How to seal the metal shed to the base

[Croolis]

Hello. Sorry it's another metal shed question. This time it's about sealant or other options. Took this image in the dark, apologies. Ignore the crappy corner trim thing, that's going to be covered over with a corner piece and sealed in place. That bit I'm not worried about.

What you're looking at is a corner of my metal shed that's sat on a frame of 2x4 that is itself covered by some angled white trim. There are bolts inside the shed fastening it to teh wooden frame.

Question is - you see the horizontal silver metal flashing that is coming off the metal wall base plate? I need to seal that against the white plastic trim beneath, as I'm getting water ingress through that bit, unsurprisingly. Lifting the shed in any way will be problematic now, also, the white plastic trim only goes a couple of centimetres further under the metal base plate and then there is exposed wood, so there's no sealing it inside, the wood would be constantly wetted from ingress, which I don't want. Need to seal it outside here.

I have some marine RTV that I use for my boat which is adhesive. But if using that, how to apply? I guess I could just do a big triangular bead that goes ~45 degrees from the white plastic to contact vertical part of the silver metal trim (not worried about how much to use, this tube will go off before I use it all). That way water will never get trapped behind the bead. Like a bathtub.

But I'm also considering tape, but I know nothing about it. Like a roofing tape or something, just lay tape across the seam. Would it be appropriate? I don't mind if it needs to be replaced every year or two, as long as it'll come off, wouldn't be too much effort.

As always, thanks for replies. I've had leaks through the roof screws, but am having success sealing those with roofing and gutter sealant, horrible black tarry stuff that never completely goes off (wear gloves!). Won't be using that down here. Hopefully this final problem is the end of the issues and I can actually start using the thing.

 

[artie]

The only lasting solution afaik is to bring the inside floor up above the level that water may enter.

 

[Croolis]

I'll make it a bit easier - can anyone recommend me a proper outdoor waterproof sealant tape that doesn't cost an absolute fortune for 11 meters? I like the look of 3M Extreme Sealant tape but that is way too pricey. Need something that will do the same job for less money. Some sort of exterior weatherproof ducting tape?

 

[Hypnotic Chimera]

Have you ruled out ingress from the red arrow areas?

 

[Croolis]

Have you ruled out ingress from the red arrow areas?

The ingress can only be from under the silver galvanised steel, between it and the white trim. Below the green wall panel, at the bottom, is an air gap, but behind the green wall panel the same silver galvanised steel piece rises to form a barrier a couple of centimetres high. So any water running down the wall can only go out and not in. So your middle arrow might have ingress there where one metal base plate meets another at the corner (I'll put sealant around that area), around the rest of the shed floor it can only be water coming under the steel.

I mean, the steel is just sat on the white trim and I don't expect it to be watertight. I think I'll use tape, it's just a case of deciding which tape. I see there are bitumen based ones, but my concern is that, if in a year or two the tape fails and I have to replace, which is fine, I might have to get rid of a load of horrible left behind tack after peeling off, which is not fine. Maybe unavoidable when using any tape fit for the purpose, dunno, hence question.

 

[Hypnotic Chimera]

What about something like Everbuild Black Jack or EvoStik Flashband? Looks like a 10m x 100mm roll can be had for around £12. Not sure on what it's made of, though - it might be butile -based which is the horrid black stuff that never goes off you mentioned above?

 

[alex robinson]

Is there a reason you don't want to go for the big thick bead of silicone option? That sounds the simplest option.

 

[Croolis]

Is there a reason you don't want to go for the big thick bead of silicone option? That sounds the simplest option.

TBH, I am thinking the tape is going to be easier. I would have to cut it along its length to get it to size. I've bought a roll of the butile type stuff, a B&Q brand, this evening. And that is definitely what it is - a sticky roll of black stuff.

I'm already wishing I'd bought this stuff for the sealing of the leaky screwholes in the roof - cutting out squares of this stuff and just covering the screw heads, in my head anyway, seems easier than the fun times I had on Sunday squirting that black sealant crap from a caulk gun. It's going to rain all day tomorrow, I'll find out if there's still roof leaks then.

I have both the marine RTV sealant then and the tarry tape. I've got until Thurs evening to make a decision which one to use on the shed base.

Votes?

Shed is 3m by 2.5m btw. Very rough calculation says I should probably have enough RTV if I choose that in a single tube. I stand to be corrected on that if anyone knows.

 

[stuart little]

I have a 6 x 3 metal shed which I set on a piece of black tarp. stuff to stop weed growth - I kept the edges inside the shed, then put down a floor, then taped the tarp to the inner walls. It has remained dry for the 16 years it's been there, I use it to store my hard wood with no problems. The front is also protected by a covered 'mower port'. (that's like a car port, but smaller)

 

[Fergie 307]

I'm guessing that the designers envisaged the edge of the galvanized section hanging over the edge of the base. By putting a shelf under it you are inviting water to puddle on top of the white plastic, and then find it's way underneath the wall.
Is there any reason it had to be done that way?

 

[Croolis]

I have a 6 x 3 metal shed which I set on a piece of black tarp. stuff to stop weed growth - I kept the edges inside the shed, then put down a floor, then taped the tarp to the inner walls. It has remained dry for the 16 years it's been there, I use it to store my hard wood with no problems. The front is also protected by a covered 'mower port'. (that's like a car port, but smaller)

Yeah lol, that's an idea. I spose I could do something like that still, it's probably possible to lift the shed up one wall at a time and slip some DPM under there and lift up the inside edges like you did. I have plenty of access to small magnets at work, use them to pin the edge to inside of wall. Going to think that one over.

 

[Croolis]

I'm guessing that the designers envisaged the edge of the galvanized section hanging over the edge of the base. By putting a shelf under it you are inviting water to puddle on top of the white plastic, and then find it's way underneath the wall.
Is there any reason it had to be done that way?

No, the shed designers had the idea that the user is going to put it on a flat surface like a poured concrete base etc. The instructions actually state that whatever it is sitting on should extend, from memory, I think it was 10cm further out than the outer metal base plates. Whatever the reason, it's done now innit?

The shed base design was aimed at raising the roof of the metal shed, 'cos it's for short people (unlike my towering and manly 5'8" stature) . So to raise the roof I decided to make a regular wooden joisted shed floor with OSB floorboards on it, but then adding a small stud wall that added total 240mm height to shed (and put a 240mm step in the doorway as a consequence). I decided to cap off the top of the stud wall with angled plastic trim because I was using feather edge boards below.

So the way it is, is as intended. I did consider making the floor smaller so the galvanised section would overhang as you observe, but when you look at the way those base plate pieces are underneath, there are large empty spaces because the metal folds upwards to create the shelf bit that the metal wall sits on (I can't describe that well without a picture I can't now get). Couldn't tell if shed would have been stable on its mount if all of the base plate wasn't touching down on something. The instructions suggested not, dunno. And I'm too amateur night to guess.

I was always aware that, unless I was very lucky, I was going to get water ingress there and it was going to need sealing. There are many examples of people on t'internet talking about this <shrug>.

 

[Fergie 307]

Ok fair enough. One thing that occurs to me is that if you can lift a wall at a time then could you fit some closed cell double sided foam tape under it, the sort of stuff that is used for sticking trim on cars. It comes in various thicknesses. If the gap is small then it will get squashed between the two surfaces and should form a pretty effective seal. You could actually use anything with a bit of give so it will conform to the gap, strips of smooth rubber matting or an edge trim, there are a huge variety available. Two examples below but there are dozens of different types and sizes. Google car edge trim for example. You can usually buy it by the metre.

 

[Fergie 307]

Out of interest what provision does the manufacturer make for a seal between the building and the base, presumably there must be something?

 

[Croolis]

Out of interest what provision does the manufacturer make for a seal between the building and the base, presumably there must be something?

Nah. It's a 300 quid metal shed. What you see in the first pic is what there is - a horizontal metal flange. There are some pre-drilled holes so you can screw it down so it doesn't blow away .

 

[Croolis]

It's worse than I thought. Got the hose out, sprayed it down from above and had a really good look at what's going on. The weight of the metal shed on the white plastic trim is actually making it bend downward towards the shed wall . As a result, the water is pooling and heading inward nicely, nowhere else for it to go. Bit of a fail in design on my part. Dammit.

Here's a pic of it in profile. As well as coming in at the top of the stud wall, the water must be running back under the trim, and then down the front of teh stud (there's a Tyvek wrap, must be running down behind that) and getting under the stud base plate and coming out onto the OSB. It's not just dripping from the top plate , it's coming in under the stud base plate.

I don't think I can lift the shed to just take the trim off. It's screwed down and some of the screws are under the metal. Or slip anything in. There's no guarantee that the same thing wouldn't happen even if I could - can't be sure the stud top plate isn't angled downward/inward slightly like the trim (shouldn't be, did good repeat cuts on the mitre with a stop block, but some of the lumber was bent and twisted a bit) .

So I need to put something angled at ~45 degrees in (probably more plastic trim arrgh) to carry the water to the edge of the existing trim and over, seal it at the top so no water gets in behind this new trim. I'll put some of that tape down first to cover the seam between the existing trim and the metal plate as previously discussed. I'll add another feather board all around I think as well to give the OSB better protection (the feather boards do extend lower than the OSB now, but I can add another it easy and cheap so why not).

If anyone's got any ideas, I'm all ears. What to use to fill that angle, or any other suggestions. Bit annoyed and tired now lol.

EDIT: the required angle isn't 45 degrees, of course, it's much shallower than that. Top of teh silver only rises about a cm...

 

[Croolis]

I wonder if I could just put two layers of tape down, with another piece of tape trimmed narrower in between them and located against the metal rise, like a sandwich with the filling off to one side. The top layer of tape would then angle downwards.

 

[John Brown]

Excuse me for not taking the time to do a proper drawing, but I'm tired.
You need to lift the shed and have some waterproof membrane where I've marked in red. You have to have overlap by design. Anything else will fail. IMO.

 

[Inspector]

If it isn't too late you might want to find a place that sells products for the camping RV market. They have sealing tapes and rubberized sealing products they use to seal the top of the trailers (caravans) and motor homes. Not cheap but very effective and fairly long lasting. If you ever have to do a prepare you only need to get through to clean sound material and apply the new. They will stick to themselves better than silicone does.

Pete

 

[Fergie 307]

Excuse me for not taking the time to do a proper drawing, but I'm tired.
You need to lift the shed and have some waterproof membrane where I've marked in red. You have to have overlap by design. Anything else will fail. IMO.

Not dissimilar to how I have always done the joint between shed walls and base, although having the wall flush with the base makes life much easier.
The DPC roll you can get for walls is cheap and would be flexible enough.
I think John is right though, you are going to have to lift it to do a proper lasting job, and to correct whatever is causing the plastic trim to bend down.