Thread: stone foundations covered in concrete?

Hi there! I've recently got a job surveying homes for replacement costs, and have a lot to learn (makes it interesting!). I'm glad I found this forum!

I've had a few cases of houses built around 1900 that appear to have poured concrete foundations. Since this seems unlikely for the era, I wondered whether it's common to repair/protect stone (or slump block?) foundations by covering them with concrete. Or are they old houses with newer foundations? I've come across a concrete block foundation on an old house, too.

All help for this poor newbie much appreciated!

Kristi

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Kristi,

I work in the Twin Cities also and have done over 4,000 home inspections in the metro area. Most of the foundations you'll see from 1900 to 1910 are going to be stone and mortar. Most of these will have a concrete skim coat on the interior. The interior will typically be smooth concrete but look as if it's covering large stones (which it is).

From 1910 to about 1930 you'll run into actual poured concrete foundations. What you'll see is the lower 4 feet of the wall will be poured concrete and you'll actually see form marks in the concrete. Most of these houses were actually raised up years ago so the upper three feet of foundation wall will be concrete block.

From 1930 on you'll find mostly concrete block foundations.

Starting in the late 1970's homes you might find wood foundations, then in the late '80's they started pouring foundations again. So from the 1970's to new construction your most likely to see poured concrete, block, or wood.

These are not set dates by any means. On some of the older places you'll run into a combination of river stone, sand stone, brick, poured concrete and concrete block. And some of these will have totally new foundations under them.

If you have any questions you can send me a private message.

Stone rubble walls are not concreted over, the parging is a cement based product. It is not typical to see full parging over stone rubble, and if its present it has been done at some point after initial construction.

That is great information! Had to look up "parging"...now I'll have to look out for it, too. The region-specific info is very useful, and directly contradicts what I learned in training (no surprise there! I trust your knowledge more than theirs). What I've been seeing makes much more sense now. And Ken, your offer of help is very generous and just the thing I've been wishing for.

I'd never have guessed they were building wood foundations in the 70s! Where does slump block fit into the timeline?

...Aha, I just found a couple photos of the type of thing that confused me. The first two photos are from the same 1910 house, outside and in. The foundation seemed from the inside to be a strange mixture of stone and a couple kinds of block. You could only see stone in a few places where the exterior covering layer had cracked, or inside where it looked like the foundation bulged inwards (I guess that area was parged? - left side of second photo).

Is the third photo an example of cracked parging? Does it sometimes detach from the underlying layer?

I really can't tell whether someone poured a cap over the top of the foundation in the first photo and parged over the exterior with subsequent settlement/cracking.

However the second photo appears to be a stone rubble tied into a newer concrete block foundation.

And mortar has been lost over the years and someone has used canned foam to fill voids which should have been mortared.

Originally Posted by Raymond Wand

Stone rubble walls are not concreted over, the parging is a cement based product. It is not typical to see full parging over stone rubble, and if its present it has been done at some point after initial construction.

I should have clarified. I was referring to cut limestone foundations. To see a stone rubble wall around here it would have to be pre 1880's.

The photo with the foam shows a layer of concrete (or something like it) about 1" thick, (mostly) covering the limestone foundation. In areas where it isn't damaged it's flat, looking similar to poured concrete. I thought mortar was only between bricks/stones/whatever - no?

Hmmm, maybe part of the foundation is poured concrete, and the layer over the stone is for continuity. It was obviously one of the combo-foundations Ken was talking about, that's just one more facet of it.

I have seen stone and mortar foundations that people have built forms in front of and then poured in a concrete facing/parge coat of sorts in from of the stone.

I'm not all that happy with the practice and do not find them all that stable. When I see them, I'm always wondering what is happening behind them that I can not see.

Be aware that, 1900 homes, you will be seeing dug out basements that have had concrete poured to stabilize the wall to a new footer on the retaining wall section.

The first photo showing rubble stone may have a small red flag. It seems that the lowest piece of wood (skirt board) (which would be covering a wood sill) may allow water to fall on the parged stone.

This could wick back and upwards to rot the sill. Hopefully you probed with an icepick or a hacksaw blade to find decay which may not be observable from the cellar. Decay on the exterior part of a sill can engender a "roll out" of walls.

Awesome inspections provided by a top level member of The American Society of Home Inspectors ASHI

MORE great information! You guys are gems!

Saw another instance of damaged foundation covering today. In the past I have seen them flush with the exterior of the siding, with a gap at the top, and it has occured to me that there was significant potential for moisture infiltration and wicking. Now that Ken describes roll-out of walls and the reason for it, I wonder whether I've seen that, too. I agree with Tom, it seems like a lousy practice.

Unfortunately, in my job we are taught a hands-off approach, so I'm not allowing to probe anything - nor do I have time for it if I want to make any money. We're expected at minimum to be able to measure and sketch the exterior, find dwelling hazards and liabilities, take photos of them, the home, and outbuildings, and describe the construction materials and foundation type(s), all in 15 minutes. Some insurance companies demand more. Home (or "risk") surveying for insurance companies is a far cry from home inspections! But I'm still eager to learn more than I need to do my job...maybe one day I, too, can be an inspector!

Originally Posted by Kristi Silber

MORE great information! You guys are gems!

Saw another instance of damaged foundation covering today. In the past I have seen them flush with the exterior of the siding, with a gap at the top, and it has occured to me that there was significant potential for moisture infiltration and wicking. Now that Ken describes roll-out of walls and the reason for it, I wonder whether I've seen that, too. I agree with Tom, it seems like a lousy practice.

Unfortunately, in my job we are taught a hands-off approach, so I'm not allowing to probe anything - nor do I have time for it if I want to make any money. We're expected at minimum to be able to measure and sketch the exterior, find dwelling hazards and liabilities, take photos of them, the home, and outbuildings, and describe the construction materials and foundation type(s), all in 15 minutes. Some insurance companies demand more. Home (or "risk") surveying for insurance companies is a far cry from home inspections! But I'm still eager to learn more than I need to do my job...maybe one day I, too, can be an inspector!

With the type of insurance related work you are doing I would be very careful when it comes to reporting on the foundation of a home. A poor parge coat on a stone foundation does not mean that it has a problem. You have to explore and investigate and even then it you might not find the cause.

Point well taken. However, my job isn't to investigate and explore - much as I may want to! What I would do is write it up as a "concern" - take a photo and briefly describe what I see. If I notice some chimney flashing that is poorly installed or damaged, that's what I say. It's not part of my job to go up in the attic and look for signs of leaks. I'm not even supposed to tell the homeowner my findings unless there is an imminent threat to his/her safety. I imagine something like damage to the parging or whatever is only significant to an insurance company because it statistically says something about the general upkeep of the "risk" by the insured (unless they have statistics saying that it increases the likelihood of more severe problems). It's all pretty superficial. The construction data I collect goes into a statistical program that estimates replacement cost, calculated right on the website I use to enter it (it's bizarre seeing RC that's 3 times higher than the property last sold for). After going through Mueller's Quality Assurance dept, it goes to the insurance underwriter, and they presumably use another statistical program that also incorporates dwelling hazards and liabilities (including certain breeds of dog and other animals) to determine insurance premiums. Good thing my agent doesn't know about my pet python!