Rotary blasting v shot blasting hull ?

[Jamboat]

As the title really, our hull needs taking back to metal due to still having some patches of mill scale

We were/are considering Aqueduct marina for shot blasting & 2 pack but then spotted Otherton boat haven's ad for rotary blasting which they say takes hull back to metal. Any thoughts ?

[Mutts]

Any shot blasting utilised on a narrow boat will always remove corrosion / paint to restore bare metal.

Rotary shotblasting............If you want to pay a fancy price for a fancy name.

( I could go into how we open or decrease air flow over turbine wheels and turbine nozzles by rotating aforesaid items in a clockwise or anti clock wise direction under a constant stream of glass beads)

Conventional shot blasting..........Does exactly the same job (Removes paint / corrosion)

[Bloomsberry]

Rotary shotblasting ? Never heard of that before.

 

Just googled it and the results displayed refer to a rotary shotblasting machine that cleans small items so not sure what relevance it has for cleaning narroboat hulls (unless it's a big machine !)

[Grebe]

In my working days I used this 'aid memoir' when dealing with metal cleaning and surface finish matters.

 

It is important that they paint/coat the bare metal as soon as possible after blasting. Certainly well within 4 hours. If they do not, make them do it again before they coat it.

SURFACE FINISH INFORMATION.doc

[WotEver]

In my working days I used this 'aid memoir' when dealing with metal cleaning and surface finish matters.

 

It is important that they paint/coat the bare metal as soon as possible after blasting. Certainly well within 4 hours. If they do not, make them do it again before they coat it.

I guess that first note is supposed to read

Limit of Coarse finish...

[Grebe]

Thanks WotEver.

 

Yes coarse it is.

 

I've only been using it since 2002 and never noticed.

Edited September 23, 2016 by Grebe

[RichardN]

We have just had our hull re-blacked in Aqueduct but not by Aqueduct. Here are my thoughts

 

Consider how and where you will use your boat. We tend to move our boat on at least 70 days in any one year and move significantly. The boat does spend time in brackish and even salty water, I swear you can see the anodes getting smaller in salty water. Occasionally we have a cracking time doing things like the BCN Marathon Challenge which involves somewhere between 80 and 95 locks in 24 hours. We want something heavy duty and want it to last at least 5 years.

 

As already pointed out surface preparation is key. Spend serious money on that. Loads of information out there eg http://www.steelconstruction.info/Surface_preparationThere are some tools not mentioned there eg the bristle blaster but some sort of shot blasting is the gold standard.

 

Aqueduct has great facilities and enabled us to get Andy Russell in to do painting and MWT Civil Engineering in to do the Zinga and blacking all under cover. Aqueduct is horribly expensive, they are busy and we suffered a bit as we could not get everything we wanted from Aqueduct. I would make the same decision again as the location works for both MWT and Andy Russell but there are other places, someone mentioned that the guys in Mercia Marina are way cheaper then Aqueduct. Andy Russell's reputation is fantastic, even undercoat feels like glass when he puts it on, amazing and very hard working talent. The guys from Aqueduct spent time watching what MWT did, nice, you know someone is doing a good job when an experienced outfit comes to look and learn. So far I have only seen MWT's prep work and zinga remedial work and I am very impressed.

 

10 years ago our boat was shot blasted and painted with a super zinc rich paint called Zinga with 2 part Hempel Blacking on top. The shot blasting and original painting was not perfect but the boat was in great condition when first lifted out after 5 years so loads of mechanical damage to the coatings but apart from one area no real rust, just a sort of tarnish and no pin holing.Our mistake was to take the boat up and down the Chesterfield shortly after blacking, we should have waited a month so a fair amount of damage in the first month. It was actually painful

 

5 years on we have a load of "tarnish", lots of damage but no flakey rust or pin holes. So very impressed with the coatings,

 

We wanted the same people back to re-black our boat as before and get it done whilst the boat was being re-painted. Ideally we would have wanted them to shot blast but Aqueduct could not free up the shot blasting bay. Real shame as we had some issues with minor rusting under rails and overhangs in the superstructure, basically the areas that you know are hard to get to prepare and paint. Shot blasting with an angled nozzle would have sorted that but it was not to be. Cost wise it would have been better as a 2 man team costs around £500 per day with consumables but shot blasting is two or three times as quick and costs around £900 per day and would have taken less then a day including the first coat of Zinga (note: only required where we had beaten up the original coating.

 

The Zinga coating is fabulous but it is horribly expensive, around £20 per kilo. As we are at the 10 year mark anything that looked vaguely suspect both above and below the water line was taken down to bare metal and re-coated so we spent £200 on Zinga. This had to be done by hand :-( but MWT have some serious tools and know how to use them. I get to see the finished product tomorrow.

 

I will post a link to some current photos shortly but here are photos from 5 years ago: https://indigodream.wordpress.com/2011/07/10/boat-blog-a-look-at-indigo-dreams-bottom/

 

Edit to add that we have the Hempel 45880 two part blacking which is I believe what Aqueduct now use. I suspect we could get 10-15 years out of it if we kept fenders down . .

Edited September 24, 2016 by RichardN

[RichardN]

Should add that the Hempel does go a bit grey with time