Expert: Dan Griffin - 1/6/2008

Question
QUESTION: Our bedroom wall has a fairly  big crack starting from the edge of roof level running close to half way down the wall.  Initially it seemed just a surface crack but now is right through the wall from outside to inside.  The building is only 2 yrs old.  Could this be serious and how best should we repair it.

ANSWER: I do not expect you to be a building expert, but the question is almost impossible to answer without knowing what material the building is made from.

About the only material that would make sense for the problem you have is cement block. It would be unusual to have the cement block exposed on both side of the wall depending on where you are.  It is not great news, but cracks in CMU walls are not unusual.  The building is not on the verge of falling down.  I suspect it is a stair step crack following the block joints.

If I am correct about the CMU, and if the outside is painted, it would be best to grind/dig/chip the mortar out of the affected joints at least 1/2" deep.  You can then tuck point the joints with mortar or a good urethane caulk.  A nice treatment with the caulk is to rub course sand into the wet caulk to achieve a similar look though not important if you paint.

---------- FOLLOW-UP ----------

QUESTION: Thanks for your response - yes it is a cement block material. do we grind/dig/chip from both sidesof the wall - eg. from the inside of wall and the outside wall as the crack seems to go right through ?


Answer
I guess I should ask how big the crack is.  Are you seeing daylight?

Let's assume they are hairline or under an 1/8".  I would concentrate my efforts on the exterior.  The inside can probably be handled by a careful application of painter's latex caulk and fresh paint.  You don't want to end up with a big smear of caulk on the face of the block that shows through the paint job forever.  This is just as true on the outside.  It is very hard to do a good caulk job on hairline type cracks, so on the outside I think it is just better to remove some material to be able to perform an adequate job of sealing.