Cat litter - bear with me here.....

OK, as most of you know I have a shed that is struggling in terms of water-tightness to the point that I am thinking of naming it the Costa Concordia.

This shed, and the heavy duty base it is sat upon is less than 3 years old - that, coupled with the fact that I really can't afford a new shed at the moment has led me to scheming ways to make it watertight.

The base is made up of a 2" x 4" studwork frame, all screwed (no nails) with 18mm OSB on top. The underside of the studwork was wrapped in damp proof course (so no wood in contact with the concrete underneath) and the top also had a run of damp proof course that the OSB was then screwed down on top of - thereafter, the half width of the damp proof that was sticking out (with the other end sandwiched between the frame and the OSB) was then folded over and stapled to the top of the OSB to make sure that no edge of the OSB was left exposed. Then a flat run of damp proof course was stapled down on top of that to bring the course in far enough that there was no exposed OSB outside the shed (the base is wider than the building by about four inches all round, as per the instructions from Yardmaster).

The shed is screwed down tight - tighter than a tight man's tight thing, but water is somehow managing to get in, and looking at the shed yesterday it is at a low level - ie, either between the metal frame of the shed and the damp proof course, OR between layers of the damp proof course.

So, my plan of action is:

- Use weatherproof expanding foam filler around the inside of the shed at the foot of each wall
- Dry the inside of the shed somehow (*)
- When the weather improves, use some self-adhesive flashing tape around the outside of the shed at the bottom of the walls and over the sides of the base to make sure water runs off to the ground.

Now, to the (*) drying the shed somehow. The OSB floor is fairly saturated, and almost certainly will need to have hardboard laid on top to stabilise it for the future - however, it will need to be dry before I can do that. I was wondering if cat litter might be a reasonably low cost solution to start the process off - use it to sprinkle all over the floor to absorb the moisture, renewing it a few times as needed until the better weather arrives.

Once things warm up, I could then either/or:
- Use an electric heater to heat the shed whilst leaving the door open a wee crack to promote air circulation
- Use a portable air-conditioner in dehumidifier mode to suck the moisture out of the air
- If the weather is warm enough, throw open the doors and let Mother Nature do her bit.

Would cat litter work? Or am I being totally nuts?

 

It's an idea, FC. But some cat litter tends to dissolve into a mess or transform into a paste which would be a pain to wipe up or get rid of, if your shed floor is as wet as you say, and the floor would turn clay grey.

 

I wouldn't mind scraping up a paste with a shovel if it came to it - as I say, I really doubt that the floor itself will remain in service as it is; if it drew the water out and allowed me to get it out of there (even as a sort of mud in a bin bag), I would be content. Depending on how the floor dries, I am thinking of either laying sheets of ply over the top, or get some lino (or both).

 

I think that would just be hiding the problem if you just laid ply or line over it. You need to get the floor dry and keep it dry until you can seal it off. I had basically the same problem when the Observatory was erected. Water was seeping in underneath the unsealed base and I couldn't do anything until a dry period where I could dry out the floor and then seal the base.

 

I'm trying to visualise the joint between the DPC and the OSB, is there a lip outside allowing rain to pool and track inside? Could you post some photos of it

 

I get condensation forming on the insides of the roof of my metal shed, it runs down and drips off in some places. I'm certain that's why mine feels damp in there all the time.

I recall others insulating their metal roofs to stop this.

Mine only has a tiny vent, opening the doors helps but at this time of year when it's misty/foggy there is not much else I can do.

 

Wood pellet type? Tell me more....

As for straw, I reckon I would struggle to get enough around here without paying through the nose for it.

Sorry, I didn't make it clear - I would only be putting the ply over it once it was fully dry and sealed; Although it hasn't mis-shapen yet, there is a bit of flex in the OSB due to being soaked, and I have a feeling that it will never be quite right even once it is dried out. Replacing the OSB is a non-starter as the whole shed would have to come down, and if that happens I guarantee I would not be putting the damned thing back up. I am hoping that the ply over the top will stabilise things a bit, but only once everything is sorted.

I will try, but light could be an issue - failing that I will do a wee drawing, bear with me.

There is only small points of contact between the base and the ground (think of it as being up on very short stilts) and there is airflow underneath it. The root cause is without doubt rainwater getting in on the top of the floor - whether that is tracking over the bottom frame of the shed, or under it is the unknown. As above, I will try and get pics.

Definitely not condensation - there is tons of it, and it is worse after rainfall. I had it almost dried out at some stages over the summer, but when it rained it simply re-soaked.

 

OK - it is tipping it down out there, so I can't really get much of an image, but I will try to explain; my drawing skills are nil by the way, so I apologise in advance.

Here is a drawing of the side view, which shows how the ground slopes back (from the front to the back of the shed), so the framework under the floor is levelled by sitting on various blocks at the right levels to support the base and have it flat. The very front edge sits on the ground, but water can pass underneath it and washes out the back (I have tested this extensively)


The floor assembly comprises of a 4 x 2 frame, braced between lengths with the braces being offset to give the most support. Everything is screwed together with long screws, no nails.

The brown line on the image below represents the floor framework. The black is the DPC wrapped around it. The red is the 18mm OSB sheets, screwed down to the frame (with a bit of DPC sandwiched in between, which is then folded over and stapled to the top of the OSB, thereby sealing its edge.

The yellow is the stainless steel frame bottom strip that is screwed down to the floor along its length and then supports all the shed frame from there.



Here is the best photo I could gather given the weather. Ignore the wood going vertically, it is not part of the shed, it is purely a hanging basket holder and comes off with two screws. Initially, I had the front face of the wood also covered with DPC, but ripped it off in a bid to try and find the water's entry point. The corner photographed is the worst corner (the opposing diagonal corner is dry as far as I am aware).



you can just see the silver of the stainless steel bottom frame piece between the green of the shed and the DPC - the 'ledge' that you see protruding out is roughly a similar width round the whole shed.

I wondered back when it first leaked if the water was wicking between the layers of the DPC, so sealed between them with silicone (used it like a sort of glue in between them as much as I could, but couldn't really get much in as everything was tight as a drum.

I am now wondering if the water is wicking between the stainless steel frame and the floor (so under the yellow bit on the second picture), but there seems to be a hell of a lot of water in there for it just wicking in.


Just to give an idea of how it all fits together, the brown on the image above is the floor, the green is the wall, the yellow is the stainless steel frame and the blue shows the directions the screws are put in. Although the sizes are exaggerated above, and the frame is not very large, I doubt very much that the water is getting in between the wall and it.

 

Oh, and a couple of last bits:

I wouldn't ordinarily be tackling anything like this until the summer, but there is stuff in the shed that is at risk of damage and I don't have anywhere else to move it to. Even if I don't effect a cure at the moment, if I can improve things a bit and get us on the road to a cure I will be happy.

I have managed to get an extended loan of a blow heater which I can use to help the drying process; I also have a rechargeable floodlight if I need to do some work in the dark (although that eats in to wine time, and that isn't good )

I think that the job won't be anything like done until the better weather and I can get that self adhesive flashing and lay it over the outside ledge.