Waterproof concrete

[Squaredy]

5 minutes ago, ucoulddoit said:

Just seen this thread and looking at the dates, might now be too late to comment? Anyway, after a quick scan through, I didn't see any mention that visqeen serves two purposes. In addition to reducing dampness, it provides a slip membrane. Once the initial setting involving heat of hydration (the chemical reactions) has finished, the concrete will gradually cool and hence shrink. If cast directly onto the ground or hardcore, the friction can sometimes resist the shrinking, creating a crack in the middle if the tension in the concrete exceeds it's strength. That's what the mesh or fibres are usually there for, to resist the early thermal cracking tension forces. The slab should be able to easily slide over what it's sitting on. Waterproof concrete will keep the water out, but cracks through the slab won't! Not relevant here, but a basement structure in a high water table would have water pouring through cracks if not properly detailed and designed. Having said all that, long lengths of slab are obviously more prone to early thermal shrinkage cracking and joints if needed (can be saw cut a day or so after casting) are usually 5 to 6m spacing. I guess the garden room is about this size in which case no joints needed if adequately reinforced and with a slip membrane.

 

Andrew

Thank you Andrew I appreciate your input.  It is not too late for my project - I am waiting for my spuds to finish so I haven't started groundwork yet! 

 

I think I will be using a membrane under the slab as well as using waterproof concrete.  I had leftover plastic DPM from another job, or is there some huge advantage of using Visqueen? 

 

And yes I was hoping it would just be of a size that it can be cast as one with no joints. 

[ucoulddoit]

5 minutes ago, Squaredy said:

 

I think I will be using a membrane under the slab as well as using waterproof concrete.  I had leftover plastic DPM from another job, or is there some huge advantage of using Visqueen?

Visqeen is a just a trade name and a DPM plastic sheet should be fine.

 

Andrew

[bankhouse builder]

what floor finish are you having if you are covering the concrete over you could use a tanking slurry we used to do a lot of floating floors on the housing sites before underfloor heating came into vogue that was insulation on top of the slab dpm and weyrock on top you can have carpet or even timber floor finishes.