The answer depends on the location of the repair to be made, living works or dead worksâeuros? In other words, below the waterline or above it?
Why do a repair yourself?
The life of a boat is not only about peaceful anchorages. There are all the "side effects", which sometimes sound like a small collision with a pontoon or another boat during a failed maneuver. Or a pebble that suddenly slips under the hull, or a floating object that wants to end its drifting life.
There are many reasons why you might one day have to fill a small, unsightly crack that is detrimental to the integrity of your boat's hull.
These modest snags of life are easy to repair and bring a certain satisfaction after repair. We know the procedure to follow: cleaning, sanding, degreasing, filling, sanding, surfacing, and finishing.
But which products to use? At the ships, we are offered epoxy sealants and other polyesters. What are their advantages and disadvantagesâeuros?
What is polyester or epoxy repair putty?
A repair putty is a paste used to fill cavities of varying depths.
It is made with a binder that gives it certain mechanical qualities. For the nautical industry, the binder will be epoxy resin or polyester resin.
The composition of the putty also incorporates filler to give it a spread-like consistency. The denser the filler, the stronger the putty, but also the harder it is to sand.
The two-component mastic
The putty is presented with two components, a base and a hardener. It is the latter that will trigger the catalysis, the chemical reaction that will link the molecules together to harden.
The transition from a paste-like state to a solid is a temperature and humidity sensitive step. It is therefore important to follow the manufacturer's instructions for the timing of the application.
Except for specific products, it is forbidden to work on a wet support and it is not recommended to operate with a high humidity level. The drying time will be long at low temperature and fast at high temperature.
On a glass/polyester shell, which product should I use?
The answer will depend on where the repair is located. Above the waterline, you can use either a polyester or an epoxy filler. Below the waterline, epoxy is usually the choice.
Why choose epoxy putty?
Epoxy putty is a waterproof material, so it is this characteristic that is naturally retained for work under the water. In fact, in such a restrictive environment, i.e. under salt water and therefore subject to a certain pressure, the material must not be porous to avoid water infiltration.
The other advantage of epoxy for repair is that it does not shrink. After drying, the sealant has not shrunk.
With epoxy, you must scrupulously respect the dosage recommended by the manufacturer, who sometimes offers practical packaging
The drying time of epoxy putty - even fast-drying epoxy putty - is several hours. Epoxy putty often allows a longer working time before curing than its polyester counterpart.
However, this type of sealant, like all epoxy products, is much more expensive than polyester.
Finally, it is quite sensitive to weather conditions. For an optimal result, it will be necessary to take care to work on a relatively dry day and at more than 15° and less than 30°.
Why choose polyesterâeuros sealant?
Above the waterline, you can choose polyester filler which offers many advantages, starting with its affordability.
We also appreciate its ease of use, especially when it comes to mixing, which can be somewhat imprecise.
Because it is softer than epoxy, it is also easier to sand. And finally, the drying time is only a few tens of minutes.
However, as with all polyester resin-based products, there is a noticeable shrinkage during curing. It is as if the putty had shrunk as it dried.
On the other hand, this putty is not very waterproof, so it will be necessary to cover it with an insulator to protect it. You will use gel-coat to stay on homogeneous materials or a sufficiently waterproof paint.
What is the compatibility between these 2 products?
Be careful, an epoxy base is totally incompatible with polyester, but not the other way around.
For example, an epoxy-based repair should not be covered with polyester, such as gel-coat. The polyester will not stick to it. You must therefore continue your repair cycle with epoxy products.
On the other hand, epoxy can be used on polyester putty, but polyester-based products will be finished.
