Removing Antifouling and Re-Painting

[GregB]

As mentioned in a previous post, I had to lift up my C29 to for a
loose propeller. As it was going to take a few days to machine the
shaft, I decided it was time to removed 20+ years of anti fouling as I
knew from the purchase survey that this was well overdue.
The marina I used is in the north part of Lake Macquarie and they are
able to remove the paint by fine garnet blasting to the gel coat. The
quote for this was $1850. Ouch? So this is how I did it myself. I have
done this twice before.

Most paints including antifouling can be soften with Caustic Soda.
Preparation
I used a concentration of 250-300 g per liter of water. About 3 heaped
table spoons. The caustic soda must be added to cold water as it is
exothermic reaction and the water will get quite hot. After the water
has cooled somewhat then add a small amount of wall paper glue powder
and stir well. In about 5 - 10 minutes the liquid will turn into a
gel.

Method: Apply the gel with a paint brush to about 0.5 x 0.5 m section
and wait about 20 minutes for the paint to soften. At this time about
1 to 2 mm of paint can be scraped off. I use a scraper with a hard
metallic blade that is designed to be pulled. The caustic soda will
not harm the gel coat or fiber glass. When a section is cleaned of
antifouling it should be rinsed with water to remove any remaining
caustic soda.
The caustic soda is only active when it is in solution (ionized). So
in hot weather is is necessary to spray the applied area with water to
keep it wet. I have also read that the applied area can be covered
with plastic strips to stop it from drying out, but I have not tried
this myself.
The area above the waterline should be protected with masking tape
especially if it has been painted.

Safety Aspects: This concentration of caustic soda is definitely
corrosive. It ill burn your skin if left for more than a few minutes
but not immediately on contact. It is dangerous for eyes so good eye
protection is mandatory. I use chemically inert gloves old clothes and
a discardable cover overalls and plastic boots. The caustic soda
solution does not smell and gives off no gases. Face protection is
advised but not mandatory as the scrapings do not need to come in
contact with your face.

Results: I took me 5 days to scrape the hull of my C29 clean of 4 to 5
mm of antifouling. I needed to applied the gel 3 to 4 times in the one
area.

Painting. This is some what a personal preference, but I will describe
my efforts. I used Alltex industrial/marine paint system. I applied a
primer coat of two pack type 504 and two coats of two pack protective
paint type 540 and then two coats of ablative copper based antifouling
No. 5. The only critical process being the time between the last coat
of 540 and the No 5 where the antifouling must be applied before the
540 cures.

Total cost was under $1700 including lift out and day hard stand
costs, paint and accessories. and I have about 1/3 of the paint left
over.

I can provide additional information on request.

I will post some photos in the files sections. Hull1 to Hull4.jpg

Greg Barnicoat
S/Y Viggan

[Maeling]

Thanks Greg, copied your recipie and advice for the future.

Did it soften the gelcoat at all. I once tried commercial paint
stripper. Didn't get far before scaring myself with soft gelcoat and
went back to sanding.

Geoff Raebel

[feebz]

Top stuff Greg

I too have printed out your technic,

I wet & dry the old anti foul back to the base coat/ primer every
time i slip, i get stuck into it with 60 or 80 grit emry paper and a
bucket of water and a hose soon as they finish with the water blaster,
if i could use the blaster myself and spend 20 to 25 minutes instead
of the 10 to 15 minutes the boys at the slipway do, it would only
take half and hour instead of the hour or so to rub it back,

i like rubbing it back every slip it keeps me well intouch with
the hull

Happy rubbing shane

[GregB]

Geoff
I have not seen any deterioration in the gel coat.
Initially when the antifouling is thick the caustic solution does not
come in contact with the gel coat.
However when the scraping finally comes down to the gel coat then I
rinse off the surface with high pressure water and then wet sand with
a 3M abrasive pad with a 60 to 80 grit rating. This should remove all
the caustic and also gives a good surface binding for the primer.

I have been more concerned where the gel goat is badly cracked or
missing where I make sure it is well rinsed and properly dried with a
heat gun. I then repair this section using two component car bog as it
it much cheaper that so called marine filler. Car bog is usually used
by many professionals as well.

I have also read that one of the recommended storage vessel material
for liquid caustic soda is HDPE (high density polyester) and note that
gel coat on30 year old boat is usually polyester based.

I also agree with Shane.
That each year before applying the new antifouling to wet sand the
surface back so that the remaining old antifouling is essentially
removed.

Greg

[feebz]

Hi
i make my own bog out of polyester resin and talcom powder, (no
name baby powder), for big jobs you can mix the resin and powder up
in a 20liter bucket (or ice cream bucket) and keep the lid on it and
scoop out what you need then add the catylist, just like car bog, for
most of my work though i drop the hardner in first and mix well, then
add the talc, when i'm repairing boats that have cracked the join
inbetween the hull & the deck were there has been an impact from a
whalf or another vessel the mix resembles a greenish candy type (less
talc), i also use the candy bog (as i call it) for a bit of a mud mat
fisrt on some jobs, then use the whiter fluffyer bog (more talc) for
the bulkier jobs that will require building up and sanding, or doing
little nicks here and there, also filling ozmosis scollops & repais

cheers shane

[Maeling]

Apologies, Shane, I suspect you know at least as much as me about
building moulds.

Oh to stay with antifouling, yes I wet and dry mine each year, too
labour intensive for boatshed who just slap new paint over old getting
a good buildup going

Geoff Raebel

[feebz]

Hi Geoff ,
Apologies for what, all is good here,

> >   cheers shane- Hide quoted text -
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