and perpendicular to the base arm
Note: Spray formboards with form-release oil
Metal wedges inserted into the ends of the form ties will
when cutting.
to facilitate their removal after the concrete has
keep the formboards from spreading. The next step is to
pour the footings before pouring the foundation walls.
Foundations and Concrete
249
been poured. But be careful not to spill the oil
the anchor bolts, pins, form ties, and the like. Use
P R O T I P
onto the rebar, anchor bolts, or old foundation
a cutter-bender to cut and bend bars on small
because the oil will weaken the bond with new
jobs. When rebar is delivered, store it above the
if you’re retrofitting anchor
concrete.
ground—dirty rebar doesn’t bond as well.
bolts to existing mudsills, begin
with a wood-cutting bit to drill
anchor bolts. Place 1⁄2-in. or 5⁄8-in. anchor bolts
adding steel
through the sill. then switch to a
no more than 6 ft. apart in one-story house foun-
rotary hammer bit to drill into
Structural steel used in renovated foundations
dations and no more than 4 ft. apart in two-story
the concrete foundation.
includes rebar; anchor bolts to attach framing to
foundations. In earthquake zones, 4-ft. spacing is
Because the tip of the wood bit
concrete; pins (or dowels), which tie old founda-
acceptable, but conscientious contractors space
invariably hits concrete as it
tions to new ones; and a plethora of metal con-
the bolts every 3 ft. There also should be an
clears wood, you’ll ruin the bit
nectors, including the popular Simpson Strong-
anchor bolt no farther than 1 ft. from each end of
before long. But rotary hammer
Ties, which strengthen joints against earth-
the sills. For maximum grip, use square washers.
bits are too slow and ineffective
quakes, high winds, and other racking forces.
When pouring a new foundation, use J-type
at cutting wood.
anchor bolts; the plastic bolt holders shown in
rebar. Rebar in foundations is not specified by
the bottom photo on p. 234 will position the
all building codes, but it’s cost-effective insurance anchor bolts in the middle of the foundation wall.
against cracking caused by lateral pressures of
When retrofitting bolts to existing founda-
soil and water against foundations. Rebar also
tions, use 5⁄8-in. all-thread rod cut to length. Rod
can eliminate concrete shrinkage cracks.
lengths will vary according to code specs and sill
Common sizes in residential construction are
thickness. For example, a 10-in. rod will accom-
No. 3 (3⁄8 in. in diameter), No. 4 (1⁄2 in.), and
modate a washer, nut, and 1-in.-thick mudsill
No. 5 (5⁄8 in.). One common configuration is
and will embed 7 in. in the concrete. You can also
No. 4 rebar spaced every 32 in. or 48 in. on center.
buy precut lengths of threaded rod, called retrofit
In footings and foundation walls below grade, bolts, which come with washers and nuts. Drill
place rebar back 3 in. from forms and at least
through the mudsill into the concrete, clean out
3 in. above the soil. On the inner side of the
the holes well, inject epoxy, and then insert the
foundation walls, rebar can be within 11⁄2 in. of
rods and bolts. The procedure is essentially
the forms. You should run rebar the length of a
the same for epoxying rebar pins to tie new
foundation, tying the lengths together after over-
concrete to old.
lapping them at least 12 in. Use prelooped wire
Because bolts, all-thread rods, and other tie-
ties to join them. (Wire ties don’t lend strength;
ins are only as strong as the material around
they simply hold the bars in place before and
them, you should center bolt holes in the top of
during the pour.) Use wire ties to attach rebar to
Masonry anchors:
1. Anchor bolt holder (monkey paw)
2. Anchor bolt holder
3. Simpson SSTB anchor bolt, used
with seismic hold-downs
4. J-bolt anchor
3
5. Square plate washers
2
6. Concrete screws (high-strength
threaded anchors)
4
7. Lag screw within expansion shield
8. Pin-drive expansion anchor
9. Wedge expansion anchor
10. Expansion shields for
1
5
machine screws
10
6
7
8
9
250 Chapter 10
embed rebar at least 7 in. into the top of founda-
tions, and at least 4 in. into the side of 8-in.-thick
walls. Extend rebar epoxied into the old founda-
tion at least 18 in. into new formwork, and over-
lap rebar splices at least 12 in.
attaCHing tHe mudsill
Builders may attach new mudsills at different
stages of form assembly. But here are the essen-
tials. Before nailing up the mudsill (to the bottom
of the pony-wall studs), predrill for anchor bolts,
as described earlier, making sure that no bolt
occurs under a stud. If local codes require metal
termite shields, tack them to the underside of the
mudsill after drilling it for anchor bolts. Then,
using a pneumatic nailer, end-nail the sill to the
studs, using two 16d nails per stud. If there isn’t
enough room to end-nail upward into the sill,
jack the mudsill tight to the studs and toenail
down from the studs into the mudsill.
Once the mudsill is nailed to the studs, insert
anchor bolts into the predrilled holes, screw on
Retrofitting anchor bolts requires drilling in tight spaces.
washers and nuts, and tie the free ends of the
Bolts should be centered in the sill and embedded at least
bolts to the rebar. At this point, the nuts should
7 in. into the concrete.
be just snug; you can tighten them down after the
concrete has cured. If you end-nailed the mudsill,
make sure the studs are tight to the top plates
the old foundation and drill them 6 in. to 8 in.
deep, or whatever depth local codes require. Use
an impact drill if you’re drilling concrete. Drill
holes 1⁄8 in. larger than the diameter of the bolt so
there’s room for epoxy. For example, for 5⁄8-in. all-
GeTTinG a GooD epoxy BonD
thread rod, drill 3⁄4-in. holes; for 1⁄2-in. rod, drill
5⁄8-in. holes. If you make the holes larger than
When you’re done drilling into the foundation, you need to clean each hole thoroughly
that, the bond probably won’t be weaker, but you
because dust clinging to the sides of the hole greatly reduces the epoxy’s bond
may waste a lot of expensive epoxy.
strength. For this, use compressed a
ir to blow dust from each hole and then a hole-
Note: To anchor mudsills in retrofits, threaded
cleaning brush in a repeating blow-brush-blow-brush-blow cycle. Before blowing, put
rod and epoxy have largely replaced expansion
on a respirator mask and eye protection. then fit a tube into the hole and attach a
bolts. These chemical bonds are almost always
blow nozzle. Continue the cycle until the hole’s clean.
stronger than mechanical ones, and epoxy’s com-
to avoid air pockets in the epoxy, fill each hole from the bottom with a long-nozzle
pressive strength is roughly four times greater
injector. the epoxy should flow in easily. As you insert the threaded rod or piece of
than that of concrete.
rebar, twist it one full turn clockwise to distribute the adhesive evenly. if no epoxy
Pins. Concrete cold joints are inherently weak.
oozes out of the top of the hole
Cold joints occur when new concrete is butted
when you’ve fully inserted the
against old or when separate pours create seams.
threaded rod, you didn’t use
To keep cold joints from separating, you need to
enough epoxy or the epoxy
join them with rebar pins. When drilling lateral
leaked out. Leave the failed bolt
holes to receive rebar pins that tie old walls to
new (or secure a foundation cap), angle the drill
in place, and drill and insert a
bit slightly downward, so the adhesive you’ll
new one next to it. or remove
inject into the hole won’t run out and so pins will
the bolt and refill the hole com-
be less likely to pull out.
pletely with new epoxy.
Local codes and structural engineers will have
the final say on sizing and spacing rebar pins.
But, in general, drill 5⁄8-in. holes for 1⁄2-in. rebar
to be epoxied; drill holes at least every 18 in. and
Foundations and Concrete
251
mercial stake puller. If you leave the stakes in
until the next day, you’ll likely be able to pull
them only if you remembered to oil them first.
Otherwise, cut the tops of the stakes off and leave
the rest embedded in the new concrete.
Hammer the outside of the formboards, then
use a concrete vibrator to drive out the air pockets.
For this, insert the hoselike vibrator into the
forms. As the concrete approaches the tops of
forms, signal the pump to shut off so that the
concrete doesn’t spill over the sides. When the
forms are full and vibrated, use a trowel to flatten
the top of the wall and sponge off any globs on
the stakes and forms. Allow the concrete to
cure three days at a minimum and seven days
for the optimum before removing the forms and
shoring, replacing the siding, and tightening
down the washered anchor bolts. For further
protection against moisture, apply below-grade
waterproofing to the outside wall and footing
Rebar epoxied into the old
before backfilling.
foundation is spliced to steel in
a perimeter wall of the new
This Simpson HD8A hold-down ties framing to the
foundation. Part of this new wall’s
foundation and transfers tension loads between floors.
footing underpins (flows under)
the old concrete. The chalkline
Capping
immediately above the rebar
marks the top of the foundation
above. Jack up any studs that have separated.
a Foundation
(see arrow).
You may also need to brace the pony wall if it’s
loose, which is often the case if you have to
Capping an old foundation with new con-
demolish siding to remove it. Pony walls should
crete is relatively rare but is done when the
be plumb and aligned with the forms.
existing foundation is in good condition and
needs to be raised because the house’s framing
pouring ConCrete
is too close to the ground, allowing surface
After installing the outside formboards, you are
water to rot sills and siding.
almost ready to pour. If you are using a 2-in. hose
the new cap must be 8 in. above grade. at
(interior diameter) to pump the concrete to the
P R O T I P
the very least, that means shoring up the struc-
site, make sure there is at least a 3-in. clearance
ture, removing the existing mudsill, shortening
between the edge of the formboard and the out-
if you
the pony-wall studs, drilling the old founda-
have a septic tank, show
side edge of the new mudsill to accommodate the
the driver of the concrete-mixer
tion, epoxying in rebar pins to tie the new con-
width of the pump nozzle. If necessary, notch
truck where the tank and fields
crete to the old, and pouring new concrete atop
the forms so the nozzle can fit. The top of the
are so he or she doesn’t drive
or around some part of the existing foundation.
form should be slightly higher than the bottom
over them. after the pour, make
that’s a lot of work. so if the existing founda-
sure the driver doesn’t rinse and
of the mudsill.
tion is crumbling or lacks steel reinforcement,
empty the truck’s residue on your
Fill the footing to the bottom of the wall
you should replace it altogether.
yard. you may want to plant a
forms before filling the forms. Some concrete
on the other hand, if the house lacks pony
lawn there someday.
may slop over from the walls onto the footing
and bottom formboards, but slopover isn’t a
walls and the joists rest directly on the founda-
problem if you remove the concrete from the
tion, you have basically two options: (1) grade
form bottoms before it sets up. That will allow
the soil away from the house to gain the neces-
easy removal of the forms once the concrete
sary height, which may not be possible if the
has cured.
foundation is shallow, or (2) jack up the house
When the concrete begins to set but is not
at least 8 in., which means hiring a house
completely hard, pull out the perforated steel
mover. Here again, replacing the foundation is
stakes holding the bottom formboards in place.
usually more cost-effective.
To do this, remove the duplex nails and then use
either a pipe wrench to grip the stakes or a com-
252 Chapter 10
Cubic yards of Concrete in slabs of various thicknesses*†
AREA (sq. ft.)
1.0 in. 1.5 in. 2.0 in. 2.5 in. 3.0 in. 3.5 in. 4.0 in. 4.5 in. 5.0 in. 5.5 in. 6.0 in.
10
0.03
0.05
0.06
0.08
0.09
0.11
0.13
0.14
0.15
0.17
0.19
20
�
�
0.06
0.09
0.12
0.16
0.19
0.22
0.25
0.28
0.31
0.34
0.37
30
0.09
0.14
0.19
0.23
0.28
0.33
0.37
0.42
0.46
0.51
0.56
40
0.12
0.19
0.25
0.31
0.37
0.43
0.50
0.56
0.62
0.68
0.74
50
0.15
0.23
0.31
0.39
0.46
0.54
0.62
0.70
0.77
0.85
0.93
60
0.19
0.28
0.37
0.46
0.56
0.65
0.74
0.83
0.93
1.02
1.11
70
0.22
0.32
0.43
0.54
0.65
0.76
0.87
0.97
1.08
1.19
1.30
80
0.25
0.37
0.49
0.62
0.74
0.87
1.00
1.11
1.24
1.36
1.48
90
0.28
0.42
0.56
0.70
0.84
0.97
1.11
1.25
1.39
1.53
1.67
100
0.31
0.46
0.62
0.78
0.93
1.08
1.24
1.39
1.55
1.70
1.85
200
0.62
0.93
1.23
1.54
1.85
2.16
2.47
2.78
3.09
3.40
3.70
300
0.93
1.39
1.85
2.32
2.78
3.24
3.70
4.17
4.63
5.10
5.56
400
1.23
1.83
2.47
3.10
3.70
4.32
4.94
5.56
6.17
6.79
7.41
500
1.54
Renovation 4th Edition Page 59