Blacking a previously epoxied boat

[Gus94]

I have the dilemma of whether to go back to bitumen or to do another 2 pack epoxy. Does anyone know if I need to shot blast every single time epoxy is put on? Or just wire brush it?

 

And if going back to bitumen, will that be easier? (I guess wire brush and slap it on?)

 

Boat has not been taken out for a decade by the way… Fingers are crossed.

 

Any advice is very much appreciated, I have never blacked a boat. Thanks.

[Arthur Marshall]

I'm pretty sure mine was just jetwashed last time and then two packed.

[nicknorman]

I guess it will depend on exactly which product was used. In our case it was Sigmacover 300 coal tar epoxy, done in 2011. It is great stuff but unfortunately, like all great stuff, someone in EU said it was too toxic and so it was taken off the market. We took it out again in 2016 but really needn't have bothered, once the slime was jetwashed off you couldn't see the waterline. Anyway as per the instructions we abraded it with an orbital sander and overcoated with the last remaining stocks of Sigmacover 300 I could find. That lasted quite well and again we took it out in 2023 - again not really any rust apart from rubbing strakes but we had to put on SML Ballastic blacking 2-pac. Which I don't think was as good. It has been OK though.

Next time I think we will be better off with a shot blast, but we have done 3 overcoats and 14 years since the original shotblasting and I don't think it will need doing again until around 2029 so we will have been 18 years between shot blastings.

 

So to get around to answering your question, probably doesn't need shot blasting, just follow the instructions of the original and new (if different) coating manufacturer. And I would put on 2 pac again, the cost difference is not that much, it is mostly about the preparation (ie the cost of man-hours). But if you are having it done by someone else,  make sure they follow the correct procedure and don't just slap it on after a quick jet-wash.

Edited February 19 by nicknorman

[David Mack]

The existing 2 pac epoxy is probably mostly fine, apart from any scrapes and scratches. Going to bitumen would be a backward step. I would jetwash, then lightly abrade the sound areas. Any bare hull exposed, take back to bright metal with something like a flap disc (which will leave a surface with a key whereas a wire brush will polish any firmly attached rust). Then two coats of epoxy just over the bare areas overlapping onto sound coating, and perhaps a band along the water line. Then one to two coats over the lot - mostly for cosmetic reasons.

And don't put the boat back in the water until the coating has fully cured - check the manufacturers data sheet. The full job will probably take a week. Those boatyards that do it in 3 or 4 days aren't giving the coating long enough between coats or for final curing.

[nicknorman]

...edited due to being wrong!

Edited February 19 by nicknorman

[blackrose]

2 hours ago, Gus94 said:

I have the dilemma of whether to go back to bitumen or to do another 2 pack epoxy. Does anyone know if I need to shot blast every single time epoxy is put on? Or just wire brush it?

 

 

Don't black it unless you want to continue doing that every 3 years.

 

Ideally try to find out which epoxy was used last time and use that again. You MUST print out and read the technical data sheet for epoxy as it's not as simple as slapping on bitumen blacking.

 

How long ago was it last epoxied? If it's still in good condition - first ask whether it really needs to be re-done. A decent epoxy job should last 8-10 years. If it does need doing but it's still in good condition you'll have to pressure wash the hull as soon as it comes out of the water as usual and then you'll need to key the sound epoxy with a medium grit paper and do as David says above with any rust patches. Brush off any dust before applying any paint. Surface preparation is "key" 🙂 I would say thoroughly abrade the existing paint rather than lightly. A boat painter I know uses a belt sander for prepping old epoxy. 

 

Then follow the technical data sheet for your epoxy paying attention to mixing ratios (Jotun publish a mixing by weight document rather than by volume which is a lot easier with a cheap set of digital kitchen scales) and also minimum/maximum overcoating times. 

 

If you have a choice then choose winter grade epoxy hardener as that is essential even in summer if you want to get 3 coats on and you only have a week out of the water. I would recommend Jotamasic 90 if you can't find out what was previously used.

 

If you do decide to paint the hull with bitumen and then years later decide you want to go back to epoxy, the hull will definitely need to be grit blasted to get all the bitumen off.

 

Edited February 19 by blackrose

[BEngo]

Our experience.

 

Jarrah was built 1989.. Blacked  regularly with bitumen.  Blasted, outdoors,  in 2010.  Two coats Epidac 2. 

Out again in 2015, to heated,  covered slipway. Pressure wash,  rusty bits to bare metal with sanding disc and  angel grinder.  Aggressive wire brush over the rest, removing the grey look. The bottom was really hard yacker as my Aussie mate would say. Two coats Epidac 2.

 

Rinse and repeat in 2019 with Survey. Coating in good order, No problems.

 

Slipped again last year. Previous coatings still all excellent except on rubbing strakes and a couple of areas of mechanical damage at the bow. No more Epidac 2 (EU tar ban) so used SML Ballastic 2 pack.  Followed SML advice .not to use wire brush, but to get rusty bits to bare metal and to prep the rest with something that would leave a profile.  Went for angel grinder and sanding discs.Bottom even harder work than previously!  The 2 pack looks fine 10 months on.

[blackrose]

24 minutes ago, BEngo said:

 Went for angel grinder and sanding discs.

 

If you prep bare steel this way either inside the bilges or the outside, just be careful how much good steel you're taking off. As I've said before, every 0.1mm of good steel counts when it comes to a survey. 

[Gus94]

Thanks for all the tips! Saved me going back to bitumen.

 

On 19/02/2026 at 17:21, blackrose said:

 

Don't black it unless you want to continue doing that every 3 years.

 

Ideally try to find out which epoxy was used last time and use that again. You MUST print out and read the technical data sheet for epoxy as it's not as simple as slapping on bitumen blacking.

 

How long ago was it last epoxied? If it's still in good condition - first ask whether it really needs to be re-done. A decent epoxy job should last 8-10 years. If it does need doing but it's still in good condition you'll have to pressure wash the hull as soon as it comes out of the water as usual and then you'll need to key the sound epoxy with a medium grit paper and do as David says above with any rust patches. Brush off any dust before applying any paint. Surface preparation is "key" 🙂 I would say thoroughly abrade the existing paint rather than lightly. A boat painter I know uses a belt sander for prepping old epoxy. 

 

Then follow the technical data sheet for your epoxy paying attention to mixing ratios (Jotun publish a mixing by weight document rather than by volume which is a lot easier with a cheap set of digital kitchen scales) and also minimum/maximum overcoating times. 

 

If you have a choice then choose winter grade epoxy hardener as that is essential even in summer if you want to get 3 coats on and you only have a week out of the water. I would recommend Jotamasic 90 if you can't find out what was previously used.

 

If you do decide to paint the hull with bitumen and then years later decide you want to go back to epoxy, the hull will definitely need to be grit blasted to get all the bitumen off.

 

 

 

It has been about 15 years. It looks good from the towpath, but needs to come out for survey/valuation so might as well do the overdue touching up.

 

So for this touching up, do I need to get 3 coats on any bits that have been taken back to shiny metal, and then just one coat over the whole (abraded) lot? So basically one full coat and hopefully not too many touch up areas, so maybe 5l should do it?

 

Cheers for your help!