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Wet Shed

Bawnmore

Bear with me, as this might seem like a basic question. We have a single block shed here in the house that used to be a cow shed - we didn't build it, we bought the house a few years ago and the shed was already there. Probably built around the same time as the house (70's).

The old corrugated roof was in a state when we bought the house, so we put a new roof on this year (timber + underlay + corrugated) at the beginning of the summer and the roof is bone dry.

With the bad weather recently, the walls on the inside are wet to touch and ground of the shed is wet. Is it fair to say that this is just the way it'll be (water coming through walls/floor) or is there something we could be looking into (maybe rendering the exterior of the shed or similar)?

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Bawnmore

I can see people are screaming out for an update here but it looks like the damp is coming straight up through the ground. There'd be no damp proof membrane in the shed (was a cow shed) which I'm guessing would be the reason.

I've been keeping an eye on it and can see it beginning about a day into heavy persistent rain. It's also only really to the front of the shed where the door is which suggests it's coming from the ground in front of the shed. I'm thinking of the following as remedial work:

Add guttering to front of shed (put it on the long finger after building the roof) - have done this over the Xmas break but problem persists.
Add a french drain to the front of the shed - started digging this today.
Add a liquid epoxy DPM to the shed floor.

So questions:

I'm assuming above seems like a reasonable plan? Have also considered adding a plastic DPM and screeding above, but obviously more costly.
There seems to be a lot of epoxy DPM products out there - any particular product worth looking at?

10-10-20

Thanks for the update! :) I think your message got a bit lost after the big boards.ie move.

What type of block is the shed? What is the intention for use of the shed?

Also I presume there is no DPM in the walls? This would be a significant issue even if the drain, external walls renderered and a gutter added as that moisture is still going to propagate upwards.

Epoxy DPM's - I don't know much about, but I'd wonder if they can be used as a finished surface or whether they would need a further wear-surface on top.

Bawnmore

https://www.boards.ie/discussion/comment/118391316#Comment_118391316

Ah it's as much of a blog as anything at this point 😅

I'm not actually sure what type block the shed is - single skin concrete block I'd imagine. I'd be assuming there's no DPM in the floor or the walls. The walls themselves have only ever really been wet when the floor has been soaking. It's been raining a few days here now (in the West) and the floor is fairly soaked now towards the front of the shed to about half way through.

Intended use of the shed is for storage and as a workshop that'll be used infrequently. Epoxy DPM's seem to be usable as a finished surface but I'd be skeptical they'd be usable with how wet our floor gets. I also know absolutely nothing about anything, so that might be a right or wrong assumption in fairness.

Bawnmore

Here's a few photos of the shed that might help.

corner of hells

I'd try a French Drain first.

My father had a similar issue around a very basic block shed and used a French Drain to resolve it.

Car99

Not a very big floor area, break it out , bit of hard-core and blinding , dpm , fresh concrete mix it yourself for a bit of excercise and save money.

Odelay

I’d do the gutters first.

Furze99

What sort of block walls? 9 inch cavity blocks maybe or hardly single 4 inch blocks?

If there's no render on outside wall, that's what I'd be doing first. Spatter coat and at least two good coats of render with waterproofer in mix. Then paint it with a decent exterior paint. Concrete will absorb a lot of rain esp when wind driven and this soaks down to floor level. People overestimate rising damp. Render first, paint and put up gutters.

Bawnmore

https://www.boards.ie/discussion/comment/118396031#Comment_118396031

Have started a digging for a French drain. No harm having one there regardless of other changes.

https://www.boards.ie/discussion/comment/118396070#Comment_118396070

It's about 28msq so I was hoping to avoid it, but would definitely do if there isn't a much easier job.

https://www.boards.ie/discussion/comment/118396101#Comment_118396101

I did a temporary setup of the gutters during the week. Ugly, but carries all the water away. Doesn't seem to have made much/any difference.

https://www.boards.ie/discussion/comment/118396282#Comment_118396282

I might have been wrong on the rendering. I'm assuming if it doesn't appear like blocks that it's been rendered in some way, is that right? Can you tell from the images above?

looksee

Around the doorway appears to be a 2x4 frame, flush with the wall on the inside but recessed maybe 2" on the outside. However the window appears to be recessed both inside and out with about 2 to 3 inches of wall either side. There is no sign of any block pattern showing through so presumably it must be rendered - render on a 4" block perhaps? Or maybe mass concrete. though there is some evidence of block ends in the window.

I have an old pigsty that is recently re-roofed, with a mix of old stone walls, recent flat laid 4" blocks, and one end built up with mass concrete, presumably filling in a doorway. It has some concrete render, some rotten lime mortar and some bare shuttering marks on various walls on the outside, a concrete floor (which is fine/recent) and something that appears to be a mix of earth and some sort of mortar/concrete in another part. This part is actively wet but I haven't decided what to do about it yet. I am watching this thread with interest.

Furze99

https://www.boards.ie/discussion/comment/118396629#Comment_118396629

Chip away at the outside and see what comes off. If it's been rendered, you should be able to knock a bit off with a suitable chisel and see what's underneath, blocks maybe. As pointed out above some walls like this were often built by raising two temporary sheets of plywood and then pouring concrete in. When set, builder removed the shuttering and carried on up or sideways. Such mass concrete walls can also absorb a lot of water. I built a shed with blocks a while back and hadn't time to render before winter rains. Surprised at the amount of water that came through on wind driven rain, was sweeping it out.

Bawnmore

Had a look just now and it looks to be blocks alright, rendered both inside and outside. See images. Walls don't seem to be letting in water at all. Looks to all be coming up from the ground.

Have included an image of the floor surface too. I'm thinking one of 3 things:

I'm going off the idea a little of a liquid DPM. I don't know much about these, but the floor gets wet enough eventually that it looks like it's been rained on directly. The seems like it might stretch the bounds of a solution like this.
Fill the channel through the middle, put down a sheet of DPM and a new layer (cement/screed?) on top.
Tear it out and build up with DPM from scratch as suggested.

Wildly Boaring

A small thing

Any ventilation?

This type of set up will never be dry anyway.

And yes you'll need to sort the floor.

But looking at the photos looks like rafters are sealed up.

You need plenty air flowing through.

looksee

Its hard to know, but it does seem as though there is not a lot of seal between the bottom of the walls and the floor. However I agree about the damp coming up - I know 'rising damp' isn't as much of a thing as is sometime claimed, but a thin concrete floor on wet earth is likely to seep through. In the end it depends on how much dryness you want. You will never get it 100% dry and snug, but keeping it dry enough for storage should be possible. I am coming round to the idea of (someone 😀) scraping up the top surface of the rough stuff that is down and putting a dpc and a layer of concrete on my own one.

Bawnmore

https://www.boards.ie/discussion/comment/118400018#Comment_118400018

In terms of ventilation at the moment, there are 2 metal wall vents (you can see one in the 1st photo of the last post above), the window is completely open currently, there's about an inch on all sides of the door and there's a big gap between each of the rafters and the wallplate that hasn't been sealed off. So lots of ventilation currently at least as it's a work in progress.

I'm under no illusion it'll ever be fully dry, but I'd definitely prefer if the ground wasn't like being outside at the same time 🙂

10-10-20

I'd go for option 2 for a few reasons:

You can do it in multiple pours.
Other than for the top of the door-frame, you don't really care about a loss of head-space, right? You can adjust that door to suit anyhow.
You can deploy a proper DPM and stop that primary source of moisture.

You should just ensure that the new screed has some expansion capabilities, use some expansion foam strips around the edges. Looking online it also seems that a 50mm screed is possible with traditional sand & cement, but you can get it down to 35mm if you use a specific screed product.

mickdw

It looks like it's had a very skimpy coat of plaster with it not even returned to windows etc

The shed is built off a flat slab it seems.

Water will make it's way in at this joint.

If that was mine, I would dig out around the edge of the floor slab externally, possibly blackjack (bithetene) the side of the slab and about 9 inches up wall and replaster over the work again. This will prevent water seeping in at floor joint.

Keep external ground lower or do french drain as you suggested.

You also likely have a problem with driving rain going under door.

Bawnmore

https://www.boards.ie/discussion/comment/118400100#Comment_118400100

I'm leaning towards option 2 alright. Height isn't a big deal, so I'm not too bothered about adding a little extra to the floor. The same amount could be taken off the bottom of the door no problem.

https://www.boards.ie/discussion/comment/118400129#Comment_118400129

I'm actually not too worried about the floor joints but it might be no harm doing this either in fairness. The side of the shed that gets the most rain is actually bone dry, even at the floor joints. When it's raining heavy, the 1st patches of wet tend to be in and around the groove through the floor rather than from the edges.

The door is just something I threw together from timber lying around to have something there - will replace it with something more sealed at some stage.

Bawnmore

I've been keeping an eye on this and I've noticed 2 things:

Sometimes it might rain heavy for days on end and the shed will stay bone dry.
Other times it'll be misty type rain for a morning and the shed will be wet.

So it might be fair to assume that:

It's not coming up through the ground after heavy rain.
It's probably not coming in through the joint between the brickwork and slab.
It's likely just the moisture from the air on very wet humid days.

It'll never be fully sealed, but I'm going to focus on sealing the main parts (door/window/between joists) since it needs to be done anyway and see where I am then.

Wildly Boaring

I'd say just maintain some ventilation too though.

Create a draft with opening opposite eachother

10-10-20

https://www.boards.ie/discussion/comment/118558514#Comment_118558514

Sounds like dew on the cold concrete surfaces. They are probably already damp with retained water, but the added moisture is then noticeable by the dark marks.

Car99

Cover a few areas of the floor with 2ft squares of polythene , when you notice damp on the floor again lift the squares of plastic and if it's dry underneath you will know if the damp has come from above o

JustJoe7240

Find it very hard to believe that much water is coming up through the floor, I'd imagine the rain Is beating in under the roof with a lack of facia and soffit, Very tidy job on the roof. It's a lovely shed

Bawnmore

https://www.boards.ie/discussion/comment/118562839#Comment_118562839

I'm going to do this alright. Read it recently and that'd give a pretty clear indication its not coming up from the ground.

https://www.boards.ie/discussion/comment/118562862#Comment_118562862

I can see why it might seem like its coming in under but I'd be reasonably confident it's not. It could be lashing rain for days on end and the shed will be bone dry.

Thanks - myself and a buddy spend a few weekends tipping away at it and I'm very happy with how it's come out.