Cellar floor grouting advice needed please

[Carol]

Can I pick the collective brains again? The last lot of grouting (or is it pointing) done on our cellar floor got very wet with a surprise small flood and now it is dry it has turned completely to powder. The floor is a combination of very old small flags and old stone tiles (which someone thought would look like the flags) and it was partly re-pointed recently in a standard lime mix. It had about a week of drying out before the rains came!

Generally floor is a very dry one, this cellar was used as the town document store during the 39-45 war as it was considered the safest and dryest, but obviously recent weather conditions have been extreme. Should we use a different mix if floor is likely to get the occasional soaking? And if so what ratio of lime/sand etc, please?

 

[DaveBrigg]

Somehow your post seems to have been overlooked. In the absence of any of the experts, I can start you off and hope that someone with more experience will contribute too.
I remember Adam Hart-Davis demonstrating the effect of adding pozzolans to lime mortar when he cast a miniature archway and then immediately dropped it into the sea to harden. There is more detail about recreating lime that will set and be strong in very damp conditions here: on http://www.azom.com/news.asp?newsID=2854

And from buildingconservation.com
" The durability of pozzolanic lime mortars of correct mix design is proven beyond doubt. A pozzolan is defined as a material that is capable of reacting with lime in the presence of water at ordinary temperatures to produce cementitious compounds. The essential difference between these and modern hydraulic hydrates is that the reaction takes place in solution. The pozzolanic reaction products and the compounds produced on ageing will differ and depend on the calcium to silica ratio in solution. Modern hydraulic hydrates derive their hydraulic properties from the subsequent hydration of compounds of principally calcium and silica produced by solid state reaction in the kiln. The chemistry is of the same chemical nature, but it is not the same.

Pozzolans vary in reactivity, and historically include naturally occurring volcanic Italian pozzolana and Santorini earth as well as artificial forms including brick and tile powder. The varieties most used in the UK are the metakaolin Metastar 501, certain brick dusts of known reactivity and Trass from Germany, but other forms include HTI (ceramic ‘high temperature insulation’) and PFA (‘pulverised fuel ash’). The ground slags are not true pozzolans as they may themselves be cementitious; these are classed as latent hydraulic binders. The addition of ten per cent pozzolan improves durability and strength and slightly reduces porosity and permeability. The pozzolan reacts with the lime and does not set in isolation as occurs when hydraulic lime or cement is added. Pozzolans are added to lime putty mortars where there is doubt about durability and the reduced porosity is not disadvantageous.


To quote Vitruvius from De Architectura in the first century BC: ‘If to river or sea sand, potsherds ground and passed through a sieve, in the proportion of one third part, be added, the mortar will be the better for use.’"

 

[Schoolmarm]

Yes but this doesn't necessarily mean stronger or better in future after it has set.

A normal lime plaster was recommended on a site I read to protect peoples walls inside houses if they lived in flood prone areas.
Am unable to find it though. It said things like; lime plaster a meter up, plastic skirtings, plugs and electrics a meter up etc.