There is no user manual for all aspects of homeownership, from moving, to taking occupation and to maintaining and understanding common and uncommon defects. Albert van Wyk has more than 38 years’ worth of building experience and has put all he has learned into a concise, easy-to-use reference book entitled, The Proud Home Owner. He has granted HomeTimes exclusive access to republish portions of his book to help homeowners make better decisions around buying and selling, as well as maintaining their properties.
This chapter is the most important one in the manual. Study it and make sure that it is applied correctly in your new home, even if this is the only tip that you use from this book.
The purpose of the damp proof course (DPC) is to prevent rising damp to get to floor level and to limit it to the plinth.
A house is built on the ground with soil and water below and around it. We cannot prevent water to get in under the house, but we can prevent any damage to the house with good construction methods.
Damp can be identified early when paint and plaster are starting to blister and peel on the walls. Rising damp is usually noticed at the bottom of the walls first because this is where it comes from.
It is the upward movement of water through masonry (bricks), plaster and concrete with capillary action. Moisture moves from areas of high content to areas of low content. Rising damp can only rise to an approximate height of 900mm from ground level in the Johannesburg area, because the atmospheric pressure will prevent it from rising higher.
A wet area about 1.5m from the floor is not rising damp, but be on the lookout then for a leaking pipe in the wall or a leak from the top.
Rising damp is due to a construction mistake, and should not happen if the house was constructed correctly.
Make sure that the damp proof course (DPC) in the outside walls, the vertical DPC at every change in the floor levels, and the membrane under the surface bed, are correctly installed and pay extra attention to the details which I will explain next, as this could become an expensive mistake for your account 5 years later.
It used to be common practice to build the outside walls of the plinth with face bricks, but clients and architects do not like to do this now; rather they insist that it is also plastered.
My advice is: Construct the plinth with the best quality face brick you can afford. This will be a good investment and you will never have peeling and blistering paint on the plinth.
There is still the same amount of moisture behind the face brick walls, but no plaster and paint to peel and blister.
Albert says: “Rising damp is because of a construction mistake and ignorance”
The damp below the line cannot be prevented, but it has risen way above where it has caused a lot of damage and where it has extended to the inside of the house.
Moisture moves naturally from an area of high content to areas with low content. In this case it moves horizontally, but vertically in the case of rising damp. Damp on walls where there is a change in the floor level will be visible if the wall on the high side was not protected or water proofed.
The correct thickness of the membrane is 375microns and the correct installation is important.
- A 20mm bed of river sand on top of the filling will protect the membrane from damage.
- Joints of the membrane must be sealed with adhesive tape.
- Wire mesh can be used to secure the plumbing and electrical pipes. The electrician and plumber must repair all damage to the membrane before concrete is placed.
Efflorescence is a deposit of white powder on the surface on mainly clay bricks and pavers. Bricks are made with soil and water and then baked in a kiln. The colour of a brick depends on the soil that is used because no colouring is added.
There are mineral salts in all soils. There is no efflorescence visible on the bricks when they arrive on site from the kilns. When water penetrates the bricks it is attracted by the mineral salts. The water will later evaporate and leave the white salts on the surface. Rain as well as the water in the mortar will also do it.
You should investigate it if you notice white powder again after it has been clean for a period. This is a sign of moisture or damp in the wall. It could be a leaking pipe or rising damp. Although it is unsightly, is it not harmful and can be left to disappear after some time in the sun.
Be alert to excessive salts on the wall before it is plastered, as this could affect the plaster and cause de-bonding. The efflorescence can be removed by scrubbing it with chemicals which are available in the trade, or with clean water.