FRP Coatings

The specification of an FRP coating will depend on the substrate and the operating conditions where it shall be applied. However, below are shown some general indications for FRP coatings both for steel and concrete substrates.

1- Substrate preparation.

1.1 Concrete substrate

a) For concrete, the following is required:
- Cure must be complete, that is, 30 days old at least.
- Compression resistance should be 200 Kg/cm2 or higher
- No surface grease or oils
- Curing accelerators should not be used, as they act as de-moldants, hindering a good adherence.

1-High pressure water cleaning or sandblasting shall be applied to the entire surface so as to open pores and eliminate loose or weak material from the surface
2-Where cracks or fissures appear, including joints, an elastomeric cordon shall be applied, leaving a strip not adhered to the concrete so as to avoid cracking of the coating.
Q = uX l where
u = maximum unit deformation
l = maximum opening variation

1.2 Steel substrate

1. As a prior requirement for steel substrate, the following is necessary
2. no oils or grease on surface
3. no prior chemical attack and no porosity
4. 
   

1 – sandblasting to white metal shall be applied to entire surface so as to obtain a clean coarse surface free of weak or loose material.

2 – Primer
Apply a primer that has high elasticity, with a mean thickness of 0.1 mm with the purpose of impregnating the concrete or steel and thus avoid the absorption of the next layer of FRP.

With the aim of enabling a spark test for porosity at a later stage, in the case of a concrete substrate, a conductive veil of carbon or similar material shall be applied. to provide conductivity for the spark test of the coating. For a steel substrate this is not necessary.

3 – Reinforced coating
Two multidirectional fibreglass mats shall be applied, of 450 gr/sq.mt. weight each, and in some cases a bi-directional E type fiberglass cloth of 600 gr/sq.mt weight, achieving an average thickness of 2 to 3mm.

4 – Surface topping
This will consist of four layers of resin with 1/64” fiberglass scales applied with pistol or roll. Each layer has a thickness of about 0.125mm so as to ensure that said scales are laid parallel to the substrate. Thus, the final thickness of this coating shall be 0.5mm approximately.

5 – Topcoat
Four layers of resin with fiberglass scales of 1/64” size, applied with pistol or roll Each layer has a thickness of about 0.125mm, so as to ensure that the fibreglass scales are laid parallel to the substrate. Thus the thickness shall be about 0.5mm.

So as to control this application, each layer is pigmented in different colours. The last layer shall contain surface agent to help surface polymerization.

If no fibreglass scales are available, application must be carried out using surface veil and a topcoat of surface agent..
Fiberglass scales possess low permeability, thus avoiding formation of bubbles through the osmotic process, and reducing also the possible diffusion of chemicals.

Final thickness should be about 2.8mm and 3.8mm respectively.