How to seal the bottom of the shed?

[MattR85]

Hi all,

Just wanting some ideas on how to best waterproof and seal off the bottom of my shed.  There are sides with significantly bigger gaps of which one side I can only seal from the inside, as it's against a retaining wall & fence (not able to access the outside edge)

Appreciate any help on this.

[Vis-á-vis]

You need a floor under the shed with a rebate at the edge for the shed walls to sit in. I don’t think you’ll ever be able to adequately seal that shed on a concrete floor. Sheds either need a slab built to fit with a rebated edge or an internal floor. 

[MattR85]

Well that ain't happening... So anyone else?

[MitchellMc]

Welcome to the Bunnings Workshop community @MattR85. It's great to have you join us, and many thanks for your question about sealing a shed floor.
 

You've chosen a particularly un-even location to place your shed on there. Are there any other options you could consider? At a minimum, you'd need a level surface or a rebated slab, as @Vis-á-vis has mentioned.

You could level the area with cement and then apply a gasket of Sikaflex 11FC directly under where the shed walls will sit on the concrete. While the 11FC is still tacky, the shed would be placed on top and secured to the concrete with Dynabolts. This will pull the shed down into the sealant and give a reasonable seal to the walls. However, the gaps you have currently are well outside the realms of this method.

Have you considered creating a floor within the shed of pavers? That wouldn't stop water from entering the shed but would keep the contents above it.

Please let me know if you have any questions.

 
Mitchell
 

[Vis-á-vis]

Even with a relatively flat surface it is very difficult to seal anything going from one plane 90 degrees to another. That is why houses have flashings and are built above the earth or the have membranes continuing into the earth or terminated on a footing. You can’t really do any of these things in your situation. Only other thing you could do is pour a new slab inside the shed. It doesn’t need to be very thick if you aren’t storing heavy equipment. Even if you could come up 50mm on the inside then you’d have a raised platform that water can’t enter. If your shed is say 3x3m then you’d only need .5m of concrete. That is about 50 bags and mixing two bags at a time in a wheelbarrow could be done in a morning. 

[BoeingFan]

@Vis-á-visAm I reading that right; 50 bags to get half a metre of concrete? I've been considering concreting the bottom of a large shed, which is currently just dirt, and wasn't sure how to work out how much concrete I'd need.

[MitchellMc]

Hi @BoeingFan,

@Vis-á-vis is spot on with their calculations. For a slab 3000 x 3000 x 50mm, that is 0.450 cubic meters or 50 x 20kg bags of concrete. If you need to change the measurements, here's a handy online bag calculator from one of our suppliers.

Mitchell

[BoeingFan]

Thanks @MitchellMc for that calculator, I've bookmarked that now.

Cheers,

Jason

[Ari]

@MattR85 I have a similar shed with a similar gap to uneven pavers.  Instead of sealing to waterproof it, I installed garage shelving and hung loads of S hooks in the gaps between the roof and walls so everything is hung up or on a shelf.  Water enters in a heavy rain but but it's no problem.

I guess it depends on your reasons for wanting to seal it but it could be a simple option.   Cheers.