Property Repair Systems

How to Fix Damp below DPC - Diagnosing Damp Issues Below Your Damp Proof Course and How To Cure Them

This project is sponsored by Property Repair Systems

Summary: How to detect, test for and remedy damp below damp proof course. In this guide we show you how to diagnose damp issues below your damp proof course including the tell tale signs of damp concrete floors, damp skirting boards and white fluffy salts known as efflorescence. Using our check list you can easily identify your particular issue and then see how to fix it.

Testing for Damp

If you would like to check for damp for yourself, click the below and purchase a Property Repair Systems Damp Meter. If you need any help with any type of Damp below dpc, timber repair or maintenance problems, Property Repair Systems will be pleased to give you completely free, no obligation advice on 01626 336180. The information you need may be in the project below, if not, call them.

Property Repair Systems Damp Meter

Damp Detection Meter

Damp Below Damp Proof Course Level

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 penetrating dampness.

Diagnosing Damp Causes and How to Fix Them

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 a leak testing check list - one can be seen here).

Remedy - 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).

HydraDry

Tanking Slurry Powder – brush on to waterproof walls and floors

Injection Course

Wall and floor Membranes – cavity drain ‘tanking’ for floors and walls

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 a leak testing check list (see the one mentioned above).

Remedy - 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 prepared 'slot'.

Symptom - white, fluffy salts, plaster possibly blowing off the wall - efflorescence - you have a water source which needs to be found and eliminated. Again, use the water leaks check list mentioned above to help you trace the source.

Remedy - 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, 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. Click the image to the left to purchase Property Repair Services Hygrometer.

Property Repair Systems Hygrometer

Hygrometer

Remedy - 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 also.

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.

Remedy - 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 salting.

As mentioned at the top of this project page, if you still require some additional help and advice please contact Property Repair Systems free of charge on: 01626 336180

Don't fancy doing this project yourself? We work with Checkatrade to ensure that we recommend only reliable and trustworthy tradesmen.

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