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

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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)

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highly water repellent surface
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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.

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