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Vactan under two-part epoxy?


blackrose

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I think I already know the answer to this but will pose the question anyway:

 

I'm still prepping my water tank and have finally come to the end of my patience with it. In the end I decided to paint it with Armourguard epoxy paint as the water tank liner from HCL was the best part of a grand. The paint cost about £130

 

I'm going to put on 2 coats of ST and 2 coats of PW. https://www.boatpaint.co.uk/acatalog/Reactive_Resins_Epoxy_Steel_Coatings.html

 

I've had to remove another cement-based epoxy product called Cementitious Coating 851 which was 10 years old. The inside of the baseplate and hull sides are virtually like new steel but the underside of the deck (top of the tank) is badly corroded as the cement coating hadn't been properly applied by the builder. They were supposed to use 2 x 1mm coatings of the cement and it looked like they'd only used 1 coat so the water had got underneath. I guess the top of the tank is always damp rather than fully immersed so it's always going to be the worst part.

 

Getting all the cement off and prepping the bottom and the sides of the tank was hard work, but laying on my back inside the tank holding an angle grinder above my head to do the top of the tank has been a nightmare and I've really struggled with it. You can see some of the cement is still in the corners.

 

The finish isn't perfect and I'm just wondering if I should use half a bottle of vactan that I've got left over from another job to convert the rust under the deck before applying the Armourguard. Instinctively I feel it's the wrong thing to do, but I can't carry on with the angle grinder and wire wheels.

 

Should I just get the rest of the dust out and slap the first coat of Armourguard ST on?

 

Hoover marks in the dust - I haven't wiped it out yet. That's the cabin bulkhead on the left of the picture, hull side on the right.

CAM00722_zpszwpkrfpr.jpg

 

This is the bit of the tank that extends under the gas locker at the bow. That's the baseplate on the bottom.

CAM00720_zpsjiwh62jv.jpg

 

CAM00732_zpsxvfczxsw.jpg

 

The rest of the pictures show the underside of the deck/top of the tank.

 

CAM00724_zpsl1ykba4o.jpg

 

CAM00729_zps3gqxe3j4.jpg

 

CAM00730_zpsp7n58dss.jpg

Edited by blackrose
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You have done a bl**dy good job on that with wire wheels and sanding discs! I think Vactan could be a good idea, but I'd start by talking to the Tech Services department at the paint makers.

 

N

 

Thanks. No sanding discs, just a pneumatic needle gun/chisel to get the cement epoxy off and then wire wheels on an angle grinder to get the rust off. The pneumatic chisel was good for getting the cement coating off the flat bits, but the needle gun attachment was useless - 6 bar isn't enough pressure.

 

I talked to Reactive Resins who make the paint. They said they couldn't comment on Vactan as they didn't know the product and wasn't sure if it was compatible. They also said Armourgurd could cope with a bit of rust as long as I got all the loose stuff off.

Edited by blackrose
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Havig used various rust killer remedies over the years im not entirely convinced of their effectiveness.

 

Despite the claims they wont convert rust more than a few microns thick. You still have to get down to bare metal as best you can.

 

If you do use vactan or a similar - Holts rust remedy is basically the same - I would clean it off before painting in 2 pack, the idea being the vactan coat removed from the high spots will leave perfectly clean metal leaving the vactan in the low spot pits.

 

2 pack won't stick very well to vactan unless it is abraded before hand.

 

Warm up the panels a bit before applying the paint. Drive the moisture out of the remaining rust, seal it from moisture and oxygen ingress with a good coat of paint and you stop the rust for good.

 

 

  • Greenie 1
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They say that Armourguard can be painted onto damp surfaces. This is the epoxy primer.

 

http://www.reactiveresins.com/Armourguard-ST.html

 

Thinking about it I'll probably just use the epoxy straight onto the steel. Paint adhesion is only as good as its weakest bond and that would probably be the Vactan. It's the same as painting a two-pack epoxy on top of a single pack paint.

  • Greenie 1
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I've used Armourguard quite a bit of late (well deck and side locker floors), and my water tank was done exactly as yours (though I copped out and paid somebody else to do that).

My intuition is that as long as you have removed 99% of any rust I would put the Armourguard on directly and not use Vactan etc.

Armourguard and many other primers are designed to bond to steel and to stabilise any rust (to some extent) so using Vactan will interfere with the operation/bonding of a very good primer. I think that Vactan and other rust converters are really a second best approach and so should only be used when it is not possible to get back to (or very close to) bare metal.

Trouble is it's (hopefully) going to be many years before I know if I am right.

 

..............Dave

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I'm concerned about the effectiveness of vactan on treating anything other than surface rust. It won't penetrate into scale and can actually encourage you not to get rid of all the rust.

Also, it's water based. Can this really be a suitable primer for epoxy?

No, you're right, probably not.

 

The Armourguard people said my prep was good and even asked if they could use some pictures of my job on their website!

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