INJECTED DAMP-PROOF COURSE
When most people talk about damp-proofing this is what they mean and
involves drilling a horizontal line of holes into the brickwork at the
base of walls and then injecting a damp-proofing fluid into the wall in
order to provide water-repellent or pore blocking material throughout
the cross section of the brickwork in order to from a damp-proof course
to prevent any ‘rising dampness’ from the ground. The effectiveness of
this form of damp-proofing is reliant on a number of factors such as the
suitability of the wall for treatment and the type of fluid used for the
damp-proofing treatment.
Most damp-proofing fluids used nowadays are bases on silicone resins,
aluminium stearate or sodium/potassium siliconates and are either spirit
based or a concentrated solution which is to be diluted with water.Both
spirit based and aqueous damp-proofing fluids do not block off pores and
capillaries in brickwork but line them with a water repellent material.
This fluid alters the surface tension of the brickwork and instead of
the normal upward capillary action is reverse as the meniscus is
inverted which tends to reverse the upward path of moisture.
One of the problems with chemical damp-proofing systems is that,
contrary to popular belief, they do not completely saturate the
brickwork with damp-proofing fluid or force all the water out of the
bricks as the damp-proofing fluid advances through the thickness of the
wall. The effectiveness of an injected damp-proof course can be affected
by the type of brickwork, porosity and thickness of the wall and also
the effectiveness of the operator. Instead of forming a continuous water
repellent band the fluid follows the path of least resistance in the
brickwork in a process known as ‘viscous fingering’ where fingers of the
injected fluid form when the fluid fills larger pores or cracks in the
brickwork. When a wall is wet it also causes more viscous fingering and
therefore the damp-proofing fluid will have even less effect than
intended. The only way to reduce viscous fingering is to use a
low-pressure injection or gravity diffusion damp-proofing system.
Most manufacturers and installers of chemical damp-proof course will
concede that an injected damp-proof course will not itself stop rising
dampness from the ground and it is only likely to control rising
dampness and that for rising damp to be stopped then specialist
water-proof rendering has to be undertaken at the same time. So what
they are, in effect, saying is that chemical damp-proofing does not act
as a total damp inhibitor and the system relies on the effectiveness of
the waterproof plaster. This is usually a dense render comprising of 3
parts sharp sand and 1 part cement with an integral waterproofing
additive such as Sika 1 added to prevent the passage of moisture through
the render and on to the finished internal plaster. Unfortunately the
use of these hard and impervious plasters can result in moisture and
salts becoming trapped behind the plaster causing them to be displaced,
usually higher up a treated wall, where they can easily evaporate.
Alternatives to pressure injection damp-proofing include :-
Freezteq- ( Frozen damp-proof course system . British Board of
Agrément Certificate 92/2849)
Involves drilling holes at the base of walls to within 25mm of the wall
thickness and then inserting frozen ice sticks of damp-proofing fluid
into the holes and then after they have melted and diffused into the
brickwork repeating the process of inserting the frozen ice sticks of
damp-proofing fluid a further three times with the entire operation to
be completed.The sticks come delivered unfrozen in plastic sachets and
the damp-proofing fluid is a clear liquid and once frozen they look like
ice-pops.
Advantages- no injection pump is required as the damp-proofing fluid
diffuses into the wall slowly as the ice-stick melts.
Disadvantages-Time consuming. Fluid needs to be frozen, then sticks
inserted four times over to achieve full damp-proof course
Slurry injection- ( e.g. Vandex Injection Mortar DPC)
Involves drilling 18–20 mm holes on a mortar line, roughly at 230 mm
apart from both sides of wall at an angle of around 30º downwards to a
depth equivalent to the thickness of the wall.Holes from either side are
staggered to give an overall spacing of 115mm.The holes are then flushed
out with water to remove any dust. The damp-proof injection mortar is
then mixed with water, but only enough for a round 30 minutes use as it
solidifies after this, to form a smooth paste and then injected into the
wall using a caulking gun. By means of a chemical reaction between
reactive salts in the structure, moisture, and the chemicals ( bentonite),
a crystalline growth will take place which will block all pores and fine
cracks. This creates a barrier through which moisture cannot pass. The
mortar will tend to tend to fill any fine cracks or voids and will set
to form a solid damp-proof material and also replace any material
removed by the drilling operation.
Advantages-good for thick walls and stone walls which may be unsuitable
for pressure injection. Sodium bentonite has proven water-proofing
qualities
Disadvantages- Time consuming and messy.Large holes are drilled into the
walls which can be unsightly even when they are plugged with mortar.
Silane(cream d.p.c.) diffusion - ( e.g. Peter Cox-Drywall
Diffusion DPC- British Board of Agrément Certificate 02/3976 or
Safeguard Dryzone BBA 97/3363)
Drilling 10mm holes into a mortar joint and then injecting a
damp-proofing cream into the holes. This thixotropic silane cream is
intended to form a barrier against rising damp. As the cream slowly
diffuses it releases a silane vapour which reacts with the silica in the
masonry to form a water repellent resin.
Advantages- no injection pump is required as the cream can be injected
using a caulking gun or hand-pump.
Disadvantages- can be messy as the cream never seems to come out of the
tubes as neatly as required
Siliconate transfusion - ( e.g Wykamol Siliconate K DPC- British
Board of Agrément Certificate 02/3961)
Holes are drilled into the wall and then a series of transfusion units
and tubes are fitted into drill holes. The transfusion units are then
filled with enough aqueous potassium methyl siliconate fluid to saturate
the brickwork and this is then gravity fed from the units into the
brickwork in order to provide a layer of damp-proofing fluid across the
cross-section of the wall.
Advantages-slow release of fluid ensures a better distribution of the
damp-proofing fluid and lessens any viscous fingering.
Disadvantages- time consuming.
If you need any more information about the effectiveness and suitability
of chemical damp-proofing systems then please call us on 020 8226 3101
or e-mail
enquiries@dampbuster.co.uk