Garage damp where floor meets wall.

[turnitup]

I have now edited/shortened this port as it was VERY long.

The garage that is attached to our house has damp patches where the wall meets the floor at various points along two walls (only after it has been raining).

The 2 x problematic walls are:

1. The wall opposite the double garage doors (basically the rear wall of the garage) which has paving/patio slabs on the outside that are built up against the garage wall - with no visible drainage in place.
Paving is rather uneven and water that lands on the first two rows actually runs towards the garage wall (I would assume that the concrete base/bed has sunk or dropped over time).

2. The wall opposite the main house which has (on the outside) an approximately 18" wide cement slab with a runoff channel in the centre that runs towards the front of the garage where there is a drain (due to an inconsistent pitch, water does not run effectively).
Between the edge of this slab and the neighbouring fence, is about a 6" drop to what must be the ground level.

Here are two pictures showing the outside of each problem area - you can see a small amount of water pooled in the channel down the side slab in the one photo.

Back paving issue

• turnitup
• 30 Mar 2010
• 1

Side of garage

• turnitup
• 30 Mar 2010
• 1

On the inside, all of the way around the base of the garage, there is a single course of bricks, above which is the DPC and then garage block walls.
The damp patches are all coming from that first course of bricks BELOW the DPC.

The top/surface of the slabs/pavers on the outside are an inch or so above the DPC --- I realise this is vague, but I do not know how to do an accurate measurement --- bottomline is that water lying on these these slabs/pavers are definitely higher than that first brick course, but not by a huge amount.

Here is a picture of a damp patch on the inside.

Damp!

• turnitup
• 30 Mar 2010
• 1

What I would like to do (reason explained in one of my posts to follow) is as follows:

At the back where the patio/pavers are - lift the first two rows, or perhaps all of the paving and re-lay them so that the water runs away from the house and garage walls.

On the side of the garage - get the water to run AWAY from the wall and then also ensure that whatever channel is in place runs properly towards the drain.

In both cases, I would also consider covering each area with a fixed awning type of affair with proper guttering in place, so that 99% of any rain is kept away from the slabs and walls in the first place.

Thanks in advance for any thoughts and advice.

Steve

 

[turnitup]

Apologies in advance - I don't usually do this, but I desperately need a single *bump* here as I have had two contractors out who have both stated that they do not do this type of job, so I may need to undertake this myself.
Steve

 

[hotrod]

Hi Steve, a quick summary, right, I think the obvious 2 major issues here that are contributing to the damp (although I found your post a bit hard to follow to be honest - but I tried my best to stick with it) are as follows:-

1. The flags / 'cement slab' externally need to be set with a fall away from the external wall of your house.
2. The DPC should be approx 150mm above external ground level - and from your post you are suggesting the DPC is actually below the external ground level. Is that correct? How have you verifed the position of the DPC?

If both the above are true, as a start, it's time to get the shovel and pick out

 

[r896neo]

As hotrod has said, The ground level outside should be at least 150mm or two bricks below the dpc. If this is not possible without major work then you may get away with digging /cutting a channel 4inch wide channel down to the required depth and then fill this with clean stone. Ideally try to get a slope on the base of it or at least not big hollows in it.

Your other problem which is much harder to deal with is the fact that the damp proof membrane under your garage floor is clearly not overlapped with the dpc in the wall meaning any damp in the cavity caused by your high outside ground level is simply soaking into the floor slab.

I had a customer with the same problem last year and a full land drain next to the affected wall sorted the problem but this was due to the wall being at the base of a slope.

 

[turnitup]

Hello and thanks for the replies.

Sorry about my confusing initial post - I had originally posted a very long explanation that was even MORE unclear so I shortened it last night and probably left it with less flow.

ps. I have reworded it again this morning.

I can confirm (I have tried to make this more apparent in my rewording this morning) that in both cases water is not running away from the walls properly.
This issue is a lot worse at the back --- I was cleaning the pavers with a hose a few weeks back and a pool of water about an inch deep collected right up against the garage wall. From about the second row of pavers, the water then runs away from the walls towards the rear garden.

On the side of the garage, if you look closely at the picture, you can actually see that there is a constant green moss growth along the sourface of the cement slab where it meets the wall --- so I would assume water does not run away from the wall properly?

Re: the DPC --- I realise how difficult it must be to try to help if I cannot provide the proper facts and I do apologise --- due to the outside of the house being pebbledashed, I do not know how to tell exactly where this is positioned --- the only place I can see the DPC is on the inside directly above that first course of bricks as it sticks out about 1/2 an inch all of the way around (you can see the line in one of the pictures).

When you refer to the outside ground level - is that the surface level of any slabs etc, or the actual original ground level beneath any slabs and pavers?

If the trench is the only solution then I would have to go that route - the only problem being that it is not my house and although the owner is happy for me to do any work at my cost (the reason and relevance of why I am doing this would take this thread WAY off course) - I fear that chopping down may complicate things a tad due to the inspection plate that you can see in the one photo, so there may be technical hitches with me just getting stuck in if you know what I mean.

Is there a chance that I might get a result by trying to fix the "surface area" of each slab so that water runs AWAY from the walls and then covering the entire slab area with a fitted awning structure so that 99% of any rain cannot even get to the slab in the first place?

If this is all beyond the scope of my train of thought, then could anyone recommend the type of contractors to get hold of to come and quote?

I called two seperate "Damp Fixers" and both came around and said that they do not do this type of thing as there is no rising damp inside etc.

Thanks again.

Steve

 

[r896neo]

all references to 150mm below dpc are to the top surface of the paving slabs.

It is not just a case of water pooling against the side of the house causing the damp but also the earth/bedding for the slabs will hold a lot of water and because it is against the house the water soaks out of the earth into your wall.

As you obviously don't mind long posts i'll just explain whats happening.

If the sodden earth is below your dpc then it will only rise up the wall until it hits the dpc but if the earth is touching the wall above your dpc, water will seep into your cavity and then seep into the inner leaf of the wall. It will then climb that wall until it hits your inside dpc and then will not go any further.

BUT Because the concrete slab forming the floor of your garage is below the dpc water will seep out of the inner leaf below the dpc and form pools of water at the joint of floor and wall.

In normal construction there is a membrane under the slab which in run up the wall past the dpc/ tucked in underneath it this forms a continuous barrier against water.

So in conclusion, Simply re-bedding the slabs so water falls away from the house will help but will not fix the problem. To fix it you need to reduce the ground height outside to below dpc.

The outer dpc will probably be at the same height as the inner one so transfer the level that way or check at the garage door reveal and you may see it.

 

[turnitup]

Thank you very much for that.

I realise this is bottom-feeder stuff for many, but this gives me a clear understanding.

If I may ask one more question - if I create a trench-like channel right up against the wall that ends up beneath the DPC as a sort of natural seepage/drain, then how does this alleviate the rising moisture problem --- will there not be moisture "beneath" that same course of bricks that will rise up through those bricks and then still seep back into the garage?

EDIT - I am not questioning your knowledge in any way as you obviously know what you are talking about!

Should I then seal the garage floor and the inside face of that lower course of bricks as well so that any moisture trying to get in cannot and is forced to expel via the "exposed outer face"?

If that is the case, then is it better to dig down beneath DPC level and leave that "trench" open, or fill it with gravel as I think I have read about in other threads?

Aaaarrrggghhh --- so many questions.

Thanks

Steve

 

[r896neo]

Am not quite sure what you mean by

''will there not be moisture "beneath" that same course of bricks that will rise up through those bricks and then still seep back into the garage?''

Whatever the case i think you have got the message, the first thing to try is digging the trench at least 150mm (preferably a little more if possible) below dpc and fill it with clean stone. Don't worry about sealing the inside as water will chose the path of least resistance and much more easily flow into the clean stone trench than it will try to seep through the wall.

Of course this will definately help but may not cure the situation in which case you should extend the width and depth of your trench but more importantly drain it to somewhere via a land drain/ french drain.

 

[turnitup]

OK - got it.
Thanks for all the help and patience.
Steve