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Direct to rust paint - number of coats


lxs602

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I have been changing the insulation and trying to sort out the wiring on my boat and I was disappointed to find that the steel shell had been painted only up to the gunwhales, above which it was quite rusty, especially under the windows, with even a couple of perforations in the bathroom.

 

After scraping off the loose rust with a wire brush, I have painted over almost all of it with Hammerite direct-to-rust hammered finish paint. On shining a light at an angle, I can still see lots of dots of rust despite a thick coat, and I was thinking to do a second coat as what says on the tin. It has been a rush job, which I have been trying to sort out within 1 1/2 weeks of annual leave, without any budget available, before moving in. The mechanic/fitter I have been working with suggested that with sticking tin foil over the top before installing rock wool, it would be fine. What do you think?

Edited by lxs602
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I don't think direct to rust paint will stop more rust coming, at least it never has on my old tub. It might slow it down a bit, I suppose. Vactan doesn't stop it coming back, either. If there's rust, and water about or a humid atmosphere, it's always going to return.

Whether it matters much I dunno. If you can't see it, and it's well insulated and not going to suddenly become an unexpected window I wouldn't worry about it. I don't...

Someone will probably be along soon with better advice!

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If you've gone to all the trouble of getting the wooden lining off I'd stick on 1" thick Cellotex or Kingspan foam boards.. Stick them on with a flexible adhesive/sealant like Stixall or Stick like Sh*t from Toolstation or Screwfix. You don't have to cover the entire board with the adhesive, as long as you fill any gaps with hand held sprayfoam and tape between boards/joints/ edges with aluminium tape. 

 

If you use rockwool you'll need to add a vapour barrier otherwise water vapour will pass straight through and condense on the cold steel. 

3 minutes ago, Arthur Marshall said:

I don't think direct to rust paint will stop more rust coming, at least it never has on my old tub. It might slow it down a bit, I suppose. Vactan doesn't stop it coming back, either. If there's rust, and water about or a humid atmosphere, it's always going to return.

Whether it matters much I dunno. If you can't see it, and it's well insulated and not going to suddenly become an unexpected window I wouldn't worry about it. I don't...

Someone will probably be along soon with better advice!

 

Yes I've never thought much of Hammerite. It doesn't do what it says on the tin.

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10 hours ago, blackrose said:

 

 

Yes I've never thought much of Hammerite. It doesn't do what it says on the tin.

And it's not compatible. It's OK for things that are a one off, on small areas,  but in the end if you want a lasting job you've got to do the prep, and apply when atmosphere is dry etc etc.

I see a lot of people recommending celotex, this must leave gaps compared to a good foam job, is it possible to use something like Thinsulate in addition?

Edited by LadyG
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4 minutes ago, LadyG said:

And it's not compatible.

What is not compatible?

 

Cellotex and Kingspan

stixall and sticks like sh*t

toolstation and screwfix

sprayfoam and aluminium tape

rockwool and vapour barrier

hammerite and metal

 

All / none of the above.

 

 

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3 minutes ago, rusty69 said:

What is not compatible?

 

Cellotex and Kingspan

stixall and sticks like sh*t

toolstation and screwfix

sprayfoam and aluminium tape

rockwool and vapour barrier

hammerite and metal

 

All / none of the above.

 

 

Kingspan and people 

It is flammable and carcinogenic 

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9 minutes ago, rusty69 said:

What is not compatible?

 

Cellotex and Kingspan

stixall and sticks like sh*t

toolstation and screwfix

sprayfoam and aluminium tape

rockwool and vapour barrier

hammerite and metal

 

All / none of the above.

 

 

I've ammended my post, lol.

It's the Hammerite that I find is difficult to deal with after it has been used once it's then a hard surface to sand lightly if it needs to be overcoated. I would have to use power tools to get is back to a good flat paintable surface.

I used Rustoleum Combicolor to coat my boat first time round, (after sanding the previous gloss paint ) and it is still there! Easier to overcoat when you decide that you made a mistake with the colour ;)

Edited by LadyG
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11 hours ago, lxs602 said:

The mechanic/fitter I have been working with suggested that with sticking tin foil over the top before installing rock wool, it would be fine. What do you think?

I think steel/moisture/ aluminium foil sounds like a battery and a recipe for a corrosive reaction between the two dissimilar metals.

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In the end you get a better result if you remove all the rust, but that can be difficult. From the position you are in, I would get a drill-mounted wire brush and go over the surface with that to remove the paint and the surface rust so far as possible, and then paint it with an epoxy primer designed for rusty surfaces. Drill mounted is better than angle grinder mounted because you can periodically reverse it when the wires get bent over, so it always cuts rather than polishing. Epoxy is the best option for paint as it forms the best barrier - being a 2-pack means you do need to mix it and use everything you have mixed, but they are moisture curing and some will cure at very low temperatures so it is about the only paint which will will still work properly in winter. I appreciate that you are short on both time and budget, but it sounds like this has gone rather deep so leaving it would not be a good option, particularly if it is already perforated in some places, as it is going to get worse and you will then have to take out everything you put in, taking even more time and money.

 

Having done this I would agree with the use of a proper foam insulation material. Celotex and Kingspan are much cheaper as seconds boards and the best technique is to stick foil tape on the back face of the edge, sticky side facing out, then fill any gaps between boards with spray foam and trim off, and seal the top with another piece of foil tape. You then have a perfect moisture barrier. If you aren't going over the roof then tape it there too. Foil tape from builders' merchants or online is not expensive and it works way better than anything else - get a wider tape than you think you need as you then don't have to worry about getting something sticky in a perfectly straight line.

 

Alec

Edited by agg221
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Sanding down would be ideal, but I think I 'm now too far along with the Hammerite... If Rustoleum is better perhaps I could use that for a second coat. I'm worried that just one coat will flake off quickly, more so than one coat. I will definitely take off panels in two or three areas in 12 months time to see how it is doing.

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27 minutes ago, lxs602 said:

Sanding down would be ideal, but I think I 'm now too far along with the Hammerite... If Rustoleum is better perhaps I could use that for a second coat. I'm worried that just one coat will flake off quickly, more so than one coat. I will definitely take off panels in two or three areas in 12 months time to see how it is doing.

 

I think that you will find one thick coat is more likely to flake or fail than two or three thinner ones. Both from the different expansion rates between the steel and paint and solvent entrapped below the cured surface of a thick coat.

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32 minutes ago, lxs602 said:

I'm worried that just one coat will flake off quickly, more so than one coat.

If you've painted over rust, then that bond is going to fail anyway, unless you have removed all the loose rust and used a product designed for rusty surfaces. At one time hammerite might have been such a product, but it has been reformulated (presumably to reduce VOCs) and I doubt the current version is any good.

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26 minutes ago, David Mack said:

If you've painted over rust, then that bond is going to fail anyway, unless you have removed all the loose rust and used a product designed for rusty surfaces. At one time hammerite might have been such a product, but it has been reformulated (presumably to reduce VOCs) and I doubt the current version is any good.

I removed the loose rust. It is designed for rusty surfaces but it's unfortunate if it's been reformulated. The VOCs are still rated high though.

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1 hour ago, lxs602 said:

I'm worried that just one coat will flake off quickly, more so than one coat

 

 

If your one coat is going to flake-off then putting addtional coats will not make it adhere any better - it will still flake off.

 

Sorta like building your house on unstable sand, rather than proper foundations.

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19 minutes ago, Alan de Enfield said:

 

 

If your one coat is going to flake-off then putting addtional coats will not make it adhere any better - it will still flake off.

 

Sorta like building your house on unstable sand, rather than proper foundations.

I'd thought that filling in the dots of rust still showing through the paint would reduce condensation on these spots and then rusting underneath and then flaking off the surrounding paint. I don't know if it would ioccur like this in practice. It is just my theory of course. Hence whether a second coat would give more comprehensive coverage.

3 hours ago, Sea Dog said:

I think steel/moisture/ aluminium foil sounds like a battery and a recipe for a corrosive reaction between the two dissimilar metals.

I thought tin foil as a moisture membrane between steel and rockwool was standard?

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7 hours ago, frangar said:

Painting at this time of year unless the boat is out of the water in a heated building just isn’t going to work well. The steel will be damp and the paint won’t cure unless it’s an epoxy designed for such conditions. 

I got it as dry as I could manage. Hope the stove being lit helped.

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19 minutes ago, ditchcrawler said:

I would have thought you would get as much condensation on the tinfoil as you would on the steel that its next to

 

Not only that, the aluminium foil would probably soon perforate by galvanic action if any conductive water got between it and the steel.

 

To the OP, the foil, if you use any, goes over the insulation as a vapour barrier. The last thing you want is wet Rockwool/glass wool insulation.

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45 minutes ago, Tony Brooks said:

 

Not only that, the aluminium foil would probably soon perforate by galvanic action if any conductive water got between it and the steel.

 

To the OP, the foil, if you use any, goes over the insulation as a vapour barrier. The last thing you want is wet Rockwool/glass wool insulation.

What should I use between the rockwool and the steel then? I am also using PIR enertherm boards (similar to celotex) on the walls. Wouldn't there be a galvanic reaction between the foil covering on the boards and the steel?

1 hour ago, ditchcrawler said:

I would have thought you would get as much condensation on the tinfoil as you would on the steel that its next to

As long as the steel is protected

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5 minutes ago, lxs602 said:

What should I use between the rockwool and the steel then? I am also using PIR enertherm boards (similar to celotex) on the walls. Wouldn't there be a galvanic reaction between the foil covering on the boards and the steel?

As long as the steel is protected

 

Just paint. The vapour barrier is to prevent moisture in the air making contact with the cold steel.

 

I think that you can get Celotex with foil only on one side. In fact, if you are fitting a vapour barrier, I don't see that it needs any foil facings apart from helping to  keep the gas in it.

 

Anyway, nothing would induce me to use Rockwool for thermal insulation on a boat where you are always subject to window frame to cabin side leaks. If cost was an issue, I would use 50mm self extinguishing expanded polystyrene on the hull sides (keep wiring away from it) cut to fit a tight as possible, with any gaps filled with offcuts and then a vapour barrier. I used the plastic silvered "bubble wrap" stuff, but builders polythene sheet would do with any joints taped.

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5 minutes ago, Tony Brooks said:

Just paint. The vapour barrier is to prevent moisture in the air making contact with the cold steel.

To which end you need to stop the water vapour getting anywhere near the steel. So your vapour membrane should be on the inside (warm) face of the insulation. Glue celotex/kingspan to the inside of the shell. Fill any significant gaps with sprayfoam and trim back, then tape all the joints with metallised foil tape, so that the foil facing on the celotex/kingspan and the foil tape form a continuous gap-free vapour barrier.

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On 31/01/2023 at 17:10, Ex Brummie said:

As you do not need to achieve any aesthetic  result, why not a couple of coats af Waxoyl instead? That is how my inside was treated 35 years ago and on the occasion when I've needed to access it, there is no rust.

Thanks for the suggestion. I will put a coat of waxoyl over the Hammerite. I'm sure it's not ideal, but this has all been very fast.

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On 31/01/2023 at 15:24, Tony Brooks said:

 

Just paint. The vapour barrier is to prevent moisture in the air making contact with the cold steel.

 

On 31/01/2023 at 15:34, David Mack said:

To which end you need to stop the water vapour getting anywhere near the steel. So your vapour membrane should be on the inside (warm) face of the insulation. Glue celotex/kingspan to the inside of the shell. Fill any significant gaps with sprayfoam and trim back, then tape all the joints with metallised foil tape, so that the foil facing on the celotex/kingspan and the foil tape form a continuous gap-free vapour barrier.

I will put rockwool on the ceiling, with a vapour membrane between the warm surface and wood ceiling panels.

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