Is there a damp proof membrane in a 60's house's concrete floor?

[Pennyw]

Hello all,

We have a 10 year old downstairs shower set on the existing concrete floor of a 60's house.
We have had signs of dampness on the other side of the wall which we think was probably caused by the failure of the tile grouting which is now dry.
It had not been used for over a year to allow it to dry out.

We decided to replace the whole shower unit, tray, tiles and door. It is set in an alcove and took up the tray and it was pretty damp underneath. The tray had been set on uneven concrete slab and had cracked from underneath plus the silicone seal around had failed.
The shower trap had been set hard in the concrete so didn't flex at all.
It has all been exposed now for about 2 weeks but the concrete floor is still showing damp with the damp tester.
We thought the waste pipe could be leaking but it doesn't seem to be.
But we think the damp is coming up from the floor so we asked our builder from 10years ago.
He said that if we dug all the way down under the waste trap to well below the foundations to the dirt we wouldn't find any damp proofing at all like a dp membrane!
We can't believe that there is none!
Surely there must be something there to prevent the damp from the ground coming up.
Please advise as we can't bear to redo it all only to find the damp is coming up again.

Many Thanks in advance
Penny

 

[tell80]

If you posted pics of what you have exposed it would help?
Are any of the alcove walls outside walls?

 

[Pennyw]

Thanks for the reply. I hope you can see the pics as I'm a novice at this.
There are no outside walls.
It doesn't look damp or feel damp as the mortar mix is very sandy but damp meter shows it as being damp.
The floor seems to be the only area in the shower around the trap that is now damp apart from about 3" up the right hand wall.

 

[stuart45]

A DPM became part of the regs mid 60's.

 

[Pennyw]

The house was built in 1961 and in the 20 odd years we've been here no other damp areas in the house have appeared.

 

[KenGMac]

You can try to use a fan to "assist / force" the final dry out of the base material, could be that because the damp area was / is in an alcove there was minimal air flow, it is air flow that dries things out [think of a washing line and a good going breeze? ]

Given that this is the only are of dampness, could be that the failures of Mastic / tile grout Etc, have been the predominant cause?

Ken.

 

[Tigercubrider]

Many houses had bitumen painted on solid concrete floors and vinyl tiles fitted on top.
A lot can happen to a house in 60 years .
You can probably add a liquid DPM but let it dry first

 

[tell80]

Pennyw,
As you suggested, the tiles & tray seem to have been the damp culprits.
Does the RH studwork appear to be solid wood - its very dark looking - check that its not rotten?
Is the damp on the other side of the wall high or low?

 

[^woody^]

but damp meter shows it as being damp.

The damp meter will normally show a corner of a ceiling being damp, along with your dry hand.

Damp meters are designed for and intended for use on timber

 

[Pennyw]

Thanks very much for all the replies.
KenGmac - Yes I think we will get a fan in there and open doors and windows for another week at least.
Tigercubrider - What type of Liquid DPM would you recommend please? I have seen epoxy type mentioned on websites.
tell80 - That is a breeze block wall and it is quite dark anyway and quite porous I think. There is a corner timber next to it which is for the stairs above which is still a bit damp at the bottom.
woody - You are probably right although it says it is for timber and masonry. If we didn't have the blooming meter(like the old days)we would be blissfully unaware that it was actually damp!
Thanks everyone. All very helpful.
Penny

 

[Tigercubrider]

I’m no expert on damp

but I had a slight issue in a corner that was parquet and used the bitumen stuff that is used to fix them
Can’t remember the name

edit

synthaprufe

 

[Nige F]

I
edit

synthaprufe

or as tell will tell anyone who'll listen - it's tarmac.?