fieldstone foundation rehab

huangyhg

fieldstone foundation rehab
i have seen this condition before in inspection only projects and when have had to remediate, generally took an approach of installing as much of a new foundation as possible. in this case, it is an historical renovation and the existing foundation must remain. i have a fieldstone foundation which the mortar has essentially turned to dust. i need to develop a spec and repair plan. the stone is in good condition so it is a matter of replacing the mortar. thinking of removing mortar in small sections and grouting solid with some sort of grout/mortar modified to almost be injected into wall to fill all voids. i can think of a host of issues but wanted to see if anyone had any experience with this or product/procedure reccomendations.
the city of colorado springs, colorado, has a standard repair which consists of shotcreting both sides of deteriorating rubble foundation walls. i never was able to detemine if there were any calcs to back the method. i guess you'd have to clad the visable faces of the wall with thin stone to achieve the look of original finish.
perhaps one of the shpo's could provide a cost effective method.
jjeng:
i don't know your loads or existing conditions but my two cents are to be careful about even attempting this repair. if the wall is part of the historic fabric of the building and needs to remain, your primary option is to repoint.  rebuilding is a second less desirable approach.

historic rehab standards generally discourage disturbing anything in the building unless you absolutely have to, but my two cents is that the second option is really the right way to go.

to repoint you must fully expose both faces of the wall (thus disturb a lot of landscaping etc), but you probably will not be able to repoint the full depth of the mortar joints.  if joints on both wall faces are raked and repointed, it may tend to trap some existing deteriorated mortar within the wall, but over time its likely that load the wall is carrying will be transferred over to just the repointed faces. keep in mind that the outer, buried face of old rubble walls are usually a real mess and extremely rough. so the load path down a repointed rubble wall may be well, problematic.  imho repointing is not really a good or permanent repair strategy for this situation. although it is done frequently!!  
consider instead tearing the wall down in sections and rebuilding it using the original stones and an appropriate soft mortar.  you will probably need to temporarily shore and all that but at least in the end the wall repair will be good for another century, yes?
by the way however you proceed do some research on repair mortars- using a conventional portland cement based mix may not be appropriate for your building, either historically or structurally.  nuff said. good luck