Lecture 5 тсп 1

1.

COURSE: TECHNOLOGY OF CONSTRUCTION PRODUCTION
Lecture 5
Installing Foundations,
and Keeping Water Out of Them
A practical, step-by-step look at how precast foundations go into the ground — and the methods builders use
afterward to stop water from getting in.
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2.

LECTURE 5 ROADMAP
What We'll Cover Today
PART ONE
PART TWO
Installing Precast Foundations
Waterproofing the Foundation
• Cranes, crew, and the step-by-step setting process
• Horizontal vs. vertical protection, and why both matter
• How accurate the work must be, and how fast it goes
• Six waterproofing methods, and when each one is used
• Strip and combined (two-piece) foundations
• The foundation-to-wall detail, and one rule you can't break
• Finishing work, then backfilling toward the first floor
• Special cases: columns, piles, and timber buildings
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3.

BEFORE WE START: A QUICK RECAP
Getting the Backfill Moisture Right
Before any soil is compacted into a backfill layer, its moisture content has to sit inside a target window around that soil's “optimal moisture”
(written W₀). Too dry, and the soil won't pack into a dense, stable layer. Too wet, and it won't compact either — it can squeeze out from under the
roller and settle later.
0.8–1.2 × W₀
0.9–1.1 × W₀
0.2–0.3 m
Target range when the soil starts out too DRY — water is
added to bring it up
Target range when the soil starts out too WET — it is dried
out before use
How far each compaction pass overlaps the one before it, so
nothing gets missed
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4.

PART ONE
Installing Precast
Foundations
Getting factory-made concrete foundation blocks into the ground — accurately, safely, and on schedule.
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5.

HOW THE BLOCKS GET INTO PLACE
Moving Foundations with a Crane
• Precast means made off-site in a factory, then simply lifted into
place — unlike cast-in-place concrete, which is poured on site.
• Precast foundation pieces are almost always installed by crane:
usually a crawler or wheeled mobile crane, sometimes a tower
crane already on site.
• A tower crane is normally parked at the edge of the excavation
pit.
• A mobile or crawler crane's position depends on the building's
width — it may work from the pit edge, or drive down onto the
pit floor itself.
A tower crane (left) and a crawler crane (right) setting precast foundation blocks.
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6.

ONE COMMON SHAPE: THE “CUP” FOOTING
Setting a Cup-Type Foundation, Step by Step
A “cup-type” foundation is shaped like a deep socket — much like a wine glass holds its stem — so a column can simply be set down inside it later.
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Blocks arrive straight off the delivery
truck — site space is too tight for large
stockpiles.
The crane lifts and lowers each block into
place, guided by two or three installers.
Surveyors check the block's position
against the marked axis lines, and its
elevation.
If it's off, the block is re-lifted, the base is
corrected, and it's set again.
Why this matters:
A crew of a crane operator and three installers works through this cycle repeatedly — setting, checking, and (when needed) correcting — for every single foundation
block on site.
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7.

HOW PRECISE DOES IT NEED TO BE?
Tolerances You Can't Skip
“Axis” means the marked centerline a block should sit on; “elevation” means its height above a fixed reference point. Both are checked with surveying
instruments.
±13 mm
20 mm
10 mm
Maximum shift of any block away from its marked axis line
Maximum error in a cup's bottom elevation — fixed with
mortar or reinforced-concrete packing
Maximum error in the finished top bearing surface, checked
once all foundations are in
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8.

WHO DOES THE WORK, AND HOW FAST
A Four-Person Team
Don't forget the steel
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15–20
The crew: one crane operator plus three installers
Foundation blocks this crew typically sets in a single shift
Technology of Construction Production · Lecture 5
• Foundations include embedded steel connector plates
that will later tie the cup to the floor slab above.
• Once those plates are welded in place, they're coated
with an anti-corrosion coating so they don't rust away
over the building's lifetime.
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9.

A DIFFERENT SHAPE, A DIFFERENT SEQUENCE
Strip (Ribbon) Foundations
• Strip foundations form one continuous band, so installation always starts with the two
corner blocks that anchor the run.
• A taut guide line is stretched between those corner blocks, and every ordinary block in
between is set against it.
• About every 20 m along a straight run, another corner-style block is set, and the
process repeats.
• Vertical joints between neighboring blocks are staggered, the same way bricks are, so
no long crack line can form.
Corner “beacon” blocks (dark) go in first; a guide line runs between them so the in-between
blocks (hatched) follow a straight, level path.
Technology of Construction Production · Lecture 5
• Blocks rest on a 100 mm sand bed — or straight on the leveled pit floor, if the natural
soil is already sandy.
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10.

TWO PIECES, ONE FOOTING
Combined (Two-Part) Foundations
Some foundations are built from two separate precast pieces: a flat base
plate, and a “pedestal” (a socket piece) that sits on top of it and holds
the column.
• The base plate is installed first; its position is checked both in plan and in
elevation.
• The pedestal is then set on a fresh mortar bed on top of the plate.
• The pedestal's final height is fine-tuned just by making that mortar layer
thicker or thinner — an easy way to compensate for the column's actual
manufactured length.
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11.

THE LAST STEPS BEFORE MOVING ON
Closing Out the Installation
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Cut the lifting loops
Pack the vertical joints
Level the top surface
Every block has steel loops cast in just for the crane
to grab — no longer needed once it's set, so they're
cut flush.
Ordinary soil is tamped into the gap between blocks
to a depth of about 40 mm, then the rest is sealed
with mortar.
The whole foundation's top is smoothed with
cement mortar, checking the “installation horizon”
— the reference height the rest of the floor will be
built from.
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12.

WHAT HAPPENS NEXT
From Backfilling to the First Floor
All of this below-ground work — from excavation through to this point — is often called “zero-cycle” construction: everything that happens before the visible
building starts rising.
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Partial backfill: soil goes back around the
foundation, up to the top of the block
(not higher yet).
Foundation beams are placed on the
block tops or on small support piers,
ready to carry the wall above.
Vertical waterproofing is applied to the
foundation's outward face before it's
covered again — today's Part 2.
The plinth (the short wall section just
above ground) and the floor over the
basement complete this stage.
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13.

PART TWO
Waterproofing the
Foundation
Keeping groundwater and rain out of the one part of the building that touches the earth.
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TWO KINDS OF WATER, TWO KINDS OF PROTECTION
Horizontal vs. Vertical Waterproofing
• Vertical waterproofing protects a foundation from moisture
and groundwater held in the surrounding soil — used on strip,
slab, and pier foundations alike.
• Horizontal waterproofing mainly blocks “capillary rise”:
moisture creeping upward between two materials stacked at
different levels, the way a paper towel wicks up water.
• Horizontal protection is used on every foundation type,
without exception.
Left: horizontal waterproofing along the top of a strip foundation. Right: a vertical coating being applied before backfilling.
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15.

MATERIAL REQUIREMENTS
What a Waterproofing Material Must Do
• Impermeable — blocks water completely, not just slows it down
• Water-resistant — keeps working after long-term contact with moisture
• Mechanically strong — survives the stresses of the surrounding soil
• Plastic and elastic — flexes slightly without cracking as the building settles
• Chemically resistant — stands up to whatever is in the soil and groundwater
+10°C
Minimum air temperature for applying most waterproofing materials —
colder, and they won't bond or cure properly
• Durable — expected to last for decades, since it's very hard to repair later
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16.

SIX METHODS, ONE GOAL
The Waterproofing Toolkit
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2
3
Coating (Painted)
Membrane (Adhesive)
Plastered
A liquid material brushed or rolled on, usually in two
or three layers.
A rolled sheet material, glued or heat-welded onto
the surface.
A cement-based waterproof render, troweled on like
ordinary plaster.
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Penetrating
Injection
Mechanically-Mounted
A chemical that soaks into concrete's own pores,
sealing it from within.
Sealant pumped directly into cracks or joints, under
pressure.
Sheets or membranes physically fastened to the wall,
not glued.
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METHOD 2, THREE VARIATIONS
Membrane Waterproofing: Three Ways to Apply It
• Heat-welded — the sheet's underside is heated with a torch until it softens, then
pressed onto the surface (shown here).
• Glue-applied — no torch needed; a separate bitumen adhesive (mastic) bonds the
sheet in place.
• Self-adhesive — the sheet already has a sticky backing built in, so it needs neither a
torch nor a separate adhesive.
Heat-welding a membrane sheet to a foundation wall.
Polymer membrane sheets can even be applied directly over an existing, older
waterproofing layer during a repair — no need to strip it off first.
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METHOD 1
Coating Waterproofing
• Applied as a liquid with a brush or roller — almost always in two
or three layers, never just one.
• Most coatings are bitumen-based: one- or two-component
polymer and bitumen-polymer resins, or bitumen-rubber mastics.
• Modern polymer additives resist cracking in cold weather far
better than plain, old-fashioned bitumen.
2–3
layers, typical for a full
coating application
A coating being brushed onto a foundation wall.
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METHOD 4
Penetrating Waterproofing
A chemical compound is brushed onto the concrete surface and soaks into its own pores
— sealing capillaries from the inside, rather than just sitting on top like a coating does.
• Usually combined with a coating or membrane layer, for extra protection.
• Also makes the concrete's surface layer somewhat stronger, as a side benefit.
Technology of Construction Production · Lecture 5
100–200 mm
How deep the sealant typically penetrates into the concrete
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20.

METHOD 5
Injection Waterproofing
• Used to seal an existing crack, cold joint, or leak path that's already letting water
through.
• Sealant materials include acrylic gels, resins, various polymer compounds, foams,
and rubbers.
• The material is pumped in under pressure through small tubes (shown in red) until it
fills the void and cures.
Sealant being injected along the base of a wall through a row of small tubes.
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21.

METHOD 6
Mechanically-Mounted Waterproofing
• Instead of gluing or coating, the waterproofing material — steel or plastic sheets, or
a dimpled membrane like the one shown — is physically fastened to the structure.
• The toughest, most robust option: besides blocking water, it also resists pressure
from shifting ground.
• Reserved for especially demanding conditions — for example, foundations where
groundwater is high and under significant pressure.
Workers fastening a dimpled “profiled membrane” sheet against a foundation wall.
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22.

PUTTING THE PIECES TOGETHER
A Strip Foundation, in Cross-Section
Plinth
Horizontal waterproofing
• Vertical waterproofing runs down the outward-facing side
of the whole foundation.
Vertical waterproofing
• A profiled (dimpled) membrane and geotextile fabric
protect that vertical layer and let groundwater drain instead
of pressing on the wall.
Foundation
• Horizontal waterproofing sits along the top of the
foundation, right where the plinth begins.
Profiled membrane
Geotextile fabric
• A drainage pipe at the base carries that water safely away.
Basement floor
Drainage pipe
Gravel bed
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23.

A COMMON BUILDING BLOCK, ONE IMPORTANT RULE
Precast Block (FBS) Strip Foundations
A strip foundation can be precast (built from standard rectangular blocks, often called FBS
blocks) or cast-in-place (poured as one continuous piece).
IMPORTANT RULE
A precast-block strip foundation, fully coated in vertical waterproofing before backfilling.
Bitumen-based materials must NOT be used at the joint between the footing pad and the
first block row — that joint can shift slightly, and bitumen won't tolerate the movement.
Use a thicker mortar joint reinforced with ribbed steel rods instead.
Everywhere else, the sequence is: horizontal waterproofing on top of the foundation, vertical
waterproofing on the outside face, then the blind area around the perimeter.
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24.

A LIGHTER-DUTY FOUNDATION TYPE
Columnar and Pile Foundations
Columnar (isolated column footings) and pile foundations meet the ground very differently than a continuous strip or slab — so their
waterproofing needs are simpler too.
Only ONE direction needed
Why less is needed here
• Only horizontal waterproofing is required, applied where the
foundation meets the wall material above it.
• Its one job is stopping capillary moisture from creeping up into the
wall.
Full vertical waterproofing isn't needed because these foundations don't
present the kind of continuous below-ground surface that strip or slab
foundations do.
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25.

THE FIRST LINE OF DEFENSE
The Blind Area (Apron)
• A blind area (or “apron”) is the sloped strip of concrete running all the way around a
building at ground level.
• Its job is simple: carry rainwater and melting snow away from the foundation before
it can soak in nearby.
Wall
• It must be wide enough that water actually clears the foundation zone, rather than
sliding off just next to it.
Concrete apron (sloped)
Sand
Compacted clay
Base soil
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26.

THE COMPLETE PICTURE
A Complete Foundation Waterproofing Scheme
• Vertical waterproofing (often two layers) is covered by a thin protective film so
backfilling doesn't tear it.
• Thermal insulation sits right beside the waterproofing, so the wall is protected from
both cold and moisture at once.
Tin flashing
Load-bearing basement wall
Horizontal waterproofing
Wall
• A tin flashing cap keeps water from ever reaching the top edge of the vertical
waterproofing.
• Free-draining backfill soil lets any water move down and away, instead of pressing
against the wall.
Free-draining
backfill soil
Vertical waterproofing
(2 layers) + film
Thermal insulation
Floor insulation + waterproofing
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27.

ONE MORE VARIATION
A Special Case: Timber-Framed Buildings
Depending on the exact foundation design, the rolled waterproofing sheet can instead be laid on top of a pile-cap beam, or directly on
the heads of individual support piers.
This detail matters especially for timber buildings, where the bottom-most course of logs or timber acts as the tie beam connecting the
whole wall structure to the foundation — so that layer needs its own waterproofing right at the contact point.
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28.

TODAY'S LECTURE IN NUMBERS
Key Numbers to Remember
±13 mm
20 mm
10 mm
15–20
Axis tolerance
Cup-bottom elevation tolerance
Top-surface elevation tolerance
Blocks set per shift
20 m
+10°C
2–3
100–200 mm
Beacon-block spacing
Minimum application temperature
Coating layers
Penetrating depth
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29.

WRAP-UP
What We Covered Today
Part 1
Part 2
• Precast foundations are set by crane, checked and adjusted against
strict axis and elevation tolerances.
• Horizontal waterproofing stops capillary rise; vertical waterproofing
blocks groundwater.
• A small crew sets 15–20 blocks per shift.
• Six methods exist — coating, membrane, plastered, penetrating,
injection, and mechanically-mounted — each suited to different
conditions.
• Strip and combined foundations each follow their own installation
sequence.
• Finishing work and controlled backfilling lead into vertical
waterproofing.
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• Never use bitumen at an FBS footing-pad joint.
• Columnar, pile, and timber foundations each have their own
simplified requirements.
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30.

FOR DISCUSSION
Questions to Think About
1
Why might a crew choose a combined (two-piece) foundation over a single precast block, even though it takes an extra installation step?
2
If you inherited a site with high groundwater pressure, which waterproofing method(s) from today would you prioritize, and why?
3
Why does bitumen fail specifically at the FBS footing-pad joint, when it works fine everywhere else on the same foundation?
4
Why do columnar and pile foundations get away with only horizontal waterproofing, when strip and slab foundations need both directions?
5
What would likely go wrong if backfilling and vertical waterproofing were done in the wrong order?
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31.

END OF LECTURE 5
Thank You
Next time, in Lecture 6: earthwork and excavation — how the ground itself is prepared before any
foundation goes in.
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