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Good Craftsmanship Guide

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Kevin Ellement

on 22 March 2010

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Transcript of Good Craftsmanship Guide

Good Craftsmanship Guide
Substructure
Cavities
Wall ties
Mortar
Thermal insulation
Openings
Lintels
Cavity trays
Bonding
Movement joints
Separating Walls
Appearance
Cold weather working
Additional guidance for timber frames
What to do:
locate dpc at least 150mm above external ground or
paving level
Do not use masonry cement as if it is OPC.
More masonry cement is needed - refer to manufacturer’s recommendations to keep mix proportions consistent
Problems to avoid:
Low strength
Variations in mix
Poor durability
What to do:
keep mixers and plant clean
store materials correctly
ensure that the mix is correct for:
- bricks/blocks being used
- location in building
- exposure of area
do not use washing up liquid
Note: do not
overdose; “more
is not better”
Do not use
unauthorised
additives such as
washing up liquid.
Problems to avoid:

Water crossing the cavity

Thermal bridging (cold spots)
What to do:
Follow the manufacturer’s instructions for built-in insulation (see packaging)

Support the bottom row of boards/batts using ties insulate the whole wall area, including below dpc
Install boards/batts with staggered joints

Butt boards/batts closely with no gaps
Ensure that insulation is fitted tightly against lintels, cavity trays and cavity closures.

Maintain a minimum 50mm clear cavity between partial cavity fill and the external leaf
Keep partial cavity fill securely in place using the
correct clips for the type of tie

Ensure that horizontal joints in partial cavity fill
insulation coincide with wall ties
Problems to avoid:

Water crossing the cavity.

Poorly fitted frames
What to do
Build masonry around:

The frame in-situ.

A profile/template (frame fitted later)
Ensure openings are of the correct size and square.

Butt brickwork closely against the frame (if built-in)
Provide vertical dpcs at jambs (either separate or
combined as part of a proprietary cavity closer)
Install dpcs in one continuous length.
Where separate vertical dpcs are used ensure they
protrude about 25mm into the cavity
Problem to avoid
Inadequate structural support
lintels should extend beyond the opening at each
end by at least the following
Problem to avoid
Water crossing the cavity
What to do
provide cavity trays where required by the design–over lintels, roof abutments, air bricks, meter boxes, etc.
Install cavity trays in one continuous length
extend trays at least 25mm beyond the cavity
closers, and cover the ends of lintels
Provide weep holes at max 450mm intervals (at least two per opening) with fair-faced masonry
Problems to avoid
Problems to avoid
Unstable walls

Differential movement

Poor appearance
What to do
Problem to avoid:

Excessive cracking
What to do:

Provide movement joints in the outer leaf to minimise cracking:
Use correct filler material in joints, e.g. for clay brickwork:

- flexible cellular polyethylene
- cellular polyurethane
- foam rubber

Ensure sealant is at least 10mm deep to ensure a good bond
Problems to avoid:

Poor sound insulation

Inadequate firestopping
What to do:
Ensure block type and thickness complies with design
Do not use cracked or damaged blocks
Use only butterfly or other approved ties
Maintain clear cavity width (where applicable)
Bed all blocks and fully fill perpend joints
Fill all gaps, however small
Bond external walls to separating walls:

Tooth alternate courses where blocks of the same
type are used.

Carry separating wall through to the cavity and tie the inner leaf to it where the separating wall uses denser blocks than the inner leaf of the external wall
Problems to avoid:

Unsightly brickwork

Colour variations

Materials damaged/stained

Finished work stained
What to do:
Ensure materials are stored correctly, away from site traffic
Protect bricks/blocks from rain, mud splashes, etc
Handle materials carefully during construction
Do not use chipped or fractured bricks for facework
Keep mortar mix and colour consistent (sand variations may be significant)
Unless blended before delivery, mix bricks from different batches to avoid colour patching
Use a gauge rod marked with heights of openings to keep courses to the correct height
Keep work level, plumb, and to design bond
Keep perpend joints plumb
Problem to avoid:

Frost damage
What to do:

Cover materials to prevent them becoming saturate and damaged by frost
This Good Craftsmanship Guide
highlights key problems with brickwork
and blockwork and gives guidance on
how to avoid them.

Problem to avoid:
Rising damp
What to do:

Keep cavities uniform and to the width specified in the design – at least 50mm.

Strike mortar off all joints as work proceeds.

Keep cavities clear of droppings and debris.
Bed ties a minimum of 50mm into each leaf.
Keep ties clean.
Ensure ties are level or slope outwards slightly.
Ensure drips face downwards in centre of cavity.
Much of the guidance in previous sections applies also
to timber frame. This section highlights additional
problems specific to brickwork and blockwork used as
cladding for timber frame homes.
Problems to avoid:

Moisture damage to the timber frame.

Masonry cladding not tied to frame adequately.

Damage due to movement of the timber frame.

Inadequate control of fire.
What to do:

Repair any damage to breather membrane.

Fix ties to the studs, not the sheathing.

Use the fixings specified in the design.

Space ties in accordance with the design, but not more
than 600mm horizontal and 450mm vertical.

Spacings at jambs of openings set ties within 300mm of the masonry reveal at 300mm maximum vertical spacings.
Full transcript