Summary:Checklist, tips and waterproofing guide how to waterproof your home and other buildings. In this easy to use 7 step guide on how to solve damp problems in the home, diagnose any waterproofing and damp issues you may have including chimney stack damp, external wall damp, damp internal plaster, damp solid or concrete floors and damp basements or cellars. Find out how to spot each issue and what you need to do to fix damp issues including what products to use.
There are many effective ways of waterproofing buildings, but firstly you need to be sure that you have a dampness problem that requires such treatment. Many dampness problems do not require waterproofing at all – they arise from plumbing leaks, poor roof, gutter and downpipe maintenance.
Waterproofing – Common Defects and Solutions
First you need to correctly diagnose the problem, see our diagnosing and analysing damp project, then you may need to refer to our finding water leaks project.
If you need any help with diagnosis or leak detection call the Property Repair Systems experts for free help on 80.
We will take some of the major defects that genuinely require some form of urgent waterproofing from the top of a typical building down to the foundations, they are as follows:
1. Chimney Stack Damp
Water penetrating the masonry of the stack itself, usually visible in the loft space or even in the ceilings below (stains).
Eliminate Building Faults
- Lack of a ventilated capping on the chimney stack
- Poor pointing
- Rotted ‘spalling’ bricks
- Birds nesting
Waterproofing Options and Procedures
- Render the stack – use a Primer and then sand and cement, incorporating a waterproofer. Thorough cleaning and priming are essential because old stacks are heavily contaminated with soot, salts and resins.
- Apply a water repellent – this must be a product that is suitable for high levels of salts. A standard silicone based product in solvent is not usually sufficient.
- Apply a waterproofing coating – cement based Tanking slurry or Bitumen based products can work, but will probably not adhere long term.
2. External Wall Damp – Penetrating Damp Above Damp Proof Course
- Poor brickwork
- Lack of window cill ‘throats’ or ‘drips’
- Blocked cavities in cavity walls
- Cavity wall ‘trays’ or ‘weeps’ missing
- Wires or pipes entering the property
- Poor mastic or mortar around apertures
- Render the walls – use a primer and then sand and cement, incorporating a waterproofer. Thorough cleaning and priming are essential because old masonry can be heavily contaminated with ‘salts’ and other chemicals
- Apply a water repellent – this must be a product that is suitable for high levels of salts. A standard silicone based product in solvent is not usually sufficient
- Apply a waterproofing coating – cement based tanking slurry or a bitumen based product
- Slate hang the walls – a favourite in conservation areas, to satisfy planning regulations
- Air Gap Membrane – fix this plastic dimpled material with plastic plugs and then render with sand and cement
- Masonry Paint – use an algae resistant masonry emulsion
3. External Wall Damp – Penetrating Below Damp Proof Course level
Bear in mind that walls are always damp below the damp proof course to some extent, but only from naturally rising dampness. Visible wetness should be treated with suspicion and investigated further.
- High ground levels – garden, path or road
- Materials or objects up against the wall – piles of soil, debris, building sand, garden walls or posts
- Poor drainage – blocked gullies, soakaways, surface drains, drives sloping down towards the building
- Render the walls – use a primer and then sand and cement, incorporating a waterproofer. Thorough cleaning and priming are essential because old masonry can be heavily contaminated with salts
- Apply a waterproofing coating – cement based Tanking slurry or a Bitumen based product
- Air Gap Membrane – fix this plastic dimpled material with plastic plugs and take down to foundation level, to meet a French Drain (perforated pipe)
4. Damp Internal Plaster – Above the Damp Proof Course
- Chimney leaks (see Section 1 above)
- Penetrating dampness (see Section 2 above)
- Bridged damp proof course (see Section 3 above)
- Hidden water leaks – old mains water supply pipes, buried central heating pipes
- Neighbour’s concrete floor laid above the damp proof course – common fault on party walls when timber floors are replaced.
- Render the Walls – use sand and cement, incorporating a salt inhibitor/waterproofer. Plaster finish with a skim coat of Multifinish. Thorough removal of old plaster is essential. DO NOT use any type of bonding or browning plaster on the walls, or as ‘dabs’ to secure beads
- DO NOT apply a waterproofing coating – Tanking slurry, bitumen based products or Unibond – used above the DPC these will simply drive the moisture upwards and outwards into other areas
- Air Gap Membrane – fix this plastic dimpled material with plastic plugs and then plaster with Bonding Plaster
5. Damp Internal Plaster – Below the Damp Proof Course
- Plaster taken down to the solid floor, wicking moisture from a non waterproof wall surface or an unsealed floor to wall joint
- Raised external ground levels
- Apply a waterproofing coating – cement based Tanking, then render and plaster skim.
- Air Gap Membrane – fix this plastic dimpled material with plastic plugs and then plaster with Carlite Bonding.
- Floor to wall Joint Seal – cut out the gap to at least 25mm x 25mm and fill with a waterproof mortar.
6. Damp Solid Floor
When concrete, brick, slab, slate or quarry tiled floors are in a sound and otherwise decent condition but feature areas of damp.
- High external ground levels
- Lack of a damp proof membrane
- Apply a waterproofing coating – cement based Tanking. NOT a full vapour barrier. Can be screeded over with sand and cement.
- Apply a vapour proof coating – Epoxy based paint, two part system. Ideal for new wood floor protection. Can be screeded over with sand and cement
- Air Gap Membrane – lay this plastic dimpled material dimple face down and cover with tongued and grooved boards (chipboard or MDF), or a sand and cement screed
- Floor to wall Joint Seal – cut out the gap to at least 25mm x 25mm and fill with a waterproof mortar. This should be carried out in conjunction with Items 1-3 above, to eliminate vapour at the floor edge
7. Damp Basement or Cellar
As in the above point where brick, slab, concrete, slate or quarry tiled floors are damp but still in a good condition and also surrounding wall surfaces feature damp brickwork or stonework and where there is also liquid water ingress present.