Installing concrete lintels into sandstone walls

[geordiesworld]

Hi all. I have pulled out some old rotten wooden lintels above some upstairs windows in preparation for installing some prestressed concrete lintels. These windows are quite small, although others are larger downstairs. I have taken away sandstone lumps and lots of lime mortar and cut the lintels to the correct length to enable them to fit retaining the correct bearing length and Im ready to actually set them in place. My question is what mortar mix should I use to bed these lintels in and build back up above them to the top of the wall at the eves, some 8 inches of sandstone rubble .. the mortar is very fryable and breaks down easily. SHould I use a lime mortar mix similar to that that came out or a more opc mix.
What mix should i use to build back the stone above ?
What mix should i use to form new pads for the ends to bear on ?

Cheers
George

[stoneyboy]

geordiesworld,
Assume you are working internally so appearance (mortar colour) will not be an issue. Use a 9:2:1 building sand:lime:opc mix.
end

[geordiesworld]

Cheers

Yeah thats what I settled on about after using 1 : 1 : 5 to 1 : 0.5 : 4.5 cement lime sand. Seems to set quite quick so Im using bit less lime, dilute it with more sand. I did gather up a bucket of old mortar and pulverized it and filtered out any lumps to end up with a quite fine powder of the old mortar, added water only and it mixed up quite well. Applied it to some other bits and pieces of pointing internally and its set fine. Just not enough of it to do all the work .. !

Thanks for replying.

George