Sealing a shed on a concrete base

TheBrooder · 4 Nov 2013 at 18:29

Hi

The shed has no floor so sits directly on the concrete base and I've never been able to successfully seal the bottom of my shed, there's always some water that finds it's way underneath. Based on the advice of people working in the DIY stores I've tried an exterior mastic, which seemed to absorb the water and turned to glue, and I've tried an exterior silicone which was better but is still allowing water to get through.

Can anyone suggest another method that doesn't involve dismantling it and adding a wooden floor?

Maccapacca · 4 Nov 2013 at 18:41

Black jack and epdm

Ugly but it'll work

Nightglow · 4 Nov 2013 at 18:42

No idea as to the size of your shed, but you could raise it high enough for it to sit course of bedded engineering brick?

You only need to raise it 100mm so it can sit on some 4x2 while you laid a bedded course of brick.

You need a hard brick, so it's frost resistant, & unaffected by water absorption, then paint with Black jack.

Cosmic182 · 4 Nov 2013 at 18:45

If you can't be bothered doing much (i.e too lazy) or not too worried. Use clear sticks like **** "poo" That will tbh be perfect. pretty much invisible, high strength, waterproof and provides a great seal in dry or wet conditions. Otherwise if you can be bothered, as said raise it up and put a course of blues/engineering brick or similar around.

http://www.screwfix.com/p/evo-stik-...tracking url&gclid=CMuinZXly7oCFZMdtAod3D8A5g

Maccapacca · 4 Nov 2013 at 18:48

Cosmic182 · 4 Nov 2013 at 18:51

That would absolutely ruin your concrete base/shed if ever dismantled. Not to mention looking naff

TheBrooder · 4 Nov 2013 at 19:08

Thanks all!

This is the shed - http://www.auchan.fr/jardin/abris-c...in-28mm-courmayeur/achat4/24624/C369142/Liste

It's just under 10m2 and uses 28mm planks so it's a bit heavy to lift without dismantling. Also, I'm pretty sure engineering bricks will be hard to source here as everything is built in heavy concrete block or stone.

I was looking at sikaflex or tec7 but I've been told it's better to lift the shed and drop it on a thick bead of the stuff to get a proper seal. I just want to find something I can run around the bottom and it's done if possible. The Evo stick stuff looks like it could work.

How is the water getting in do you think, is the water soaking through the porous concrete, because my silicone seal looks pretty good i.e. no gaps. I made sure I ran a wet finger over it to push it into any gaps.

Cosmic182 · 4 Nov 2013 at 19:12

Best bet is to dismantle it and put a course of bricks round and wherever the bearers are, or some treated timber bearers for it to sit on. You can seal and seal, but both are porous materials so enough water and it will penetrate through causing damp eventually if it hasn't sealed properly. A shed that price and that big should have been on a decent base raised anyway.

TheBrooder · 4 Nov 2013 at 19:49

Yeah I thought it may come to that. I may buy the wooden floor that goes with it for around €270 and be done with it. I'm a bit cheesed off as if I'd have bought the floor in the first place I could've gotten away with simply raising it up off the floor without the hassle and expense of doing a 14m2 reinforced concrete base on my own in 35C heat... oh well, live and learn!

BF-Bert · 4 Nov 2013 at 23:13

Does the floor slab extend past the outside of the shed?

TheBrooder · 5 Nov 2013 at 06:38

BF-Bert said:
Does the floor slab extend past the outside of the shed?

Yes

DXP55 · 5 Nov 2013 at 13:37

Could you use a stihl saw and cut all round shed and knock cut bit of concrete off - then take off bottom board all round shed - staple some damp proof membrane all round to overlap concrete then put bottom boards back on. Done membrane bit on few sheds but never cut base off first as we planned it like that.

That looks to good a shed to leave it.

dave

TheBrooder · 5 Nov 2013 at 13:43

Not really, the boards all slot onto each other so I'd either have to dismantle it first or try and somehow lift it and pull the bottom boards off.

I'm resigned to the fact that I'll have to dismantle it, raise it up, buy the floor and put it all back together again :/

Thanks anyway!

bitslice · 5 Nov 2013 at 14:38

Why dismantle it?

Get a car jack inside the shed at one end
On top of that jam a beam of wood between the car jack and apex beam
Jack one end up

Support those two raised corners and repeat for the other end of the shed.

That should give you enough room to get a DPC and 150mm of brick down.

Cosmic182 · 5 Nov 2013 at 14:45

Brooder- The way you just wrote ^ definitely the best way. I know its a pain in the **** but just take your time. Once it's done you won't have a problem again with it can be sure for certain that you will of sorted the problem. If you try jacking it up, you will knock everything out of plumb more than likely (especially the doors) and risk doing worse damage. Up to you though

DXP55 · 6 Nov 2013 at 13:59

If I was to jack up that shed I would cross batten it first to keep it square - easy job really.

dave

snappyfish · 19 Sep 2017 at 02:08

DXP55 said:
If I was to jack up that shed I would cross batten it first to keep it square - easy job really.

dave

Love digging up old threads...

Exactly same problem for me.. Taking it down and building a decent 4x2 base on concrete blocks.. Only way :rolleyes:

TheBrooder · 19 Sep 2017 at 05:59

Well a storm destroyed my shed and the insurance paid us the full amount, so that solved the problem!

Kemik · 19 Sep 2017 at 13:54

TheBrooder said:
Well a storm destroyed my shed and the insurance paid us the full amount, so that solved the problem!

Easiest answer to a OcUK thread ever!

snappyfish · 21 Sep 2017 at 23:04

Kemik said:
Easiest answer to a OcUK thread ever!

Sealing a shed on a concrete base

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