Slab-on-Ground: Thickness, Base, Vapor Retarder and Capillary Break
"Slab-on-Ground: Thickness, Base, Vapor Retarder and Capillary Break" is lesson 4 of 7 in the Concrete (C-8) Learning Hub. It opens with "Minimum Thickness and Strength" and works through 5 short steps, then a worked example you can check yourself against.
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Steps in this lesson
Minimum Thickness and Strength
Site Preparation and Base Course
The Vapor Retarder and Where It Is Not Required
The Capillary Break
Keep the Steel Up Where It Works
The worked example in the course applies this lesson to a realistic job in 5 steps, from "Check thickness" through "Vapor retarder for the heated room".
What you'll be able to do
Explain the main idea of "Slab-on-Ground: Thickness, Base, Vapor Retarder and Capillary Break" in plain language you can use on the exam.
Apply this step with confidence: "The Vapor Retarder and Where It Is Not Required".
Apply this step with confidence: "The Capillary Break".
Apply this step with confidence: "Keep the Steel Up Where It Works".
Test yourself on the worked example and the quick-check quiz inside the classroom.
The diagram for this lesson, exactly as it appears in the Learning Hub.
The first steps of this lesson
Step 1: Minimum Thickness and Strength
A concrete floor slab supported directly on the ground must be not less than 3-1/2 inches thick (2025 CBC 1907.3; 2025 CRC R506.1, which sends expansive soils to R403.1.8). R506.1 says the specified compressive strength comes from Table R402.2. CBC 1907.1 and 1907.2 split slabs into structural slabs-on-ground, which carry vertical or lateral loads from the structure to the soil or foundations, and nonstructural slabs, which still must meet 1904.2, 1907.3 and 1907.4.
Step 2: Site Preparation and Base Course
Under R506.3, everything inside the foundation walls has vegetation, topsoil and foreign material removed. R506.3.1: fill must be free of vegetation and foreign material and compacted for uniform support, and unless approved the fill depth may not exceed 24 inches for clean sand or gravel or 8 inches for earth. R506.3.2: where the slab is below grade, place a 4-inch-thick base course of clean graded sand, gravel, crushed stone, crushed concrete or crushed blast-furnace slag passing a 2-inch sieve; no base is needed on well-drained or sand-gravel soils classed Group I in Table R401.4.1(2).
The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.
Independent exam preparation. Contractors Classroom is not affiliated with the Contractors State License Board, and no course can guarantee a passing result.
