Painting antifouling - is new barrier coat required?

[cooties]

I'm going to paint on an ablative paint soon on a 2-year-old boat which currently has a barrier coat and the sparse remnants of another ablative that doesn't do its job anymore.
Do I just sand away the existing paint, stopping at the barrier coat, followed by application of the new paint? Or is it recommended to also apply at least one more barrier coat before applying the antifouling?


The instructions for the antifouling only provide for situations of bare fiberglass or existing paint. For existing paint, if it's in "good condition" recommendation is to sand, solvent-clean, and paint. If the existing paint is "soft or in poor condition", recommendation is to sand down to bare fiberglass, add barrier coats, then paint. So, I'm not sure exactly what to do.. and whatever happened to gelcoat in these considerations? Boat has gelcoat, then barriercoat, then I presume "poor condition" paint, or what's left of it.

[slug]

Nothing wrong with an additional tie coat of epoxy primer

Follow the instructions

Remove old paint

Apply tie coat

Antifoul

[mikedefieslife]

Just sick a tie coat on. Each anti-foul manufacturer has a tie-coat for use with their anti-fouls.

For example, I'm currently putting on Seajet 039, but over the old antifoul (once abraded) I used Seajet 015 as a tie-coat

The TDS of Seajet paints is usually very good and lists which primers you should use in which situations. I've International/Interlux not to be so good with recommending their own primers and tie-coats.

[cooties]

Thanks all



BTW the old mostly-gone antifouling I have is Seajet 039. It's instructions say never to dry sand..I assume for environmental reasons. I've ordered a Festool 150 rotary sander and some dust collection equipment, so I presume I should be OK...


Should I get a full-face mask for the epoxy tie coat or would a half-mask be OK?

[CassidyNZ]

I use an ablative antifoul. Only once in the last three applications have I sanded back to the base which was actually not gelcoat but an old application of Coppercote. Every other time I have just sanded a key onto the last coat of antifoul and painted straight onto it. My antifoul lasts two years minimum and the last one was 30 months. If anyone thinks a tie-coat will improve on that, dream on.

I often think that paint manufacturers create tie-coats and primers and then publish instructions that indicate that their product won’t work unless the pre-coats are used first. That way they promote the sale of twice as much paint. But if one has drunk the primer cool-aid, I guess that’s all good.

Personally I think that if a paint manufacturer publishes information that implies their product won’t work without a tie-coat/primer, I would be better off moving to another paint manufacturer. YMMV.

[Miguelso]

I have been using ablative antifouling for 20 years, never used a tie-coat and most of the time I don't sand either. I use a good quality green scotch brite with the hose and give the hull a good rub. Works for me...

[mikedefieslife]

Originally Posted by cooties

Thanks all



BTW the old mostly-gone antifouling I have is Seajet 039. It's instructions say never to dry sand..I assume for environmental reasons. I've ordered a Festool 150 rotary sander and some dust collection equipment, so I presume I should be OK...


Should I get a full-face mask for the epoxy tie coat or would a half-mask be OK?

You should never dry sand any antifoul. I've never been to a yard that doesn't though. If you really must, then you want a respirator half face is fine, eye and skin protection. You might want to make sure your neighbours in the yard are ok with it too. Most don't care, as I said every yard I've been to in Southern Europe and now the Caribbean they dry sand the boats.

Originally Posted by Miguelso

I have been using ablative antifouling for 20 years, never used a tie-coat and most of the time I don't sand either. I use a good quality green scotch brite with the hose and give the hull a good rub. Works for me...

Isn't using the scotch brite just the same as sanding with 600 grit?

[CassidyNZ]

Where I live (and antifoul) dry sanding is allowed only when full vacuum extraction is used.
Wet sanding (my preference) is not permitted in 90% of the yard due to permeable surface and the hard stand that is concrete is reserved for those “in the know”.

So I rent a vacuum sander for a day - $100 including sanding discs. Get my boat done in 4 hours.

[HankOnthewater]

I do like Cassidy in post #5: I generally do not use tie coats. Even though manufacturers and paint suppliers suggest to do so. When using same or similar paints there is in my view absolutely no need for it. Sofar I never had never an antifoul failure. Not using a tiecoat saves time (on hardstand) and money. The other side of the coin, you gamble a little when using a different brand of antifoul,
Yes, I fix loose and flaking antifoul and put a tiecoat on those fixes. I try to minimise the sanding.
Over the last few years I do only my own boat and occasionally help out my fellow boat owners.

However I suggest to use a tie/barrier coat if you use a different kind of paint.

If you are unsure, try a little on your old paint without a tiecoat (in a big yard there are always people using the kind of paint that you plan to use). Paint a square ft or so, and see what the paint does, if it dissolves the bottom layer.... or shows other unwanted effects, use a tie/barrier coat.

[HankOnthewater]

Re sanding: wet sanding with airtools works best (for me) but if the antifoul is waterblasted clean, smooth and free of dirt, what is the purpose for sanding? A new layer of antifoul will stick very well to an unsanded antifoul surface, ie for ablative antifoul type of paint.
Yes, over the years there is often a large built up of antifoul, and going back to the gelcoat, or first barriercoat might be beneficial, now and then.

If there is a large built-up of antifoul, are we putting too much paint on every year? If that is the case, it is plain silly: applying expensive paint and on the next haulout we sand it off again, and we repeat the cycle......Should we more selective how much paint we apply, on which places?

[mikedefieslife]

One thing I don't understand is wet sanding. If I wet sand the paper or disc is clogged instantly, especially with Micron Extra, a bit less of with slightly harder paints.

Normally I'm only sanding to remove the growth (and there is usually that **** ton of it) that doesn't come off with pressure washing and scraping.

Acid can be used on shell growth, but then you've completely ruined the old antifoul surface, so probably need a tie-coat anyway.

[wingssail]

Originally Posted by cooties

I'm going to paint on an ablative paint soon on a 2-year-old boat which currently has a barrier coat and the sparse remnants of another ablative that doesn't do its job anymore.
Do I just sand away the existing paint, stopping at the barrier coat, followed by application of the new paint? Or is it recommended to also apply at least one more barrier coat before applying the antifouling?


The instructions for the antifouling only provide for situations of bare fiberglass or existing paint. For existing paint, if it's in "good condition" recommendation is to sand, solvent-clean, and paint. If the existing paint is "soft or in poor condition", recommendation is to sand down to bare fiberglass, add barrier coats, then paint. So, I'm not sure exactly what to do.. and whatever happened to gelcoat in these considerations? Boat has gelcoat, then barriercoat, then I presume "poor condition" paint, or what's left of it.

I have never used a tie coat OR a barrier coat, OR a primer, epoxy or otherwise. I just sand the old paint off, as much as I feel like, and then, after cleaning, put on new paint. Plus I repair spots with epoxy filler and sand those. Now days I pay some guys to do all of this, and they either dry sand or wet sand as is their practice (and what's allowed where they work).

We've gone down to the bare hull a couple of times (it is not gel-coat, btw). I plan to do it again this year.

Our paint has pretty much always stayed attached and has worked as advertised to prevent fouling.

IMPORTANT: While I don't follow the barrier, primer, tie-coat rules I DO pay attention to the compatibility instructions. Make sure that the paint you are applying can be applied over the specific old paint you already have.

[CassidyNZ]

Originally Posted by mikedefieslife

One thing I don't understand is wet sanding. If I wet sand the paper or disc is clogged instantly, especially with Micron Extra, a bit less of with slightly harder paints.

When wet sanding, the more water you use (within realistic parameters) the better. I have an articulated panel on the end of a broom stick with garden micro sprayers fitted and a garden hose connects to the upper end. The system constantly provides a wet surface on which the sanding medium works, washing away the swarf as you sand.

I use 80 grit sanding screens and can generally do my whole boat with one screen. Never clogs, doesn’t get blunt, can sand my whole boat in a morning on my own.

Our yard now doesn’t allow wet sanding because the yard surface is not paved and the removed paint soaking into the ground creates an untenable bio-hazard. But given a choice I would wet sand every time, no question.

[Chotu]

Over the decades, using ablative since it first came out, I’ve done nothing but scuff up the substrate, remove the dust and roll on the new paint. Never had a problem

As far as an epoxy barrier and then primer: if the primer is still there below the paint you’re good. With the epoxy, it IS your hull now so no need to add another layer of it.

[keepondancin]

You will like the Festool system. I use a Rotex 125, lighter when overhead, collects almost all the sanding dust. I would think using scuff pads you are still putting a lot of dust in the air. Eye protection is important, along with a mask, if you can find them. and gloves. Just be a bit careful with the Rotex, on thenon-randem setting, it is a bit aggressive. Great tools. Follow the manufacturers directions, they know the best.