPC is on the surface, how should i do this? Do i just fill in the gap and treat the surface, if so using what.

Not sure on the date the house was built but i think it was the 30's

 

[ianbuildingplans]

Sounds like your screed is mastic asphalt, I think in those days it acted as the damp proof membrane as well as a levelling screed. Be careful with those Asbestos tiles, you should really have them removed and disposed of by a specialist.
-Ian

 

[mointainwalker]

you should really have them removed and disposed of by a specialist

Sounds as if you are implying they are required to removed by a specialist which is not the case.

If the OP is confident about doing it, no reason why they cannot be removed with due care and damping/soaking beforehand to ensure no fibres floating around.

Need to find out about local disposal possibilities though.

 

[browfish]

Is it the tiles that contain the asbestos of the black bitumen adhesive?
I lifted the tiles in the area i was working in with a paint scraper (the come up whole very easlily. However i stitch drilled and area of the floor to break an area of slab up to excavate a new foundation. Bit late i know but i wont do anymore if it is the bitumen.

 

[r896neo]

no the asphalt is fine

 

[Saycheese5]

I had a similar experience the other day. My tiles are of a dark brownish colour and seem to be hard vinyl (house built in late 40s). If they were also partially made of asbestos they would look fibrous I suppose. One area of the screed seemed hollow so I took some of the cracked old mortar off and discovered that there was no Damp Proof Membrane (DPM) once I reached the concrete. In those days builders seemed to apply the DPM on the top of the screed (mortar) rather than between the concrete and the mortar. So that black stuff is very likely to be the DPM which was also used as an adhesive for the tiles. Those tiles also help to insulate the floor. You can buy a tin of DPM and apply a few coats with a brush. Once dried, you can apply a very thin screed on top. I wil apply mortar on mine since I seem to have problems with self levelling compound which cracks with the heat of direct sunlight.

 

[mointainwalker]

Those tiles also help to insulate the floor.

Anything , even a sheet of newspaper ...

also help to insulate the floor

...but that is incidental.

Once dried, you can apply a very thin screed on top.

How thin ?

 

[Saycheese5]

Fill in the gaps where the tiles have been taken out. I would apply the same thickness as the vinyl foor tiles, mine are around 3 to 4 mm.

 

[mointainwalker]

Please say how long you would expect a "screed" of 4 mm to last .

More or less than two days ?

Or do you mean a self-levelling compound ?

 

[browfish]

having removed a section of slab to case a new strip foudation, i discovered the slab was laid on a 12 to 18" layer of flint stones. This i guess can not absorb moisture or form capillaries so i guess is my damp proof layer. Has anyone else ever come across this?

 

[Saycheese5]

I have used self levelling compound twice and it has cracked under the heat of the sun, that's why I decided to buy a bag of mixed cement of sand mortar and apply it to fill the gaps where the vinyl tiles were taken off because they were broken. I haven't put my laminate flooring yet but the floor is now levelled and I walk on a regular basis on the areas where I've laid a thickness of 3 to 4mm of mortar and it's still there. So my floor is made of a very thick layer of concrete, then a good inch of the original mortar, then the DPM and finally vynil tiles or a very thin layer of mortar to replace the broken ones to make the floor levelled. Why shouldn't such a thin sreed of mortar last???

 

[mointainwalker]

Why shouldn't such a thin sreed of mortar last???

That's like asking why a sheet of wet newspaper won't carry a 10kg weight. It doesn't have the physical structure and mass to be able to do so.

 

[Nige F]

Do 2 things - 1 google Pudlo . 2 ask for " old un " to give an answer I`ve seen these floors with no apparent dpm and a very thin screed - like a wall render but more dense

 

[Saycheese5]

Mountainwalker, as you metioned if I were to put a weight of 10 Kg on a sheet of wet newspaper, it's logical that it will go straight through it. What's not so logical is that I haven't gone through my 4mm screed of mortar, it's still in perfect condition. If you think someone is not doing the right thing, then please provide some practical advice so that everyone can benefit from it.

 

[mointainwalker]

My practical advice is that a concrete screed of 4 mm thickness has no chance of lasting any length of time.