Cracking in Stucco
By John R. Schneider
Oct 5, 2002, 00:33

For the past two years Iíve noticed small hairline cracks forming in the exterior stucco and in some of the walls and ceilings of the interior rooms. At first I wasnít concerned, but the cracking seems to be getting worse. Some of the cracks run up the corners of walls and are 1/4 inch wide.  The house is only 5 years old and on a fairly level lot.  How do you tell if the cracks are normal or if they are something to be concerned about? Does this have something to do with the foundation or soil? Someone told me the soil around here has adobe in it.  

B. P., Dublin

Hairline cracking to interior and exterior surfaces of a building is very common, particularly in wood framed construction, and is usually the result of building movement or building settlement.  Buildings have a tendency to move because they are subject to the forces of nature and ground movement, as well as the effects of expansion and contraction of the framing system and finished surfaces.

If you think about it, a house is only as stable as the ground that supports it.  Houses built on adobe soil will experience more movement than most homes because of adobeís great potential for expansion and contraction.  Most of the soil here in the Bay Area has some adobe content, and when this soil moves, vibrates or settles, so does the house that sits on it.  The catalyst for adobeís ability to expand and contract, is moisture.

During the winter months when adobe soil gets wet, it expands.  During the spring and summer as the rains begin to stop and the soil starts to dry out, the adobe actually contracts and shrinks.  This movement of adobe soil is the biggest contributing factor to hairline cracking in the surfaces of a building.

Cracking in stucco and sheet rock most commonly occurs at the outside corners of window and door openings, the inside corners of walls and ceilings and sometimes at joints in the finished surfaces. This is usually where building movement is most evident. Most of the time, minor cracking at these locations is not a structural concern, and is   considered to be cosmetic.  However, large or progressive cracking can be an indication of a structural compromise.

With the winter and spring rains and long dry summers we have had the past two years, the soil has had the opportunity to move more than normal.  This can make hairline cracks become bigger and more noticeable, and can cause doors and windows to shift and bind in their openings.  This may be what you are experiencing with your house.

Normally, it is during the summer months that cracks in stucco and sheetrock become seem to occur.  This is when the soil under the house is the driest, and most compact.  Often these cracks are not new cracks, but existing cracks that have merely opened up and are now move visible to the eye.

So how can you tell if cracking is serious?  A basic rule of thumb suggests that a crack is cosmetic if it is less than 1/8th of an inch wide, and if the edges of the crack still line up with one another.  Take a look at one of the cracks you are concerned about.  If you look at the edges on either side of the crack, and the edges still line up (if you were able to push the crack back together), then the crack is considered minor and cosmetic.

On the other hand, if the crack is more than ľ of an inch wide, and edges of the crack have shifted or moved in relation to each other, the crack is considered to be serious.   It is the shifting or slippage of the opposite edges of the crack that often indicates unusual movement of the components of the house.  This shifting can be an up or down movement of the edges, a shifting that causes one surface to rise above the other, or a tilting of the surfaces so that the crack is wide at the top and tight at the bottom.

Large cracks and cracks that have shifted, indicate that some part of the framing system and /or the foundation, has moved and created enough stress for the surface materials to break apart.   If the foundation on one side of the house has settled more than the other side, cracking will occur. Cracking will also occur when a vertical support post under the house settles or moves.  Large cracks should always be investigated to determine the cause before any repairs are attempted.If the cracking is minor, the crack can be usually be caulked and painted over.

Ideally, the crack would be cut open slightly, to allow the caulking or patching material to fully seal the void between the two edges.  Otherwise, the caulking will only be on the surface of the material, and will separate or break apart whenever the crack moves in the future.

John R. Schneider is a licensed general building contractor and a certified residential code specialist. He is president of All About Homes, a residential inspection company, and has been performing code and construction consultations since 1985.  Readers may address their comments to John Schneider, 24326 Mission Blvd. Suite 7, Hayward, Ca 94544.  Fax number: 510 537-8666, or on the web at   Please include your phone number.  Schneider will answer questions of general interest in the paper. He reserves the right to edit the letter for brevity and clarity. Readers are encouraged to contact a competent contractor or code consultant for specific information regarding questions they may have about their homes.

Copyright 2002, John R. Schneider, all rights reserved

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