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I have a 30 year old stone 12" high stone wall that needs to be patched up.

There are small voids where stone has fallen out.

My question is what is the ratio of portland cement to sand used to set the new stones in the wall?

Is the ratio different for the mix used for the mortar between the stones on the facade of the wall? Thanks for your help

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Since you asked it's 6 parts sand/1 part cement/1 part hydrated lime; it won't stick without the lime. Unless you absolutely need to use a specific sand you're much better off buying a bag of premixed mortar. You can take a piece of the existing mortar to a masonry yard and get a color matched dye if you need an invisible repair.

A helpful pneumonic device for mortar is "MaSoN wOrK." The capital letters represent the standard mixes in decreasing order of compressive strength.

  • Type M has the most cement and is used almost exclusively below grade.
  • Type S has the highest tensile strength and is used for outdoor load-bearing work such as retaining walls.
  • Type N, the 6:1:1 mix above, is used indoors and out for soft stone and brick work.
  • Type O is limited to non-bearing use indoors.
  • Type K isn't a thing anymore, outside of restorations. As you get to this end of the spectrum there's less cement and more lime so things are a sticky mess.

You'll find bags of Type S and Type N in the home center. You can use the same mixture all over the wall. I'd suggest N based on your description.

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  • Thanks Matthew...as portland cement is 60% calcium oxide (lime) I take it there would be no need to add additional hydrated lime. Also isn't a certain amount of water added to the sand cement mixture ? How much ??
    – provlima
    Nov 20, 2017 at 11:03
  • The lime in Portland cement has been sintered to limestone or clay in a kiln. It will cure into a solid piece, but won't bond to already cured cement without the addition of slaked lime (calcium hydroxide). [ See: quikrete.com/productlines/portlandcement.asp ] As far as adding water goes, slowly until it's the texture of peanut butter a good rule. The exact amount varies with local conditions.
    – Matthew Gauthier
    Nov 20, 2017 at 13:50
  • Where do I purchase a small quantity of hydrated lime and what ratio to the portland cement sand mix?
    – provlima
    Nov 21, 2017 at 21:49

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