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New garden shed on existing larger slab?

New Contributor

New garden shed on existing larger slab?

G’day all,

Read a few of the questions on here about ‘Weatherproofing existing shed’ and ‘How to waterproof existing garden shed?’ etc.


I’ve got an existing slab off my driveway.

I’d like to bolt a small garden shed directly on to (3m x 2m x 2m).

The slab it stills on will be bigger that that so water will likely sit (there is a little bit of a slope)

I had planned to pressure clean the concrete and then bolt the shed straight to the slab and just put some pavers in there to keep the contents off the ground. Lawnmower etc so nothing too precious.  


Should I apply the bitumen backed flashing tape directly to the bottom of the shed and then bolt it on? Or foam tape etc.


Any advice would be appreciated



Bunnings Team Member
Bunnings Team Member

Re: New garden shed on existing larger slab?

Hello @rpreston


Welcome to the Bunnings Workshop community. It's wonderful to have you join us, and thank you for sharing your question about your shed.


Using bitumen backed tape is a good idea. However, it does present a problem when the tape forms a valley depression where water can sit in. It will accelerate rust formation on your shed. I suggest instead using Selleys 310g Roof And Gutter Silicone Sealant - Translucent, once the shed has been bolted down on the cement base. I recommend putting the seal both outside and inside. Selleys Roof and Gutter Silicone are suitable for use on Colorbond and other BlueScope Steel decorative sheet metals, galvanised metals, rigid PVC, rubber, glass, terracotta, concrete and glazed tiles.


My number one recommendation is to double-check the assembly of the roof. This is to make sure that there will be no leaks inside the shed.


If you have any other questions regarding your shed, please don't hesitate to post them.


Let me tag our experienced members @TedBear and @tom_builds for their recommendations.


If you need further assistance, please let us know.




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Experienced Contributor

Re: New garden shed on existing larger slab?

Hey @rpreston

A garden shed will make good use of that slab. Bitumen flashing tape is more often used in roofing applications, as @EricL said I would instead aim to seal along the base of the shed with a silicone sealant. 


Provided that water rubs off the slab and doesn't pool in any great depth, a good application of silicone will keep the floor of the shed dry (as long as the roof is watertight) and you won't have to put down pavers to keep everything up off of the concrete.


Keep us updated with your progress, and best of luck!


Re: New garden shed on existing larger slab?

Cheers Tom. Much appreciated mate.

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