Adhesion after bad weather

Adhesion determination after cycles of exposure to weathering, conducted after air-conditioning in four cycles of heating/freezing and four humidification/freezing cycles. The adhesion test must be conducted as specified in EN 1015-12 that is, determining the bond strength in MPa by pull-off through direct load perpendicular to the surface of the plaster mortar applied on a support of a size not smaller than 550 mm x 150 mm x 50mm.

In the UNI EN 1015-21 a test method is specified to determine the compatibility of a single-layer mortar for exterior plaster with predetermined types of support (UNI EN 1015-21).

The samples must be subjected to two tests, namely the determination of water permeability and determination of adhesion (according to UNI EN 1015-12).

For the first test we require a metal cone (diameter of 200 mm and height of 200 mm), a graduated glass closed tube (or transparent plastic) with a minimum capacity of 1 l and a device for fixing the graduated tube. For the adhesion test needed a freezing cabin capable of maintaining a constant temperature of (-15 ± 1)°C, an infrared lamp device capable of maintaining a vertical plaster surface at (60 ± 2)°C, a sealed container to keep the water level of 15 mm, of water-resistant wedges of 10 mm thickness for the support of the samples and a thermocouple.

To carry out this test you have to prepare 1,5 l of mortar. After 10 minutes from mixing completion, the mortar must be applied on the supports. Before the test, to counter a false setting, you must mix the mixture by hand using a trowel or spatula for (5 to 10) s.

The permeability test is performed on two panels with at least two supports that represent the "worst condition" (with a thickness of (10 ± 1) mm and (20 ± 1) mm). On them the mixture of fresh mortar must be applied, keeping the vertical support during the application.

The samples will have to cure for at least 28 days under standard conditions, then the thermocouple should be fixed at the center of the sample face and subjecting the samples to two sets of air-conditioning that consists in four cycles. The first set consists of four cycles heating-freezing, the second of four cycles of humidification-freezing.

After 48 hours under standard conditions, position the cone on the plaster surface using a water resistant sealant. So, once the sealant has set, we must maintain a violent pressure of water of 100 mm on the surface of plaster and record the amount of water required to maintain this violent pressure in a period of 48 h.

After this test you have to put the samples under standard conditions for at least four days and then you can perform the adhesion test on the samples.

Instruments used to perform the test: Climatic cabinet for curing, Pull-off