Damp patches concrete floor

[Decca2]

I live in a 40 yr-old terraced town house with the garage on the ground floor.

A spreading damp patch has suddenly appeared in the garage concrete floor.
There are no water-pipes under the floor, or leaks from pipes in the garage. My neighbours do not have any damp showing in their garages.

What could cause the sudden appearance of damp after a prolonged dry period? Anyone got any suggestions for tracing source or treating floor?

 

[bogwort47]

Hi

If the patch is spreading from a point away from the walls, then there are 2 options as I see it. A drain is running under the floor and has a problem or, particularly if you are built on clay then it could have dried out, cracked and allowed ground water access to the under side of the floor. Where is your house? High, low, flood plain, bottom of hill etc?

The other option is if the damp is spreading from a wall. Is it an internal wall or external or shared etc? The most likely explanation for an external wall is watering during a dry period. If the ground level is above the DPC outside the wall then it is possible that the waterproofing applied to the outside of the wall as built has failed. Mine went after 10 - 15 years. If soil has been added above the DPC since build then this equally with watering can cause the problem. Before saying anymore, it would be helpful to know exactly where the leak is please.

 

[Decca2]

Thanks for a thought provoking response. The house is built on sandstone, well above the flood-plain. There appear to be 2 sources of damp, about 1m apart, both against an internal dividing wall and below the dpc. There is no sign of dampness in the wall (or ceiling!).

 

[JohnD]

might be a leak from the adjacent room, especially a radiator?

how do you know there are no pipes under the floor? where does the water main run, and the waste pipes?

photos would be interesting

//www.diynot.com/forums/viewtopic.php?t=129539

 

[bogwort47]

I agree with JohnD and let us know what you have on the other side of the wall and double check exactly where your water service pipe is and also where your drain runs are and do not forget that drains from your neighbours can sometimes run under your property or join up with yours. Also outside drains which might take run off from car washing can be faulty and cause water to spill/leak under your floor and come up between the floor slab and the wall if there is a problem with the join in the 2 DPMs.

Sandstone should not give you a problem unless the land slopes towards your house and then there is chance of a spring under the house. Springs sometimes move about over many years as a result gradual ground changes but usually, land works or changes to stream courses etc are the cause.
Do not dismiss the possibility that it could be someone else's leak showing up.
Good luck and please keep us posted.

 

[Decca2]

I'll be happy to post pics & diags. How do I upload these to forum?

 

[JohnD]

here ->>>>> //www.diynot.com/forums/viewtopic.php?t=129539 <<<<< here

 

[Decca2]

Plan View and photos of garage uploaded.
Key Facts:
1. There has not been rain for past week
2. No car in garage for past week
3. Garage and rear doors left open with through draft for last 3 (hottest days) with no sign of drying!
4. Front of garage is Macadam, to rear of house is communal lawn that has not been watered.
5. 7 Sunnybank middle house in row of 9 built on flat ground with river valley ~3/4ml Nth.
6. Neighbouring garage floor bone-dry.

I've now covered garage floor in plastic sheeting to:
a) Ensure their is no water coming from above.
b) So that condensation from below will locate source of dampness?

 

[JohnD]

i reckon leaking pipe under floor

 

[Decca2]

Looks like that BUT there are no records of underfloor pipes OR any services routed that way!
Mains water comes in across driveway under front door and runs up through 1st floor kitchen to cold water tank in attic. Then feeds hot water cylinder on 2nd floor. All hot and cold feeds to ground floor run at ceiling height.
All pipework in garage appears dry.

Will report tomorrow on plastic-sheet findings.

 

[JohnD]

have you got a stopcock outside the house?

 

[bogwort47]

Hi

From the information you have supplied I am guessing that there is another garage the other side of your wall near where you have the damp patches.
Correct?

Plastic sheet is a good idea, however unless you put some talcum on it you may not see any evidence of drips from the overhead pipes as they can disappear/evaporate before you check next time - the talc will leave an image of the drip.

Do any of the overhead pipes run directly over the damp patches? If so, are there also joints in the pipes possibly over the damp patches. If there are joints, are they compression or soldered? Do these joints look the same as others in the garage? Are there any stains on the connectors, may be green white or brown? The stains may well look dry - particularly if it is a hot water pipe.

Do you have a water meter? If so read it, use no water overnight, draw some before for drinks and the loo if you want but do not flush. Read the meter again before using water. You need to note all numbers and make sure the 'spinner' is completely still. If the spinner is completely still and none of the digits have changed and this is very important, the last digit has not moved at all - even it still shows the same number. Anything less than this, then you have a leak somewhere in your water system.

Failing that, you are looking at drains, someone else's water pipe or ground water.

You mention a river. If you let me have your post code, I'll check out your local geography to see if there is a chance that it could be ground water. That is, after all other possibilities have been eliminated.

Just because it is not on the plans does not mean there are definitely no pipes or drains under the floor. Was your house built on virgin ground? If not then then there could also be left overs down there.

My gut feel is that the most likely cause is an overhead pipe - but in a garage - not my preference - even with lagging, water pipes are very vulnerable in an unheated space. Do the leak test first and then let's see where we go. At a guess the overhead pipes are not part of the original build? Is this correct please?

Hope this helps a bit - keep smiling - I've just been through a similar investigation and concluded that I have a ground water problem on a chalk hillside!

 

[Decca2]

Hi bogwart47
If you can access the Plan and photos posted to the Forum you'll see the layout but to answer your questions:
1. Yes there is a garage the other side of the wall but it is completely dry.
2. No, none of the overhead pipes (original build), are above the dampest patches and they show no sign of leakage or stains (although I first suspected frost damage to the soldered joints in these pipes).
3. As we have guests staying it will be another week or so before I can do a thorough water-meter test.
4. Postcode SK9 1ND
5. The townhouses are built in the grounds of a former large house but mine is close to the road and unlikely to have been built over the site of the old house.

 

[Decca2]

Hi John,
After a cooler night, there is absolutely no sign of water on top of the plastic sheets covering the garage floor. As a control, I placed a saucer of water on the corner of the sheet and there was very little evaporation. Tonight I'll spread some talcum.

There is a stop-cock located 10m from the front door, as indicated on my Plan.

 

[JohnD]

OK. As you have an outside stop-cock:

1) wait until it is very quiet (evening, perhaps). Turn off all radios, appliances etc. then get someone with sharp hearing (young) to stand in the garage, quietly, with the door shut while you turn the stop-cock off, then on, then off. see if they notice a noise. I once had a pin-hole in an iron water main (it was at the elbow where it turned up to come through the kitchen floor) and there was a slight hiss. but too quiet to notice as it was there all the time. But when it turned on and off you noticed

2) make sure all internal taps are off, cisterns and tanks are full so not drawing water. Get a large glass tumbler and put it under the kitchen cold tap, stood up so the spout of the tap is immersed in the water. Turn the tap on. Now go and turn off the outside stopcock and watch the glass to see if the tap is sucking water out of it (this will happen if there is a leak under the floor). It might be quite slow so give it ten minutes. Be sure not to use ant hot or cold water in this time.

If not, try to persuade your neighbour to do the same

BTW this is how you attach a picture

Untitled

• Decca2
• 24 May 2010
• 1

Isn't there a tap or drain in your utility room?

BTW I am very suspicious of those pipes on the wall just above where the wet patch is.