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Block walls - cracks in mortar joints

pyroman's picture

I recently looked at a home I was considering buying. I stood in the unfinished part of the basement looking at the block work and I could see daylight thru some hairline cracks of the mortar joints. Not big open gaps, but just slivers, maybe 1/32" wide or a hair more or less (no pun intended) some of them running maybe 12 to 20 along a horizontal mortar joint, while others smaller in length. The cracks were horizontal, none vertical and only a few here and there. Foundation seems otherwise solid other than at one point it must've been hit because there is an ever so slight "push in" of part of the wall in which there is also a diagonal ladder step crack spanning several rows, but that was in another part of the foundation.

Are these hairline mortar cracks where I can see daylight of concern I should worry about?

Edited 1/10/2005 1:04 am ET by Pyrotechie

I did measure twice and cut once, and still messed it up.

(post #64097, reply #1 of 16)

" some of them running maybe 12 to 20 along a horizontal mortar joint,"

Really need to see & know is my first take.

Horizontal cracks like that may indicate inward bowing of the wall....go back and take a level, plumb bob, string line and a good eye.  Check it out!   All the walls! Check upstairs for small cracks in the walls that might indicate movement.

I'm assumming the basement has back fill around the perimeter....the force of settling and or freeze thaw cycles  may have broken the block bonds.  It might be a minor problem or it might indicate structural problems with the basement walls.

Find an experienced  competent inspector or block foundation contractor......add another set of eyes and mind to your experience.

I did an inspection for a young couple moving back to our community...they had the check book out, chomping at the bit to have this "sweet, cute little love nest"!

Same problem as you describe, but the sellers had neatly patched and painted the basement walls which had a total 3" bow  in the plumb line at the center of the wall and  a 6"  horizontal string line bow down the 30' front wall.  All four walls were similarly bowed!  Almost all the floor joist had pulled from the main center beam a small amount....some had had truss nailing plates added as a "fix"!

Be cautious....................Iron Helix


.......Iron Helix

(post #64097, reply #2 of 16)

You say you can see daylight.  Does that mean that there is no backfill on the other side of the wall?


(post #64097, reply #3 of 16)

The house sits on a slope of a mtn....approx 50% of the foundation is backfilled. The upslope is backfilled all the way up to within 2 or 3 block rows. On either side where the slope goes down that much is backfilled with part of the foundation block showing due to the slope. This is where daylight was seen.

The walls were painted wi th drylok only where backfilling occurred. THere were brown stains coming thru the drylock. Thisis in TN they have heavy red clay soils there. THere is a stairstep crack in the block work where it appeared to have been hit, the recess is about 3/8" (the inward bow of the crack) .On the inside can't see it much at all due to the dryloking hiding the crack. The inspector says it is evidence the wall is done moving as the paint shows it has not moved. Here is a few pics. DSC1046shows the stair step crack, others just show foundation in general. You may need to magnify the pic to see the crack. It begins on the upper left a few rows down and goes to the right.


Edited 1/10/2005 11:30 am ET by Pyrotechie

I did measure twice and cut once, and still messed it up.

(post #64097, reply #4 of 16)

So, as I understand your description.....the horizontal crack is to the walkout side of the basement......right? Hence the daylight?

What did the inspector say about the horizontal crack?

Does the step crack at the corner appear to have been repaired? And if it was patched,  has it opened up again?

Was the horizontal crack patched? Same follow up.

Are ther any cracks in the upper story walls?

Does the basement floor have any cracks in it?

................Iron Helix


After Thought.........

Are the upper two block courses poured with concrete  & rebar as a "bonding course and lintel over the basement doors/wondows?   If it is then the crack might be a result of the floor and block settling down and away from the bond beam.

This might be even more important if the rear walkout footings were constructed in the same manner as the buried footings instead of as a frost footing.

Edited 1/10/2005 6:01 pm ET by Iron Helix

.......Iron Helix

(post #64097, reply #7 of 16)


Yes the daylight is on the "walkout" side of the basement.  There has been no patching at all of the crack. However, on the inside of the basement I looked at the wall with the step crack and I cannot see the crack unless I get up to it and look for it. The owner drylocked the wall  about 2yrs ago. The drylock has "sealed" the crack making it hard to see with the eye unless on top of it. The blocks are actually broken, the bottom half of the stairstep crack is bowed inside the house about 3/8" the top half is of course shifted about 3/8".

There is no basement floor. This is a 3 level home that is roughly 40 block high. The first level (and consequently the first few block rows) form the crawlspace which is all dirt. The midlevel is 850 sq ft of unfinished area with a wood subfloor and non PT joists. The third level is a log cabin.

I did measure twice and cut once, and still messed it up.

(post #64097, reply #9 of 16)

40 courses high and no steel or filled cells? Run, Forest, RUN!

(post #64097, reply #10 of 16)


I get a bad feeling about this one....

Did the current owner actually build it  or contract it?  Some construction details need to be clarified/confirmed.  Contact the participating contractors.

The sheared/cracked block step crack at the corner is of concern...although it may not have moved since it was drylok'ed supposedly two years ago.  Why did it shear?

Horizontal crack reasons need to be found.

Did you crawl the crawlspace and look at the footings and floor construction?

Is the construction 12" block in the bottom 2/3 rds and 8" in the upper floor?

How is the building insulated where the block walls are?

The 40 courses without poured cement/rebar/bond courses and  on a hillside of clay in a wet climate.......Wicklund is right...Run!

If you are in love with the place and can't pass it the services of a structural engineer to sleuth out this enigma.   Too much I can't see from here.

May set you back a few hundred $$$, but that is better than buying a perpetual problem that you may not be able to sell without a loss.

....................Iron Helix


Went back to your posting about LOG homes and your questions....realizing now that those photos belong ontop of the photos of this basement.

I hope the price is "Dirt Cheap" cause you are going to spend a lot of time and money on this piece of property!

If the owners criteria for construction of the non-PT porch extends to the rest of the house's construction.... be forewarned, cause "Dirt Cheap" is how it was also built!

Edited 1/11/2005 6:54 am ET by Iron Helix

.......Iron Helix

(post #64097, reply #11 of 16)


Yeah my log home posts are related to this post. I did rescind my offer to buy the home. I offered $147K for it. It may be there is concrete/rebar in the block cells on the upslope side of the foundation and none elsewhere since there is no "ground push" on those other sections. I dunno, can't verify it and I didn't have a hammer drill to drill into the block to see. Owner said there was crete/bar in them, but, when I can see daylight thru blocks, I dunno, I have to wonder.

This was built by a father/son, not contracted. Not sure about the foundatin, though. The inspector said the wall looked like a piece of machinery hit it knocking it in to make the stairstep crack and only hit  it just enough to make the block offset (misalign) with the upper block by 3/8".

I could not check the crawlspace. This is about a 40 block high home. In the TN smokies when you build that's pretty much what you get, a steep sloped lot that you have to build high foundations on to get the views vacationers want. The crawlspace was inaccessible. As a result of the foundation being so many block high it afforded the owner to have a mid level, a "basement" level that is unfinished and consequently inaccessible but I was able to get in that area at least. The inspector remarked that the joists were not PT that carried the floor in the unfinished area and the crawlspace was not ventilated. Can anyone spell ROT.

In TN it doesn't get cold enough either that they insulate the blockwork. It's pure blockwork, backfilled, sealed, and house on top.

I did measure twice and cut once, and still messed it up.

(post #64097, reply #12 of 16) glad you could back out!!!!   I could see the $$$$$$ flying off into the wind.... never to be seen again!  Great tax deduction!  Gotta have a profit first!

'What a crazy story! 

....................Iron Helix


.......Iron Helix

(post #64097, reply #14 of 16)

Iron, yes as explained earlier I had a contingencyon the inspection and an out and I exercised it.

Last night the seller contacted my agent and said that they are willing to repair all areas of objection I have in order to keep the sale. The main area of objectoin is the decking that is all rotted and is non PT wood. There are two broken windows presumably due to log shrinkage...

I dunno.

I did measure twice and cut once, and still messed it up.

(post #64097, reply #15 of 16)

An above grade block wall is not terribly difficult to repair, particularly if the footing is still good.  Get an estimate, and negotiate it into the price.

(post #64097, reply #16 of 16)

I would want to know:

A.  The condition of the crawlspace.

B.   The size and specs on the footings as well as their condition.

C. Comfirmation of a frost footing at the exposed downhill sections.  Signed affirmation or denial by the seller.

D. Why there is a horizontal crack in the block wall?

E. Is there concrete and rebar in the block foudations and walls? Signed affirmation or denial by the seller.

I would consider calling in another inspector to do a structural and construction method analysis. 

And still I would be leary of the seller's truthfulness as well as his construction skills and methods.

You are still hot to buy and I would have been history!!!!

Good Luck...................Iron Helix


.......Iron Helix

(post #64097, reply #13 of 16)

Don't buy the house.  Keep looking for something that is not problematic from the get go.  Surely your offer to purchase has a clause that you can back out based on the home inspector's findings.



(post #64097, reply #5 of 16)

I could be wrong but it seems to me that block walls that tall should be be filled with mortar and rebar and you shouldn't be able to see daylight.

Second issue is the wall properly waterproofed on the exterior and if they are why are they using drylock on the interior?







(post #64097, reply #8 of 16)


The owner lied to the home inspector. Said the walls were poured with rebar. But that I can see daylight suggests strongly this is not true at all.

yes the exterior was sealed properly. Dryloking is prob preventative since no foundation seals forever, I dunno.

I did measure twice and cut once, and still messed it up.

(post #64097, reply #6 of 16)

I couldn't see the cracks in the pictures, but here are a few rules of thumb. 

Cracks greater than 1/4" in width or misalignment are cause for concern. .

Horizontal cracks can mean pressure from the backfilled dirt, hydraulic pressure (water), etc pushing against the wall.

Stairstep or ~45* (or >) cracks can indicate uneven pressure on the foundation like perhaps a point load from above, a large tree root pressing up underneath the footer, or even a cracked footer.

Again, small cracks I would not worry about.  I'm not there so I can't really give you much more than that.