Holes in gelcoat caused by grit blasting

[JonB]

Help please from anyone who's experienced hundreds of holes in the underwater gelcoat following grit blasting to remove old antifoul. My Etap28i is now covered in holes through the gelcoat to the mat layer beneath ranging from 10mm to pin-head in diameter. I'm told that West epoxy will fill the holes eventually when applied as liquid but it doesn't. Does it mean that I have to fill each hole with epoxy filler before appying epoxy paint? Very grateful to hear from anyone with experience of the situation.
Regards
JonB

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[Guest]

If you have good supply of West System or similar ... you could use Micro-balloons mixed with the resin as filler, which allows sanding of the filler to remove proud areas etc.
or
a proprietary marine filler to fill the holes.

It sounds as though either the blasting was too aggressive or the gelcoat was suffering from air-bubbles / porosity or micro-blistering. Normally GRIT would not be used - as this is particularly abrasive and sharp. It is usually better to use sand or slurry blasting - less aggressive and leading to less damage to gel-coat.

You MUST fill that gel-coat - as if you don't you may create your own water ingress into the laminate - especially if there is any area of poor laminate where resin failed to fully wet-out the fibres etc.

But you can be glad that you have exposed weak areas of the gel and will remedy that with your filling ...... you may also have broken / removed micro-blistering .... so in all most likely done yourself good !!!!



<hr width=100% size=1>Nigel ...
Bilge Keelers get up further ! I only came - cos they said there was FREE Guinness !

 

[vyv_cox]

International's Gelshield should cope with this, it's quite viscous. Watch the minimum temperature requirements, though. As Nigel says, you can increase the viscosity with microballoons but don't overdo it as the aim is to get liquid into the holes.

I must say that filling many small holes will be a very difficult task to achieve with 100% success. If the situation is really bad it might be better to bite the bullet and take all the old gel coat off, replacing completely with Gelshield (or the West equivalent, I don't know their products so well).

Gelshield 200 is the solvent-based epoxy system and it definitely has some filling capability. A primer may be advisable for good adhesion.

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[oldsaltoz]

G'day JonB,

This is a good question, however the answer may not be so good. Pin holes in the gel coat can be caused by poor lay-up. What you need to establish first is just how much gelcaot you have left, I suspect not enough.

If this is Not the case, you only need to replace the missing gelcoat. Dab a little epoxy resin onto the holes to wet them with a short bristle brush, then spread some gel coat with a plastic squeegee, or credit card, in a hatch pattern, when it's gone off, sand it smooth as required.

If this IS the case, you need the sand the area below the water line, fill and fair with closed cell balloons (not all Microballoons are closed cell), sand again and apply at least 3 coats of epoxy resin, sand lightly and apply some anti osmosis paint. International Interprotect (I think) then an epoxy top coat, and antifoul.

Note, Many of the professional osmosis treaters are now putting on one layer of woven rovings, sanding it and then applying the 3 or 4 coats of epoxy resin.

There are a number of web sites available on this subject, and no doubt other readers will have some ideas, but the above would be my approach to a long term cure.

Hope this helps

Andavagoodweekend. Old Salt Oz /forums/images/icons/cool.gif

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[steffen]

Hi Jon,
Your in for some hard work plus a financial drain. I did same with my 32 foot fin keel (approx. 22 mtr sq).
Applied 2-comp epoxy primer with special thinner to lower viscosity, dab into holes carefully with a brush.
Fill in the holes with epoxy+micro balloons; normal filler is not recommended for underwater.
Then apply 4 layers of epoxy (Gelshield 200= solvent poor or Gelshield= solventless).

Check www.yachtpaint.com There's a load of info about how to use, min/max times between layers etc.

Happy sailing, Steffen

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