Evaluation of capillary water absorption in rendering mortars made with powdered waterproofing additives

Several additives, such as powdered stearates, oleates, silanes and silicone films, are used to avoid water absorption in renders. This paper looks at the effectiveness of six powdered waterproofing additives after 28 days of curing at: 0.00%, 0.25%, 0.50%, 1.00% and 2.00% w/w on the whole composition. The waterproofing efficiency is analyzed by capillary water absorption tests, while water immersion tests are also carried out after 20 and 90 min. Powdered silicone and sodium oleate showed the best resistance to water penetration, while metallic soaps in the form of calcium stearate and zinc stearate showed the lowest efficiency in this respect at low dosages. The results are useful for understanding the long-term durability of renders and the minimal waterproofing dosages according to the EN 998 requirements.