How to Recognise and Treat Salt Damp
What is salt damp?
Modern buildings are constructed with a "damp proof course" which may consist of a strong sheet of polythene plastic. Older buildings may either lack this damp proof course, or have been constructed with an less effective course which can break down over time.
Without a damp proof course, porous stone work and mortar may suck up water from the ground. As this water evaporates from the wall, it leaves behind salt deposits, for example Sodium Chloride (NaCl or table salt), Sodium Sulphate, (Na2S04), Calcium Chloride (CaCl2) and Calcium Sulphate(CaSO4·2H2O or gypsum) which attack the wall. This reminds me of the method by which irrigated soils increase in salinity until they are unsuitable for agriculture.
The salt deposits in the wall eat into the materials used to join the bricks or stones together. They can also ruin plaster and decorations. The water itself attacks vulnerable building materials, softening plaster, rotting timber, rusting metals and harbouring mould.
Dealing with Salt damp
Salt damp can cause continuing harm to your home, so it is important to take action against it.
1. Recognising salt damp
Step one is recognising salt damp. It can occur in a variety of forms. On my house it one wall was damp to the touch, while others were dry and crumbly.
I was convinced that I had several different problems and that one method of treatment would be ineffective.
However, I am told that symptoms range from blistering paint, through crumbling mortar to visible gaps between bricks.
2. Silicone injection treatment
There are several methods of dealing with salt damp, and you should do some research regarding the treatment most suited for your property.
However the silicone treatment appears cost effective and less intrusive than methods that involve removal of bricks to insert other damp courses. It is also a good choice for owners of heritage style homes because the original materials of the home are conserved.
Holes are drilled at intervals along the base of the wall and a damp proofing liquid is inserted. This liquid seeps through the wall material immediately surrounding the hole and is absorbed into the brick or stone by capillary action. The brick or stone then becomes part of the damp course, thus protecting the property.
Logic would suggest that treating the whole length of a wall would be more effective than spot application, because water will seep into a new place if it is blocked at one point only.
3. Planning the treatment for spring or summer
The timing of treatment is important. We were advised by both the technical experts and a real estate agent to get the treatment done in spring or summer.
After the silicone barrier is created, the wall needs to dry out and shed salt. This process takes about six months and must be allowed to complete itself before old mortar and plaster can be scraped off and new render applied.
The old mortar and plaster helps draw the salt out of the wall, so it has an important function during the six months of treatment. The length of this process is a source of frustration to some, because they would like the wall fixed and beautified in one step. However, good things come in their own time!
4. Plugging the holes
After treatment, holes may remain in the bricks where the silicon was inserted. Ultimately, you will want to re-point the bricks and refresh the mortar between the bricks. Indoor areas which were damaged will require clearing and re-plastering. However, until this is done an all purpose foam gap filler may be applied to the holes to seal against moisture.
The foam filler should come in a compressed can and be available at major hardware stores. When you remove the top of the can a tubular applicator is revealed which can be inserted into the hole in your wall. As the foam filler is applied, it expands and dries, sealing the drill hole. It is recommended that you fill 2/3 of the drill hole and do not overfill.
Wear gloves, safety glasses and a nose mask if you decide to attempt this task yourself.
Check your plumbing
5. Seal other sources of damp
Rising damp can be associated with falling damp and penetrating damp, so check your plumbing is not leaking and keep all gutters clear.
Ensure that down-pipes and water tank overflows guide water away from the house and into areas of the garden which will benefit.
Extend your downpipes
Young, D. 2008 Technical Guide: Salt attack and rising damp: a guide to salt damp in historic and older buildings, Heritage Council of NSW, Heritage Victoria, South Australian Department for Environment and Heritage, Adelaide City Council, available online from: http://www.adelaidecitycouncil.com/assets/acc/Development/heritage/docs/salt_attack_rising_damp_technical_guide.pdf