We love them too!! You can definitely install concrete floors on a wooden subfloor or wooden substrate. Concrete floors (or overlays) are of similar thickness and weight to tile, so you should be fine structurally to install concrete on any surface (provided your floor is adequately prepared and you hire an experienced concrete artisan).

There have been lots of recent product developments that challenge traditional thinking of what 'concrete' is. With traditional concrete, you would definitely need to reinforce and check the structure before any application or overlay is applied. If the concrete contractors use the latest high performance products, the concrete floor or overlay could actually be lighter than tile and usually only 3/8" thick.

Depending on the flex in your wooden subfloor, hairline cracks are natural and expected to appear on the surface. This comes from the concrete slab being a single, solid piece of rock and the wood underneath is flexible and changes and shifts consistently. When the foundation of the house shifts, the concrete is subjected to various flex points and pressures which take the form of tiny hairline fractures in the material. Seams, contraction joints and schluter strip help curb this, but if doing concrete on any flexible surface you can expect movement.

If you need a concrete top coat it generally runs between $12-$18 per sq/ft (plus floor prep on wooden subfloor - usually $1/sq ft), prices are depending on the sealers, waxes and acid stains you want applied. You can maybe find cheaper contractors in your area, just make sure they have plenty of experience and are using the best products, for guaranteed results.

Good luck convincing your architect! If installed correctly, these concrete floors have more longevity and style options than other flooring options.

Thanks so much for this detailed response!

what colour is this please?

This is a standard grey concrete overlay with a black water based stain on top. Make sure you do test areas on the floor to make sure the stain achieves the color you are looking for. Hope this helps!

Thanks I've got 6 sample stains yet to be tested leaning towards ebony or stonebeige maybe both if I can work out how to use both together...

All concrete reacts differently, so test areas will show you how everything will react. Also make sure you apply your sealer/waxes on samples to see how the finished concrete will look. Usually sealers/waxes amp up the color a bit. You can also add layers to water based color, to increase the intensity or add depth. Good luck!