Expert: Bruce E. Johnson - 4/12/2009

Question
QUESTION: I'm planning on buying a house and have found that most houses have something wrong with the foundation. So, I've found one that I'm considering buying but there are some items with the foundation that may be major issues - or maybe not.
 It looks like there has been considerable effort to control moisture in the crawl-space - new 6 mil plastic and a sump-pump added just in case.  The lot is sloped slightly away in the back of the house but mostly level in the front of the house.  Gutters in the front of the house have tubes to run the water away toward the sides of the house which slope toward the back also.  There are some mature trees nearby the house.  House was built in 1980.  I've attached one picture of one of the corners, but there are other similar patterns on each corner of the house. (though the other corners are mainly hairline stair-step and much less severe) There does not seem to be any issues at the center of any walls except the section of foundation at the garage which shows a 1/8" to 1/4"(max) sliding/bulging OUTWARD of a couple of the blocks above grade.  I cannot see below grade because the garage foundation was separately outlined/footered within the main foundation outline and then completely filled and capped with a slab. The picture attached is my main concern, I suppose... and it shows a stair-step separation and possible lack of mortar?  Above grade from the outside it looks like a 1/8" crack at grade that stair-steps up to a hairline crack to the top of the wall.  Note broken block section in bottom-left of corner under the plastic - wonder what that is?  Well, I hope that's enough information to give a guess as to whether things could be minor/normal or major!  Thanks for your help!

ANSWER: Hi Richard, most masonry foundations are generally unfinished or poorly pointed (good solid mortar joints) on the interior, especially in production housing.  I'm sure the exterior of your walls are better pointed with nicely struck joints.  What really holds the block together is the fill cells that are filled with concrete and the bond beam which is a hollow block on the top course with a bar of reinforcing steel in it and filled with concrete.  Just looking at your photo: I don't see any signs of mildew or mold around the joints in question.  If a lot of moisture were present there would be mildew or algae growing in all the obvious places.  It looks to me like the underside of this house is in decent condition with a good vapor barrier in place.   What you are looking at in the masonry can be easily pointed up to make it more esthetically pleasing but as long as the block has concrete filled cells and a bond beam I don't see any major structural damage from this photo..I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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QUESTION: Thanks Bruce!  Very educational!  That helps a good deal to understand what's going on in the foundations I'm looking at.  :)
Correct me if I'm wrong, but if I understand you correctly - I think that you are basically saying that a crack here and there is nothing to worry about and maybe I should seal the crack (just in case) to prevent moisture... but by itself this is nothing serious... in fact it's normal...?

Well, that answers that - but if the foundation is locked-in at the top and the bottom, (like it's supposed to be) then that still leaves the middle courses the ability to slide, right? (generally speaking)  

Maybe this foundation isn't properly "locked"?  What do you think of this photo? Looks like the top course and next lower courses have moved out a bit. This section is along the middle on the side of the house. I think it is pretty close to a "corner" of the garage foundation outline because I can't see this from within the crawl space.  What's your take?

Thanks again for your insight!

Answer
Hi again Richard, if you have ever seen a masonry block it has two hollow cells in it.  When the blocks are laid the cells line up to make a vertical tube.  These tubes are called filled cells when they have a piece of rebar coming out of the footing up through them and they are filled with concrete.  This rebar is then tied to a "header" course of block which has the center removed and a horizontal bar of rebar is installed.  Most foundations have a concrete filled vertical cell at least every 4 feet and a continuous header block upon which your house sits.  That is what locks the blocks into position.  I can't tell from your photos whether this foundation has been done properly or not.  I see some areas that need to be repointed with mortar but I don't see any foundation failure going on.  If you have concerns of this nature you may want a structural engineer to physically look at the foundation to make sure all is okay.  The best I can do is tell you how the foundation should have been built.  I am enclosing a quick sketch.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com