Showing posts with label Materials. Show all posts
Showing posts with label Materials. Show all posts

Wednesday, April 4, 2018

Damp-proof membranes (DPMs)

April 04, 2018 0

Damp-proof membranes (DPMs)

DPMs are sheet or liquid membranes designed to resist damp
caused by capillary action. They do not have to perform as
well as tanking membranes, which must resist water pressure.
DPMs may be positioned under site slabs providing the hardcore
is smoothed with 25 mm minimum rolled sand or preferably
25 mm smooth blinding concrete. This position is more
vulnerable to damage than placing them over smooth finished
site slabs. In this position the membrane can prevent
satisfactory bonding between slab and screed, so a thick
screed is needed, ideally at least 63 mm.
DPMs must be carried up to lap or join DPCs in walls. Brushapplied
membranes are better than sheets in this respect.
Care must be taken not to penetrate membranes when laying.
Any pipe ducts must be in position before screeds are poured,
as any subsequent chasing could well damage the DPM.


Concrete – some types and treatments

April 04, 2018 0

aerated concrete A lightweight concrete with no coarse

aggregates, made of cement, lime, sand and chemical admixtures

which cause bubbles to make a cellular consistency. It

has low strength but good insulation properties. It is easily cut

and nailable. There are many grades, some unsuitable below

ground. Water absorption will impair its thermal performance.

bush hammering Tooling concrete or stone with a compressed

air hammer to remove 1 to 6 mm of the outer skin to

reveal a surface texture that improves its appearance.

granolithic finish A thin topping of cement, granite chippings

and sand laid over a concrete slab, preferably as a

monolithic screed to provide a good wearing surface. Can be

made non-slip by sprinkling carborundum powder over the

surface before final trowelling.



glass-reinforced concrete (GRC) Precast concrete, reinforced

with glass fibre to make thin panels with improved

strength and impact resistance.

polymer-impregnated concrete Concrete made with a

polymer to improve the strength by filling all the voids normally

left in conventional concrete. Water absorption is thus

reduced and the concrete has greater dimensional stability.

refractory concrete Concrete made with high alumina

cement and refractory aggregate, such as broken firebrick, to

withstand very high temperatures.



Brickwork and Blockwork

April 04, 2018 0

Brick sizes

The work (actual) size of the standard brick is
For the co-ordinating size, which includes the width of one
mortar joint, add 10 mm, i.e.
225  112.5  75 mm
Metric modular sizes:
190  90  65 mm
Other less available brick sizes:
215  102.5  50 mm
215  102.5  73 mm
215  102.5  80 mm

215  102.5  65 mm

Weights of bricks

kg/m3

Blue 2405
Engineering 2165
Sand cement 2085
Fire brick 1890
London stock 1845
Sand lime 1845
Flettons 1795
Red facings 1765
Diatomaceous 480