soft sand in mortar?

[robgil]

Its all ive got, can it be used? should i mix it with a bit more lime? or hair perhaps?

 

[MdB]

The smaller the grain size, the more lime is required. I'm not sure why though. For top coat, silver sand / putty in ratio 1:1.5 to 1:2 is used though this ratio may just be to give it a good finish.

I've used builders sand + lime for non structural stuff and it has been fine. I think it shrinks a bit more than graded sand but I'm not sure of this. If you want to use it for structural stuff then I would wait for a better expert then me to come along and comment.

 

[Louis Henry]

I ran out of sharp sand and worried a bit but then had a good look at the original mortar. It used totally rubbish sand from about two fields away. So I stopped worrying and used the soft builders sand which I had around (and it was a nicer colour). It does shrink a bit more and I did put in a bit of extra lime, but really just to reassure myself. I use hair if I'm using it on lath, but if the substrate is not likely to move I don't bother. Builders on a high class job were finickity but on a little cottage like mine they used whatever was to hand.

 

[Gervase]

Get enough of the sand to fill a measuring jug and dry it (pop it in a low oven for half an hour or so). Put the dry sand in the jug and slowly add enough water from another measuring jug to just the level of the sand. That's the ratio of lime to use.
Say you have 600ml of sand in the jug and it takes 200ml of water to bring it level with the top of the sand, then you'll have a 3:1 ratio. If it takes 240ml, then you're looking at 2.5:1; 300ml, then 2:1 and so on.

 

[robgil]

Cheers guys, i use3d the soft sand and added some crushed chalk i had lying around. Gervase ive often heard this method and though i dont doubt it or the 3 to 1 mix ratio in the olden days they would (if i remember correctly) pour a ring of sand then slake the lime in its centre, i dont think they cared too much about ratios.

Here we go,

For general mortars the quicklime was then usually slaked to a crude powder (technically, a dry-hydrate) on site. One of the most popular methods to achieve this was to place a one-third measure of quicklime broken down to the size of nutmegs within a cubic yard of ringed sand, and then apply the minimum of water necessary to slake it, before quickly drawing the sand over it as it both heated and broke down in slaking. After slaking was completed the pile would be turned over dry to fully integrate the sand and lime. One option was then to add extra water to bring it to the working consistency of mortar ready for immediate use.

http://www.buildingconservation.com/articles/mythmix/mythmix.htm