How to build a home book excerpt about slab construction

 CHAPTER 6 The Slab:

[Below is an excerpt from the book  How to Build A Home and Work with Contractors - "Working for Subs"

The major activities discussed in this chapter are the slab and foundation work. The quantities shown in schedules throughout this book are based upon an average sized home (see Chapter 3.)

Detailed Schedule - Part D*

• Call for Portable toilet.
  
• Deliver OSHA equipment (Chap. 6) to job ( hard hats, fire extinguisher, MSDS (Chap. 4) binder, 1^st aid kit, safety glasses, etc.)
  
• If Block Foundation w/Slab:
  
  • Call slab subcontractor for date to start.
    
  • ORDER: ____8”standard blocks (w/garage); ____ bags mortar, ___#4 / #5 rebar, _____MAS (a Simpson mudsill anchor) anchors 4ft oc (on center -see Glossary;) _____ rolls mesh; _____sqft 6 mil Visqueen, _____ yds. sand (add for sand under Plumbing at Fill); ___ 24” grade stakes, ____2x8 #3 spruce for footings steps, L-shape 10”x36” rebar, 8d cut nails.
    
  • Order: ____Lin. ft. (= twice the perimeter) of 2x4 utility grade lumber for braces & stakes (slab: 10” above grade & foundation: 13” below –verify for location).
    
  • Call-before-Dig 811, 72hr in advance, liability avoidance is good for 15 days: _________________date of call.
    
  • Batter boards Shoot grade and set batter boards, need 5 lbs. 12d double head nails.
    
  • (FHA / LG&W energy inspection?)
    
  • Set Electrical Conduit for floor & island receptacles.
    
  • Dig footings per code (10” x 24”); for monolithic slab set (3) #4 rebar or (2) #5, Slab edge insulation may be required.
    
  • After footings dug, drill piers (or postholes) if needed, insert rebar & concrete fill in piers.
    
  • Pour brick fence footing and porch post piers at same time.
    
  • Take Photos of rebar (steel reinforcing rod, see Glossary) in place.
    
  • Call footings inspection or Engineer required if greater than 5 blocks high (in TN).
    
  • Call PLUMBER to roughin below slab piping.
    
  • Pour footings 10” thick; Set blocks; plumbing roughin (wait, plumber calls Inspection)
    
  • Set block foundation & fill cores with concrete & rebar per code.
    
  • Set 6”PVC (by plumber) downdraft cooktop vent pipe and 1” electrical conduit?
    
  • Set 2x8 above block with cut nails for form boards & stake
    
  • Backfill dirt to elevation for 4” slab.
    
  • Level grade around lot; Dig & pour 4” dia. postholes at 4’ oc inside slab area.
    
  • Pier/Post Hole Inspection -Engineer to survey footings & postholes.
    
  • Verify termite spray (phone ________________), call 2 days in advance.
    
  • Lay Visqueen and wire mesh; Wait for SLAB Inspection.
    
  • Pour slab (& Trowel).
    
• If Conventional Foundation: Order brick ties, 12” blocks, termite shield.
  
• If Monolithic SLAB:
  

• Pour Patio/porch now (block out if any brick inlay).
  
• Slab 10” above grade & foundation 13” below (TN).
  
• 2x10 (2x6’s) perimeter, 2X4 stakes (2x perimeter), rebar (2x perimeter + trenches), stakes (60) 24”; 6 x 6 wire mesh (750 sqft/roll), Visqueen, backfill dirt / sand for plumbing piping.
  
• Set 2x8 above brick ledge + 2x4 = 10”high form boards & stakes; Backfill dirt for 4” slab.
  
• After Forms are set, drill piers (or postholes) if needed, insert rebar & concrete fill in piers.
  
• call licensed ENGINEER to inspect –phone ______________________.
  

• Order: Spray foam slab insulation (Sill Sealer & 12” black poly -TN)
  
• Order: Roll of tie wire, 6 lb of 12d nails for forms.
  
• Call PLUMBER to roughin below slab piping.
  
• Termite spray
  
• call Plumbing and slab inspections.
  
• Get Release of Lien from each sub (or Notice to Owner provider –in Florida) before payment.
  
• Call for Trash container delivery or trash sub.
  

*Detailed Schedule – Part D in this chapter continues the sequence of construction tasks following Part C in Chapter 4.

See Appendix B for the complete Detailed Schedule. Dimensions and amounts are based on codes in Tennessee, Colorado, and Florida, local requirements, and the Uniform Building Code that change annually in some cases, so verify all in this book before acting on them.

Preparation for Slab:

Be sure to discuss with your slab contractor the steps required to pour the slab, including: who furnishes formboard nails, when he can begin, and what things you will have to do, materials to order, when and who will call inspections, etc. Ask the sub once forms are set for his guess of the number of yards (cu. yd.) of concrete for footings and later for the slab, when he will need delivery, the size of loads (8 yd. or 10 yd. truckloads) based upon soil conditions (heavy trucks sink in loose uncompacted dirt,) manpower available, and frequency of truck delivery desired (-e.g. 30 min. apart.)
Ask if calcium [chloride] should be added for accelerating the concrete setting if cold weather, which allows completion in one long day . Concrete sets up faster in warm weather, so your sub will be able to trowel the finish before normal quitting time in the summer. Calcium chloride will corrode the steel rebar surface to an extent, but the trade-off is not being able to finish the slab before dark. Consult with the concrete supplier when ordering about the percent calcium to add. Three percent (3%) Calcium is a lot, one percent is common. 

Any slab section not finished before concrete setup should be terminated with an expansion joint by inserting a temporary 2x4 form to square the edge of the open pour. This will prevent what is called a cold joint, that is subject to weakness at the irregular intersection. Add rebar ties through the smooth junction protruding into the next adjoining pour to tie them together.

Have the slab sub sign a subcontract agreement in advance. Get his insurance, contact numbers, and other information as described in Chapter 5 before he sets foot on the lot to begin. The best time to get the information is at the time you meet with or call him to award the contract. This procedure should be repeated every time you hire a subcontractor. Call the sub a day before delivery of materials are due to arrive, and let him know that everything is being delivered as scheduled. This keeps him reminded to show up on time without insulting him by calling with no information and implying that he might need a reminder.

When you call for a portable toilet, have the unit placed far back from the front lot line. If the toilet is near the curb all the other builders' subs, their laborers, lookers / passers-by (idea thieves), and neighbors on a walk will use your facilities and other builders will avoid having to rent their own. You will also have an odorous site element that you have to call to have emptied every few days. If you can avoid this nuisance, it will be worth requesting the placement further back on the lot. This won't eliminate the unauthorized use of your port-a-potty, but it will reduce the abuse.

Slab Form Materials Order:

According to Detailed Schedule – Part D the builder will have to order several items prior to the arrival of the concrete slab subcontractor. Be sure to determine from your materials supplier what the lead time is (between ordering and delivery) then add at least one half day to that. Also ask your sub what day he will begin, and get his advice before ordering the things he will need to do the job.

He may want you to supply 12d (twelve penny) double-headed (for ease of withdrawal when stripping the forms) nails for forms and batter boards, and bailing wire for tying rebar, as well as any number of items you could have omitted from the materials list. Although the sub can cut and bend L-shaped rebar on the job, he will probably prefer that you order a number of these pieces pre-formed. Verify the length required for these pieces with codes. This is a small extra expense, but your subcontractor will appreciate the gesture. We used number three spruce (SPF -spruce, pine, or fir) or lower grade that the sub could cut for braces and stakes and could cut into short end forms where the grade sloped, since this is considered junk lumber and not expensive to toss after use. Attempting to cut used concrete formboards to use for framing later is hard on saw blades, but can be done to an extent. The 7-1/4” height of the 2x8 is just about right for stepping (in tiers) a footing that will hold 8” blocks. Use standard blocks, since heavy weight blocks cost more and are hard to carry as well as over-kill for residential compression strength requirements. We used type N mortar for laying foundation blocks which satisfied the codes. Our subs would tack a 2x8 to the outside of the concrete blocks with 8d (eight penny) cut nails. These were set with a reveal at 3-1/2” above the block to match any 2x4 formboards elsewhere at the slab edge.

Verify with your local code authority whether two or three number 4 rebar or number 5 rebar are needed due to the foundation wall height. The energy code calculations, performed by you, or perhaps an architect or engineer, will dictate whether slab edge insulation is required. A 24” wide footing for residential loads is extreme overkill with a high factor of safety, but often required by code. Be sure a footing pad is placed below where any point loads will occur due to a support post.
In Tennessee we dug our own footings and poured concrete ourselves when first starting our business as a cost saving measure. We learned very early that pouring your own concrete is hard work and requires experience and skill, also you won't save any meaningful amount by avoiding hiring a subcontractor to do this. When we first began, no rebar was required in footings by the code authorities in Tennessee, but later they began demanding it. We had installed it anyway as insurance against failure. The frost line was only about four inches deep, but the codes called for a twelve inch depth of footing. Florida with no frost line calls for a thirteen inch depth, unnecessaryly for compacted soil. If there are any brick fenceposts to be installed later, this pour would be a good time to set those footings also.

Call your plumber well in advance of having formboards set. Then call him a day or two ahead of the completion of forms as a reminder. The plumber will use the slab edge forms as a guide for setting his below slab piping. You will have to verify the locations of his risers afterwards, since they always get one or two wrong (see Photo 8, Chap. 7,) and you will have to break out a big chunk of slab to relocate the piping in the future walls. The plumbing inspector will leave a tag, once successful with piping layout. Your slab contractor can then begin after the plumbing has been backfilled with sand (not dirt, due to lack of proper substrate compression.) If there are any downdraft cooktops or other appliances requiring under slab vents, it's a good idea to set them now. The plumber can use PVC piping below the slab to accomplish this, which has good compressive strength. See Chapter 7 for more about Plumbing.

After the slab is formed is the time to add electrical conduit (liquid-tight, PVC, without joints) below the slab for things like floor receptacles or island appliances. before laying the vapor barrier The electrical sub will have to lay conduit under the slab to the island. If there will be a downdraft range in the island he will need to know this, as an electrical receptacle is also needed, and may require a separate conduit. My electrical subcontractor once said to just lay a 2x4 on edge where the conduit will lie, and his guys would break it out later and grout it over. However, it would have been best to break it out the next day when the slab is still green, since it took a jackhammer to get it out once the cement set up. You, the builder, will probably have to locate any floor or kitchen island receptacles for the electrician if he is to come on the job at this time, or they will end up in the center of the room, since the floorplans are considered only diagrammatic in character and not exact unless dimensioned. Be sure to place a stake with a small note attached for the electrician, and also show him the stake. We used to attempt to locate the great room floor receptacle beneath the proposed spot for a coffee table to serve a floor lamp beside a center-of-room couch, thus the need for a furniture layout on your floorplans.
Prior to laying a vapor barrier below the slab and after the plumbing, you may be required to drill four inch diameter postholes down to stable ground with the depth dependent upon how much backfill had been added to the soil. Our concrete sub dug with a hand posthole digger (used to joke that he had a “PhD” -acronym) A gas operated auger works better. The backfill dirt may have been added thirty years prior when the subdivision was developed, but it could still be insufficiently compacted despite the settling time. These postholes will help support the slab and prevent sagging (or deflection, for the structural engineers.) We used to take a piece of no. 4 rebar and put our weight behind it to test the depth of the posthole. If there was any give into the soil, further drilling was required. Though not scientific, it was effective.

Either code enforcement or a privately hired engineer will have to be called prior to the pour and after the forms and postholes are dug to sign off on an inspection certificate that will be placed visibly on the job. This was a Tennessee requirement and may vary elsewhere. The subcontractor will wait for this clearance before laying the concrete.
In Tennessee 6”x6” woven wire steel mesh was laid over a Visqueen vapor barrier and supposedly (and ineffectively) kept the slab from cracking. However, we used to joke that our guarantee was that the slab would crack, since this was very commonly unavoidable and harmless, as most cracks seldom exceeded about 1/4”. The mesh did provide the function of preventing the crack from widening over time in most cases. The vapor barrier sealed the crack to some extent. To be accurately placed the mesh was theoretically supposed to lie in mid thickness of the slab, but this wavy flexible material never does what it is expected to do. The sub seldom lifts it off the bottom during the pour. Mesh chair supports were required in Florida, but not Tennessee, and subject to failure with workers stepping on them.

Ordering materials on time, avoids theft, weathering, site clutter, and vandalism. You do not want your slab forming materials lying around more than a couple of days, as wire mesh, Visqueen and stakes are common items that may be stolen, because they are lightweight and portable. You will not have a problem with long rebar, blocks, or utility grade lumber being stolen, since these are too cumbersome for most thieves to handle for the small return they bring.


Once the slab subcontractor has given you a start time, you should telephone call-before-dig to have the ground marked for below grade utilities (electrical, gas, water, telephone, cable, & sewer) preferably before delivery of materials, so that the ground will be uncluttered. The marking service will use different colors of spray paint on the earth where lines and cables lie beneath. The call-before-dig service guarantees you freedom from liability for damaged utilities usually for fifteen days if they mark prior to your excavation, so mark your calendar to call them again prior to tampering with the earth after that time.    [continued in book]
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