Instructions for painting GFK

Instructions for painting GFK: construction

If you want to paint GRP, you can either do it with previously unpainted material or with repairs with already painted parts. For example, you can find GRP in vehicle construction, boat building and model construction, as well as in the construction of ponds, streams or pools.

Instructions for painting GFK: painting

Modern pool basins are made of fiberglass and need a new coat of paint from time to time.

Some even have a so-called gelcoat. This is an additional coating that is commonly used as a sealant in boatbuilding.

Depending on these requirements, the type and finish of a coating of GRP is adapted to the use of the material. A hull made of GRP is subject to completely different environmental influences and loads than, for example, a bumper made of the same material.

Last but not least, the tools, environmental conditions, and craftsmanship available are all important factors in considering how to paint your fiberglass.

GRP repair painting

When it comes to a repair coat, it must be distinguished whether the entire old finish must be removed from the GFRP, whether only a firm base is to be created or whether it is only a matter of repairing the gel coat.

Instructions for painting GFK: paint

GRP boats require a special boat finish.

Is the old paint of poor quality and should completely down, must first be worked with paint remover and then sanded. Even better: sand off the old paint completely.

If the old paint is of high quality and should only be repainted, then it is sufficient to sand the substrate well. This is also the only starting point, in which it is reasonable to paint GRP without primer, since this is already present in the intact paint system. However, it should be painted over with the same type of paint. Careful with 2-component paints on 1 component paints, which solve the Altlack under circumstances so strong that everything is wrinkled and must completely down. When in doubt, definitely test at a non-critical point.

When it comes to repairing a damaged gel coat, it is easy to do with a gelcoat repair kit or gel coat filler. Just follow the instructions of the manufacturer on the package.

Step 1: Sanding - Prepare the GRP for painting

For old coatings, use sandpaper starting with grade P 60, otherwise use 120, in increments of 240 and 400 to 600. Then remove dust completely and very thoroughly. The best suction and wipe dry with towels.

Step 2: GRP priming

Especially easy is the handling of primer spray. When you paint GRP, choose a primer that fits the color system. For example, acrylic primer or a bonding agent for the 2-component paint that you have chosen. It is recommended to apply the primer in two coats. Allow to dry completely.

Instructions for painting GFK: paint

Boats or pool areas are not rigid. Therefore, a flexible primer should be used.

Depending on the GRP color, an already pigmented primer can provide sufficient coverage of the paint buildup.

Tip: delete GRP - with what? Depending on the load, you can choose between common 1-component paints (eg car paint) and 2-component paints that create more stable surfaces.

If you have decided on a varnish, it is best to use the primer, putty knife and, if necessary, gelcoat and antifouling on boats from the same manufacturer in one system, as these are optimally matched in terms of their ingredients.

In this step, unevenness and the structure of the grinding are compensated. If there are coarser unevenness, first fill with filler (eg with epoxy filler) and then sand and dust again. Then filler or filler is painted on or sprayed (eg 2 K filler). Dry well after manufacturer's instructions, before further processing. From the spray can, for example, also spray filler in question.

Step 3: Prime again

After this step can be re-primed to optimize the adhesion of the lake. Also, this layer must be completely dried before the color coat can be applied in the next step.

Step 4: Paint or spray paint or basecoat

Instructions for painting GFK: coat

After priming, GFRP can be rolled or painted.

Depending on your own skills and equipment, the paint or top coat can now be applied with a brush, roller or spray gun. Depending on the paint and the color request, different numbers of layers are painted.

The color or base coat is best applied in two coats. In many cases, this completes the GFRP coating. For example, if you paint fiberglass in model making.

However, if you want to achieve a particular depth of the paint or a special resilience, such as UV protection, or osmosis protection and the like, as is often required for boats, working with even one or two layers of additional protection.

Important note: Regardless of whether it is car paint, 1 K boat paint, 2 K boat paint or acrylic paint: let the paint dry (see manufacturer's instructions), make an intermediate sanding with very fine sandpaper, remove dust and then apply only the next layer of paint.

Step 5 (optional): clearcoat, topcoat, antifouling

For increased UV protection as well as strong mechanical loads, a clear coat (eg clear coat, 2 K clear coat or gloss coat) is now also used for special protection in conjunction with the previous layer construction with one- or two-component lacquer. Boats at sea, for example, are particularly stressed. There may be advisable an additional coating with so-called antifouling, which provides protection against fouling. However, it is also a biocide that must be used responsibly.

Special feature: paint GFK gelcoat

Instructions for painting GFK: paint

Gelcoat can be applied directly on GRP.

In boatbuilding, the GRP is often painted directly with gelcoat, without using other paints or as the first sealing layer. This is of course also possible, especially since the polyester resin gel coat or epoxy gel coat (corresponding to the GFRP laminate) can also be colored. It is primarily a professional seal in three to four shifts.

Especially polyester resin is not only very harmful to health, but also extremely sophisticated in terms of processing and environmental conditions. For example, all material must have the same temperature - including the tools, the workbench, etc., and that must be between 20 and 25 degrees, with no drafts. The solvents must not evaporate too fast and not too slowly, otherwise the hardening will be impaired etc.

The processing by a layman can quickly lead to not insignificant damage. Thus, in the case of fiberglass painting, the costs can quickly become higher than the execution by a specialist.

Author: Christiane Baldwin

Photo Credits:
  • Cover picture: Pixabay / Hans
  • pool color: Amazon / LS-405
  • Boat paint: Amazon / Halvar
  • Primer: Amazon / Yachtcare
  • Color: Pixabay / MH83
  • Gelcoat: Amazon / PHD

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