What is a chemical
damp proof course
Chemical damp-proof courses
are inserted to control the vertical passage of moisture from the
ground upwards through building materials (brick, stone, concrete)
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 Damp Proofing Trade).
We specialize in finding
out the real cause of your dampness and then giving you the facts.
Only when you have those facts should you make any decisions about
products. In many situations no specialist products are required -
only general maintenance items available from B&Q and Homebase.
If you do need anything special we may offer to supply it - but you
have no obligation to purchase from us.
Most chemical damp proof
courses are not required and have no useful effect. There are simple
reasons for this, which are happy to discuss by letter, E Mail or
How is a modern chemical
damp proof course installed
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. If the installer does
not follow the basic rules the damp proof course will be useless.
Additional rules apply
to cavity walls, vertical damp proof courses and internal walls.
So called DPCs 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,
to act as an effective '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.
Check the source of your
damp for yourself - it is not difficult - click
See our Article about installing
different types of Damp Proof Course - click
See our Shop for damp proofing
pumps and equipment - click
For help with installation
methods and rules call our experts on 01626 872886 .
- E: Mail us at email@example.com
What types of damp
barrier can be used as a damp proof course?
Historically, a variety
of materials have been installed during the building process - stone,
slate, lead, zinc and stainless steel and more recently (and currently)
However, once a building
has been erected it is more difficult to insert a physical DPC (although
stainless steel sheet can be vibrated into walls, via saw cut slots),
so other methods have been developed for remedial action;
1. Water repellent - liquid,
paste, gel, or cream by injection - amateur and professional
2. Pore blocking - cement
based mortar, by injection - mainly professional
3. Osmotic - passive or
active, via embedded wires - mainly professional
with types of damp proof course call our experts on 01626 872886 .
How are different
types of damp proof course installed?
1. Water repellent type-
holes, usually between 10-12mm in diameter, are drilled either into
the mortar joints or via the bricks or stones and the chemical is
injected using a high pressure pump (liquids) or low pressure hand
pump or skeleton gun (creams, pastes and gels). The chemicals spread
through the damp masonry, over a period of several months, to join
up and form a continuous water repellent layer. This is NOT a solid
vapour barrier - it prevents further liquid water from passing through,
thus allowing the wall to dry out.
2. Pore blocking type
- the cement based injection mortar is mixed with water to form a
'slurry' and injected from a re-usable, plastic bodied, heavy duty
'gun'. It rapidly sets, giving off great heat, to form a solid plug
in the wall. The holes are generally 18-20mm in diameter and this
method is only really suitable for thick, stable stone walls. The
injected mortar then slowly generates impermeable 'salts', which over
several months block the pores in the wall and prevent moisture from
rising. This method requires large drilling machines, expensive drill
bits and mortar guns, making it uneconomic for amateur use.
3. Osmotic types
- the old, 'passive' system used copper wires, which unfortunately
corroded, but the latest Lectros Active System utilises a titanium
wire, connected to a special mains powered control box, which is run
around the walls rather like a ring main. Bent at regular intervals
to form anodes, the wire loops are inserted into large holes drilled
into the wall (internally, externally or both if necessary). The wire
is hidden in formed "chases" or existing, raked out brickwork
joints and the whole system is earthed. The electricity from the mains
supply passes through a transformer, through the anodes and to earth,
setting up an electrical field, which repels the damp. The holes are
filled with a special mortar, to ensure good conductivity. This method
requires large drilling machines, expensive drill bits and special
mortars, making it uneconomic for amateur use.
with methods of damp proofing call our experts on 01626 872886 .
Why are Injection
Creams better than liquids, gels and solid sticks
The technical review below
summarises the problems of the last generation of liquid damp proofing
systems. Our New Generation Creams are infinitely better for the following
- no pressure is used
in placing the cream in the hole, so no losses down cracks and crevices
- gradual spread of the
cream giving even distribution, unlike liquid short term squirt
and stop techniques
- no solvents to evaporate,
so no smell, no health hazards and nice slow spread
- not caustic and non-staining,
unlike the old water based DPC Fluids (Siliconates)
- no solid stick to push
into a ragged hole and a lot cheaper
with Silicone Creams call our experts on 01626 872886 .
Do pressure injected
liquids work as a damp proof course
Unlike a physical damp-proof
course these injected liquid damp-proof courses do not form a 'discrete
impermeable plane', but more of a 'diffuse band'. When fluids are
injected into a heterogeneous substrate such as brick/mortar they
do not totally fill up the porous structures and neither do they completely
push out the water in front of the advancing injection fluid as is
so often claimed. Instead, the fluid tends to 'finger' within the
substrate, a process known as 'viscous fingering'. The fingers of
the injected material form when the fluid takes the lines of least
resistance such as the larger pores and cracks. Unfortunately, such
pathways are not the most important elements in the conductance of
water up the wall. Furthermore, the damper the substrate the greater
this fingering is likely to be, especially with solvent based systems
since these are not miscible with the resident moisture. Fingering
is also increased by injection at high pressure. Reduction of the
phenomenon is obtained by low pressure injection or, better still,
by gravity diffusion of the DPC fluid.
with pressure injected damp proof courses call our experts on 01626 872886 .
Why can liquid pressure
injection be incomplete
The result of the damp-proofing
fluids forming fingers give rise to non-impregnated 'pools' within
the wall through which water can continue to rise. In the case of
pressure injection damp-proof courses, this suggests that it is unlikely
that the diffuse band of the damp-proofing agent will be totally complete.
The resultant chemical damp-proof course may therefore not stop rising
dampness by causing an immediate cut-off of rising water above the
damp-proof course like that effected by a physical damp-proof course.
Instead, a relatively rapid decline in the moisture gradient should
occur above the inserted chemical damp-proof course due to the 'control'
exerted. Thus, in practice, the rising ground water should be reduced
to such a level that, in association with specialist replastering,
it should no longer cause decorative spoiling or damage.
with pressure injected damp proof courses call our experts on 01626 872886 .
What other factors
reduce the effectiveness of liquid systems
The efficacy of the water
repellent damp-proofing systems can be affected where there are detergents
(surfactants) impregnated into the wall by, for example, past leakage
from sink waste pipes. A similar problem may occur when walls are
sterilised against dry rot infection by biocide formulations containing
surfactants. The overall effectiveness of a remedial damp-proof course
can be investigated by examining the relationship between the distribution
of free moisture (water due to rising dampness or other source of
active water ingress) and contaminant salts (chloride and nitrate).
Where rising dampness is still active capillary moisture will be found
to the full height of salts. The absence of capillary moisture in
the presence of salts arising from rising dampness indicates that
drying back has occurred and that the damp-proof course is effective.
Intermediary stages are also found which demonstrate different degrees
of control of the rising dampness. If chloride and nitrate are not
detected in a sampled profile it is possible that the ingress of moisture
is due to recently developed rising dampness or more likely through
rainwater penetration, condensation, plumbing defect or other sources.
with pressure 'salts' analysis call our experts on 01626 872886 .
How do you test a
chemical damp proof course
When evaluating the efficacy
of remedial damp-proof courses care must be taken not to misinterpret
electrical moisture meter readings; high readings might not indicate
that the damp-proof course itself has failed. They may reflect a number
of possibilities including contaminated or inadequate plasterwork.
Thus, an accurate assessment of the efficacy of a damp-proof course
can only be undertaken by determining full moisture profiles linked
with analysis for contaminant salts. It is also important to give
consideration to the expected performance and limitations of the installed
system as described above.
NOTE: It is identified
in BS 6576:1985 that where timber suspended floors are encountered
the damp-proof course must be injected, where possible, below joist
level; this is to protect the embedded timbers from dampness and the
risk of fungal decay. However, given the likely efficacy of injection
systems the embedded joist ends could still remain in contact with
damp masonry even if above the injected damp-proof course and may
therefore remain at risk to fungal decay. It would be considered prudent
that in all cases where a damp-proof course is installed in relation
to a timber suspended floor, action is taken to protect any embedded
timbers just above and certainly below the injected damp-proof course
to prevent potential decay! Boron Gel, injected Boron Paste and the
insertion of a plastic membrane can all be used to protect vulnerable
joist ends and bearings. Do NOT bag joist ends in plastic - this can
lead to serious decay, due to condensation and lack of breathing.
with testing a damp proof courses call our experts on 01626 872886 .
Learn from the
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DIY Master Class in Dampness and Condensation - become your own
Expert in 1 hour! Buy our "Dampness in Buildings" reprinted
book by the great expert Graham Coleman. A great read, short and to
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This book was written by
Graham Coleman, who is a Lecturer in dampness and who has set many
of the examinations.
He confirms in his book
that a Damp Meter is not be be used to confirm that rising damp is
present and he also explains how proper tests can be performed.
In practice these tests
are rarely needed - simpler, less expensive options exist - but in
'legal' Cases Graham is often involved as an Expert Witness.
here to see our Dampness Guide for using a Damp Meter - page 1
here to see our Dampness Guide for using a Damp Meter - page 2