Fiberglass Gel Coat Restoration

A while back I was working on a boat in a local yard when I happened to strike up a conversation with a fellow that owned the boat next to the one that I was working on. I immediately noticed the shine on the hull (It was a sailboat, about 35 years old) and I asked if it had recently been painted. The answer was no but that he had just applied a product called Poliglow to the hull topsides. I have to admit that the hull was clean and the shine was impressive especially considering the boat’s age.


Here’s a picture of the hull I’m talking about.

Now I’ve seen this stuff on the shelves for years under various brand names Vertiglass, Poliglow, Vivilon to name a few and I have to admit that I have never paid much attention to them preferring instead to use the “sand and conpound method” in my attempts to restore aged gel coat. After checking out the finish on the aforementioned boat I decided that maybe this deserves more research. Off I went into cyberspace and a few hours later I was able to compile enough data to make me think that this may be a viable way to re-store and maintain the appearance of fiberglass gel coat. Especially interesting was a post on one of the sailing forums by a fellow who seems to have had considerable experience with this method and abviously knew what he was talking about. We’ll discuss that further in a bit. Next, let’s start with the basics and discuss the three most common methods of gel coat restoration and some of the pros and cons of each.

1- Sand, Compound and Wax

Abrade it down using whatever, compounds, sandpapers, scotch pads, necessary. It all does the same thing, and then slowly reduce the grit size to create a smooth finish and then keep it protected because if it goes bad again, you may not have any gel coat left to restore it.

Note: This removes Gel Coat

2-Wax, Wax and More Wax

Wax it and keep it from getting worse. This may or may not improve the oxidized appearance, depending on the original condition of the surface. Wax is not very viscous and may not be a great aesthetic solution, but you keep it from getting worse and you don’t reduce the gel coat.

3-The “Shine in a Bottle” Method

Disclaimer: Before we go any further I just want to point out that I have NOT done this myself but may in the very near future. The method that I’m about to describe has been compiled from various sources of information that I have uncovered in my search.

Seal it and restore the surface gloss and color using a thin sealer that is tough and durable. There are good ones and less than good ones. A couple of well-known brand names are Poliglow and Vertiglass. I suggest that some re-search is in order before you jump in the try this. The main argument against the above products is that, while they do provide a shiny surface and are a good aesthetic solution some are not very durable and vinyl fenders may abrade the surface.

A post on one of the forums indicated that “what you want is a high solids, metal interlocked, acrylic-copolymer designed for high durability with UV absorbers” commonly known as commercial grade floor wax and to look for a Product with 20% solids or higher.

A product that fits the bill is Zep High Traffic Floor Finish, available at any Home Depot store. It’s reasonably priced, has UV absorbers and can be easily removed, if desired with available products. It is also reported to be very durable.

Material List

-Zep High Traffic Floor finish (available at Home Depot)

-Bar Keeper’s Friend (powdered, available at most hardware stores)

-TSP (Trisodium Phosphate, powdered and available at hardware stores in the paint department)

-3M scrubbies (white, fine)

-Microfiber rags (white or laundered)

-Latex gloves
Surface Prep and Application

  • Clean the Hull. First use “Bar Keeper’s Friend” and a fine 3M scrubbie. Removes surface dirt and Gel Coat Chalk.
  • Wash the surface with “TSP” (trisodium phosphate). This removes any surface oil and silicone.
  • Use a garden sprayer and mist surface with water, examine for water beading to ensure that no silicone or oil is present.
  • Dry the surface prior to application.
  • Apply wax with a damp Microfiber cloth and “wipe” it on. Dries in minutes, is self-levelling and continue for 4-6 coats until desired gloss is achieved.

The first 1-2 coats will probably look somewhat blotchy but after you get 3-4 coats applied the surface should develop a good even shine.


Re-apply 1-2 coats each season.

Ok over decals and makes for easy dirt removal

Wood Epoxy Boat Hull Construction

I guess that before we move on from our discussion of fiberglass and composite boat construction that we should include a segment on a technique known as “Wood / Epoxy”. This is a building method that became popular in the late 1960’s with the introduction of epoxy based resins. This was at about the same time that production boat builders were making the switch from wood to fiberglass, utilizing mainly polyester resins as a building material. Until now most boats both production and home / custom built were constructed mainly of plywood, both in sheet form for hard chined hulls and various diagonal strip planking methods for curved hulls.

I remember that as a kid growing up on here in the north shore of Lake Ontario that wood boats were everywhere with sheet plywood and cedar strip being the most popular. Fiberglass was this wonderful new material that made for bright shinny curved hulls and sleek looking boats that almost overnight seemed to take over the lakes and rivers. For while wood was still popular with custom and home builders. It was at about this time that someone decided that it would be a good idea to cover these wooden hulls with lightweight spun glass cloth saturated with polyester resins. It seemed like a great idea at the time effectively turning the exterior surface of a wood hull into a hard piece of plastic. For a few years fiber glassing your wooden boat was the thing to do. It wasn’t a difficult process although a little messy and somewhat smelly.        This went on for a few years until after some time boaters realized that the fiberglass cloth was delaminating from the plywood hull material. It was later determined that polyester resins, in damp conditions, over time will separate from plywood. So much for all the hard work.      At about the same time Epoxy resins, even though they have been around since the 1930’s were beginning to show up as a boat construction material. Their increased cost was prohibiting them from seeing considerable use in production boats however with the custom and home builders who’s predominate material was still wood then began to utilize epoxy resins as a hull overcoat, both with and without light glass cloth re-enforcement. This was possible because of epoxy’s superior bonding strength to wood, it’s superior film strength and it’s superior hygroscopic properties. Remember a few posts back we learned about polyester resin’s hygroscopic properties, well epoxy is far superior in this regard. It does however have a couple of disadvantages. It degrades rapidly when exposed to UV and it also doesn’t like high temperature situations. This means that it makes a poor gel coat in that it must be over coated, preferably with a light colored paint or coating.

Lets’ now skip forward to a few months ago when I was contacted by a potential client to perform a survey inspection on his 26 foot wood epoxy Thunderbird sailboat. For those of you that aren’t familiar with the Thunderbird it is a 26 foot sailboat, designed by a naval architect named Ben Seaborn in 1958. It became incredibility popular with home builders in both North America and Australia as both a racing and cruising sailboat with one design racing fleets and an international class association. They were quite popular in my area here however the numbers have dwindled in recent years. As with many marine surveyors these days I generally shy away from wooden boats for obvious reasons but after a short discussion with the owner a few things came to light. The boat was constructed by the owner in 1977. The hard chined hull construction is GIS fir plywood sheeting over mahogany framing and the exterior hull surface is covered in light glass cloth saturated with epoxy resin. The hull interior is coated out in epoxy resin only.

I then decided to accept the assignment. At the inspection my findings were, that after 37 years of constant use, electronic moisture readings were not far off what I would normally see in dry plywood and percussive tests showed no structural issues. I found this very interesting that the plywood was in very close to new condition. I often inspect fiberglass boats that haven’t fared nearly this well. It looks like this epoxy is pretty good stuff. I guess that it’s just one of those things that just makes you want to go HMMMMMM now isn’t it?????

Fiberglass Boat Construction Part 3 Cores

Back to our discussion of fiberglass boat construction. Last time we looked at the various materials used in cored hull and deck construction. We learned that the most common materials are End Grain Balsa Wood and various types of Closed Cell Foam. The next question is, that since these materials are rigid and do not bend, how do boat builders manage to shape them into the compound curves necessary for hull and deck construction. Core materials are supplied in various configurations other than standard sheets. It can be supplied in narrow strips and small blocks attached to a scrim which is a thin flexible material that hold the blocks together and the small gaps between the blocks, called Kerfs allow the material to be shaped into both single and compound curves. Below is a diagram of core material showing the blocks, scrim and kerfs.

Core Close up1_Layout2

Here we can see a Balsa core material laminated into a boat hull. The kerfs are easily visible between the blocks.

This is a side view diagram of sandwich core construction as used in boat hull.

Cored GRP Hull2_Layout4

When performed correctly sandwich core construction can provide strong light structures but the trick here is to ensure that core materials are installed correctly. As we’ll see in future posts this has been somewhat of a problem for boat builders over the years.

Surveying Fiberglass Boats in Sub-Freezing Temperatures

Every winter I get request to survey boats when the ambient temperatures are below freezing. Surveying fiberglass boats in sub-freezing temperatures just doesn’t work and here’s why.

As we have previously discussed fiberglass as a material is hygroscopic (it absorbs moisture over time) and as such, during the winter months when the ambient temperatures are below freezing any moisture contained in fiberglass structures, such as boat hulls and decks freezes as well. During the freezing process crystallization of the substance occurs, adding small air pockets which make electronic moisture detection virtually impossible. Also because the substance is frozen it becomes very hard rendering percussive sounding tests useless as well. It is for these reasons that I do not recommend surveying of fiberglass boats when the ambient temperatures are below freezing. Any surveyor who claims that their inspections are valid under these circumstances is, in my opinion simply not being truthful and should be seriously questioned.

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