remedy for disintigrating mortar
Hi group:
I’m in the middle of several remodel projects of older (late 1800’s construction) masonry buildings with either stone or brick foundations (with mortared joints). Most of them have areas, some larger than others, where the mortar is turning back into its constituent parts (mostly sand). They are not damp (at least not any more), so I don’t have a problem with water leaching out the lime — just seems to be so old that it’s had its day.
I’ve been thinking about different ways to remedy this — so far the best (cost/labor efficency basis) I can come up with is to use a parge coat of fiberglass reinforced mortar (like the “Quickwall” brand for use with dry stacked block) on the interior of the basement walls. The problem with that is I’m not sure I could get it to adhere properly to the existing structure (some of the building basement interiors already have a parge coat of some junk — maybe even gypsum or plaster based, that is very poorly adhered in spots — but bonded just good enough in others to make it a royal pain to get off).
Does anyone have suggestions for getting rid of the old parge coat and for what to do to stabliize the walls that is cost efficient and will last? If a fresh parge coat is the best choice, then I’d also appreciate suggestions for getting it to bond properly.
Thanks for any help.
Replies
"that is cost efficient and will last"
Those 2 terms, IMHO, are mutually exclusive in the scenario you present. The few times I have had to deal with this issue, it was replacement work, it took time, and it cost.
"If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man." - Mark Twain
Was this stuff parged to begin with? If not, better to repoint. Use a soft mortar for those old bricks.
Repointing is the proper way to repair and restrengthen the walls. When repointing a wall with decaying mortar I would make an assumption that the mortar is a soft mix. When these walls where built they usually had a lime that was a lot harder to mix well. Todays lime is made in a way that makes it much easier to mix well in the mortar. The lime is what makes the mortar "sticky" and helps keep the mix together. I would recommend you use a mortar mix that is soft and durable. That is fairly easy to achieve. Mix 6 parts sand, 2 parts masonry lime, and 1 part portland cement. This keeps the mortar flexible and yet strong and durable. Reef out the martar joints an inch or so and replace with the fresh mortar mix. This should take care of your problem.
Curly
Restoring the past for the future.
Curly: You sound like a stone mason! Need some good advice on fixing a stone structure that was built in about 1820. It is a pile of stone about 4 ft tall, used to back up a tombstone. About a foot of stone off the top is missing, courtesy of vandals. The exposed mortar is quite strong, surprisingly. The interior mortar seems to be crummy. It scrapes out w/ little resistance.I have the original stones. They are granite, and randomly shaped.
What mortar mix do I use to reset the missing pieces so it looks like the original - or almost. Noticed that the sand in the original mortar mix is quite coarse, and widely distributed in size of grains. Also it tends to be round, telling me it is creek bed sand. This is a "Historic" marker, but not registered & protected. I am going to recreate the original tombstone - I have a sketch of it to show me layout & spacing of text, and a section of the original stone still exists in a local museum, and gives me the exact shape of every letter except for three. Those I have to fake, but not a problem.
Thanks.
DonThe GlassMasterworks - If it scratches, I etch it!
Don,
I'm not a mason I have just worked with many and had to teach a few as well about old stone work and how to keep the building in good shape, rather than making things worse by using the wrong products.
It sounds like you want to get some creek sand from somewhere nearby and try doing a test batch or two to match up the colors. From your description, I think maybe the face had been repointed in the past. Hence the harder motar on the outside. Use the same mix I mentioned in the earlier post and use white portland cement rather than grey.
Have fun,
CurlyHand Hewn Restorations Inc.
Restoring the past for the future.
Curly: Nope - doesn't look like it was ever repointed. Stones are random shapes & the mortar looked really old, w/ a significant qty of the surface mortar washed away, exposing the sand grains. We were able to get prety coarse sand from HD - it was patio paver block stuff that had a large variation in size w/ lots of big stuff. I suspect that the work we did "restoring" some of the wall may some day look like the old stuff - except that we used gray premix that we added the sand to. I'll do your recipe next time, and use white portland.
We were extremely lucky - where we had to re do the wall around this grave, we found the original stones for the outside of the wall. The inside stones are missing, so we used the best we could find. Looks like the wall had an exterior layer of stone, an interior layer & rubble in the middle. There was some mortar holding the rubble, but not very good stuff. The mortar on the exterior was very strong, and tenacious, holding to the stones quite well.
BTW - this grave site is in Northern VA, near DC. It is the parents of BG Archibald Henderson, longest serving Commandant of the Marine Corps. Old Alexander, the father, is the father of the chain store, having opened two stores in separate towns w/ his name during Revolutionary War times. He & his wife died in 1814 & 1816. Vandals broke the marker in the 1970's. It was marble, about 3 ft wide & 4 ft tall. I will recreate the marker in gray GA granite at the request of the local Sons of the Revolution who are locating as many Revolutionary War Vet's graves as possible. My grandson Cleaned up and did a lot of repair work on the site for an Eagle Scout project. I created two simple stones w/ the names & dates of birth & death in the same font as the original stone. We embedded them in the wall. I am going back to complete the project next spring after the thaw by making a new marker , repairing the cairn it was attached to and replacing it. Hopefully I can build it so it can withstand all but the most determined vandals - meaning those who would bring wrecking bars & hammers.
Thanks for your advice - you have pointed me in the right direction.
DonThe GlassMasterworks - If it scratches, I etch it!
Sounds like you are having fun with this project. Glad to hear the Eagle Scout angle. Remember that grey portland cement really does not belong in any old work. It was not invented till the 1870's as I remember. Too hard and wrong color for historic work.
Good luck and keep up the good work.
CurlyHand Hewn Restorations Inc.
Restoring the past for the future.
Curly: Thanks. You just told me something I didn't know - about gray being invented in the late 1800's. What is the difference between the two? I don't think I have ever seen a bag of white portland. Now that you mention it, the mortar did look quite white - or bleached out. I was passing that off to weathering, since the larger particles of sand were exposed in the old mortar. It also appears that they used a very lean mix - lotsa sand, not much portland. I tried to approximate their mix ratio, but even as lean as we mixed it, it seems they mixed it leaner. I passed that off as the relative cost s between portland & sand back then, concluding that the portland was a fairly expensive item & had to be stretched.
DonThe GlassMasterworks - If it scratches, I etch it!
if it's 1800's your mortar has no portland in it... it's just lime & sand... without see'n it... i'd say
A. there are areas where with an airhose you could blow it out completely
B. some stones/bricks are loose
c. the parge coat was added 50 + years ago (unless it was a finished wall in which case it was also a lime & sand mix)
most of the info above is correct as far as a lime mix being self healing (if it's even 5% portland it's not and won't be)
old brick being not fired as well as brick of today is very soft... with a lime mortar have'n a compression value of around only 250psi (vs 2000 for type N mortar) it allows alot of movement you do not want to stop this movement ie; I'm sure you have no expansion joints... if your mortar is harder than your brick (and it will be if you use a portland mix)... this movement will result in cracked bricks...
all that being said... nothing lasts forever and you can't spend 400k fix'n your problem...
so how i fix this... and i fix it alot... i pressure wash what needs fix'n try'n not to make myself more work than need be... and use'n grout bags and tuck point trowls... i use a pretty wet mix of lime, sand & about 10% portland i add some dish soap to the mix... the lime & dish soap make it easy to squeeze out of the bag... on the really deep joints i'll do it in passes and pack it in... this might not be the 100% best way but it should give you another 100 years...
pony
Don,
White portland gives you the color of the older mortar as well as some strength. The white that I use is called Federal White. I don't know what is available in your area, but if you ask at the masonry supply yard they will probably have a white available.
Sand and lime where the primary and sometimes only ingredients in mortar. The lime is what makes the mortar "sticky". Cement, i.e. portland is used for strength. Used in small quantities you can get a fair bit of strength and yet maintain the flexibility you what with old work. I'll repeat the ratio I use and recomend to all of my clients and subs for mortar; 6-2-1. ^ parts sand, 2 parts lime, 1 part white portland cement. You can change the color with different sand colors, dirt, brick dust, dyes, etc... Stucco or parging repairs are usually done with a 7-2-1 or 7-1-1 mix. The stucco usually needs to be even more flexible. And lastly, white wash should be, 7-1 lime to white portland.
That will be 2 goats and one virgin for this great and useful advice.
CurlyHand Hewn Restorations Inc.
Restoring the past for the future.
Thanks. You want those goats washed or unwashed? Billys or Nannys? Old or young? You gonna supply the rubber boots?
Not as many questions on the virgins.
I just finished reading the note from Ponytail above yours. The way he described what you can do to some old mortar describes the interior stuff holding the rubble in place in the interior of the wall. The stuff exposed to the elements is very hard - you need a chisel to break it up and clean it off the stones. Judging by the joints I had to break, I'd say that the wall has never been repointed. There are no boundaries between exterior surface & the inside surfaces of the exterior stones. No changes in appearance. Looks continuous to me. There are no signs that there was ever a second layer of mortar applied. Stones are very clean. But, given their age, any small qtys of mortar on them would probably have weathered off.
Has the composition of lime changed w/ history? I assume it is still the same old stuff - fired at a high temp to drive off the water, then when you slake it, it returns to its original composition. It essentially gives you a matrix of limestone w/ a bunch of sand suspended in it. I can see how it would deteriorate over time - the limestone is partially soluble in water - just like the KY caves.
DonThe GlassMasterworks - If it scratches, I etch it!
Don, the chemistry is a bit more complicated than your description, but you've got it essentially correct. A key part of the series of chemical reactions involves carbon dioxide (from the air), that's why you can keep wet lime mortar indefinitely if it's kept in an airtight container.
Modern powdered "hydrated lime" is chemically the same as "slaked lime" from the old days. Powdered hydrated lime has just enough water added to keep it stable. Old-time slaked lime was a putty resulting from the chemical reaction resulting from the addition of water to "quick lime" (quick lime being the result of "burning" limestone -- or sometimes seashells in coastal areas).
I find that modern lime -- because of its purity -- is much whiter than old lime. Usually I add yellow ochre pigment to color it slightly.
When matching old mortar, it's important to match the original sand for both color and aggregate size. Also, old mortar often has visible chunks of lime, so I match that aspect also. And, because the old lime has been exposed to 150-plus years of weather, I "instantly weather" new work by misting with a spray of water before the mortar sets too much ... exposing the aggregate. In a day or two, I mist it again with diluted muriatic acid to clean off any lime on the stones, then rinse thoroughly with water.
BTW -- I don't add any portland except at or below grade.
Allen
Edited 11/2/2004 10:03 pm ET by Allen
Yopu say you don't have a problem with lime leaching out, but that is exactly what you describe.
Lime mortar is self healing by virtue of the fact that as water moves through the mortar, the lime continually regeneratees by disolving and re-adhereing, so that a crack will soon fill. Burt over a hundred years or so, the lime will leach away and leave the mortar weak.
You need to re-point these joints
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