Roman cement - experience?

I have a neighbour who has some pouzzolane granules and sand for sale.
I’m thinking of using it to make a 7cm slap to insulate (acoustic & thermal).

My main question is, has anyone used a recipe NHCL5 & pouzzolane & Salt water?

Any tips greatfully received. Thanks

Are you intending to use NHL5 because it will be exposed to salt water? Pouzolane is often volcanic dust, if you are looking for an insulated mix might be better with vermiculite. I would probably put down a rigid sheet insulation and then screed on top but I may not have understood your project?

I am thinking of using salt, due to recent articles which give me the impression that:

  • in a humid environment, cement acts like a sponge and does all sorts of nasty stuff, whereas roman cement, which uses volcanic sand, NHCL5, and sea water creates a particular chemical reaction which makes it really ‘humid environment friendly’.
  • pouzzolane is apparently a very good thermal and phonic insulator (perhaps not as good as vermiculite, but a good bang/buck compromise)

I am paying 90€ the m3 for pouzzolane.

In the context of pouzzolane, I have heard good reports, but I have heard nothing about people using salt water mix (which was only reported by scientists in 2017).

I had to chuckle on reading this thread…

When I first saw the Title… my brain went into overdrive…with the following result…

Roman roads seem to last a lot longer than modern ones… so, although I have no experience of Roman cement, IMO there is every chance it is better than the modern-day stuff… :rofl::joy:

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You are quite right Stella, apparently, archiologists have beev scratching their heads for centuries, wondering why Roman seawalls had lasted 2000 years.

It seems the answer was discovered in 2017 - sea water and volcanic ash/sand together with lime creates a certain (very rare in nature) chemical reaction which builds a crystalline structure, reinforcing the bonds between the materials.

Richard, being the smartarse he aspires to being, thought ‘wouldn’t that be cool for my bathroom floor’.

The pouzzolane should arrive this morning.

If you hang about for a couple of thousand years, I’ll let you know if I stumbled on the right recipe :wink:


The use of NHL5 on sea defenses has been quite common for hundreds of years as cement is attacked by salt water. I can’t see any benefit from the pozzulans in either insulation, thermal or sound wise. Yes you can get sodium silicate formation which can also be helpful in a densifier for finishing concrete worktops.
I think I would still use an insulating layer as it’s a bathroom.

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I’ve got chunks of real Roman concrete ??? A kind of well construction, this being a historic corner on an elbow bend of small ferocious river, in winter.
I adore all that stuff and dearly wish to discover the truth about what the Romans were up to, and why. Their closest road …only five minutes away. Still dreaming of mini musée with arts éspace, here… there are photos of Roman concrete on the internet…they had to do lots of layers…one on top of another… not massive solid walls full of it…I can show you my photos, although I think you are not talking about the same thing at all…:smiley:

OK will do - thanks