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Foundation Maintenance Tips

To understand foundation maintenance one must first understand the soils that support them. The Plasticity Index (PI) of soil is a numerical designation applied to all soil types. The PI soil ranges from a low of 15 to a high at 85 nationwide. The PI of soil in the Austin area ranges from a low of 15 to a high of 70. The higher the number, the more active the soil is with seasonal changes to the moisture content of the soil. The moisture content of the soil under and/or around the foundation is a function of regional climate and rainfall. The regional climate alters the moisture content of the soil, which causes volumetrical changes to the soil thus creating shrinking of the soils in dry weather and a swelling of soils during wet weather. It is this shrink-swell cycle that creates havoc in foundations of all types.

In most parts of the country, you consider the foundation one of the maintenance free parts of the house. However, in a large part of Central as well as other areas of Texas , proper care of your foundation requires special effort and may be an important factor in maintaining the value of your property. The homeowner must maintain constant and/or consistent moisture content in the soils around the foundation in order to reduce foundation movement.

As stated above, the problem is our soil. In this part of the country the soil has a large amount of clay content. The characteristics of clay are, it expands when moisture is added and contracts when the moisture is taken away, very much like a natural sponge. The soil has what the Department of Agriculture classifies as a high shrinks well ratio. In their words, "this characteristic alone may be responsible for the failure of sewer and water lines, foundations and walls, power line and pole alignment, and cracks and heaves in pavement".

To understand how a foundation affects the soil beneath it, first picture the area before the construction site was developed. There was a uniform distribution of moisture during the rainy seasons and dry seasons. The construction of a building over a plot of ground protects that inner most area from the elements and actually creates a terrarium affect. It creates and maintains its own moisture and protects the center sub-surface from any weather or atmospheric conditions…Which means the soil in the center part of the foundation will always be in an expanded state…. If the clay soil around the perimeter of the foundation is permitted to dry out, it will contract. The foundation will no longer be evenly supported by the soil it rests on. When this happens, the construction materials will deflect or bend until they reach their maximum bending moment, when that extreme is reached they will crack. The crack will indicate the greatest stress point.

One of the first questions people typically ask "Are there any cracks in the slab"?

The answer to that for almost any slab…is yes. Most slabs come with cracks because as concrete cures, or sets, the surface sets at a faster rate, causing very tiny cracks to form. These tiny curing cracks become a weak point in the slab and it will open wider if other causes of stress are placed on that area; such as movement caused by the variations of moisture content in the clay soil supporting the foundation area; or the consolidation of the base material used in the foundation area site preparation.

Quite often people will mistake superstructure movement caused by poor workmanship, expansion and contraction of building materials due to temperature changes, improper bracing or sizing of framing materials, curing of building materials, etc., as being caused by foundation problems. It is not the same and the urgency of correcting a superstructure condition may be greater than any slab condition, also, the method repair will have nothing to do with the foundation.

Are cracks a major concern?
Cracks are, in most cases, a cosmetic condition that may indicate a sign of movement. These cracks will appear in the most rigid building materials first, such as: the outer foundation wall, masonry veneer, ceramic floor and wall tile and the interior sheet rock surfaces. Other indications of structural movement are doors and windows that do not fit square in their frames, doors creeping, cracked caulking along side of the door or window frames, cracked or wrinkled sheet rock tape, walls out of plumb and floors not level and the framing pulling apart.

Is the slab performing the function for which it was intended?
Let's think of the basic design. Grade beams are placed under the load-bearing walls to support the superstructure. All material placed between the grade beams mainly provide a surface to walk on. That surface is the concrete slab, but for all practical purposes it could be a wood frame flooring system supported by the grade beam or piers…. I cannot think of any situation where a crack in the floor system would render it nonfunctional. The function of the grade beam is to support, or carry the load of the superstructure, transferred to it by the load bearing walls. The movement of the grade beam or footings and piers result in cracks and deformation of the members in the superstructure.

What is the normal procedure for stabilizing foundation movement?
Proper foundation area drainage should be a primary concern and is always a key factor in structural stability. The soil should be graded in such a manner that will provide a gentle slope away from the foundation. The current building standards require grade away from the foundation walls to fall a minimum of six inches (6") within the first ten feet (10'). Steep downward slopes or terracing near the foundation will almost assuredly cause movement as will negative drainage that permits water to pond next to the foundation…. Vegetation (trees and shrubs) growing near the foundation can cause foundation problems. They extract a great amount of water from the soil and send their roots under the foundation for the water reserves created by the slab. Vegetation growth near the foundation may cause uneven moisture distribution resulting in structural movement. Roof guttering and downspout systems installation to facilitate drainage away from foundation walls is also recommended.

If there are signs of movement as mentioned above, it is important to first determine what caused the movement. Next, would be to decide the best way to correct the condition…. In this writing I will only address correcting the movement caused by the moisture variation in the clay soil beneath the foundation. If there are signs that the foundation has already moved it means there may be a great deal of catching up to do. It is important to remember that clay accepts water very slowly, so water will have to be applied very slowly over a long period of time for it to reach the depth where the moisture content is constant the year around. That is a depth of about 15 feet below the surface. Therefore a minimum of 90 days and as much as 180 days may be required to achieve maximum results.

Placing piers under the grade beam is a popular method to stabilize foundation movement promoted by foundation repair companies, it is very expensive and after completed some houses continue to experience movement. The average cost per pier is about $425, but this cost may very from $250 to $750 depending on the number and type appears used…. If done properly, watering around the foundation that has moved due to moisture deficiency in clay soil, will return the soil to its original volume and once again provide a uniform support for the foundation…. Methods for watering, to stabilize the foundation varies from using soaker hose placed on the surface, to automatic subsurface irrigation systems. The cost for putting in a watering system to stabilize a foundation on clay soil will range from the cost of soaker hose to approximately $35 per perimeter foot around the foundation. I have seen slabs on clay soil, in a negative drained yard, in a serious down-warping condition return to near its original form after a watering program was properly implemented. The key to a watering procedure is regularity and uniformity. During dry weather it will require considerable more water around the foundation than normal lawn care demands.

The big question that is always asked: Will this crack or other foundation movement become a problem in the future?
Without extensive soil and structural examination and analysis, only someone with supernatural powers (a clairvoyant) could answer that question. A Real Estate Inspector can look at a building and give an opinion as to the condition at the time of the inspection, but, they cannot honestly state what its condition will be at any point in the future.

In summary...
The Central Texas area has clay soil that shrinks and swells with variations in the moisture content. This phenomenon can cause foundations to move. During damp weather less moisture is needed. During dry weather the foundation needs much more moisture to maintain stability. Where applicable, soaker hoses should be placed at all (4) of the foundation elevations, approximately one to two feet from the edge of foundation. This will allow for an even distribution of water to soak into the soil. Do not place soaker hoses against foundation. If soil has dried and cracked, water may travel along cracks and accumulate at the bottom of the grade beam. If too much water collects under the foundation, the soil may become too wet and lose its load bearing capacity, therefore causing your house to sink into the ground or the soils may swell under moderate amounts of water and cause that area to heave. During dry weather months proper watering will keep the soil from separating and/or pulling back from the foundation. We recommend watering daily during these periods. Remember, the goal of a watering program is to maintain a consistent level of moisture in the soils near and/or under your house. Proper lot grade and/or drainage are also required to ensure that water does not pond or pool near foundation. Together, this should help minimize the risk of foundation movement and/or possible foundation failure.

Remember, when you have a foundation on clay soil…foundation maintenance should be a top priority.

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