maybe got a damp floor - please advise

[wwwebber]

Hi folks - need some help in diagnosing some possible damp in my kitchen floor - I'll start from the beginning :-

Our new kitchen diner was once a 3rd reception / small kitchen / downstairs toilet. There were approx 3 walls that separated them. To create our new kitchen diner we removed all of these internal walls completely. At the base of the walls we found that they sat upon some black powdered type soil ???.

Anyway - we filled these "trenches" in with mortar and then levelled things off self levelling cement. I noticed that as the cement dried out the areas where the walls once stood took longer than the rest of the floor to dry. I figured that the mortar still contained moisture so thought nothing of it.

We've now had our new kitchen installed but we seem to be having a problem along where these walls once stood. Whenever it rains these areas on the floor start to darken and then can feel damp to the touch. I've dried them out using heaters and fans but they still kept coming back. We've had a dry spell lately and they appeared to dry out completely until it rained again this week .

I'm confused here as these areas are in the middle of the room so have a I got damp ? and why is it present only where the walls once stood ? and what can I do about it ?.

Cheers.

 

[Fafhrd]

Sounds like deliquescent salts from long-gone coal-fired cooking or water boilers, hence the black stuff - soot. Deliquescent salts extract water from moist air, and can migrate through concrete and brickwork.

Even though it is not actually rising damp, a DPM Is usually the cure for this type of dampness, trapping the salts below a clean new concrete floor.

 

[regsmyth]

Does the existing floor have a membrane underneath that was cut against the walls you removed.
It sounds like the exising floor is dampproofed but the bit where the walls were wasn't.
You'll have to dig up your infill to find out.
If so, try to fit a polythene dpm to overlap the dpm in the existing floor. This might be more tricky or messy than it sounds.

Even in the middle of a house, the soil underneath will be damp. The fact that yours is quickly affected by rain is evidence of that.

 

[wwwebber]

Thanks for the replies guys. Can I remedy this without digging up the floor ? I ask this because I have a brand new breakfast bar standing along where one of the walls once was and I'd have to dismantle it to dig up the floor. Can it be tanked or sealed at all ?.

 

[noseall]

Sounds like deliquescent salts .

Never heard that one before, though a few of us are familiar with hygroscopics.

I have just read the Wiki on the word and deliquescent is similar in nature to hygroscopic. I like the instant coffee explanation whereby if you leave dry coffee granules on the kitchen side they will eventually become sticky due to water absorption.

 

[Nige F]

Juvenile Deliquescent