rpuddle

How to stop water coming through soil bank

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I've just built a timber garage on my concrete base that was dug out of the soil at the bottom of our garden. The level of the garage is below the soil at the back end and water appears to be seeping through the soil, onto the concrete and into the back wall of the garage (I've circled the bank of soil on the image attached). I'm just wondering the best way to stop water coming through that far bank? Wall of bricks / concrete? Or is there a better way of doing this?

 

Thanks

bb4d8281-d3bf-455e-b122-06a8295a75c7.jpg

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Dig it out and put a French drain in?

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Posted (edited)

Probably you need to look at digging out behind and maybe the sides and making a French drain. 

 

If considered beforehand then perhaps waterproof concrete upstand off of the slab but it really needs to be homogenous or you're getting into water bar territory.

 

Then there's membranes. You're getting into the realms of underground houses.

Edited by Onoff

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You might even need a continuous waterproof strip around 3 sides that sits 6" above ground level and projects down the sides of the main slab. Needless to say any cladding should be 6" above ground.

 

Got any pictures?

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Posted (edited)

Yep - you need the garage to be above the ground, which means lowering the ground level immediately around the garage, or at least the part where the seep is occurring.

 

TBH I would also be concerned about the two sides - though "lowering the level" may just be for say 20-30cm next to the wall, putting in some sort of channel, and maybe part filling with gravel. That is a variation on the French Drain option.

 

Alternatively you tank it, which (put unkindly) is relying on a big waterproof plaster if done afterwards.

 

Ferdinand

 

Edited by Ferdinand

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Posted (edited)

I don,t see any easy way with the floor level below ground level --too late now but the slab should have been above ground level

 

you could i suppose use blocks  to jack up garage all round -then throw some plastic sheet in and just make your floor higher --that would be best solution -probably don,t even need to cement blocks if you going to fill with concrete--and don,t forget to put a run on floor to wards the doors

If you work out the other proper soutions  I think you will find  what I suggest as alot cheaper than trying to tank or lay franch drains ,which need to connect to somethinbg lower -like main drains

Edited by scottishjohn

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Dig a path around the garage?

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Posted (edited)
2 minutes ago, Onoff said:

Dig a path around the garage?

6" deeper than the top of garage  slab--that should work 

 

Edited by scottishjohn

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Only guessing but thinking there is no DPM under that slab?

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There doesn't appear to be a DPM under the slab, although the builder told me there would be! Don't even ask about the story behind the slab, and it's finish.....

On the left hand side (against the dividing wall) we've used a circular saw to cut away an area for the water to drain to and then run to the front of the garage, and the front and right hand side have gaps for the water to drain way, but the back has no such option. There is a DPM between the slab and the timber but the back of the garage there is not a lot of space (probably 35cm) so I'm not sure what my options are now. Don't think there is space to dig out the concrete at the back. May have to cut away the earth bank and push things further back from there? 

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Posted (edited)
12 hours ago, rpuddle said:

I've just built a timber garage on my concrete base that was dug out of the soil at the bottom of our garden. The level of the garage is below the soil at the back end and water appears to be seeping through the soil, onto the concrete and into the back wall of the garage (I've circled the bank of soil on the image attached). I'm just wondering the best way to stop water coming through that far bank? Wall of bricks / concrete? Or is there a better way of doing this?

 

Thanks

bb4d8281-d3bf-455e-b122-06a8295a75c7.jpg

You really need to lower the level of the ground at the back, simply that is the only real "long term" solution. A french drain will work but that requires dropping the level of the ground and back filling with washed gravel, which will still sit against the garage, so it's a sort of half solution really.

 

If you don't want to drop the level then excavate down the back of the slab, pour a foundation with a seperation gap from the garage slab and build a small retaining wall, back-fill the high side with washed gravel then make up your ground level to the wall, leave a gap down the back of the garage. This will keep the water back and leave a nice ventilation gap so the timber can breath. 

 

Ideally this section would have been built in block/poured concrete and waterproofed. 

Edited by Carrerahill
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The OP needs to either fight gravity or use gravity.

 

In my experience rainfall prefers to wriggle horizontally over the surface of the ground by following a gradient. To solve the garage problem I would dig a drainage trench around the external perimeter of the garage and then channel the water off somewhere.

 

Water will find its way through any untanked masonry defences.

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20 minutes ago, rpuddle said:

There doesn't appear to be a DPM under the slab, although the builder told me there would be! Don't even ask about the story behind the slab, and it's finish.....

On the left hand side (against the dividing wall) we've used a circular saw to cut away an area for the water to drain to and then run to the front of the garage, and the front and right hand side have gaps for the water to drain way, but the back has no such option. There is a DPM between the slab and the timber but the back of the garage there is not a lot of space (probably 35cm) so I'm not sure what my options are now. Don't think there is space to dig out the concrete at the back. May have to cut away the earth bank and push things further back from there? 

 

Basically, the cheapest option is to drop the ground level to below that of the finished level of the slab all the way around.

 

Basically your slab is a bowl in a bath of water and the lip of the bowl is under the surface of the water - simple as.

 

 

 

 

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Posted (edited)

How is the garage clad?

 

If say horizontal boards you could drop in a 3 sided edpm or similar waterproof membrane.

 

Btw, if your slab has no dpm is the timber frame sat straight on the potentially damp concrete or is there a dpc under the sole plate?

 

20200313_102926.thumb.jpg.6a50b26a7398cb0fd68686d89f9b3850.jpg

 

Depends to some extent how free draining the ground is...

Edited by Onoff

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I think the OP has already got the garage in place...

 

20 hours ago, rpuddle said:

It all went up guys! Thanks for all the help. Now got to pray it doesn't rot too quickly! 

IMG_20200308_134902.jpg

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5 minutes ago, Mr Punter said:

I think the OP has already got the garage in place...

 

 

We know. Now water's pi$$ing in through the back and he's trying to mitigate it.

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Wouldn't say pissing in. I'd say seeping at the moment! Either way, the whole thing has been a botch job, but time was against us as I had to get the thing built as the garage I rent was being emptied! It was a case of build now, worry later. Not the greatest moto but I'm working with it! I think it's time to get the hammer and chisel and start creating a runoff at the back of the slab.... 

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1 hour ago, Onoff said:

 

We know. Now water's pi$$ing in through the back and he's trying to mitigate it.

 

OK.  After he has reduced levels and installed a French drain, if the floor is still damp I suggest a sheet of DPM and a chipboard floor over.  Cheap and you get a smooth dry surface.

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6 minutes ago, Mr Punter said:

 

OK.  After he has reduced levels and installed a French drain, if the floor is still damp I suggest a sheet of DPM and a chipboard floor over.  Cheap and you get a smooth dry surface.

 

Not for long if parking a wet car in there! I'd go dpm and council slabs. Quite how level they would be looking at that slab...

 

Maybe those interlocking garage mats?

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12 minutes ago, Onoff said:

Not for long if parking a wet car in there!

 

Who on earth parks a car in a garage?  A wet one even madder!  Garages are used for storing crap you are not allowed to bring into the house.

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1 hour ago, Mr Punter said:

 

Who on earth parks a car in a garage?  A wet one even madder!  Garages are used for storing crap you are not allowed to bring into the house.

 

How many pieces is this car dismantled into?

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1 hour ago, Mr Punter said:

Who on earth parks a car in a garage?

 

Or two cars even... 🤫 It does have a dpc though...

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This bloke seems worth listening to, easy to make mistakes on french drains

 

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