What are the considerations when building a slab on grade?
Other considerations that play a role in the successful construction of a slab on grade include; proper proportioning of the concrete mix, joint design and performance, and the slab thickness. Floor Classifications Table 1 describes the nine classes of concrete floors according to ACI 302, Guide to Concrete Floor and Slab Construction.
How do you repair soil settlement on a concrete slab?
Instead, soil settlement damage to slab-on-grade foundations is commonly repaired by boring holes through the foundation and installing piers through the foundation. Another potential repair is to pump a “slurry,” a mixture of water and cement, below the slab to lift the slab.
What are the factors that affect the success of a slab?
Other considerations that play a role in the successful construction of a slab on grade include; proper proportioning of the concrete mix, joint design and performance, and the slab thickness. Floor Classifications
What's wrong with slab on grade basements?
In addition to significant cost savings during construction, a slab-on-grade will reduce the risk of problems caused by humidity and water infiltration, which are typical challenges faced by basements. What's wrong with basements? Concrete is very expensive to purchase and extremely energy intensive during manufacturing.
What is a slab settlement?
Why does concrete settle?
What happens when water moves under concrete?
What causes concrete to sink?
Why does clay shrink?
Does Aquaguard do foundation inspections?
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What causes slab settlement?
Slab settlement is simply the movement a concrete slab experiences when the soil underneath it can no longer support the weight of it. Soil changes – that is why your concrete will begin to sink and settle.
How do I prepare for a slab on grade?
2:176:18Pouring a concrete slab: Prepare the Ground & Drainage - YouTubeYouTubeStart of suggested clipEnd of suggested clipThe first thing you want to do is bring in a backhoe or a skip loader and scrape off any organicMoreThe first thing you want to do is bring in a backhoe or a skip loader and scrape off any organic material or topsoil from the area where the slab will be poured topsoil.
How big can a concrete slab be without expansion joints?
Rule #2 – In order to prevent intermediate cracking, space joints (in feet) no more than 2 – 3 times the slab thickness (in inches).
What is the minimum slab thickness for a slab on grade?
4 inchesSlab Design Criteria: Min. slab thickness shall be 4 inches, based on a minimum 3,000 PSF soil bearing pressure, 100 PSF uniform floor design load with 400 psf fixture point loading.
How thick is a slab on grade foundation?
Slab Foundation Thickness Typical Slab On Grade Thickness is 4”-6” thick. The thickness varies depending on the slab's purpose. Patios, decks, and sidewalks are usually 4”. For heavier loads such as driveways, commercial or residential slabs, we usually see the thickness of 5”-6” .
Does slab on grade need rebar?
Concrete slabs poured on the ground with a properly prepared and compacted base, and that isn't expected to support heavy loads, doesn't require rebar. The size and thickness of the pour also determine if steel bar reinforcing should be used. Slabs 5” or greater in thickness and large pads should be reinforced.
What happens if you don't put expansion joints in concrete?
Concrete expansion joints give the slabs just enough room to move which helps prevent cracks & buckling. Without these joints, even a little movement creates pressure and stress on the concrete. Eventually weak spots can crack or buckle.
How do you control joints in a concrete slab?
0:242:10How to make concrete expansion joints - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd then they use long grooving tools to get these wonderful expansion joints nice and flat. AndMoreAnd then they use long grooving tools to get these wonderful expansion joints nice and flat. And straight down the length of the concrete. They do use these tools to get a rough expansion joint.
Does all concrete need expansion joints?
Expansion joints are virtually never needed with interior slabs, because the concrete doesn't expand that much—it never gets that hot. Expansion joints in concrete pavement are also seldom needed, since the contraction joints open enough (from drying shrinkage) to account for temperature expansion.
How thick should a slab be on a grade home?
Standard concrete floor slab thickness in residential construction is 4 inches. Five to six inches is recommended if the concrete will receive occasional heavy loads, such as motor homes or garbage trucks.
How much weight can a 4-inch concrete slab hold?
A 4-inch thick concrete can support upto 40 pounds of weight. Weight should not exceed 40 lbs/sq ft on an undetermined 4-inch slab. 80 lb/sq ft in isolated areas is fine, but unless you know what the soil bearing and reinforcing is for that slab, you might be looking at cracking.
What is the best base for concrete slab?
Most concrete contractors want a mix of coarse and fine aggregate to create a compactable base that is going to be safe for settlement and drainage. Crusher run (a mix of crushed stone and stone dust) and #57 coarse aggregate are two of the best base materials for concrete slabs.
What will be a footing with slab on grade?
A home resting on footings and piers is a home with a crawl space below the first floor. A home with a slab-on-grade foundation has no crawl space.
How do you install slab on grade foundation?
5:5011:53Mini House Build Part 1 - Foundation (Slab on Grade) @Co-Know-Pro ...YouTubeStart of suggested clipEnd of suggested clipSo we have our base down with our three-quarter inch gravel. Below our moisture barrier which isMoreSo we have our base down with our three-quarter inch gravel. Below our moisture barrier which is that plastic. And then we have our sand. And then we're gonna put our Dobies. And then we're gonna put
Do you need weeping tile for slab on grade?
DRAINAGE under Slab on Grade Foundations: At the bottom of the foundation drainage trench, install rigid French drain piping (weeping tile) that can drain to a lower level. If that is not possible it should be connected to a sump pump.
Are slab on grade floors cold?
In cold climates, a slab-on-grade can easily avoid frost heave with the simple addition of skirt insulation, which protects the perimeter of the footing so that it will never be subjected to the freeze/thaw cycle, and instead remain close to the relatively constant 8 -10 degrees Celsius temperatures of the earth.
How Much Settling Is Normal in a House? | eHow
One example of a backfill problem is a house built on slab over a site that was smoothed out with backfill during grading. If the contractor is careless, the fill dirt may contain topsoil full of decomposing organic matter that makes it spongy and easy to compress over time.
How to fix soil settlement on a slab?
Instead, soil settlement damage to slab-on-grade foundations is commonly repaired by boring holes through the foundation and installing piers through the foundation. Another potential repair is to pump a “slurry,” a mixture of water and cement , below the slab to lift the slab. However, the process of installing piers or using a liquid mixture to lift the slab both can themselves cause extensive damage to a home.
Why use slab on grade foundation?
Slab-on-grade foundations are the most commonly used foundations for tract housing because they are cheap, quick and easy to install. While an acceptable building practice when designed and installed properly, incorrectly installed slab-on-grade foundations can seriously damage your home. The most common damage includes:
Why is concrete a porous material?
Because a slab-on-grade foundation rests directly on the soil below it, moisture and drainage problems can result as concrete is a porous material. If the slab and the soil below it are not properly separated by a barrier then, moisture can move up through the slab and into the living area of the home above.
What is a slab on a slab?
A slab-on-grade is a type of shallow foundation in which a concrete slab rests directly on the ground below it. A slab-on-grade foundation usually consists of a thin layer of concrete across the entire area of the foundation with thickened footings at the edges or below load bearing walls in the middle of the building.
What is the purpose of the plastic in a slab on a foundation?
The clear plastic material inside the form is a moisture barrier intended to keep moisture from migrating up from the soil through the slab. The white pipes sticking up are for the home’s plumbing and electrical.
What is the grey strip on the bottom of a slab on grade?
The picture below shows a home under construction on a slab-on-grade foundation. At the bottom of the framed wall you can see a horizontal grey strip which is the slab-on-grade foundation resting directly on the soil below.
Why does my foundation crack?
Cracking of foundation. Often, incorrectly installed slab-on-grade foundation will crack. Most often foundation will crack if the concrete is not cured properly. This problem is magnified when the slab is not poured to the proper depth or the concrete mix is wrong. Cracks in a home’s foundation can contribute to many structural problems ...
What is an expansive soil?
Expansive soils are clays that usually contain montmorillonite or bentonite minerals. These minerals cause excessive clay swelling when wetted, or shrinkage when dried. When wetted, the soils heave, or move upward, exerting pressure on basement floors and footings that can cause structural damage. Swelling soils can also exert enough lateral pressure on basement or retaining walls to damage them. When the soils dry and shrink, footings settle, but the interior of the structure doesn't move because it takes a long time for soil in that area to dry. This differential settlement also causes structural distress (Ref. 1).
Why is it suspicious to have dark colored soil?
Geotechnical engineers will be particularly suspicious of any dark-colored soils because the color, and perhaps an organic odor, indicate possible problems with excessive settlement.
Can you build slab on grade?
If you build slab-on-grade houses on poor-quality soils, you have several design options. These include heavily reinforced slabs on grade, structural slabs supported by piles or piers, and post-tensioned slabs (Ref. 2). A structural engineer can help you choose the most economical option for avoiding distress caused by the poor soils. There are code requirements for such slabs, which usually must be designed by a registered professional engineer.
What is a slab settlement?
What exactly is slab settlement? Slab settlement is simply the movement a concrete slab experiences when the soil underneath it can no longer support the weight of it. Soil changes – that is why your concrete will begin to sink and settle. Let’s focus on the three most common reasons why a concrete slab will settle. 1.
Why does concrete settle?
Let’s focus on the three most common reasons why a concrete slab will settle. 1. Changes in the soil’s moisture content. Two very common soil types are sandy soil and clay soil. Sand is not greatly affected by moisture, but it does eventually wash away.
What happens when water moves under concrete?
2. Wash-out of soil under the slab. As water moves beneath your concrete slab, it can wash away the soil supporting the concrete.
What causes concrete to sink?
3. Poorly compacted fill soil. When a home is being constructed, the soil is usually moved around or spread out to make sure the whole plot is at the desired grade level. When the concrete slab is poured on top of this loose soil, it compresses and settles the soil. When the soil moves like this, it causes concrete to crack and sink.
Why does clay shrink?
When wet, clay holds water and expands in size; when dry, it does the opposite…it shrinks. Soil dries out for many reasons: drought conditions, tree roots taking up all of its moisture, and leaking HVAC systems under your floor slabs.
Does Aquaguard do foundation inspections?
The foundation specialists at Aquaguard will be able to diagnose these issues and more with a free written evaluation and in-home foundation inspection . Call or contact us today.
How to determine slab on grade?
The only method to directly measure the k value is by a plate loading test taken on the compacted sub-grade (or sub-base, if used). A general procedure for this load testing is given in ASTM D1196, Standard Test Method for Nonrepetitive Static Plate Load Tests of Soils and flexible Pavement Components for Use in Evaluation and Design of Airport and Highway Pavements.
What is the quality of a floor slab?
The quality of a completed floor slab is dependent on; an appropriate design, the quality of the materials used and the knowledge and experience of the workmen who place and finish the concrete. Other considerations that play a role in the successful construction of a slab on grade include; proper proportioning of the concrete mix, joint design and performance, and the slab thickness.
Why are concrete floors so complex?
This means the facility could potentially experience tall rack post and other extremely heavy loads, or require very restrictive floor flatness and levelness criteria to assure the proper operation of the equipment that stores and moves goods. As a result, floors can account for more complaints than any other part of a building, primarily because they are so critical to the proper use and operation of the building and also because any problems that develop are so readily exposed to view . To address this situation, careful attention must be given to the many factors that influence floor performance which include:
What is a sub base?
Special sub-bases are used for a variety of reasons. They can consist of materials such as crushed stone, recycled concrete, asphalt, lean concrete and rigid insulation. They may be placed to improve sub-grade support values, to expedite construction or to avert sub-grade frost heave in a freezer warehouse or ice rink. Sub-grade support can be considerably improved by installing a cement-treated sub-base (soil cement), controlled low-strength material (CLSM), or lean concrete sub-base. Generally cement treated and lean concrete sub-bases are 4 to 6 inches thick. A modulus of sub-grade reaction of 400 to 500 psi/inch can be used in calculating the required thickness of floors placed directly on lean concrete and cement treated or roller compacted sub-bases.
What is the K value of soil?
The k value used for floor slab design reflects the response of the sub-grade under temporary (elastic) conditions and small deflections, usually 0.05 inches or less . Soil compressibility and bearing capacity values are normally used to predict and limit differential settlements between different areas of a foundation and reflect the total permanent (inelastic) sub-grade deformations that may be 20 to 40 (or more) times greater than the small deflections on which k values are based. Substantial pavement research shows that elastic deflections and stresses of the slab are predicted reasonably well when the k value is used to represent the sub-grade response. This same research indicates that the control of slab stresses computed based on the sub-grade k value is a valid design procedure.
What is sub-grade in concrete?
The sub-grade is the ground on which the floor is built. The sub-base is an optional layer located on top of the sub-grade and beneath the slab bottom (see Figure 1). The sub-base, while not mandatory, can provide added benefits to the construction and performance of the slab. It is vital to consider sub-grade preparation during design and construction to assure that the concrete floor will carry the intended loads successfully and without significant settlement.
How can subgrades be improved?
The sub-grade can be improved by proper drainage and adequate compaction or soil stabilization. In cases of extremely poor soil, removal and replacement of the sub-grade with an off site compactable material will often be necessary. To construct a reasonably uniform sub-grade, special care must be taken to assure that there is minimal variation of support within the floor area (generally provided by proper proof rolling) and that the following major causes of non-uniform support are identified and controlled:
What is slab on grade?
Slab-on-grade construction is a somewhat uncommon method of home building that replaces the conventional foundation wall and basement or crawl space with a concrete slab that rests directly on grade. The technique lends itself to most types of terrain, with the exception of heavily sloped sites, and increasing the performance of slab on grade floors is simply done by adding insulation - yep, we have a guide for how to insulate slab on grade floors when building, here.
When is a slab poured?
poured, and the centre floor of the slab is poured after footings have cured. The forms of a monolithic slab are designed so that both footing and slab floor are poured at the same time.
Why do you need a basement foundation?
While we are firmly in favour of slab-on-grade construction as a concept, we recommend carefully considering your options before moving ahead with any plans. There are many legitimate reasons to begin construction with a basement foundation: 1 A slab-on-grade will require more above ground space, so in order to have the same size of home you will need to build either out or up. You may run into height restrictions where you choose to build, meaning you may have to build out instead of up. This is not always possible, certainly if your site is an urban infill lot, leaving you two options: a smaller house or a basement. 2 Despite their disadvantages, basements are often very practical since they provide a significant amount of storage space. Without a basement, everything that would have been down there must fit into the rest of the house or in the garage or shed. 3 Basements usually house mechanical rooms. Keep this in mind during the design phase should you choose a slab, as mechanical systems will now need to be housed on the main floor. And don't be stingy with that space - think about everything that may potentially need to go there: a furnace, boiler, water heater, air exchanger, water softener, septic pump, sulphur tank, central vac, etc.
What happens if a basement is poorly constructed?
Poorly constructed basements are subject to rot and mold.
What is needed in a basement?
Basements usually house mechanical rooms. Keep this in mind during the design phase should you choose a slab, as mechanical systems will now need to be housed on the main floor. And don't be stingy with that space - think about everything that may potentially need to go there: a furnace, boiler, water heater, air exchanger, water softener, septic pump, sulphur tank, central vac, etc.
How expensive is concrete?
Concrete is very expensive to purchase and extremely energy intensive during manufacturing. The process of building a basement requires 3 costly visits from a team of concrete trucks; once to pour a footing, again to pour walls, and a third time to pour a basement floor.
How thick is a foundation wall?
Typically, the construction of a single family home in Canada & North America starts with a poured concrete footing followed by an 8-inch thick foundation wall, generally 8 to 10 feet in height.
What is a slab settlement?
What exactly is slab settlement? Slab settlement is simply the movement a concrete slab experiences when the soil underneath it can no longer support the weight of it. Soil changes – that is why your concrete will begin to sink and settle. Let’s focus on the three most common reasons why a concrete slab will settle. 1.
Why does concrete settle?
Let’s focus on the three most common reasons why a concrete slab will settle. 1. Changes in the soil’s moisture content. Two very common soil types are sandy soil and clay soil. Sand is not greatly affected by moisture, but it does eventually wash away.
What happens when water moves under concrete?
2. Wash-out of soil under the slab. As water moves beneath your concrete slab, it can wash away the soil supporting the concrete.
What causes concrete to sink?
3. Poorly compacted fill soil. When a home is being constructed, the soil is usually moved around or spread out to make sure the whole plot is at the desired grade level. When the concrete slab is poured on top of this loose soil, it compresses and settles the soil. When the soil moves like this, it causes concrete to crack and sink.
Why does clay shrink?
When wet, clay holds water and expands in size; when dry, it does the opposite…it shrinks. Soil dries out for many reasons: drought conditions, tree roots taking up all of its moisture, and leaking HVAC systems under your floor slabs.
Does Aquaguard do foundation inspections?
The foundation specialists at Aquaguard will be able to diagnose these issues and more with a free written evaluation and in-home foundation inspection . Call or contact us today.