Slab-On-Grade Concrete Foundations

Slab-on-grade foundations are concrete slabs poured directly on the ground with no space between the ground and the concrete. This most often occurs in areas where the ground is not subject to freezing and therefore not likely to heave. There are derivations of this where frost underneath the structure is controlled with foam insulation or hydronic (hot-water) heating systems incorporated into the slab to prevent the ground below from freezing. However, it is usually not typically economically favorable to use the slab-on-grade in very cold climates. There is at type called a Frost protected Slab that is standard in Sweden and is gaining acceptance here.

The advantages of slab-on-grade are that it is a relative inexpensive form of residential foundation, they are very sturdy when properly designed and constructed and helps obstruct termites from entering the house. When properly constructed they offer very few spaces in the foundation itself for termites to intrude into the structure from below. This assumes that all pipe penetrations are properly sealed with stainless steel wool or adequate caulk to prevent their passage. It also reduces the amount of perimeter crack that is vulnerable to infestation making treatment easier in the event that termites do get into the house.

You must plan carefully for utility penetrations through the slab for water, electric, gas, telecommunications and any other utilities. This is often times overlooked, especially because we fail to account for changes in technology.

When planning a slab-on-grade foundation, you must bring a conduit from underneath to an accessible place outside for water. Most plumbers will direct bury the line or embed the copper lines directly in the slab. This is not a good practice because it makes repair costly and difficult if something goes wrong with the water line. If you install a 2' PVC conduit for the water line, a new one can be pulled in later if you need to. This will also prevent the copper or galvanized water line from degrading from contact with bare concrete.

The same procedure needs to be followed for cable and telephone. You can put both services in the same conduit in this case so one 2' conduit should adequately suffice in this case. Electrical services must enter a disconnect on the exterior of the house so it is not typical that you will need to provide a conduit under the slab for this. In all these cases, the conduit should terminate in one central location in the house such as a utility closet or garage.

Structural Characteristics

Slab-on-grade design calls for a slab thickness a minimum of 4" thickening to a minimum of 6" within about 16" of the perimeter for additional reinforcing steel to support exterior wall loads. If there is to be a interior bearing wall, the engineer will also call for this area to be thickened and more reinforcing to compensate for these loads.

Perimeter footers and interior footers or rafts are typically reinforced with steel bars called re bar. This adds tremendous strength to the concrete by compensating for the concretes poor tensile strength. By combining steel with concrete, you combine two incredibly strong materials in a way that compensates for the weak characteristics of each.

You will also see what is called WWF (welded wire fabric) also called as reinforcing in concrete but its true purpose is to distribute temperature changes in the concrete more evenly to prevent cracking, the proper term is controlling cracking. I say prevent cracking, but you will still have cracking in concrete, it is the nature of concrete to crack, so another step taken to minimize the effect of cracking is the process of placing control joints at specified intervals to guide the cracks to the bottom of the crack where they will not be seen and to minimize the travel of any one crack. If you see minor cracks in the bottom of the control joint, do not panic, it is normal. The design and placement is very important to the integrity of the slab. Discuss this in detail with your selected concrete sub to make sure adequate control joints are placed in the slab.

Proper Construction Means Proper Curing

The key to a good slab-on-grade foundation that has been properly designed is to allow time to wet cure the concrete. Concrete is poured as liquid, but begins to harden immediately. It is usually hard enough to walk on in a day. It should not be built on for a minimum for seven days and you must take care that the temperatures are not too cold or too hot when you pour it. The benefits of proper curing are:

Increased strength gain

Increased abrasion resistance on the surface

Less permeable concrete with increased resistance to chloride penetration and freeze/thaw damage

Increased resistance to early cracking--slabs gain strength before drying out and have more resistance to shrinkage forces.

So what is a proper method of curing. Well in warm climates, it entails keeping the concrete damp for a minimum of 7 days. This is accomplished by spraying water on the slab every day (twice a day if needed) spraying the concrete and covering it with plastic sheeting to retain the water within or using some other medium (kept wet) such as sand, straw, or blankets to do this function for at least 7 days, the longer the better. With proper planning this will be possible although if you are working with a builder, he will probably want to start framing as quick as possible after the slab is poured. Do yourself a favor and allow the 7 days for proper curing and make sure that adequate methods are employed to retain moisture in the slab during the process.

The last 2 important considerations are temperature when pouring. Concrete generates tremendous heat during the curing stage. If it is poured at very high temperatures (over 95 'F) you must take special precautions to mitigate the heat, talk with your contractor if you suspect you will have this condition to make sure he is prepared to take the proper steps to protect the concrete. Concomitantly, you should not pour concrete when the temperature is below 20 'F unless you are prepared to maintain heat on the slab until it has fully cured. This will be very expensive to do so it is best to not pour when temperatures are going to be below freezing for extended periods. You can do it , but you must make sure to maintain the internal temperature of the concrete at no less than 55 'F.

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Slab-on-grade concrete foundation

slab on grade foundations are concrete poured directly on the ground with no space between the floor and the concrete. This occurs most frequently in areas where the ground is not freezing, and therefore likely to increase. There are derivations of this, where frost is the structure with foam insulation or hydraulic (water) heating systems integrated into the plate to prevent the land under the control of freezing. Butusually is not usually the most economically advantageous for the slab-on-grade in very cold climates. This is a guy named frost protected slab in Sweden and will accept standard here.

Die Vorteile der Tafel-on-Klasse sind, dass es ein relativ Kostengünstige Form der Wohn-Stiftung ist, sie sind sehr stabil gebaut und wenn sie richtig ausgelegt ist und hilft vom behindern Termiten Betreten des Hauses. If properly designed, offering only a few placesthe foundation of termites, which enter into the structure from below. This requires that all pipe penetrations properly sealed with stainless steel wool or caulk are such as to prevent their path. It also reduces the amount of crack perimeter, the treatment of mild infections makes the case that the termites into the house is vulnerable.

You must plan carefully in order to collect the drops of supplies by the plate for water, electricity, gas, telecommunications and allother utilities. This is often overlooked, especially because it does not take account of changes in technology.

When planning a slab-on-grade foundation, you must obtain a line from the bottom in a public place outside the waters. Most installers bury the direct line of beds or directly into the copper plate. This is not a good practice because it is expensive and difficult to repair when something goes wrong with the water line. If you have a 2 "PVC pipethe water line, a new one may be revoked if you later need. This also prevents the water line from galvanized or copper degrading from contact with the bare concrete.

The same procedure must be followed by cable and telephone. You can both services in the same line, in this case make it a 2 "pipe should be sufficient enough in this case. Electrical services to separate one on the outside of the house, so it is not usual that you must provide aHead under the covers for it. In all these cases, the line should terminate in a central location in the house, like a closet or garage.

Structural features

Invite slab-on-grade design to a depth of at least 4 "thickening to a minimum of 6" under pressure within about 16 "of the perimeter of further reinforcement steel outer wall. If there is a load-bearing interior walls, the engineer will call for this presentationArea to strengthen and thicken to compensate for these burdens.

Perimeter and interior footers footers or rafts are usually reinforced with steel bars called re-bar. This adds enormous strength to the concrete to compensate for the "real" poor tensile strength. By combining steel with concrete, you can combine two incredibly strong materials so that compensates for the characteristic weaknesses of each.

You also get what is called the WWF (welded wireTissue) as reinforcement in concrete, but his real goal is to distribute more evenly the temperature changes in concrete to prevent cracking is called, is the correct term to control cracking. I tell them not to jump, but you still have cracks in the concrete, the kind of broken concrete, so a further step to minimize the effect of cracking, is the process of placing control joints at specific time intervals, the leaks, leadership lesscrack, where you do not see and to minimize the journey of a split. If you see small cracks in the bottom of joint control, not panic, it's normal. The design and layout is very important to discuss the integrity of the plate. About this in detail with particular sub chosen so that proper control joints are located on the plate.

construction is just proper care

The key to a good-on-grade foundation, haswas designed to allow time to wet cure concrete. concrete is poured as a liquid, but begins to harden immediately. Normally it is difficult enough for a walk a day. Should not be created for at least seven days and must be done so that the temperature not too cold or too hot when you pour. The benefits of proper curing are:

Become stronger

Increased resistance to abrasion on the surface

Less permeable concrete withgreater resistance to chloride penetration and freeze / thaw damage

Greater resistance to cracking the top - to gain strength from drying plates and have a greater resistance to forces of contraction.

So what is the right method to heal. Now, running in hot climates, keep the wet concrete for at least 7 days. This is by spraying with water on the plate every day (twice a day made, if necessary) the spraying of concrete and covered with plastic sheeting forretain water into or through another medium (kept moist) like sand, straw or blankets to this feature, at least 7 days, the longer the better. With the proper planning of this will be possible, even if you use a builder, he will probably want to start framing as soon as possible cast for the cover. Do yourself a favor and allow 7 days for proper curing and ensure that appropriate methods are used to retain moisture in the pot during theTrial.

The last 2 important considerations are the temperature during the casting. Cement generates heat during the great care. If you are at very high temperatures (above 95 'F), you must make special arrangements to talk about the heat, it reduces the contractor if you suspect that you ensure this condition is to ensure that he is willing to make the right to adopt to protect the concrete to be paid. At the same time must not be poured concrete when the temperature is lower20 'F, if you are ready, heat will be stored on disk until it is completely healed. Which will be very expensive to do so, shall not be paid at best when temperatures are below freezing over a longer period. You can do it, but be sure to keep the internal temperature of the concrete not less than 55 "F.

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