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feildstone foundation repair

jimk | Posted in Construction Techniques on August 24, 2009 05:39am

I have a 100 y.o. house with a fieldstone foundation. The mortar on the inside is powdery and deteriorating. What is the best type of mortar to use. Is off the shelf mortar mix ok?

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  1. Hudson Valley Carpenter | Aug 25, 2009 12:28am | #1

    This is meant to bump your questions back up the list so that it'll be seen by others with more experience than I. 

    I assume that by "fieldstone foundation" you're talking about large, relatively flat stones, laid in an interlocking pattern with mortar between them.  Is that correct?  If not, please provide a more accurate description.

    1. jimk | Aug 25, 2009 01:06am | #2

      As far as shape,they are relatively flat on the face, but basically just big, roundish boulders. I've removed a section of mortar about 2-3' wide and about 6' high.It seems that the mortar is only on the inside and outside of the wall,with the middle of the wall with no mortar. It's as if they piled stones on top of each other dry and then went back and sort of "pointed" the inside and the outside. I had expected to find mortar through the whole wall,but so far that doesn't seem to be the case?

      Picture if you had taken a bunch of irregularly shaped,roughly beach ball/basketball sized stones and made a pile say 2 1/2 ft wide and 6 ft high. Because of the way they're shaped, you end up with a lot of large joints and cavities that you can almost snake your arm through from one side to the other. They filled the joints on the inside and outside,but left the middle empty(no mortar).

      I would have thought that you would lay a course of stone,lay mortar on top of that,more stone on top of the mortar,etc, similar to a block wall.

      Is it typical to find a foundation built this way? (keep in mind its 100 yrs old ,a bit north of Boston)

      I ended up getting some type S mortar mix. Will this be ok to use?

      When I start repointing,should I fill in the interior of the foundation, or should I just follow what was done before which was just sort of filling the joints on the face of the foundation.

       

      1. kate | Aug 25, 2009 01:09am | #3

        In New England, it certainly is common to find these old foundations - I have one myself.  I, too, will be interested to hear what the mud experts here have to say.

      2. Hudson Valley Carpenter | Aug 25, 2009 01:29am | #4

        What you're describing is common in older homes with hand dug cellars, in places where the local stone is round. 

         They dug the shape of the cellar to size, then brought the stones in via a ramp and set them against the excavated dirt walls without motar.  Mortar was placed on top of the last course as a "mud sill" to rest the wood sill upon.

        The motar on the inside of the foundation was to seal the cellar from very cold winter weather.  When mortar wasn't available or was too expensive, mud was mixed with straw to do that job. 

        In neither case was the foundation structurally dependent on the mud or mortar as a bonding agent.  

        The only suggestion I have to offer is to prepare the surface of the stone carefully before mixing and applying any motar.  Needs to be real clean to get a good bond.

        BTW, how's the rest of the house?  Has much renovation work been done or are you just getting started?

        The reason I ask is that I once did a renovation of a farm house with the type of foundation you describe, for a NYC businessman who thought he could save some money by "just fixing it up a little".   Homes from that era don't lend themselves to simple renovations.  PS: I imagine that you can now appreciate why you should never dig down near the outside of that foundation. 

        Edited 8/24/2009 6:53 pm by Hudson Valley Carpenter

        1. jimk | Aug 25, 2009 02:35am | #5

          I've done a ton of work to it. Re-roof,gutted to studs,new wiring,plumbing,windows,insulation. I've been noticing sand building up at the base of the wall in the cellar. Recently, I was upstairs and heard a "clunk" in the basement which turned out to be a baseball sized stone that fell out of the wall ,so I figured I'd start chipping away and get it out of the way.My masonary experence prior to this was pouring piers for decks and thats about it,so I'm not completely comfortable with this type of work.

          Seeing the inside of the wall basically hollow was a surprise.I never knew they were laid dry like that.I guess someone had filled in the outside at some point.It's in a lot better shape than the inside is.

          The renovation seems like an endless proposition at this point ,but its to be expected with a house of this age and I enjoy the work.I've gotten a chance to tackle at lot of things which I normally would not get to do so its been a lot of work,but fun.I like learning new stuff.

          As for digging on the outside,I'd heard that before. I figured that as time goes by,the ground lends more support to the foundation,never knew it was like that from day one,that was interesting.   

          1. Hudson Valley Carpenter | Aug 25, 2009 03:55am | #6

            I guess someone had filled in the outside at some point.It's in a lot better shape than the inside is. 

            Any part of the old foundation that was laid above grade would've needed mortar of course, to provide a bond for round stones.  But the dry lay-up below grade was very common. 

            They'd make the excavated dirt walls slightly out of plumb, leaning out at the top, to make it simpler to fix each succeeding course more easily.  

            The house I mentioned was built with the foundation only one half of one stone above grade, to avoid using mortar I suppose.  There was very little mortar in that old farm house so I'm guessing that it was very expensive at the time. 

            The sill was something like a 6X6.  Every bit of framing lumber was a rough sawn "something like". 

            I'm glad that you're deriving satisfaction from the long process.  You must have great patience and persistence.  My hat's off to you for enduring and overcoming.

             

            Edited 8/24/2009 8:58 pm by Hudson Valley Carpenter

          2. Piffin | Aug 26, 2009 02:09pm | #18

            "They'd make the excavated dirt walls slightly out of plumb, leaning out at the top"That is definitely different! Ours can start at 30-36" wide at base and be 18" - 12" wide at the top. Most of the taper is wider on the outside with the interior being close to plumb.Another thing common was that fora six foot under ground foundation, they might only dig down three feet. The excavated soils were then used to berm up around the outside, giving a good grade away from the house in the finished top grade profile. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          3. Hudson Valley Carpenter | Aug 26, 2009 02:54pm | #20

            So it would seem that there were several methods/concepts in use during the BC (before cement...was affordable) period.  That's not surprising when one considers the many unique and ingenious tools which came into being from the minds and needs of farmers and blacksmiths. 

            It is we who have been indoctrinated by our modern, pizz poor public education system who have been lead to believe in following authority figures rather than using our creative abilities to solve problems by taking initiative.  

            I helped build a new home in 1968, the foundation for which was large round rocks laid dry against a mound of dirt.  No machinery was employed.

            Beginning with boulders, each succeeding course of smaller rocks was laid dry against a slightly out of plumb surface, leaning inward to form a kind of pyramid mound.  

            Two of the purposes behind that method were to raise the house so as to offer a better view and to make use of freely available materials. 

             

            Edited 8/26/2009 12:27 pm by Hudson Valley Carpenter

        2. Piffin | Aug 26, 2009 02:04pm | #17

          Practice in your area must have been different from here.I've seen photos of excavations they did by dragging a large scoop behind the team of oxen walking back and forth.And in areas where ledge was closer to surface, they hand dug.but walls were open both sides as they laid up the rubblestone walls. I have dug down the outside of several of them with no trouble whatsoever. Always seeing the sand spilling out of joints.There are others that were done for crawspace and with shallow foundations too, but just digging a trench 18"D x 24"W and rolling large stone in and filling spaces with lime mortar. 

           

          Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

      3. Piffin | Aug 26, 2009 01:52pm | #16

        What you have is a result of the way they did mortar back then.They used lime instead of portland cement.The problem with that in below ground situations is that over time, water moving through the masonry will leach the lime out of the mortar mix, leaving only the sand behind.Your foundation has already been re-pointed at least once, and that is the face mortar you see coming loose. The dust behind it is what is left of the original sand used in the first mix when your foundation was laid up. 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

  2. Henley | Aug 25, 2009 04:08am | #7

    The real question is- Is the foundation moving?

    Was the one stone an anomaly or do you have a real problem?

    The center of old stone walls are often hollow or at least
    not mortared. I wouldn't let that bother you at all.

    Water issues, heaving, large vertical cracks, movement that telegraphs into the house are the culprits to watch for.

    Type "S" is fine for most applications, perhaps not ideal but adequate.

    1. Kivi | Aug 25, 2009 02:31pm | #8

      Are they hollow (or not filled) by design, or has the sand/dirt fill  that was there slowly washed away and accumulated in little piles in the basement that always got swept up and thrown away? I would imagine over 100 years you could get rid of alot of fill this way. 

      If the rock wall was moving wouldnt the mortar that was there be more or less falling apart from the movement? I only ask this because if the wall is stable what would be the downside of him filling the voids as much as possible?

      1. Henley | Aug 25, 2009 03:08pm | #9

        As you build the wall, you toss the scraps in the back.
        often not with much care.

        Just one of the "old timers" ways I guess. I'd probably fill em up, but it's not necessary. It's lasted
        a couple hundred years, right? Yeah, the mortar would telegraph any movement right away.

  3. DavidxDoud | Aug 25, 2009 03:21pm | #10

    I asked a similar question a month ago - http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=122608.1

    here was the only definitive answer -

    "From: Jer Jul-22 5:39 am
    To: DavidxDoud (4 of 11)
    122608.4 in reply to 122608.1
    I like to do my own mix.

    1 type N portland
    1 mason's lime
    3 sand

    I usually give the lime a quarter more to give it the workability, but not too much, it depends on what you're doing. Stone, I would stick to the tried & true recipe"

    I know you want a 'soft' mix - scrub and wash the areas you want to do, and mist the rocks before you slather on the mud -

    "there's enough for everyone"
    1. TooManyToys | Aug 25, 2009 04:25pm | #11

      Ah, but what if the foundation is sandstone, like my family's 1700's farmhouse in South Jersey.Growing up we called it bog iron.

      1. DavidxDoud | Aug 26, 2009 03:30pm | #21

        "...we called it bog iron."please explain - is that because it's particularly hard? - I don't usually think of sandstone as a hard rock (as long as I don't drop a hunk on my toes...)"there's enough for everyone"

        1. TooManyToys | Aug 26, 2009 04:30pm | #22

          Not that hard at all. It's composition is dependent on the native soil in the region. There are a lot of older homes in the South Jersey region that have this as foundations.http://en.wikipedia.org/wiki/Bog_ironhttp://www.packetinsider.com/blog/nature/wp-content/uploads/2009/07/bog-iron-batsto-7-4-09-cfe1-300x225.jpghttp://upload.wikimedia.org/wikipedia/commons/5/54/Limonite_bog_iron_cm02.jpgOur old farmhouse is pretty old and my best estimate is late 1700's. Mostly built from white cedar, the exterior clapboard is held with square cut nails, as is the interior including the stairs. Beams and joists are cedar logs with mostly one side hand hewn, and the peaks in the rafters are held together with dowels, matched with roman numerals.At some point I need to re mortar the stones, but I know it needs to be a soft material.

        2. Piffin | Aug 26, 2009 09:20pm | #23

          SOME SANDSTONE HAS A RUSTY SORT OF COLOUR, SO LOCAL ( dang caps key) collocquialism might be bog iron 

           

          Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

    2. jimk | Aug 25, 2009 04:44pm | #12

      My understanding is the lime is there so the mortar is not harder than the material it is holding together. For instance,brick will expand and contract and too hard of a mortar will interfere with this and the brick will basically break itself apart. A lime mortar will have enough give in it to allow for this movement.With a hard mortar,older softer bricks will fall apart because they are softer than the mortar.

       I would assume that stone would be just as hard or harder than whatever type of mortar that is used.I may be wrong. 

      1. DavidxDoud | Aug 25, 2009 05:15pm | #13

        your rocks may vary...I am working with glacial rubble - there's everything and anything - a few miles from here, the till has been scrubbed down to limestone - limestone comes in several flavors from pretty hard to rotten - I agree with the previous poster who mentioned that the integrity of the wall is not dependent on the mortar - that's certainly the situation in my case - the mortar just keeps the vermin and some of the drafts out - I consider it a maintenance item to be dealt with every generation or two - "there's enough for everyone"

        1. jimk | Aug 25, 2009 05:39pm | #14

          To be honest,I'm no geologist so I really dont know what type of stone they are.They stone themselves aren't falling apart,so I assume they are harder or just as hard as a type s mortar.But the bottom line is I don't really know that for sure.

          It was a surprise to find out that the house is basically sitting on a big pile of rocks and the mortar is more or less an afterthought to deal with rodents and drafts.

          1. Henley | Aug 26, 2009 03:17am | #15

            Type N or Type S is well within the ratios needed. Some instances fall outside of that (Lime stone, sand stone) but
            granites, shale, slates (most common foundation stones) are fine. Mortar recipes are often argued to death. Keep it simple for a
            straightforward answer. Like most things the install is equally as important and is the
            more common problem in the end.

      2. Piffin | Aug 26, 2009 02:13pm | #19

        That is the reason with older brick walls and chimneys. Rock is plenty hard. Lime could be made locally most places, but portland cement was once a very expensive import to haul and pay freight on 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

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