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How to waterproof existing garden shed?

Finding My Feet

How to waterproof existing garden shed?



See attached pictures of the inside of my garden shed. As you can see, two of the bottom edges are wet from water seeping in. There is also some dirt seeping in along with the water. I want to make it waterproof so that stuff stored inside is not damaged.

I do not have access to these two sides as they are very close to the fence. Waterproofing would have to happen from the inside. 


Options considered include 

1. Apply this across the length of the floor on all edges - Grunt 50mm x 10m Flashing Tape - Bunnings Australia

2. Boxing in the edges and pouring concrete all around the inside edge, covering the gap between brick and concrete floor and over the bottom timber also covering up the gaps between the sheet and timber. 

3. Would spray waterproofing, or water proofing paint work?

Also note that there are some gaps between the sheet and the bottom timber, which also I would like to close and seal.


Are there any other options? I want to keep it simple and cost-effective.


Thanks in advanceShed1.jpgShed2.jpgShed3.jpgShed4.jpgShed5.jpg  

Bunnings Team Member
Bunnings Team Member

Re: Existing Garden Shed - Waterproofing

Hello @basilmabraham


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


Looking at your current situation, it appears that water is coming in from the back of the shed. A common cause for the water to pool together is vegetation and soil build-up. I understand that you don't have access to the back of the shed, this will affect the solutions that we can recommend.


Aside from water entering the shed, moisture being trapped inside will also become a problem. Using the Grunt 50mm x 10m Flashing Tape will only address half the problem as you mentioned that there are gaps between the sheets and bottom timber. If water enters through that gap then using the Grunt Flashing Tape will not be effective. In order to seal that area, you will have to tape starting at the wall of the shed and onto the bottom timber. Then tape over the bottom timber to the cement floor. The tape is flexible and can be shaped into the shed walls cavity.


Another option is to increase the cement floor height. By adding more cement to your flooring you'll be able to cover the wall gap with cement. It will prevent water from reaching the shed floor. One more method of increasing the floor height is to build timber flooring to lift the items off the cement floor. You can use plastic footings so that even if it gets wet it will not deteriorate.


Using waterproofing paint like Gripset Betta 1L Waterproofing Membrane Bitumen Rubber could work. However, the entire area has to be painted and the gaps plugged with Gripset Betta 1kg Water Plug then painted over.


If you need further assistance, please let us know.




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Re: Existing Garden Shed - Waterproofing

Hi @EricL,


Thanks for your prompt reply. 


I tried the flashing tape and it was not adhering correctly, even after preparing the surface. So I have now applied the first coat of bitumen rubber after a thorough clean. Have used the bitumen rubber as a gap filler between the timber and the cement floor. Will wait for it to set and then apply another coat.


I plan to use a cement mixture to close all the gaps between the sheet and timber. Once that is cured, will apply two more coats of bitumen rubber all the way from the sheet to the cement floor. Hopefully this will prevent water ingress. 


Will keep you posted on the progress. 


Thanks again,


Re: Existing Garden Shed - Waterproofing

Hi Basil.

"I do not have access to these two sides as they are very close to the fence."


So no room to get a shovel in and remove soil to below the slab level - like a moat channeling the water away?

Does it happen every time it rains? Gutters and down pipes patent?



Re: Existing Garden Shed - Waterproofing

Hi @Noyade 


There is no room between the fence and shed to go in and dig up. I can probably fit a showel in and try digging. The water seepage is not too much and there is no flowing water. It is just damp and remains damp. 


I will wait to see how the current fix goes and then look at options if this fails, hopefully not. Thanks for the input though. 



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