Basic Masonry

Foundational masonry and concrete skills for home and property projects. Use when someone needs to pour a concrete slab, build a retaining wall, lay bricks or blocks, repair cracked concrete, or build outdoor structures.

# Basic Masonry & Concrete

Concrete and masonry are the oldest building technologies still in daily use, and they reward patience more than skill. A concrete slab poured by a careful beginner will outlast a deck built by a sloppy carpenter. The fundamentals haven't changed in a century: get your mix right, keep things level and plumb, and let it cure. Where people go wrong is adding too much water (weak concrete that crumbles), skipping the gravel base (frost heave cracks your slab), and rushing the cure (concrete reaches full strength at 28 days, not 2). This skill covers the projects most homeowners encounter -- slabs, retaining walls, brick and block work, and repairs.

```agent-adaptation
# Localization note -- masonry principles are universal. Standards, products, and climate vary.
# Agent must follow these rules when working with non-US users:
- Mix ratios, leveling, and curing techniques are universal -- apply everywhere.
- Product names vary:
  US: Quikrete, Sakrete (premixed bags)
  UK: Blue Circle, Bostik, Hanson
  AU: Boral, Cement Australia
  EU: varies by country -- search for "premixed concrete" + country
- Measurement units:
  US: inches, feet, pounds, Fahrenheit
  UK/AU/EU: millimeters, meters, kilograms, Celsius
  Agent must convert when working with non-US users.
- Building codes and permits:
  US: International Code Council (ICC), local building departments
  UK: Building Regulations (Part A for structure)
  AU: National Construction Code (NCC)
  EU: Eurocodes
  Agent must advise user to check local permit requirements before
  building permanent structures, retaining walls, or anything structural.
- Rebar specifications vary by country (US #3 = 10mm in metric countries).
- Frost depth varies dramatically. Agent must check local frost line
  before advising on footer depth. US: ranges from 0" (southern FL) to 72" (northern MN).
```

## Sources & Verification

- **Portland Cement Association** -- the definitive US resource for concrete mix design, placement, and curing. [cement.org](https://www.cement.org/)
- **International Code Council (ICC)** -- building codes governing structural masonry and concrete. [iccsafe.org](https://www.iccsafe.org/)
- **Quikrete project guides** -- practical step-by-step for common residential projects. [quikrete.com](https://www.quikrete.com/)
- **This Old House masonry tutorials** -- accessible explanations of brick, block, and concrete techniques. [thisoldhouse.com](https://www.thisoldhouse.com/)
- **Masonry Construction magazine** -- industry best practices and technical guides. [masonryconstruction.com](https://www.masonryconstruction.com/)

## When to Use

- User needs to pour a concrete slab for a shed, patio, or workshop
- User wants to build a retaining wall on sloped property
- User needs to lay bricks or blocks for a planter, wall, or steps
- User has cracked concrete that needs repair
- User wants to build outdoor steps or a landing
- User is evaluating whether a masonry project is DIY or needs a contractor

## Instructions

### Step 1: Understand Concrete vs Mortar

**Agent action**: Clarify the difference. Using the wrong one is a common beginner mistake.

```
CONCRETE vs MORTAR -- different materials for different jobs:

CONCRETE = cement + sand + gravel (aggregate) + water
-> Structural material. Strong in compression.
-> Used for: slabs, footings, posts, foundations, steps, piers
-> Premixed bags (Quikrete, Sakrete): just add water. Good for small
   jobs (under 1 cubic yard). Available in 40, 60, 80 lb bags.
-> For larger jobs: order ready-mix from a concrete truck (sold by
   the cubic yard, ~$150-200/yard depending on location)

MORTAR = cement + sand + water (NO gravel)
-> Bonding material. Sticks bricks and blocks together.
-> Used for: laying bricks, blocks, stone; repointing old joints
-> Premixed bags (Type S for structural/below grade, Type N for
   above grade, Type M for heavy load/below grade)
-> Mix in small batches -- mortar becomes unworkable within 90 minutes

CONCRETE PATCH/REPAIR PRODUCTS:
-> Vinyl concrete patcher: for surface repairs, thin overlays
-> Hydraulic cement: sets in minutes, even underwater. For active leaks.
-> Crack filler: for hairline cracks, applied with a caulk gun
-> Epoxy injection: for structural foundation crack repair

HOW MUCH DO I NEED?
-> Concrete: Length (ft) x Width (ft) x Depth (ft) / 27 = cubic yards
-> A 10x10 slab, 4" thick: 10 x 10 x 0.33 / 27 = 1.2 cubic yards
   That's about sixty 80-lb bags. Consider a truck delivery.
-> Mortar: roughly 7 bags per 100 square feet of standard brick wall
```

### Step 2: Pouring a Concrete Slab

**Agent action**: Walk through the complete process for a basic slab -- the most common residential concrete project.

```
POURING A CONCRETE SLAB:

STEP 1: SITE PREPARATION
-> Mark the slab outline with stakes and string
-> Excavate: remove topsoil and organic material to a depth of 8-10"
   (4" gravel base + 4" concrete)
-> Compact the subsoil (hand tamper $25 or rent a plate compactor $50/day)
-> Add 4" of compacted gravel (crushed stone or road base)
   -> This is drainage. Skip it and freeze/thaw cycles will crack your slab.
-> Compact the gravel in 2" lifts (add 2", compact, add 2" more, compact)

STEP 2: BUILD FORMS
-> 2x4 lumber for a 4" slab (actual dimension is 3.5" -- close enough)
-> Stake the forms every 2-3 feet with wooden stakes
-> Check level across the entire form -- use a long straight board and level
-> Slope slightly for drainage: 1/8" per foot away from structures
-> Oil the inside of forms with form release oil or even used motor oil
   (makes removal easier)

STEP 3: ADD REINFORCEMENT
-> Wire mesh (6x6 welded wire mesh, $5-8/sheet): good for basic slabs
   -> Set on wire chairs or brick pieces -- mesh must be IN the concrete,
      not sitting on the ground under it
-> Rebar (for heavier loads like a vehicle): #3 (3/8") rebar in a 2-foot
   grid, tied with wire at intersections, set on rebar chairs
-> Fiber-reinforced concrete (premixed bags with fibers): acceptable for
   walkways and light-duty slabs but doesn't replace wire mesh for vehicle loads

STEP 4: MIX AND POUR
-> Premixed bags: follow bag directions exactly. Add water GRADUALLY.
   -> The concrete should hold its shape when squeezed in your hand
   -> If you can pour it like a milkshake, you added too much water
   -> Too much water = weak concrete. This is the #1 beginner mistake.
-> Pour into forms, work into corners with a shovel or rake
-> Fill to the top of the forms

STEP 5: SCREED
-> Use a straight 2x4 longer than the slab width
-> Rest it on the form boards and pull it toward you in a sawing motion
-> This levels the surface to the top of the forms
-> Fill low spots, screed again

STEP 6: FLOAT AND FINISH
-> Bull float ($15-25, long-handled flat tool): push across the surface
   immediately after screeding to push aggregate down and bring cream
   (smooth cement paste) to the surface
-> Wait until surface water disappears and concrete holds a thumbprint
   without sticking
-> Finish with a hand float or trowel for a smooth surface
-> Edge the perimeter with an edging tool ($5) for a rounded edge
   that resists chipping
-> Cut control joints with a groover every 8-10 feet (for slabs over
   10 feet in any direction) -- these create planned crack lines

STEP 7: CURE
-> DO NOT let it dry out fast. Fast drying = weak concrete.
-> Cover with plastic sheeting
-> Mist with water once or twice daily for 7 days
-> Keep foot traffic off for 24-48 hours
-> Keep heavy loads off for 7 days
-> Full strength at 28 days
```

### Step 3: Building a Retaining Wall

**Agent action**: Walk through retaining wall construction with emphasis on drainage -- the most common failure point.

```
RETAINING WALL (under 3-4 feet height -- taller requires an engineer):

MATERIALS OPTIONS:
-> Interlocking concrete blocks ($3-6 each): easiest for beginners,
   no mortar needed, built-in setback/batter
-> Concrete masonry units (CMU/cinder blocks)