Concrete block pitting

Is the cause of the pitting at the walls from excessive moisture/humidity?

Is this a major concern?



My biggest concern is the source of all that water. The sill plate has been getting soaked repeatedly. Did you probe it to see it it was sound?
What is the grading like outside that wall? Failed or unmaintained gutters perhaps?

Adam, A Plus

Ooops, sorry, didn’t answer your question. Doesn’t look like humidity. Looks to be from an outside source. Is this a cape with bad ice damming? Did the walls on the interior / exterior above this area tell you anything?

Adam, A Plus

The house has numerous issues. The gutters are all rusted and need to be replaced.

Drain tiles appeared plugged.

So the pitting is from excessive moisture from exterior?

Grading was tough to tell because of the snow.

I doubt if my client will purchase this house.

Needs a lot of work & money.


Need more information. Any pics of the exterior?

Are the downspouts below grade? Is there a sign of erosion or cracking of the foundation around the downspouts at grade level? Lack of adequate extensions if above grade? Though rusted, are the gutters pitched properly, filled with ice build-up, properly secured to the home? Is there evidence from the exterior of a chronic back up problem in eave area? Loose gutters, peeling paint, deteriorated brick / mortar where gutters meet downspouts and below? You really need to move snow in these areas of the exterior to get these answers. Any more info or pics?

Did the attic inspection of the eaves tell you anything about the history of water/moisture problems? Was the attic inadequately insulated, contributing to a chronic ice-damming situation?

That would be my call with the info at hand, the rusting could be from rebar in the wall

Hey, David!

I spent about 12 years in the masonry trade and a few more in management of masonry companies.

The rust and spalling you see is a past problem with concrete block. There was a period of time when manufacturers were pretty careless about what they threw into the mix for aggregate. (Believe it or not, I’ve actually seen bits of rubber tire inner tube and other rediculous trash hanging from old concrete blocks!) What you are seeing is pieces of iron that have rusted and expanded in the same manner that a steel window lintel can rust and expand and raise the brickwork above a window. Now, like brick, there are pretty strict standards regarding their composition that must be followed and iron cannot be used at all in any form.

Concrete blocks are at best, extremely porous. Water pretty much goes right through them like a sponge. If the wall was constructed without a proper two to three coat parging and tar on the outer surface prior to back-fillilng, you get a leaker.

Our masons used to put one heck of a cove at the base of the wall on the footer with a pretty thick scratch coat. (about an inch thick) After that cured they’d put in another half inch coat. On top of that, tar. Our basements never leaked. There are, of course, new and more ellaborate systems that are very succesful at elliminating moisture intrussion, but this old school way, when actually followed, was very effective. The reason that muti-coats were necessary is because mortar and concrete shrink as they give up their moisture during the curing process and crack. The multi-coats take care of the cracking problem.

You may find this interesting. As is usually the case, old school, architects and construction practices were VERY good. The ideal portland based cement cure is supposed to happen slowly over about 30 days +/-. It is, believe it or not, a chemical process and not an evaporation process. To ensure this slow and proper curing process, contractors used to bury or even submerge footings to guarantee that the process was not rushed and weakened by evaporation!!! The slower the cure, the stronger the concrete or mortar.

If you could perfectly cure concrete, (in an ideal world) the first 90% cure would occur in about 28 days and that last 10% would take another 100 years! In other words, the approximate half-life of perfect concrete is about 100 years.

I have seen hollow core concrete block retain water and it takes an awful long time to eventually drain out. That could also indicate a problem with drainage tiles.

very nice

But the point here is that they aren’t actually “retaining” the water. They are actually only reflecting a water table. I guarantee you that if the moisture in the soil outide the block disappears, so will the water in the block. Block just don’t hold water unless you coat them with a portland based paint like Hydro-halt etc.

How do you know they are not retaining water? One side of the block is painted. The other side is the soil.


I’m not pretending or pressuming to 'know". I can simply assure you this, painted block will only retain water to the degree that the paint was applied and still in tact. In fact, if you merely use a latex paint on a basement wall, portions of the latex paint will eventually baloon out and give way. The paint usually needs to be a portland based paint, that is, cementicious so that it actually bonds with the concrete block and successfully fills in all of the voids in the surface. The strength of a condrete block is varrying sizes of aggregate. That however creates a lot of voids to permit moisture through.

Concrete block are very porous! How do you think the water got in those cores? And why do you think that a good perimeter drain and water management system are so important with a concrete block foundation? :smiley:

Concrete block make a nice foundation, but if everything else isn’t done right, you can end up with a perpetually damp basement.

Now, Ray, I may have mis-understood your question.

If you are indicating that the block are saturated, and that is what you meant by “retaining water” I most definitely agree. Thats what I’ve been trying to say all along. But if you are saying that they are retaining water as in there is water build up in the cores, you usually only see that below grade where saturated soil is on both sides of the block. It’s not very likely that the block will hold water within with only paint as the dam.

I’m certainly not trying to contradict you. Just sharing my masonry and disaster restoration experience with you.

For several years after I left insurance work, the home owners insurance dept used to continue to call me and beg me to do forensics for them regarding moisture intrusion and questionable claims (insurance fraud. Most people don’t realize it and think nothing of trying to take advantage of an insurance company, but insurance fraud is a felony and can cost a home owner a ton or even time in jail.) I usually could figure out and eliminate what no one else seemed to be able to. They’d call me out to a property and share thier problem with me. I’d case the joint. Tell them what the contractor needed to do, in a formal report, and get paid pretty handsomely! It was both challenging and rewarding.

This bring another thought to mind, kinda unrelated, but a lot of people group home owners insurance in the same catagory as car insurance. They think of the whole industry as being out to get you and take advantage of you. But, my experience with home owners insurance companies was pretty encouraging. They do all they can to make sure that you get back all that you lost and as closely to original condition as possible. In the end you almost always end up with better than what you had! And, on large losses, most companies will keep the file open for quite some time so as you continue to remember things that you lost, they can be replaced. If you think about what home owner’s insurance costs and what you get back from it if you ever suffer a large covered loss, it’s one heck of a deal.

I agree the block is not waterproof. But… if you have a paint on oneside and earth on the other, and that earth is already saturated due to rain, blocked weeper, grading, or no weepers, no sump, the water has to go somewhere. If there was no paint on the interior they would have a pool? You could have only a puddle in the bottom of the blocks the water will eventually wick up or evaporate? Maybe not such a good idea to paint the interior wall after all. :frowning: In the photo above based on the photo I would concur that the blocks do not seem to be holding water. I have also found open concrete block foundations for garages to be convienent dumping areas for the weekend mechanic, oil, brake fluid, etc.

Lol, oh I’m sure. Oh there’s always a trade-off to sealing masonry!

Back in the 70’s some one started a camaign to use silicone and seal brick masonry veneer whenever moisture and salts were leeching from them, which proved to be a HUGE mistake. Typically, moisture doesn’t penetrate brick masonry very deeply. It’s too dense a material. If moisture is leeching out, it’s from an internal source via, bad roofing or flashing. Sooooo, these “on paper” brainchilds would seal the masonry. Now silicone actually is permeable, but over time the salts in the materials would eventually block all the pores in the silicone surface making it a completely sealed system. Then the moisture trapped behind the seal would freeze and whole brick faces would pop off not to mention you’s see some wicked stains similar to a fogged thermopane window trapped behind the seal. It was a disaster! they abandoned that practice pretty quickly. We’re always trying to re-invent the wheel. The Egyptians had it right all along.

I think mbryan is correct, I live in the same area as dmacy and recently inspected a home built in 1948 with the same block pitting issues. I tried to take some closeup pictures, hopefully they are clear enough.

In some pics you see the pitting and staining.

Some of the pictures show an expansion of the aggregate that caused the block to pit.

One pic shows were the block was broken, this should give a good cross section look.

I actually have a large chunk of block that broke off. The aggregate appears to have “glass like” pieces, that are shiny and reflect light. Other pieces are very soft and running your finger on it leaves your finger black. I believe the main ingrediant is “slag” or molten steel pieces. If any of you have arc welded, when you chip the crust off with the chipping hammer, this is what it looks like.

I hope the pictures post.

wallpit1 (Small).jpg

wallpit2 (Small).jpg

wallpit3 (Small).jpg

wallpit4 (Small).jpg

wallpit5 (Small).jpg

Yup, glass was one of the things that block manurfacturers had no problem using for aggregate and filler until strict standards were adopted.

Pyrite comes to mind…