NHL5

[michael]

I wonder if you could re-educate me on the properties of NHL5 hydraulic lime. Something in the back of my mind, possibly derived from this site, tells me that they used to use this stuff for marine installations such as harbour walls and the like and that it even sets under water.
The other part of my mind tells me that like all hydraulic limes whilst it does have a chemical set with water it still needs to carbonate with air to gain its strength over time which would seem to throw the underwater application out of the window.
Could somebody please enlighten me?

 

[MdB]

I believe you are correct on all counts.

It will set underwater but it won't carbonate so the strength is only due to the chemical set. It doesn't rule it out for underwater work but it won't be as strong as if it could dry out.

The same thing though applies to be lump of masonry. A meter cubed of rock and lime isn't going to carbonate in the middle for a very very long time.

 

[michael]

Surely the additional carbonated strength was needed on harbour walls in order to contend with the power of the sea or is the chemical set sufficient?
I know natural cements were also used in marine situations but these too whilst fast setting also gain strength with carbonation in air.

 

[Flyfisher]

Just guessing here but isn't the real resistance of a harbour wall mainly a result of the sheer mass of the structure, in which case the mortar only needs sufficient strength to hold things in place?