Fiberglass Finish

I am researching methods of creating a durable high-gloss finish for a series of fiberglass furniture.

Is there any good sources that provide the exact process to achieve a high-gloss finish ontop of a fiberglass material?



Gelcoats are applied to the inside of molds before the glass layup. They generally chalk and are crack prone after 5+ years outdoor explosure. Fiberglass boats are typically painted with 2K urethanes when the owner wants to restore the glossy finish, with something that is more durable than gelcoat. 2k coatings do have to be sprayed, and a respirator is required due to the isocyanate in the 2nd component. Imron available at auto refinish jobbers will stick on a lightly sanded fiberglass surface. As well any of the 2K International Paint urethanes available at a marine supply store will also stick to a lightly sanded fiberglass surface. These coatings will not cover much of the glass texture, if you see it in your finished part. Key point is a lightly sanded and clean surface, for good adhesion.


Great tips!

you mention “lightly sanded”…what grid sand paper is recommended for best adhesion?
also, Primer will be added overtop of the fiberglass…so the paint will be adhering to the primer…

So, in terms of a furniture piece…Automotive finish such as Imron is more than sufficient you think?

Thanks for the help

also, I should mention this is a coffee table…its a typical “box” with fillet edges. I am worried about paint chipping at the fillet edges. The construction is fiberglass with automotive primers and paints…

Just wondering how to achieve a product which will not chip for many many years…especially at the edges, which are the most vulnerable part.


PU clearcoat over the paint.

if the design is ‘flexy’, look into flex agents for the paints and finishes.

I am worried about paint chipping at the fillet edges.

The larger the corner radii the better.

Since fiberglass is well, a fiber… it does not like to be bent; it is glass after all. Typically, fiberglass parts require a generous radius at corners to facilitate the glass fibers “going around the corner”.

If the part has a relatively sharp corner radius, a putty (consisting of [u]Cab-o-sil[/u] and catalyzed resin) is applied to the inside of the corner (directly on the back side of the gelcoat) so that the resin/glass matrix can bridge over the corner. Unfortunately it is this weaker putty that usually chips out because it is not reinforced with glass. Milled glass fibers (1/4" length) can be substituted for Cab-o-sil but generally the effect is the same … chipping.

Paint prep sanding? 320-400 grit is good. Any smoother and you may actually encounter problems with the coating trying to run off. It also takes more time in production. Another painting process used in the marine industry is call roll-and-tip. The paint is rolled on and a brush is used to knock down (tip over) the “over-lap” marks. Not really too applicable to small work; think 100 yacht, etc.

It may be too late for this, but fiberglass parts do not like to be molded “flat”. Due to the shrinkage of the gelcoat a “flat” part will more than likely (it’s almost unpredictable in my experience) turn out concave. “Crowned” surfaces are typical solution and are a necessary “evil” of the laminating process.


So you are looking for a high quality finish with fibre glass. This is not so difficult to do. You must however be more specific with detail about size and geometry as this would dictate the process you use to produce the part. One of the reasons we like to use this type of material is that it gives huge flexibility with the types of geometry’s that you can produce.

So you are looking for a great finish, well will you produce your product from a mould? if so the surface finish of your mould will dictate the finish of your part, so you will be looking for a super gloss finish in the mould. you would then put a gelcoat in the mould and this will give you a high gloss finish (gelcoats can be coloured, you could mix your own and add pigment to colour it). I you cannot get a good finish direct from the mould you will finish it by hand using sanding paper. The grade of paper depends upon how badly fisished your surface it you will gradually work up to a high number paper, and then spray the part.

Contrary to what LMO has mentioned, gelcoat does shrink but so does the resin you use in the glass, flat panels are possible, however you should ensure that you have a symmetrical and balanced fibre layup.

As for ensuring the edges are robust, well, you do need a radius, the minimum will depend upon the weave and weight of the glass fabric, you can form a good rad. Filling the radius with filler is not really good practice, so you should take a glass tow and insert it into the corner.

As for manufacturing processes, there are many. All are dependant upon geometry, production volumes and your budget.

Hope that this helps.

With regards to lightly sanding the surface, I would play with grit selection, depending upon how you are sanding and the quality of your fiberglass surface. 180 / 220 are about as coarse as you will want to go to get good adhesion. If you have used too coarse a paper you will see the sand scratches after topcoating the primer. Machine papers tend to fill up less quickly. You are not looking for a rough surface or visible sand scratches, just an abraded surface to get good adhesion. Yes automotive grade Imron is good for fiberglass, that is what I painted my fiberglass sailboat with.

Thanks for the recommendation,

I will try this technique out and post how it goes. Fiberglass will be ready in a couple of weeks for my project.

How smooth do you anticipate that the surface of the fiberglass will be? Do you expect to see the fiber texture telegraphing through on the surface, or smooth like a gel coat?