Glencoe: Section 60 Flashcards
What steps are involved in finishing concrete
Screeding, bullfloating, edging, jointing, floating, and troweling.
Screeding:
First step in finishing
concrete is struck off using a screed which rides on the edges of side forms or pipes. Two poeple move the screed in a sawing motion. Leaves surface level with coarse finish
Bullfloating:
After screeding, bullfloating makes the surface even more even with. A bullfloat is a wide, flat metal or wood pad that is pushed back and forth over the concrete to make the surface even. Long handle.
Darby:
Similiar tool to bullfloat but with a shorter handle.
When is bullfloating done?
shortly after screeding while concrete is still wet enough to allow a slight paste of mortar to be brought to the surface. There must be no water visible on surface. Otherwise excess amounts of fines and moisture will come to the surface
When is Edging and Jointing done:
When the sheen has left the surface, the concrete has started to stiffen.
Edging and Jointing
edging produces a rounded edge on slab to prevent chipping. The edger is run back and forth covering corse aggregate particls.
Immediately following edging, jointing is done. Jointing tool is used to cut control joints 3/4” deep into slab perpendicular to slab endge.
Why is jointing done?
shrinkage causes concrete to crack, joints controls where these cracks occur.
To ensure straight joints
guide the jointer with straight 1/8 or 1x10 called a guideboard.
Hand floating:
In some cases, additional floating step is done. Wood or metal trowels called floats further even the surface and compacts the surface mortal.
If the concrete is air-entrained, floating must be done with an
aluminum or magnesium float because wood sticks to the concrete.
If floating is the last step on finishing concrete, it may
be done a second time after the concrete has hardened slightly
Troweling:
For a dense smooth finish a steel trowel is used. For large areas a power trowel is used.
When can troweling be done
cannot be started until the concrete has hardened enough to prevent fine material and water from working to the surface. Concrete troweled too early will not be durable, too late will be difficult to finish.
For a fine textured troweled surface
trowling is immediately followed by a second where trowel is held flat with circular motions
For a hard steel-troweled finish
second troweling is delayed until oncrete is hard enough to make ringing sound under trowel. Trowel is tilted slightly and heavy pressure is applied to compact surface.
Frenso
another type of concrete finishign tool. Allows concrete finishers to trowel without having to use knee boards.
Kneeboard:
distributes the weight of a finisher over surface of concrete.
Why wont the concrete finished with a fresno be as dense as one finished with hand trowel
the finisher can not put as much pressure on a fresno
Special finishes
Colors, patterns, or texture.
When are special finishes done
after concrete has been placed but before cured
Broom finish
to make the concrete more slip resistant a stiff bristled brush is dragged over the surface in parallel strokes. After bleed water is gone.
Rubbed finish
shortly after concrete is hardened and forms removed, the surface is rubbed with abrasives to create a uniform surface that is very smooth.
Salt finish
broadcasting rock salt onto fresh concrete. Roller presses salt into surface. Salt is then washed away to leave shallow angular indentations.
After finishing flatwork, concrete should
be kept moist for at least 2 days to ensure hydration continues.
If the finished floor is exposed concrete, how long should the concrete be kept moist
at least 5 days.
What kinds of materials can cover the concrete during the curing process
burlap, canvas, or waterproof. if burlap is used, it should be kept wet by sprinkling it with water.
When can wall plates be laid out and construction continues on a flatwork
when the concrete has cured enough to withstand foot traffic
Placing concrete in unusually hot weather can
reduce its strength because workers add more water to the mix.
In hot weather, water and aggregates of concrete mix should be
kept as cool as possible before being mixed with the cement.
In hot weather, forms, rebar and subgrade
should be sprinkled with water to keep it wet.
If concrete is subjected to below freezing shortly after being placed
it can loose up to 50% of its strength.
Try to insulate it
What types of concrete can be used to counteract cold weather.
high-early strength, air-entrained, and low slump concrete.
You can kill a tree by too much
gradework
No more than X inches of backfill around tree.
12
Solid wood is used for many types of construction for several reasons:
1 strong, some woods are strong as steel
2 Easily fastened with snails, bolts, screws, glue
3 Wood buildings easily altered or repaired
4 Low heat conductivity reduces heat loss
5 accepts coatings such as paint and stains
6 resists acid, saltwater and corrosives
7 renewable
Most wood in united states is harvested from
north america
Benefits of taking good care of forest resources
Continued ability to harvest lumber
protection of important water resources
soil conservation
production of oxygen and absorption of carbon dioxide
preservation of wildlife and plant habitats and endangered species
maintenance of scenic areas
Forest ecosystems are
fragile and may take thousands of years to mature
Anatomy of a tree
Tips of roots, buds, leaves, thin layer of cells just inside bark called cambium.
Cabium
layer of living tissue that produces new wood called sap wood.
New bark is created along the
cabiums outer surface
Sapwood enables
water and nutrients from the trees roots to reach its leaves.
As sapwood builds up around the tree
the inner layers gradually turn into non living heartwood which does not contribute to growth but gives strength and stability
Water in a tree
enters through roots and goes up to the leaves
Photosynthesis
carbon dioxide in the atmosphere and water are combined in the presence of chlorophyll and sunlight to create food for the tree which is carried through the inner bark
In temperate climates, trees add X annual rings per year
one
Most annual rings consist of a light band formed in X and a dark band formed in
the spring
the summer
When resources are abundant, annual rings
will be thick.
What does hardwood and softwood indicate
Two main types of trees
Deciduous tree
coniferous tree
Which hardwood is softer than soft wood
balsa
Hardwoods are cut from
broad leafed deciduous trees
Softwoods are cut from
coniferous tree
Deciduous tree
Sheds its leaves annually during cold or very dry seasons. Usually in fall
Common hardwood trees
walnut, mahogany, maple, birch, cherry, oak, ash
Coniferous tree
produces seeds in cones and has needle like or scale leaves.
Common coniferous trees
pine, hemlock, fir, cedar, redwood
What has the global economy done to wood markets
wood used to be used in the area it was harvested, but improvements of shipping and technology allows us to import woods from all over
Log:
when a tree has been cut down and its limbs have been removed.
Lumber
logs that have been sawn lengthwise into smaller uniform pieces.
Two common ways of sawing logs
flat-sawing and quarter-sawing
Flat-Sawn lumber
Most construction lumber is flat-sawn
log is squared up lengthwise and sawn into boards. You can see growth rings run across the boards width. You can see distinctive archlike patterns on the face.
Pros of flat-sawn lumber
inexpensive, and greater width
Cons of flat-sawn lumber
more likely to warp and shrink
Quarter sawn lumber
premium wood. Log is first sawn into quarters. Boards are then cut from faces of each quarter. Growth rings run across thickness of board at 60 90 deg angles.
Rift-sawn boards:
quarter sawn boards with end grain art angles between 30 to 60deg
Pros of quarter sawn boards
low tendency to warp shrink or swell
more durable surface that does not twist or cup
hold paints and finishes better
Cons of quarter sawn board
more expensive and less plentiful than flat-sawn. Hard to find.
Moisture content (MC)
Expressed as a percentage of what the wood would weight if it were completely dry
How to calculate MC
Wood weighs 60 lbs
after drying it weights 50 lbs
10lbs of water evaporated
10 / 50 = 0.2
Fiber-saturation point
when the trees cell walls have absorbed as much water as it can hold
Most trees hit their fiber saturation point when
they are at 28% moisture content.
If the tree takes in additional moisture after the fiber saturation point
it stores it in the water cambium cell cavities
Dry water until its MC is 28 does what?
drying past that point?
wood retains its shape
wood begins to shrink
Seasoning
process of drying wood.
Two methods of seasoning
Air and Kiln
Air drying
rough lumber is stacked outdoors in layers separated by thin wooden cross piece called stickers. Lumber remains stacked for one to three months.
After air drying lumber has an MC of
19%
Kiln drying
lumber is stacked in layers with stickers. Placed in kiln
Kiln:
oven in which moisture airflow and temp are carefully controlled
after kiln drying, lumber mc is
10% moisture. This takes less than 4 days.
Wood continues to absorb of give off moisture depending on
the humidity
Seasonal expansion
as the air gets damper or dryer the wood absorbs or releases moisture and expands or shrinks accordingly
Shrinkage along length of boards is
so small its usually not a problem
Shrinkage across width of wood
can cause nails to pop in studs, floorboards to gap.
How to keep wood swelling or shrinkage to minimum
maintain consistent moisture. Temporarily condition home
The size of a board will vary about X percent for each Y percent change in moisture content
1%
4%
Equilibrium
when moisture content of the wood is balanced with the humidity of air.
Most common instrument for checking the moisture content of wood
moisture meter
Stickers:
thin pieces of wood used to separate wood layers
Lumber kept outside in storage should
be kept off the ground and covered loosely with waterproof material
Wood stored indoors will
absorb and release moisture until it reaches equilibrium
Flooring and wood paneling should be delivered several days in advanced and kept indoors to allow the wood to
reach equilibrium.
Conditioning
allowing wood to reach equilibrium
Grade
general indication of quality and strength of piece of lumber.
When is hardwood used
when durability or beauty is important
Hardwoods come in these three common grades
firsts and seconds (FAS)
Select
No. 1 common
Softwood grading is divided into two common group
green: Moisture more than 19%
dry: moisture less than 19%
Grading for softwood has been developed by
governmental agencies in cooperation with producers, distributors, and users
Each major lumber trade association has
developed their own set of grading standards
Grade stamp attributes
inspection seal grade species mill number moisture content
