CONTINUOUSWAVE

My 1981 Outrage 18 has been in the family for 37 years. I just got it from my brother who kept it at a lake in Georgia. I think he left it in the water for only 3-4 weeks at a time but now the hull has some below waterline gelcoat problems (rash?). I'm not sure they are technically blisters since the spots are pretty shallow.







Q1: are these rash spots still in the "cosmetic blemish" stage?

From now on the boat will be trailered and only be launched and retrieved for day use.

Q2: is it safe to assume a day in the Chesapeake won't further degrade the gelcoat?

IF I want to repair the rash spots I'd prefer a lower effort approach for this old boat (definitely not interested in redoing/re-applying gelcoat).

Q3: could I do some light buffing and sanding and apply a one-step product to fill and hide these rash spots?

Q4: do I really need to use an actual fairing compound to effectively fill these spots, and then paint and seal?

Thank you for any advice.

ASIDE: I reviewed some older posts (links below) and I'm unclear on my options.

Products for Top-coating Old Gel Coat that are not AWLGRIP or not TotalBoat Wet Edge Topside Paint
https://continuouswave.com/forum/viewto ... oat#p47895

TotalBoat Products for Hull Repair
https://continuouswave.com/forum/viewto ... oat#p47400

Gelcoat Blister Repair: Six Questions
https://continuouswave.com/forum/viewto ... oat#p46638

This is "osmotic blistering."

It is the result of leaving a non barrier coated hull in the water too long.

For a technical explaination see "https://en.wikipedia.org/wiki/Osmotic_blistering"

For more background on osmotic blistering see this report from the U.S.C.G in May 1987.

https://continuouswave.com/whaler/refer ... isters.pdf

Here is an excerpt from an older thread:

a user DOOBEE wrote:As far as I know, Whaler always used polyester resin. The Boston Whaler company I knew was very conscientious when it came to materials and quality control. They had specific requirements for the materials they purchased and would not settle for less.
Bottom blisters became the scourge of the marine industry in the mid eighties. While not impossible, it is very rare on boats prior to that vintage. The popular theory is that EPA regulatory changes forced gelcoat manufacturers to make changes in the manufacturing process which caused the cured gelcoat to be more porous. Another common cause of blistering was oversanding the hull prior to painting.

Whaler spent a tremendous amount of money on independent testing labs trying to determine the cause of the gelcoat failure. They were never able to pinpoint the exact cause. Eventually blister block resins were developed and the point became moot (and mute). It would be fair to say that Whalers produced from the mid nineties on were less prone to blistering because they have some form of blister block resin.

There are 3 types of blistering you will find on a Whaler.

1. Air blisters were caused by poor application of the gelcoat/fiberglass layup. They are most common in the chines and strakes. When you pop an air blister it will probably have dry fibers inside.

2. Uncured resin blisters were caused by improper mixing of the resin and catalyst. These can appear anywhere on the hull, above or below the waterline. They will most likely be confined to a small area depending on the sprayer's technique. The interior of the blister will be gummy and smell like resin.

3. Osmotic blisters are caused when water permeates porous gelcoat and starts to disolve the exterior coating on the glass fibers. Osmotic blisters will typically appear to consistently cover the entire bottom of the boat below the waterline. The interior will be wet and smell like resin.

Regarding continual immersion of the hull of a Boston Whaler boat in water, see the owner's manual. I give an excerpt below:

Boston Whaler Owner's manual wrote:Any boat left in salt or fresh water for more than a few days should have the gelcoat surface protected with a two-part epoxy paint followed by an anti-fouling paint. This will retard marine growth and help protect gelcoat from possible blistering. DO NOT LEAVE YOUR BOAT IN THE WATER FOR ANY EXTENDED TIME WITHOUT BOTTOM PAINT.

Was the transom on your boat ever repainted or re-gelcoated?

Thank you for the helpful information [that identified the cause of the blisters forming].

ConB wrote:Was the transom on your boat ever repainted or re-gelcoated?

This hull has never been sanded or painted or treated or [in any way changed since its] original [manufacture].

I plan to make repairs in sections.

I would appreciate any advice on repair techniques.

I'm particularly interested in avoiding fairing compound if possible.

Q5: can the blistered gelcoat be sanded, prepped, and then repainted or resealed using a one-step product?

Q6: what are the pros and cons [of unspecified products or methods]?

RodneyBD wrote:I would appreciate any advice on repair techniques?

I don't have any first-hand experience with repair of osmotic blisters. I will offer some general advice.

The blister was formed because water was able to pass through the fiberglass resin used to laminate the hull structure.

The first step in repair of a blister is thus to open the blister and allow the water or whatever liquid there is in the blister to drain off, and allow the laminate to become completely dry. The presence of some uncured laminating resin might also occur in the blister. That resin has to either cure or be removed.

In the illustrations above many of the blisters appear to already have been opened.

If the depth of the blister was limited to only the upper layer of the fiberglass laminate, that is, the gel coat resin layer, then the strength of the hull and its integrity is not really affected. The depression created in the gel coat layer can just be filled.

If the size and number of blisters are small, you could attempt to repair each blister individually using a color-matched gel coat resin with special additives that will permit the gel coat resin to cure to a hard layer in the presence of air. This resin type is called a gel coat paste, and it usually contains some other ingredients (such as a wax) so it will form its own top layer to block air out, letting the polyester resin cure to full hardness.

If you were skilled in this method the repair would become cosmetically invisible. Also, the location of the blisters on the transom and hull side will make getting them nicely filled a bit difficult due to the effects of gravity. You will have to work out some process to prevent the repair resin from dripping out of the depression.

If the size and number of blisters is large, their repair individually with color-matched gel coat resin paste will become tedious. At this point you have to decide if the cosmetic result of the repair is extremely important.

If the cosmetic appearance is not very important, you could fill the depressions with some tinted epoxy resin with a filler, but eventually the color of the epoxy repair will shift due to exposure to ultraviolet radiation from the Sun. The repair will look very splotchy. Filling the blister depressions with an epoxy resin fairing compound can also be done.

The general remedy to cover the non-matching color of the repairs is to apply an entirely new top coating over the general area of the repair.

The top coating could be a new application of gel coat resin, but I would expect that would likely be beyond the realm of a do-it-yourself project.

The top coating could be an application of a marine paint, perhaps a modern (and expensive) marine coating like AWLGRIP paint, which, again, may be beyond the do-it-yourself level of skill.

A less expensive marine coating like TotalBoat Wet Edge Topside Paint, which is more likely to be possible to accomplish without special sprayers and high skill in the application, could also be used.

Any method of filling the blister holes will require filling, fairing, sanding, and the top coating with a water-impermeable layer to stop further occurrence of water infiltration into the fiberglass laminate hull.