2 part epoxy on a steel hull?

[Ben Wilson]

Hi guys, 

 

I'm currently weighing up the pros and cons of using epoxy as a protective coating on my steel Springer rather than bitumen as has previously been used. Sandblasting the hull is not possible and I'm instead removing the existing bitumen residue by hand, will it affect the epoxy's adhesion to the hull if its not taken back to fresh shiny steel? 

 

If anyone who has experience with using epoxy could help it would be much appreciated

 

[dmr]

I suspect the result be less good than sandblasting, but as long as you do good prep will still be much better than blacking.

Many epoxies are "surface tolerant" and I think there is one that is even able to go over existing blacking. I think Goliath used last year it so maybe he will have something to say.

 

I have used two pack quite a bit on steel (including stainless) that I have prepared with a wire cup brush and its lasted well, though none of this is below the waterline.

[Alan de Enfield]

2 minutes ago, Ben Wilson said:

Hi guys, 

 

I'm currently weighing up the pros and cons of using epoxy as a protective coating on my steel Springer rather than bitumen as has previously been used. Sandblasting the hull is not possible and I'm instead removing the existing bitumen residue by hand, will it affect the epoxy's adhesion to the hull if its not taken back to fresh shiny steel? 

 

If anyone who has experience with using epoxy could help it would be much appreciated

 

 

You need to read the epoxy can for application instructions and required surface finishing and if it says sand blasted to XYZ specification then that is what you need to do.

 

My experience of 2-part epoxy paints is that they will not properly adhere to unclean surfaces and, if there is any previous -1-part paint, then it will bubble and blister and you'll end up with no adhesion to the substrate.

 

 

[dmr]

When doing local "back to bare steel" repairs my epoxy (obviously) slightly overlaps the existing one pack paint and I have never had any issues. I have used both Armourguard ST and Jotun 87 over the usual Toplac/Rylards/Craftmaster boat paints..

 

I suspect the 2 pack reacting with one pack thing is only significant if the one pack is not 100% dry.

 

I know that reactions can occur and have had issues putting BondaPrimer over boat enamel unless that enamel has had many days to go fully hard.

[rusty69]

Having just done this ourselves, I can't comment on the longevity, but there is probably some good stuff in the thread I started:

 

https://www.canalworld.net/forums/index.php?/topic/117366-diy-epoxy-blacking/

 

[LadyG]

Won't you use brass cup brushes and maybe other gadgets to get best surface ready to Epoxy?

I hear folks saying how expensive it is compared to bitumen blacking, but surely a lot of the cost is the time to prep, then three coat then cure. I did mine in eight days. But because weather was perfect mixing and coating was a piece of cake.

PS I would not bother with a Springer as I'd be frightened I'd go thru the steel , and have a major problem. The boat is old, we know that, just cross fingers it is still floating when you come to sell it!

If in doubt maybe try Ballistic Black, ask the vendor for technical advice .

 

 

Edited July 5, 2023 by LadyG

[nicknorman]

20 hours ago, Ben Wilson said:

Hi guys, 

 

I'm currently weighing up the pros and cons of using epoxy as a protective coating on my steel Springer rather than bitumen as has previously been used. Sandblasting the hull is not possible and I'm instead removing the existing bitumen residue by hand, will it affect the epoxy's adhesion to the hull if its not taken back to fresh shiny steel? 

 

If anyone who has experience with using epoxy could help it would be much appreciated

 

I don’t think the epoxy will be enduring unless you prepare the surface as per the specification sheet, which will almost certainly specify grit blasting. With proper preparation the stuff is remarkably tolerant of scrapes etc. because it gets “ingrained” into the roughened steel. Without blasting, I think the stuff will scrape off to reveal bare steel fairly easily. It will have the advantage of not being dissolved by leaked diesel etc but you won’t get most of the benefit.

 

You say “sand blasting the hull is not possible”. This seems unlikely, surely you mean “sandblasting the hull is too difficult”.?

[Sea Dog]

Take a look at SML Ballastic Black 2 pack Epoxy Primer (not to be confused with SML Ballastic Black bitumen based blacking). The idea is that this is tolerant of any remaining bitumen. SML recommended Jotamastic 90 over the top, but you can get their advice over the phone and make your own mind up.

 

Mine was done like that, with thorough hand prep, 2 years ago and it was generally very good when hauled out this year. Notably the bows and waterline were still perfect, so it beat bitumen there and shrugged off diesel spills. I did treat some areas with Vactan before applying the 2 pack which there was concern (raised by @TheBiscuits ) could have been less of a bond than the epoxy, but found no evidence of failure due to that. However, where there had been scrapes below the waterline it was more or less back to bare metal. Very little corrosion though, perhaps because the remaining primer was still giving some protection, but I think largely because I was assiduous in getting the boat out to see how the 2 pack was holding up and caught it early.

 

My experience tells me that the 2 pack was generally tougher, but more brittle than bitumen based blacking. Whether this was down to the primer or the 2 pack system as a whole I can't say.

 

I think if your boat is lightly used or sits in a marina, it's a good solution but if you're cruising a fair bit using locks, etc, where scrapes are unavoidable, then I'd still want to have the boat out to inspect it every couple of years or so. This being the case, it's far easier and a bit cheaper to stick with bitumen, which also tends to smudge rather then scrape off.

 

Other folks experience and opinions will be different, but that's mine. As a result, my boat is now resplendent in 3 coats of SML Ballastic Black bitumen.

[beerbeerbeerbeerbeer]

20 hours ago, dmr said:

and I think there is one that is even able to go over existing blacking. I think Goliath used last year it so maybe he will have something to say.

I did

I used Ballastic Epoxy. 

But I don’t know the results yet. 
Hoping to get out the water next Spring to have a look. 
I kind of experimented. 
Some went on to new steel

Some went on to the bow where I’d prepped clean with a needle gun 

Some went on to the swim where I’d put bitumen (well cured bitumen)
A whole mix and match went on. 
Oh and Hemple epoxy went on the base after a good cleaning with a cup brush on angle grinder. 

 

[DandV]

Surface coatings adhere to the layer below them. So the overall adhesion is dependant on the weakest adhesion between layers. It is a chain. 

So if the existing bitumen is weakly adhering to the steel below, then this will not be rectified by having the epoxy adhering well to the bitumen beneath it. What will flake off will just be bitumen plus epoxy. 

We are actually finding with the very good moisture curing varnishes now available a significant  limiting factor is that UV exposure can degrade the first layer of the timber cells in about 5 to 8 years, after which the varnish can be peeled in sheets, with a thin layer of timber cells adhering to it. A problem on masts and our cap rails that are not easily protected by covers while on our moorings.

Edited July 5, 2023 by DandV

[LadyG]

3 hours ago, DandV said:

Surface coatings adhere to the layer below them. So the overall adhesion is dependant on the weakest adhesion between layers. It is a chain. 

So if the existing bitumen is weakly adhering to the steel below, then this will not be rectified by having the epoxy adhering well to the bitumen beneath it. What will flake off will just be bitumen plus epoxy. 

We are actually finding with the very good moisture curing varnishes now available a significant  limiting factor is that UV exposure can degrade the first layer of the timber cells in about 5 to 8 years, after which the varnish can be peeled in sheets, with a thin layer of timber cells adhering to it. A problem on masts and our cap rails that are not easily protected by covers while on our moorings.

Varnishing wood and coating steel are different processes. Check out Le Tonkinois if you want results on timber spars. Do not use polyurothane or any modern water based rubbish.

Edited July 5, 2023 by LadyG

[cuthound]

On 05/07/2023 at 13:24, LadyG said:

Varnishing wood and coating steel are different processes. Check out Le Tonkinois if you want results on timber spars. Do not use polyurothane or any modern water based rubbish.

 

My experience of Le Tonkinois on my cratch board, is that it is better then varnish, but fails after 3 or so years where exposed to UV.

 

I have now removed the Le Tonkinois on the outside areas of the cratch board and put three coats of Sikkens Cetol Filter 7 Plus, which has survived unchanged for 3 years on my garden gates, the top rail of which is exposed fully to the sun during daylight hours.

Edited July 6, 2023 by cuthound
To.add photo

[haggis]

I must admit that we were not impressed with Le Tonkinois when we used it on gamebird.