Skim Coat and Wall Putties Put Through Their Paces
Why is testing of skim coat so important? Substrates, regional raw materials, climatic conditions, legal requirements and other factors vary by region. Therefore, specific formulations of skim coat are needed. At the WACKER technical centers around the world, we conduct a number of tests to make sure you always get the perfect formulation for your application.
Performance is Key
Skim coat must meet certain physical and technical requirements if it is to function properly. At WACKER, we conduct comprehensive tests as regards all the critical requirements. In doing so, we seek to improve the characteristics of the fresh mortar, e.g. its workability, as well as the properties of the hardened skim coat, e.g. its adhesion, flexibility and compressive strength.
Workability
Properties such as workability are greatly influenced by both the methyl cellulose and the polymeric binder. As co-binders, polymers affect and improve application, too. For example, the polymeric binder can extend the setting time, thus giving the applicator more time for smoothing.
Coverage
When applied in an average thickness of between 0.5 and 2 mm, a skim coat creates flawless, smooth surfaces. At WACKER, we employ our own test methods to find the perfect formula for optimum coverage.
Pot Life
How long can a skim coat, mixed to a paste with water, be stored in the mixing pot under ambient conditions? WACKER conducts special tests to find the optimum solution for different regions and climatic conditions.
Properties of Hardened Skim Coat
Tensile Adhesive Strength Test
The tensile adhesive strength test determines how well skim coat adheres to its substrate. Here, the skim coat is applied to a substrate and subjected to standard curing conditions, including heat exposure, before being assessed at 14 and 28 days.
Paint Adhesion to Skim Coat
Paint adhesion to skim coat is evaluated by the cross-hatch adhesion test. Here, emulsion paint is applied to skim coat. The specimen is then subjected to standard conditioning. After 7 days, the wall is crosshatched and covered with masking tape. The masking tape is pulled off and reveals how well the paint layer adheres to the skim coat surface. The adhesion is ranked according to the classifications specified in EN 2409.
Compressive and Flexural Strength
Since walls/masonry structures experience compressive loads/tensile stresses, compressive and flexural strength of the skim coat are tested as per EN 1015-11 in order to gain an insight into the wall's characteristics.
Flexibility Test
For this test, polymer-modified skim coat is applied to a thin panel. The flexibility of the skim coat is then tested by bending it over cylinders of varying diameters to check if it can withstand the dimensional changes without cracking.
Shrinkage Test
The shrinkage test determines if hardening of the skim coat is accompanied by a volume change. The initial and final lengths of the prepared skim coat specimens are measured to provide an estimate of linear shrinkage.
Chalking Test
WACKER uses a test method for obtaining standardized chalking results: The degree of chalking is assessed by applying a skim coat to a concrete block and then rubbing with a standard weight.
Durability Test
At WACKER, exterior skim coat is tested in the lab and under real-world conditions to obtain data for long-term durability. At our Technical Center, different skim coat formulations in combination with different paints are exposed to weathering before testing. This gives interesting insights into the long-term behavior of a skim coat and the paint.
No Chance of Water Damage
Moisture is the weak spot of skim coat: exposure to rain or other sources of humidity, such as cooking, washing, or showering, can cause water damage in the form of cracking, algal growth and blistering. Hydrophobic skim coat is the solution. The WACKER Technical Centers conduct a number of tests to evalutate the hydrophobic behavior of skim coat and to find the perfect formulation.
Water Drop Test
In this test, water droplets are placed on a skim coat by means of a micropipet. The length of time the water droplets remain on the skim coat is then measured. This provides an initial impression of the hydrophobic nature of the skim coat.
Surface Absorption Test
In the absorption test, a drop of water is applied by dropper to a vertical skim coat, and the surface absorption is observed as the water rolls down the surface. A regular skim coat produces a medium to wide band of absorbed water, whereas a hydrophobic skim coat yields a relatively narrow water band or none at all.
Karsten Tube Test for Hydrophobicity
Water penetration is assessed by the Karsten tube test. The Karsten test tube is bonded to the skim coat and filled with water. Water level changes are recorded at regular intervals to analyze absorption as a function of time.
Skim Coat Hardened Properties
Ask the Experts!
Worldwide, the WACKER Technical Centers support customers in finding the right skim coat formulation for their applications. Our experts understand local conditions and know what is important. They perform all of the definitive testing methods described in the relevant standards. Drawing on many years of experience, they have also developed some test methods of their own, providing our customers with even more insight into their products.
Whatever your plans are for skim coat: Do not hesitate to get in touch with our colleagues in the WACKER Technical Centers – they will gladly help you find the perfect formulation for your task.
