Proof Courses - Q's & A's
WHAT IS A CHEMICAL DAMP
PROOF COURSE USED FOR:
Chemical damp-proof courses
are inserted to control the vertical passage of moisture from the ground
and are almost all installed in properties where no damp-proof course
exists, or it has broken down with age (not a common occurrence, contrary
to popular opinion in the Trade).
with uses call our experts on 01626 331351.
HOW ARE CHEMICAL DAMP PROOF
Chemical damp-proof courses
should be installed in a position in accordance with good practice as
described in BS 6576:1985, "Code of Practice for the Installation
of Chemical Damp-proof Courses", a minimum of 150mm (6 inches)
above external ground level, in external walls.
Additional rules apply to
cavity walls, vertical damp proof courses and internal walls.
They are installed in walls
by various methods depending on the particular system being employed,
but the ultimate objective is to provide a water repellent or pore blocking
material in a continuous horizontal band in the masonry, thereby to
provide a 'barrier' to water rising from the ground.
These days Silicone Cream
emulsion is used most commonly. It requires no special equipment to
install, no pressure and has no chemical hazards.
with installation methods and rules call our experts on 01626 331351.
WHAT IS RISING DAMP - Natural
or Man Made?
True rising damp is natural
ground water rising by capillary action through porous building materials.
The natural water in the ground under a building climbs up through
the porous parts of the walls and floors up to the point where surface
evaporation stops further climb.
Man-made Rising Damp arises
from water leaks and 'bridging' of the damp proof course. It is usually
much more damp to the touch because more water, near to the surface
is available, so the damage is more sudden and severe.
with the causes of damp call our experts on 01626 331351.
WHY IS RISING DAMP
SOMETIMES REFERRED TO AS A MYTH?
Because most dampness problems
in buildings are NOT caused by natural rising dampness.
They are entirely Man Made!
In most cases they are caused
by building defects, such as:
- water leaks inside the
building - particularly in modern buildings fitted with plastic damp
proof course and membrane materials
- water leaks under the
building or from next door or the road - particularly in older buildings,
built prior to the use of plastics
- 'bridging' of the damp
proof course - mainly by paths, roads, steps and added structures
with the MYTHS call our experts on 01626 331351.
WHAT IS THE BIGGEST
MYTH ABOUT DAMP PROOFING?
That traditional damp proof
courses (slate, stone, bitumen) break down!
Buried inside the wall structure
they do not significantly break down, so do not need replacement.
with diagnosis call our experts on 01626 331351.
HOW DOES A DAMP PROOF COURSE
The only continuous pathways
through which water can rise through a wall are the mortar beds: for
water to pass, say, from brick to brick it must still cross a mortar
bed (bottom of figure, right). It is therefore essential that the damp-proofing
material impregnates the mortar courses since these form the major pathway
for the rise of water within walls. Damp-proofing the masonry units
(e.g., bricks) alone is of very little value! Porous mortar and impervious/water
repellent brickwork will still allow rising dampness to occur. However,
if the pores in the mortar line are made water repellent or blocked
then the water cannot rise since it cannot traverse the mortar beds
to do so.
with how damp proof courses work call our experts on 01626 331351.
NEW BUILD OR NEW MORTAR
- DOES IT MATTER?
In the majority of older
properties the mortar is not alkaline, so that the water repellent formulations
based either silicone resins, aluminium stearate, or methyl siliconate
(sodium or potassium methyl siliconate) can be used. Occasionally, however,
the mortar may highly alkaline such as in a recently constructed wall
(e.g. where the physical damp-proof course has been omitted). This will
exclude the use of the methyl siliconates since the highly alkaline
conditions found, for example, in new mortars prevent the formation
of the water repellent resin.
with types of damp proofing fluids and creams and where to use them
call our experts on 01626 331351.
AND COVERING A DAMP PROOF COURSE
Care should be taken to ensure
that the damp-proof course is not bridged by high external ground levels,
blocked cavities or debris piled against the wall; ground levels should
be lowered, cavities cleaned out or the area below the inserted damp-proof
course might be 'tanked' internally if deemed necessary.
NOTE: Should minor bridging
of an effective damp-proof course occur, for example by moderately porous
plasterwork, then it is highly unlikely that the dampness would continue
to rise to its original height. If the damp-proof course is effective
the pathway for moisture should be limited within the wall itself. Any
porous plasterwork is at the surface where evaporation would serve to
restrict the flow of rising water through it.
Therefore, moisture is unlikely
to pass through this relatively narrow pathway at a rate sufficient
for it to reach the height of rise prior to the insertion of the damp-proof
course assuming, of course, that the injected damp-proof course is moderately
effective. Problems of this type together with defects in construction
of the floor/wall junction usually manifest themselves at the base of
with 'bridging' and blocked cavities call our experts on 01626 331351.
Learn from the UK's top
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Site written by: David
David Moore, B.A. (Hons.),
C.T.I.S., C.R.D.S. Technical Author
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