Halt rising damp
Rising damp. These two words can strike fear into every homeowner’s heart. Here is a solution.
By Roelof Strydom
Nowadays there are many products available to solve the problem of rising damp, and with a little elbow grease, you can eradicate this common problem once and for all. Be advised, there is no quick fix for rising damp - it requires time and some intensive labour, but if done properly, you will never see another wall with flaking paint and crumbling plaster.
Sika Cemflex slurry
Sikalite powdered waterproofing admixture
Here is a step-by-step guide on fixing rising damp on your home’s inside walls, also known as the negative side.
What to do
Step 1: Remove the skirting boards. Chances are slim that you’ll be able to remove these without any breakage. This is because they have probably been exposed to moisture for quite some time, and are likely to be completely rotten. Don’t fret about it too much as they can be replaced.
Step 2: For the waterproofing to be effective, all the affected plaster needs to be removed and the brickwork exposed. This can be done manually with a hammer and a chisel, or you can go the easier route and use a SDS drill with a chisel attachment. Mark the affected area where the plaster needs to be removed. The height of rising damp can be between 0.5m and 1.5m.
You’ll need to assess each individual wall to determine how high the plaster should be broken off. In this instance the plaster was broken off to a height of 0.5m as the rising damp presented itself in the area just above the skirting board, but to be safe we went a bit higher.
Step 3: Once all the plaster is removed, clean the area to get rid of any remaining dust. The easiest way to do this is to use a vacuum cleaner. Try and suck all the dust out of the crevices in the bricks.
Step 4: For the first phase of this wall’s waterproofing we used Sika Cemflex, which is a waterproofing and bonding agent. It can be used as a waterproofing slurry together with a membrane to waterproof parapet walls and shower floors. It can also be used as a bonding coat (no membrane) on brickwork to prepare it for plaster.
It is this second option you’ll be using to eradicate the rising damp. The mixing ratio is one litre Sika Cemflex to one litre water to 3.4kg of cement and sand. Mix Sika Cemflex with water in equal proportions and separately mix cement and sand in equal proportions. Then add the cement-sand mixture to the Cemflex-water mixture and mix it until a uniform, lump-free consistency is obtained.
This mixture will be able to cover 8-10m2. This means that if the area you need to cover is less than that, you’ll have to use less of each, or more if the area is bigger.
Step 5: Saturate the brick substrate with water and while it is still damp, apply a coat of the bonding slurry by means of a block brush and allow it to dry for six hours.
Step 6: Just before the Cemflex slurry’s six-hour drying time is over, make up a plaster mixture into which you add Sikalite, which is a powdered waterproofing admixture for mortar. Sikalite blocks the capillaries and pores in cement, thus preventing the movement of moisture.
The mixing ratio for this is 1kg Sikalite to 50kg cement to two and half wheelbarrows of sand. Again, you’ll have to work out the correct amounts according to the area you need to cover. Mix the correct amount of Sikalite with cement and sand before you add the water.
Step 7: After the six hours you can apply a second coat of the Cemflex slurry and while it is still wet, apply the new plaster mix to which Sikalite has been added.
Step 8: Once the plaster has cured, which is after seven days, apply a coat of Sikagard-905 W. No plaster primer is required before applying the Sikagard-905 W.
Step 9: Once the Sikagard-905 W has dried, paint the new plaster.