How to waterproof garden shed floor?

[xenon]

Hi,

My garden shed is currently sitting on wood base and its getting moist/wet when rain. Can you please suggest how I can make it waterproof ?

Thanks.

[EricL]

Hello @xenon 

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

One way to seal your flooring is by laying down James Hardie 1800 x 1200 x 6mm 2.16m² Ceramic Tile Underlay Flooring under the shed. You then glue the bottom of the shed to the underlay using Sikaflex 11FC.

Because you have a wooden floor, it will absorb moisture when rained on. It will shrink during intense heat and expand when it's cool. This is why it's not practical to seal the bottom of the shed with a sealant. The constant movement of the wooden floor will eventually loosen the sealant and allow water to get in.

In order to seal it properly you need an inorganic liner that does not shrink. However, there is a secondary issue and that is water will now get trapped under the tile underlay and this will accelerate the deterioration of your timber base. At the moment your linoleum and soft foam cover are actually quite practical. 

The moisture trapped under the lino cover passes through the sides and into the open air. It is worse with paint as trapped moisture in the timber will apply static pressure to the underside of the paint forcing it to lift.

Please make sure to wear personal protection such as gloves, goggles and a paint mask,

Here are some fantastic discussions you might find useful.

• How to waterproof existing garden shed? by @basilmabraham 
   
• How to seal the bottom of the shed? by @jjebw 

If you need further assistance, please let us know.

Eric

[xenon]

Thanks for the reply Eric.

What if I pour some concrete/cement on the floor? Will it hold and resolve this issue?

[Ready2go]

Personally, I wouldn't pour wet concrete onto your timber floor. Your timber still gets wet so it will expand and contract as it dries. this will just crack your concrete without giving it any protection.

I like EricL's idea if the shed is easy enough to move..

If the shed is too big or awkward to move, I would be tempted to just place the underlay sheets down inside the shed and perhaps seal them and leave them without fixing them into place permanently. that way, you can lift them easily if the timber does deteriorate and you wont be trapping excess moisture between the layers. it would also elevate your flooring slightly and keep it clearer from the moisture.

like @EricL stated: make sure you use proper PPE when dealing with concrete products, they are worse for you than people think

[EricL]

Hello @xenon 

@Ready2go is absolutely correct, using concrete will settle on the timber surface, but will crack due to the movement of the timber. 

If you decide to use the tile underlay, I suggest having a look at how your shed is anchored to the timber base. Once you've removed the anchors and the shed is light enough to be tilted, you should be able to slide the tile underlay underneath. 
 

If you need further assistance, please let us know.
 

Eric