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Old 10-10-2009, 01:10 PM   #1
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Help with 1920's foundation


I have a 1920's built house in Toronto. I'm having a problem with the foundation deteriorating above ground and am trying to figure out how to repair it. The foundation is a poured concrete which I suspect has a large quantity of lime in it and it comes about 2 feet above ground before bricks are laid on top.

I don't have moisture problems in the basement and the house sits in a soil that is primarily sand. Where I do have problems is on the exterior walls where relatively poor drainage has led to water damage to the concrete. It has repaired some time in the past with a portland cement parging, but this is mostly separating from the wall and at the worst spots there is a gravelly sandly layer between the parging and the original concrete (the gravel is mostly rounded river stone and is mixed with large stones 6-8 in in diameter). In the bad places it is obviously easy to remove the portland cement as it is cracking and a heap of sand ends on the ground as I remove it. The deteriorated region goes in about an inch or so, so I don't think it is a structural problem. Aside from a little surface spalling inside primarily on the original parging layer at grade, the interior basement walls (even where it meets grade) is quite sound and strong (I can't remove much or any material with a screwdriver). I haven't found any cracks anywhere.

I want to parge over the exterior damage for protection but don't know what sort of cement I should use. I am considering using type N mortar cement available at Rona and mixing this with concrete sand. I was advised to use bonding agent topping concoctions like Versafix, but I have serious doubt that this will not just adhere to a layer that will separate.

I can see that the portland cement traps moisture which is bad, but at the same time I am trying to prevent moistrure from getting in. So it seems to me a balance of 50/50 portland and lime would be a good tradeoff. I would then paint over with a white concrete paint. I'm doing what I can to help with the drainage issues to halp prevent future problems as well (there is an asphalt dirveway so i don't know if I have to consider repaving that.

Does this seem like a good approach? Most of what I find on the internet revolves around fixing fieldstone mortar jobs from the 1800's and while mine might have been a little old fashioned for the 1920's, it is a poured concrete foundation and I can't find much on old poured foundations.

Any advice or suggestions would be much appreciated.

Peter
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Old 10-10-2009, 04:02 PM   #2
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Help with 1920's foundation


i do not know what the proper answer is to your situation (leave that to the pros)

but i can tell you that HD and RONA sell bagged parging cement which is made exclusively for parging exterior foundations. i have used it. its quite taky and can go on a vertical wall. i put it on 1/4" thick and up to 1/2" thick (or more) in some areas which exceeds recommended use .. but it still worked just fine. no bonding agent required.

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Old 10-10-2009, 04:06 PM   #3
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Help with 1920's foundation


You have a very common construction (I have the same at my house), which consists of a concrete footer and wall, covered with a parging material. From the sounds of it, the concrete part of the foundation is OK, but the parging is falling off the wall (so is mine). As long as the concrete is sound, you do not have a structural problem, as the parging is purely cosmetic.

Personally, I don't like the appearance of the parging, so I am letting mine fall off the wall, at which point I grind it up and use it as soil amendment (it is pretty high in lime). But if you do not like the appearance of the underlying concrete wall, there are many products available to use as parging. I happen to like the Thoro Corporation products, but this is not an endorsement, there are many other companies that make a variety of parging agents. The key to getting any of them to work is

1. You have to clean the underlying concrete very carefully. Follow manufacturer's recommendations for cleaning.

2. You have to apply the parging material strictly in accordance with manufacturer's recommendations, including mixing the material, application tool, temperature requirements, and curing control.
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Old 10-10-2009, 04:32 PM   #4
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Help with 1920's foundation


Thanks for your replies. I'm still concerned about the problem I have being related to the material my foundation was made from and moisture trapping in the exterior of the wall.

The original foundation exterior is quite soft sandy and almost as white as my brick mortar (which is pretty clearly lime based). On the exterior it is crumbly except that it has been parged (looks like multiple times.). I think it may have been parged with a possibly lime based parging (it is more brown than grey) over the whole surface and again with a more modern portland based mortar over the bottom foot which is now cracking and breaking free exposing significant moisture trapping in spots. The older parging is holding better, but it is further from the ground.

My main question is to prevent moisture problems from further damaging the foundation can I use a N type mortar to re-parge the exterior, and will that allow breathablity, or will it cause moisture to get in from the exterior, or the reverse - iit has 50/50 portland and lime - does that allow moisture out? Again, my foundation has not been compromised and still appears to be stable, but I don't want the moisture problems on the outside to get worse. I've pretty much ruled out using ordinary parging cement as that was done before and seems to cause harm. Should I consider removing all the parging, reparge with a lime based (or higher lime like N) mortar, and not paint? Is that the best option?

As for painting it, should I be more worried about sealing moisture in, or not preventing moisture from getting in?

Thanks again,

Peter
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