Stopping a leak under my shed

cc58

Hi folks,

I've got a question that hopefully someone can help with. I recently purchased a new property which has a rather decent sized shed (10 X 4 metres)
Anyway it's a relatively new shed and in good condition but it's been put on top of what looks like a cement foundation so it's been done fairly well, the only issue is that the foundation wasn't laid flat and at the front on the shed it's been laid in minor V shape so when it rains the rain water flows into the middle. It's not all through the shed, only the front 60cms or so but it's annoying enough that I want it sorted. What would be the best thing for the job? The shed sits on the cement but isn't sealed to it, I was thinking of maybe doing that but not sure if that's for the best?
Any advice would be appreciated thanks 

hangryconsumer

I'm not sure exactly how you discovered this happened (maybe from seeing water soak up through into the floor of the shed?) but if you could manage to prop the shed up somehow then you could put self-levelling compound on the first 60cm and it should level it out.

cc58

hangryconsumer said:

I'm not sure exactly how you discovered this happened (maybe from seeing water soak up through into the floor of the shed?) but if you could manage to prop the shed up somehow then you could put self-levelling compound on the first 60cm and it should level it out.

I noticed it when I went in after it had rained and there were pools of water in the front left and right hand side of the shed with some lines running towards the middle but it was dry everywhere else. I used a spirit level and noticed the cement foundation wasn't level.

Propping up the shed isn't going to work, it weighs a ton and is huge, I think something more like sealing or putting a membrane down would be a better option but not sure how to tackle it 

Bendy_House

There is water INSIDE the shed? Are you sure this has come UP through the floor?

A photo and/or a sketch would help. But I'd have thought that the shed floor would be help a good few inches ABOVE the concrete slab? 
I don't really follow what's happening, tho'.

davemorton

Bendy_House said:

There is water INSIDE the shed? Are you sure this has come UP through the floor?

A photo and/or a sketch would help. But I'd have thought that the shed floor would be help a good few inches ABOVE the concrete slab? 
I don't really follow what's happening, tho'.

I think they mean it is on a concrete base, and the base is not level, so when the rain hits the base (which has a bigger footprint than the shed), it runs into the shed, instead of off the base and onto the garden. 
Op, can you retro-fit some sort of overhang roof? 

Bendy_House

Thanks Dave.
So it's UNDER the shed and not INTO?

CC, trying to 'seal' the shed to the concrete base is unlikely to be a good move as this - even if it worked - would block the essential ventilating of the under-floor area. And, if any water were still to get through, it would then be trapped and cause damp.

A PHOTO PLEASE! Sounds as tho' adding a layer of a self-levelling compound could could work? Or, Grind a small channel from the lowest point out to the edge to let it drain.

cc58

davemorton said:

Bendy_House said:

There is water INSIDE the shed? Are you sure this has come UP through the floor?

A photo and/or a sketch would help. But I'd have thought that the shed floor would be help a good few inches ABOVE the concrete slab? 
I don't really follow what's happening, tho'.

I think they mean it is on a concrete base, and the base is not level, so when the rain hits the base (which has a bigger footprint than the shed), it runs into the shed, instead of off the base and onto the garden. 
Op, can you retro-fit some sort of overhang roof? 

Dave is correct, sorry I didn't explain it well but yes there's a concrete slab base that's got a larger footprint than the shed than the shed sits on. Essentially the shed is 4 sides & a roof and there's just the slab underneath which is the "floor" inside.

There's actually already an overhanging roof which is doing a bit but still not keeping out the water fully. I'll try and take a picture when it rains again but I've popped a few below Although a self leveling compound would work technically, lifting the shed to do it would be nigh on impossible without renting some sort of crane to lift it as it's a massive structure and far too heavy / large to just jack up to front side I think. I think it would also risk damaging it to do that.
My thought on sealing it was just because it would only need to be the front portion that's leaking so I'd be leaving 90% of it open for ventilation etc it would just be the small bit that needed sealing. I guess the water that currently gets through just evaporates anyway so I wasn't too worried about water getting trapped as it doesn't flow out anyway once in but open to suggestions at this point. 

womble12345

Most sheds have 4 walls, a roof and a wooden floor which I suspect is why people are confused. Your shed floor IS the concrete base. I would channel out a 'gutter channel' into the concrete base around the edge of the shed so that any rain running down the walls goes in the gutter rather than flowing under the shed walls.

cc58

womble12345 said:

Most sheds have 4 walls, a roof and a wooden floor which I suspect is why people are confused. Your shed floor IS the concrete base. I would channel out a 'gutter channel' into the concrete base around the edge of the shed so that any rain running down the walls goes in the gutter rather than flowing under the shed walls.

ok thanks for the advice, definitely dont have a grinder that will do concrete hence why i was hoping to just use a sealant   
playing devils advocate, what would be the downside if i say used a bathroom sealant to close the gap between then shed and the concrete to try and stop the water ingress?

Bendy_House

Ah, I see

Ok, that's in some ways a better scenario, and I think your sealant idea could well work. 
I think this is what I'd do; First, I'd wait until the base and shed timber is bone dry. Then I'd thoroughly clean around the base/bottom of shed, and SOAK the whole area with a high-quality timber preserver. Soak, soak, soak - brush/spray it right under the contact points. And the vertical posts. Did I say 'soak'?
Once fully dry, I'd choose a timber finish, something designed for exterior timber obviously, microporous, and well regarded. I'd coat the bottom plank at least, in this.
Then I'd pick a sealant. I wouldn't use silicone, as that cannot be painted over, and you may wish to add another coat of finish, also going over the sealant. I dunno - frame sealant? CT40 or whatever it's called? Stixall, even?!
I'd run a hefty bead along the OUTSIDE only, and finish it off with a Fugi or similar rubber tool - leave a large bevelled finish, sealed tightly against both the shed and the concrete (these tools are great for this).
Once set, you can go over this bead when you next coat your shed. For the concrete, I dunno, but I'm sure something can also be applied on there to seal it and prevent moisture getting under the beading - water repellent, perhaps?
Leave the inside unbeaded, 'cos you don't want to TRAP water under the lower board. Keep the inside exposed so it is ventilated, and brush on more preserver every year or so.
If you want to floor the shed, then I think I'd restrict it to a slatted base, sitting on treated battens, so it's kept ventilated. That should make it a really nice shed.
Did I mention to SOAK the bottom plank AND. All vertical posts with preserver? EVERYTHING that is touching, or close to, the ground.

cc58

Bendy_House said:

Ah, I see

Ok, that's in some ways a better scenario, and I think your sealant idea could well work. 
I think this is what I'd do; First, I'd wait until the base and shed timber is bone dry. Then I'd thoroughly clean around the base/bottom of shed, and SOAK the whole area with a high-quality timber preserver. Soak, soak, soak - brush/spray it right under the contact points. And the vertical posts. Did I say 'soak'?
Once fully dry, I'd choose a timber finish, something designed for exterior timber obviously, microporous, and well regarded. I'd coat the bottom plank at least, in this.
Then I'd pick a sealant. I wouldn't use silicone, as that cannot be painted over, and you may wish to add another coat of finish, also going over the sealant. I dunno - frame sealant? CT40 or whatever it's called? Stixall, even?!
I'd run a hefty bead along the OUTSIDE only, and finish it off with a Fugi or similar rubber tool - leave a large bevelled finish, sealed tightly against both the shed and the concrete (these tools are great for this).
Once set, you can go over this bead when you next coat your shed. For the concrete, I dunno, but I'm sure something can also be applied on there to seal it and prevent moisture getting under the beading - water repellent, perhaps?
Leave the inside unbeaded, 'cos you don't want to TRAP water under the lower board. Keep the inside exposed so it is ventilated, and brush on more preserver every year or so.
If you want to floor the shed, then I think I'd restrict it to a slatted base, sitting on treated battens, so it's kept ventilated. That should make it a really nice shed.
Did I mention to SOAK the bottom plank AND. All vertical posts with preserver? EVERYTHING that is touching, or close to, the ground.

cracking advice and i think thats the way ill go. ill remember to use the timber preserver sparingly thanks again,