As we know, in the process of polyurea project, the surface preparation is very important, otherwise the coatings will peel off, or get many pinholes.

Substrate testing before spraying polyurea

For the concrete surface, the water content should be less than 8% for effective coating application, we can test by a concrete moisture testing device, or rubber mat/plastic sheet test.

The ideal PH range on the concrete is 9~12 for polyurea coatings, and the strength of the concrete should be good.

The steel substrate should be soundness, without contaminants or rust.

Testing the ambient temperature, humidity and dew point before applying polyurea, the humidity should less than 80%, the substrate temperature must be 3℃ (5℉) above the dew point, which is very important!  or you might risk of peeling off!

How are pinholes formed on the sprayed polyurea surface?

Spray polyurea is isocyanate reacted with resins, and this system don't allow to add solvents, A side and B side react very quickly within only 10 ~ 20 seconds, this reaction is different from the slow reaction coatings.

While when applied slow reaction coatings, if there is pinhole on the substrate, the gas in the pinhole can run out before material viscosity increased.

But the reaction of hot spray polyurea is too fast, the gas in the hole is heated by the hot material sprayed out from the machine, depends on the shape and size of the pinhole, some gas may completely run out, and some did not, it will become a pinhole.

Pinholes are a “nightmare” of a polyurea project, it might cause the leaking and failure of the project, so we often apply putty on the primer before spray polyurea on concrete, in order to fill the pinholes.

How should we do the surface preparation?

First, we should grind the surface, in order to remove the loose dust or oil and get a smooth surface, then apply suitable primer, if there are many pinholes, we usually apply putty to fill the pinholes, then apply another layer of primer, and spray polyurea.

For the steel substrate, grind or sandblast the surface, in order to get Sa 2.5 degree profile, and applied a layer of metal primer, then spray polyurea within the recoat window of primer.

How to choose the primer and putty for different surface?

The primer and putty are various, for different surface we have different primer and putty.

We have developed primer and putty for concrete, metal, aramid fiber, carbon fiber, wood, and foams, etc., and our no solvent putty for foam is sprayed by the high pressure polyurea machine, which is highly efficient, and can fill most of the pinholes on foams, was high appraised by our customers.