Damp below damp
proof course level - ground floor, a quick summary checklist:
Tip 1 - if a concrete floor
is damp all over it is hard to isolate the moisture source. As it dries
out the damp retreats slowly back to the points of ingress, so if you
are not able to see any isolated damp areas either ventilate and heat
or shut all the doors and windows and use a Dehumidifier.
Tip 2 - always check the
relative level of your floor to the outside ground level and damp proof
course. If the floor is below the Damp Proof Course you will need to
'tank' the overlap and seal the wall to floor joint, to prevent laterally
Symptoms and Remedies
Symptom - isolated
damp spots on a concrete floor, not touching the edges. This is probably
due to small holes in the plastic membrane (Visqueen 1200 gauge is normally
used) laid onto sharp hard core without a sufficient sand cover. A water
leak will add to the problem, so always use our Leak Testing Check List
(see Water Leak Testing Project).
- either dig up the floor and re-lay, or clean the surface and apply
two coats of an epoxy membrane (see www.epoxy-info.co.uk) or fit an
Air Gap Membrane (see www.drywallandfloor.co.uk). Membrane of this type
can be screeded (minimum 2 inches, 50mm) or a chipboard floor can be
directly laid (a 'floating' floor, 18mm board).
Symptom - damp areas
on a concrete floor, touching and emerging from the edges. This is probably
due to a lack of joint material where the plastic membrane butts up
to the wall edge. A water leak will add to the problem, so always use
our Leak Testing Check List (see Water Leak Testing Project).
- clean out the floor to wall joint until you can find the plastic membrane
all the way around the floor, chisel out a U shaped channel in the floor
at least 25mm x 25mm (1 inch x 1 inch), vacuum and then fill with sand
and cement (4:1 sand to cement) incorporating SBR liquid, both in the
sand and cement and applied as a liquid primer to all the faces of the
Symptom - white, fluffy
salts, plaster possibly 'blowing' off the wall - 'efflorescence' - you
have a water source which needs to be found and eliminated. Use our
Water Leak Checklist (click here).
- Salt Neutraliser might work if you can find and stop the leak, or
the plaster may be too damaged and need replacement to our Specification.
Symptom - damp patches
(at low level,l right down to the skirting board - sometimes the skirting
board will be rotten) that may come and go - you have 'hygroscopic'
salts that are attracting moisture from the air.
- your damp proof course may be 'bridged' by high outside ground, plaster
on the inside or debris in the cavity (cavity walls only). Clean out
the floor to wall joint until you can find the plastic membrane all
the way around the floor, chisel out a U shaped channel in the floor
at least 25mm x 25mm (1 inch x 1 inch), vacuum out all debris and dust.
Rectify any defects and 'tank' the wall area below the correct damp
proof course level (6 inches or 150mm above outside ground level) into
the floor to wall notch and then fill with sand and cement (4:1 sand
to cement) incorporating SBR liquid, both in the sand and cement and
applied as a liquid primer to all the faces of the prepared 'slot'.
Inject Quick Cream at the correct level to form a new Damp Proof Course.
The plaster will need replacement to our Specification.
Symptom - damp patches
on or around the base of chimney breasts - sometimes showing yellow
or brown stains in wallpaper or paint - you have 'hygroscopic' chimney
salts that are attracting moisture from the air, which may include tars
and other chemicals from burning wood or coal.
- these 'salts' are very difficult to hold back in the wall, even with
the replastering to our Specification carried out to perfection. We
recommend using Mesh Membrane - a type of dry lining - to allow you
to replaster using normal, lightweight plaster, with no risk of further
Learn from the UK's greatest
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
here to buy the reprint.
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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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