Patch filling holes in rudder

[laika]

7 years ago I was pretty handy at epoxy repairs. Not having done anything for years my mind is blank so I’d like a sanity check. Last time I did some extensive blister repair to my rudder “properly”. I have some small blisters I’ve ground out, little time out of the water and would like advice/sanity check on the quick and adequate approach . I don’t want to scrape all the anti foul off the rudder. I plan on filling the ground out (small) blisters using silica thickened epoxy, grinding smooth, then coating with epoxy primer before anti fouling. Last time I think I used 2 coats of hemple primer and one of primocon. I’m wondering if I can get away with one coat applied with a foam brush to avoid stripping large areas of anti foul around the repair as would seem to be required for the “good” approach with a roller.

 

[laika]

To put it another way…
What epoxy filler to use for small fills below the waterline:is colloidal silica ok?
What is the minimum barrier between such a patch repair and anti foul?

 

[Tranona]

Silica is fine, although it is very hard so difficult to sand smooth. I usually put a bit of silica in and then pad out with microballoons to get a nice smooth paste. Never bothered with epoxy primer - the smoothed filler is already epoxy, so just Primocon and AF.

 

[Jim@sea]

The rudder I have on a boat has been damaged on the bottom.
When I took it off I could hear water sloshing around inside it.
Drilled a few holes and water came out and stuff which looked like the core of the rudder was wood which had got soaked.
Laid it out in the sun to dry the inside of the rudder.
Drilled more holes along the edge, mixed some fibreglass resin with hardener and poured it down the holes.
Sanded off when set. Painted it.
So far so good.