Glencoe: 24

Question 1

Types of reinforcement for slab foundations:

Answer 1

Rebar and welded-wire mesh fabric.

Welded-wire mesh fabric keeps slabs from separating if they do crack

Question 2

What type of rebar should be used in monolithic slab?

Answer 2

two #4 or one #5 rebar located in the middle third of the footings depth. Vertical lengths are sometimes added to reinforce the thickened portion of slab.

Question 3

Wire fabric should be placed near

Answer 3

the center of the slab thickness

Question 4

Best way to place wire fabric

Answer 4

Support it on Chairs

Chairs: small metal or plastic device that supports the wire fabric at a particular height.

Question 5

Best insulation for slabs?

Answer 5

Rigid, nonabsorbent boards or sheets such as extruded or expanded polystyrene.

Question 6

How do you place insulation for the two types of slabs?

Answer 6

Monolithic: placed around perimeter where exposed to colder temperatures.
Independent: placed between foundation walls and edge of floor slabs. This type of insulation prevents heat loss from conduction.

Question 7

Termite protection in framing above concrete:

Answer 7

one method is to chemically treat the soil before placing slab.

Physical barriers such as metal termite shields. Which on monolithic slabs, shields should be located between slab and wall plate. For independent slabs this barrier is continued to cover the gap between slab and foundation wall.

Where chance of termite infestation is very high, the irc building code prohibits the use of foam plastic insulation outside the foundation walls beneath the slabs below grade because insects may tunnel though the insulation to reach wood framing.

Question 8

Subgrade:

Answer 8

Earth below slab.

Question 9

When installing a concrete slab, subgrade must:

Answer 9

be uniformly compacted (pressed down) to prevent uneven settlement.

All organic matter such as sod or roots must be removed and ground leveled off.

Holes or cracks in subgrade should be filled in with uniform material not containing large stones or lumps.

Question 10

Fill in material in subgrade in layers called:

Answer 10

Lifts:

Should be no more than 6” deep. A uniform a shallow layer of material.

Question 11

Power Tamper:

Hand tamper:

Answer 11

Gasoline powered tool to compact fill in subgrade.

Gets areas difficult to reach with power tamper

Question 12

After filling in subgrade:

Answer 12

the entire subgrade should be thoroughly compacted by tamping or rolling.

Question 13

Soil should be kept to this condition before compacted for subgrade prep:

Answer 13

not too dry and not too wet.

Question 14

Steps for installing concrete slab:

Answer 14

Prepare subgrade: press down uniformly. remove matter and fill holes in lifts. then thoroughly compact

Prepare for other trades: electrical and HVAC lines can be placed in trenches cut in subgrade.

Prepare Subbase (base coarse): Coarse fill placed over compacted subgrade. Slag gravel or crushed stone no more than 2” diameter. Remove Fines. Bring fill to desired grade then compact.

Install vapor retarder:
6-mil polyethylene vapor retarder with joints lapped at least 6” must be placed between the slab and subbase.

Install subbase radon ventilation system.

Question 15

Fines:

Answer 15

finely crushed or powdered materials

Question 16

What does the subbase do?

Answer 16

help to drain water that might collect under the slab.

Question 17

When the slab is below grade, the subbase must be at least X” thick

Answer 17

4”

Question 18

Good quality concrete will not be penetrated by water unless

Answer 18

it is driven by pressure. However water vapor can penetrate concrete.

Question 19

when installing a vapor retarder beneath the slab, 6mil polyethylene joints must be lapped X”

Answer 19

6 inches.

Question 20

One disadvantage of a vapor retarder beneath slab:

Answer 20

forces moisture to escape through top of slab.

Question 21

How do you stop the vapor retarder from causing moisture to release from top of slab:

Answer 21

put a layer of 3” thick sand over the vapor barrier.