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for yourself - look for these clues in the photographs below
1. Can you see the original
damp proof course?
Yes = it looks like
a dark line and if I scrape it looks like slate or bitumen/felt. (It
is most likely to be just under the air brick, if you have a timber
floor, as part of the original protection of the floor joists)
No = there may not
be one, or, more likely it has been covered over with soil, steps, pathways,
roadways or other building alterations. This is called 'bridging' the
damp proof course and will give you all the symptoms of rising damp.
2. Is the damp proof course
line that you can see about 6" (150mm) or more above the outside
Yes = good, that is
correct. This drop from the DPC to the ground is to protect against
splash-up by falling rain. Check that the gutters and downpipes are
in good condition and go outside in pouring rain to check that they
can cope in a downpour.
No = bad. You will
either need to lower the ground level or insert a new DPC at the correct
height and 'tank' the walls below that new level.
3. Can you see fluffy
white 'salts' on the wall?
Yes = you have rainwater
splash up or gutters overflowing. Or, under a window frame, you may
not have a clean 'drip' slot. Check the exterior walls for defects,
check gutters and downpipes, check the pointing in the joints, treat
with Ultra Proof waterproofer.
No = your dampness
may be due to 'hygroscopic salts' deposited in the wall from chimney
deposits (after burning coal or wood), or from a previous use of the
building (e.g. coal shed, animal food store, butchers shop). Treat with
Salt Neutraliser and replaster to our 'tanking' specification using
BondAcryl. In severe cases it is best to use the Mesh Membrane wall
lining system, rather than 'tank' or replaster - chimney salts can burn
back through even the best render backing coats sometimes.
4. Do you have a cavity
wall or a solid wall?
Yes = because you
see only bricks laid along their length - no brick ends visible at any
level. This type of wall should resist water penetration, because of
the air gap. If it is showing damp symptoms on the inside the cavity
may be blocked or the wall ties may be dirty.
No = this wall is
of solid construction. You can see rows of brick 'stretchers' and then
mixed rows of 'headers' and 'stretchers'. Penetrating damp or splash
up rainwater can go straight through.
5. Have you got a timber
Yes = look for the
air bricks. Even if they are present the floor itself may have rotted
and been replaced in concrete, 'bridging' the DPC and often causing
rot in the skirting boards.
No = no air bricks,
all concreted. Check you do not have partial solid floors, with sections
of timber flooring cut off from an air supply - they will rot.
6. Are you sure that you
still have a timber floor?
Yes = find the air
bricks. Even if they are present the floor itself may have rotted due
to blockage or shortage of air flow. Fit new bricks to the current standard.
No = the old air bricks
are still there on the outside but it is filled with concrete inside.
Take them out and make good with bricks and mortar, unless they are
acting as cavity wall vents or provide ventilation, via a pipe, to a
remote timbered area.
you see a water source
A. Green stuff on the wall
- look up - are the gutters and downpipes OK in a really heavy downpour?
B. White stuff on the wall
- it indicates dampness - check window cill 'drips', roof tiles and
slates, flashings and abutting structures (even stored goods against
C. Neighbours garden, road,
path or garden higher than yours - water flows downhill!
D. Water leak from underground
- is an area of garden or path strangely green at the height of a Summer
Surface salting also visible
Green 'verdigris' caused by
rain water splash up
Salting in brickwork above
Internal view - wet skirting
How to install a damp
proof course - first,
check for high ground levels, leaking gutters and downpipes, water leaks.
12mm diameter holes at 115mm intervals in the mortar course (or via
the brickwork, angled down to meet the mortar course) selected to be
at least 150mm above outside or abutting ground level
the extension nozzle to the cartridge tube and load into the skeleton
cream from the bottom of the hole outwards until the hole is full.
to our specification. Treat any skirting boards or joinery with Boron
be capped with mortar or fitted with a plastic plug
to a minimum of 1.2 metres internally, to our specification, using sand
and cement and Rendapruf integral waterproofer, is required to finish
the job and to prevent 'salts' damage to plaster finishes and decorations.
required: Quick Cream DPC, Skeleton Gun - either a 380cc or professional
Products: Rendapruf Replastering Additive (5 litre), Wall Plugs,
Boron Ultra Gel (2.5 litre), UltraProof exterior wall treatment (5 litre
or 25 litre), Anti-Mould Paint (2.5 litre), Condensation Testing kit,
Salt Neutraliser (5 litre), BondAcryl Tanking liquid (5 litre).
12mm masonry bit, electric hammer drill, eye protection.
Typical usage rates:
4.5 inch thick (115mm) single
leaf wall - 1000cc (1 litre) per 9 metres, inject from either side
9 inch thick wall (230mm)
double leaf solid or cavity - 1000cc(1 litre) per 4.5 metres, inject
from one side or from both sides.
18 inch thick wall (460mm)
solid or random fill - 1000cc (1 litre) per 2 metres, inject from both
Installing a Cream DPC
How Rising Dampness is
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Site written by: David
David Moore, B.A. (Hons.),
C.T.I.S., C.R.D.S. Technical Author