Drop test, 1st part

How to find out whether a material is water repellent or not: drop test, 1st part
before applying a paint, a plaster, a render or a repair mortar it is necessary to know if the surface to be covered or the material to be repaired is water repellent.
By definition a water repellent material does not like water and will reject it.
Pratically this means that if you try to put a water drop on a water repellent surface the drop will « refuse » to adhere: it will form a sphere on horizontal surfaces and roll off on inclined ones.
Hence the drop test described here after can be applied to determine whether a surface is water repellent or not.
(Caution: of course this test should only be used on materials that are not water sensible!)

1 – To apply the drop
carefully bring a little drop of water on the material surface you would like to test

horizontal surface

vertical surface

2 – If the material is water repellent
the water drop will form a ball which is more ore less oblate (on strongly inclined or vertical surfaces it will roll)

highly water repellent surface

less water repellent surface

3 – If the material is not water repellent
– the water drop will wet the surface and will, if the material is porous (a), be more or less rapidely absorbed by the material;
– if the material is non porous, the water drop will humidify the surface and expand over it without being absorbed (b). The water will in this case disapear slowly by evaporation.

(a) non water repellent, porous and capillary active material

(b) non water repellent, non porous  material

Drop test, continuation : in our next trick we will explain how you can find out whether a surface treatment forms a dense, non porous film or whether it « only » makes the surface water repellent without blocking the pores …