For the Attention of Oldsaltoz (Gelcoat hole repair)

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JulianCollyer

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Dear Oldsaltoz. another forum member has suggested you may be able to answer my question.

I have now stripped the paint back on the top section of my old 16' GRP fishing boat and have found hundreds of small holes in the gelcoat. Some of these holes are quite large ranging from 3mm to 20 mm square. The holes go deeper than just the gelcoat and some of the glass fibre and resin is missing. The boat will be resprayed so therefore i am not desperate to restore the gelcoat to its former glory as it is a faded cream colour and has too many holes in it. I have seen a website where they recommend using fibreglass resin and microfibres for the glass fibre repairs and then use a gelcoat resin. What do you recommend for filling my holes?

Also I have high pressure washed the many layers of paint off of the inside of the boat and it has exposed many loose glass fibres. Should I simply apply a new coat of resin to them?
 
He is in bed still (or out racing!)
He may consider that the holes are osmosis blisters which have been opened up during your stripping back operation you should examine the hull for more of these blisters, if you find one unbroken then you can pierce it and see if there is any liquid inside, if so then you have probably got osmosis ( especially if there is a smell to the liquid)
The aknowledged proper treatment is to strip off all the gell coat, wash off any smelly liquid and let it all dry out (which can take months/ say a full summer) then you apply new gell coat.
Failing this( quick fix method) you could identify and break out all the blisters, wash them out, give them a quick dry and fill with the epoxymix you mention.
Await the oracle on this!!
 
If the holes are above the waterline as you suggest it won't be osmosis. Make sure the hull is dry and just fill them with epoxy - use a filler such as microballoons. I wouldn't waste time with polyester resin and gelcoat since you're painting it.
On the inside, it depends how fussy you are. The proper treatment is to apply a flow coat (polyester resin + gelcoat 50/50). This is best applied on a new lay-up though, otherwise you may find it will not bond very well. If it was mine I would just rub down with some coarse glasspaper to remove the worst of the loose fibres and then apply a couple of coats of bilge paint.
 
G'day Julian55, and welcome to the YBW forums.

Sounds like another rushed build, not uncommon with many of the older boats, they had a tendency to add too much hardener to the gel coat, not taking into account the volume of the filler when adding the catalyst with the result that a lot of heat was produced, if not by by this mix, then by an over rich mix at the chopper gun. or a lack of resin flow resulting in voids in the layup, not a big problem then, but add a few years of sun and frost and the gel coat has nothing to hang onto; then someone has a great idea to clean the boat with a high pressure cleaner, looks great till it dries out and all these tiny holes appear. No problem we can can paint over them; add a few more years and more sunshine and frost so we end up with the same problem only worse because the problem was not treated prior to painting.

What to do:
Well, you could start by having a very very close look, particularly at the larger holes and see if you have any traces of old paint in them that is still stuck, loose bits may be a result of recent cleaning; also see if you can spot any voids between the fibres, I suspect you will find both.

What next:
You need to to roll the area with a gel coat pricker, its a roller with lots of little pins and is about 6mm wide, a small nail gun will also work, the objective is to find and break open any thin areas so we can prevent more hole developing later.

Then:
You can mix an egg cup of epoxy resin and add the required amount of hardener, add a teaspoon of Methylated Spirits and mix well then add some 'closed cell' balloons till you have a mix like thin treacle, using a squeegee or old credit card work the mixture into the holes and let it cure. Note: temperature Must be above 18*C and humidity below 73%, do not apply resin after 3PM as it will not have cured enough to prevent it taking up moisture as the air cools and will have a white shadow, indicating moisture contamination.

Do Not use micro fibres or you will be spending all next summer trying to sand it off. the balloons are very easy to sand.

After the resin has cured you need to wash it prior to sanding to remove residue left by the curing process, have a hose running and rub the surface with a plastic kitchen scourer till the water no longer forms beads, this only takes a short time, start at the highest point and work down to avoid contamination of cleaned areas.

After sanding you can wash off any dust, let it dry and apply a coat of epoxy primer then your paint of choice, a two pot polyurethane would be my choice, it will last for many years.

As for the exposed fibres inside is important that they are sealed or they will become entry points for moisture, have a close look and if you see any voids with little or no resin around the remaining fibres then a coat of resin and paint or a single coat of flow coat is in order, just remove the loose fibres first by a light sanding.

I hope this helps, let us know what you decide on.

Andavagoodweekend......
 
Thank you so much for such a comprehensive answer Oldsaltoz. And than you everyone else for your contributions. I believe the larger holes were formed by impacts on weak areas and the smaller holes were due to the gelcoat being very thin in places with voids beneath them, which were excavated by my very high pressure washer. I must say what nice people you all are in the boating world.
 
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