to diagnose dampness
Help - 01626 331351 - discuss your building problem with a Qualified
Dampness Expert (C.R.D.S.) free of charge.
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A 'damp meter',
surface thermometer and memory hygrometer (see www.dampness-info.co.uk/meters.htm)are
useful tools for this diagnosis - if not available use the back of your
hand to assess the relative dampness of one affected area to another unaffected
your damp problem for yourself using this quick summary checklist
1. Can you see any 'black
Yes = Condensation
(use our Condensation Test kit
to confirm). Check ventilation and heating - redecorate with our Anti
Mold Emulsion. If you have a cavity wall (check the brickwork pattern
on the outside - lengthwise only bricks indicate a cavity construction)
you might have some dirty wall ties, giving rise to 'cold spots'. These
can be cleaned by taking out individual bricks. Severe black mold stains
can be covered, after treatment, with Stain
and Damp Seal Paint, to prevent the marks from 'grinning' through
your final paint colour.
No = Probably not
condensation although 'salts' from rising dampness can kill off mould,
masking part of the problem - is their any patchy mould? Try using an
illuminated map reading magnifier to view the wall surface. What can
you see - strands of fungus? Give us a ring for free advice on 01626
2. Can you see a 'tide'
line or damp stain above the skirting board up to a height of about 6"
- 18" (150mm - 450mm). Are the skirting boards damp or rotten?
Yes = may be rising
dampness - check exterior ground levels are at least 6 inches (150mm)
below the Damp Proof Course level, check that the wall plaster does
not 'bridge' the DPC or go down to a solid floor. Install a DPC and
Replaster to our Specification - use Renderproof
Waterproofing Additive. Also, check your neighboring properties
- are their floor levels above yours? Have they replaced any timber
floors with concrete of filled in a basement? Councils often raise the
level of the roads and pavements over the years, people often raise
the level of their gardens, or build things (like steps) against the
No = if the damp is
higher up the wall or patchy, more likely to be penetrating dampness
- check the exterior walls for defects, check gutters and downpipes,
check the pointing in the joints, treat with Ultra
3. Can you see fluffy white
'salts' on the wall or are they crunchy beneath flaking paint or lifting
Yes = you probably
have penetrating dampness - the 'salts' indicate that wetting has occurred
and drying out is taking place - treat with Salt
Neutraliser, if the plaster is not too damaged. 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. Have you got isolated
damp patches that come and go, particularly on or next to chimney breasts?
Yes = you may have
'hygroscopic' (means "attracts moisture from the air") salts
and chemicals from burning wood and coal, which have bled through the
plaster. Sometimes they show up as brown or yellow stains, particularly
in wallpaper. 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.
No = map out the areas
of dampness and look for the highest concentration - does this area
connect to a feature - like a radiator, boiler or sewerage pipe cover?
Have any recent changes been made to the building?
5. None of the above - are
the walls and floor visibly damp?
Yes = you may have
a water leak topping up your soil under your property - follow the water
leak testing routine in the left hand column.
No = we give up -
call us on 01626 331351 for a chat and we'll see if we can help.
to find the water source - do you have a water leak?
have a Water Meter turn off all your water using appliances for a few
hours and check to see if the meter dial moves.
A. Ask your local water Authority
to test your Water Mains pipe for leaks. Particularly ask them to test
your neighbour's supplies on both sides: if you live on a hill with
properties above you check all those on the high side of your house.
This service should be free of charge.
B. If you have liquid water
in your building (on a solid floor, or in a basement) ask the Water
Authority for an analysis - this will tell you where the water comes
from - mains, sewerage or spring/ground water.
C. Test your own drains -
test the foul water by finding the man hole cover, lifting it and running
a tap to see which hole your water flows from. Block this hole with
a rubber bung (Hire Shop or Builders Merchant - 4 inch or 6 inch). Then
fill up a ground floor sink or loo with water and mark the level. Leave
over night - if not at the same level next day you need a Drains Company
with a camera to investigate. Don't forget to remove the bung!
D. Test the surface water
drains - place a Dye Bag or granules of drains testing dye (Builders
Merchant) into the drain and fill up with water. Using a torch, at night,
look for signs of the coloured dye - it glows in the dark.
old walls - you must not use modern plasters or standard render
You may only
have contaminated plaster and the original source of the moisture may
have been successfully tackled (e.g. new damp proof course, water leak
solved). Many, many Builders and Plasterers do not use this method of
replastering and in most cases the symptoms, of 'salt' contamination,
will reappear if they have used modern lightweight plasters, like 'bonding'
1. Hack off
all old plaster to at least 300mm clear of all signs of damp or salt
and at least 1 metre above ground floor level - use a meter to test
the walls and remove plaster at least 300mm above the highest level
that readings can be obtained.
- This is to ensure that the residual 'salts' do not climb above the
new plaster in the future.
the walls to remove all plaster residue, particularly around angle beads.
- old plaster will have 'salt' in it and will cause damp spots to appear
any holes or poor joints with sand and cement (4:1) using washed, sharp
(means slightly gritty) plastering sand (sometimes called screeding
or rendering sand). Do not use fine, unwashed sands.
- fine, unwashed sands often contain salt and the fine particles are
too numerous to find enough cement particles to bond together tightly
- these two problems make for a weak render, prone to the easy passage
Note - walls made with non-porous stone or brick, like granite or blue
brick, will require an adhesive to help stick the render coat to the
wall - use BondAcryl concentrate)
- normal renders and plasters stick to the wall by suction - the surfaces
need to absorb some water. Without this suction the render or plaster
will not grab the wall and may become loose and hollow as it dries.
5. Damp the
walls lightly (to reduce 'suction', which can cause excessive drying
and cracking) and apply a thin coat (maximum 1/2 inch, 12.5mm) of render
consisting of 3 parts sand - dry, washed, sharp (means slightly gritty)
plastering sand (sometimes called screeding or rendering sand) with
1 part of fresh (free flowing - no lumps) Portland Cement.
- thick coats are more likely to slump down the wall during application
and crack during drying out.
the render surface liberally all over with a nail board, trowel, metal
float or similar object.
- without these scratches the natural drying shrinkage will cause cracking,
crazing and hollowness to develop - the next coat will probably pull
the first coat off as it dries.
7. Use only
Renderproof water proofer/plasticiser in the water that the render is
mixed with, at the rate of 1 part Renderproof to 40 parts of water.
Do not use fine, unwashed or wet sands.
- Renderproof binds the sand to the cement and prevents liquid water
passing through. It also makes the mix stickier (plasticising) which
help to hold the render together. Wet sand weighs more than dry, so
it will make your mix weak. Fine sands produce a weak, powdery render,
which will not resist 'salts'. Do not allow the plasterer to add plaster
(usually 'browning') or washing up liquid to the mix.
8. When the
render surface is firm enough (but not bone dry, or it will need re-wetting)
apply a second coat to exactly the same specification - if further coats
will be needed to reach the desired thickness don't forget to scratch
liberally. In hot weather spray the render surface with water to slow
the drying process.
- excessive drying out increases the suction and can prevent one coat
sticking to another. Rapid drying always increases shrinkage, which
gives rise to cracking of the render or finish plaster.
still damp (or re-wet again) apply a skim coat of Universal or Board
Finish. Do not polish or add water.
this will produce a shiny, glazed finish which looks good, but is prone
to condensation, black mould growth and poor drying.
any decoration for at least one month and then only apply a thin coat
of breathable emulsion paint (not a heavy vinyl). Do not repaint or
wallpaper for at least three months.
- the paint or paper will fall off the wall due to the water vapour
that will be trapped underneath in the new render.
Meters, Damp Proofing and Mold Products go to the: DAMP
A Calibrated Damp Meter is
a useful tool,
for checking your walls
Then consider a Home Condensation
also known as a Hygrometer.
This shows you how much moisture
is in the Air.
This one has the Jumbo
This one has the Standard
To kill Salts you
can use Salt Neutraliser
To buy Salt
Neutraliser - go to our Shop
and Ultra Mold Cleaner
would solve this problem
with a 5 Year Guarantee.
Ask us about the answer to
Black Spot Mould - Anti-Mould Cleaner
with a 5 Year Written Guarantee
special Bonding Agent
- go to our Shop for Damp Products.
BondAcryl can be added to
Renders and Screeds to make then Waterproof.
Additive - waterproofer,
salt inhibitor, plasticiser.
This is used to make Render
(sand and cement plaster) into a 'salts' barrier
but it still allows the passage
of vapour, so allowing the walls to dry.
Or, you can use an Air Gap
Membrane on the wall.
This provides Insulation
and a nice new surface
for plaster or plasterboard
This one is the Standard
Mesh Membrane, 7mm thick..
This one is the Slim Mesh
Membrane - only 3mm thick.
Directly Plaster or fix Plasterboard
on 'dabs' of adhesive,.
Learn from the
Expert: become your own expert - save money.
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 the point.
here to buy the reprint.
READING - click to see:
Proof Courses - what are they?
Proofing Methods - different types.
Proofing Efficacy - does it work?
Want to become
Qualified in Dampness and Timber Decay?
Contact us for
details of Professional Courses
Call David or
Angela on: 01626 331351
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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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