Outdoor terrazzo: slip, weather and what actually decides it
This answer is not written yet. It will appear here once someone has put a figure or a procedure behind it. We would rather leave it visible than publish a confident paragraph with nothing under it.
If you are specifying this
We have not published products against this question yet. Send us the process, thickness and quantity and we will quote it against what we can actually form, rather than against a catalogue.
An outdoor terrazzo floor is decided by three questions, and all three have published answers. The finish is the last decision and the only one that is easy to change.
One: what is under it
A cement-bound system is unaffected by ultraviolet light and is heavy — the published assemblies run from 25 to 30 lbs per square foot for a sand-cushion build down to 5 to 7 for a monolithic one. A resin-bound system is 3 to 4 lbs per square foot and takes water and chemicals well, and ⛔ it is the one that is sensitive to ultraviolet light.
So where the base is a real concrete slab and the height is available, the cement system is the durable answer. Where the depth is not available, the resin system is chosen for its weight, and the ultraviolet exposure is dealt with in the specification rather than afterwards.
Two: is it walked on wet
This is the question most often answered without the method attached. Under ANSI A326.3 the threshold for an interior floor expected to be walked on when wet is a dynamic coefficient of friction of 0.42, with 0.50 for a shower area and 0.55 for exterior and greasy surfaces.
⛔ Three things have to travel with that number. It is measured on a mechanical friction tester and not with a pendulum. The standard states that it makes no claim about actual footwear or human walking, so it is a material property and not a prediction about a person in shoes. And it does not set a threshold for shower floors, where the figure is a manufacturer declaration.
Three: how are the joints spaced
A floor that is ground together with its substrate moves with it, and an outdoor base moves more than an indoor one. The finished flatness allowance for a cement-bound floor is 3 mm over a two-metre straightedge, and the movement joints behind the surface are what let the base move without opening a crack through it.
What this page does not tell you
It does not give a slip rating for any floor we supply, because we hold none and the 0.42 above is a material property measured by a named method rather than a result. It does not give a joint spacing for your project, because a spacing is a property of the substrate and the joint rather than of the stone. And it does not give a lead time, because that moves with the batch and the port.
What we do not say here: every figure above is a published standard or a published system weight with the source named, and none of them describes a batch we have made. Where we hold nothing, this page says so rather than estimating.