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Direct to rust paint - number of coats


lxs602

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On 03/02/2023 at 14:37, Tony Brooks said:

 

That is correct, but make sure it is not one of the high tec permeable membranes that are used under roof tiles.

 

The vapour membranes available at stores nearby are polythene, flame resistance category E. Isn't that a fire risk?

 

 

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.

 

I was told by someone that you shouldn't put waxoyl over a layer of paint? I would have to use a second layer of Hammerite.

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17 minutes ago, lxs602 said:

 

The vapour membranes available at stores nearby are polythene, flame resistance category E. Isn't that a fire risk?

 

 

So you painted your steel with Hammerire that is almost certainly combustible. Your cabin lining is what, plywood, hardboard, block board, OSB, match boarding, tongue and groove? All of which are combustible. Then how are you going to decorate it? Would it be with more combustible paint or varnish

 

It seems, even Kingspan/Celotex type insulation will burn if exposed to enough heat.

 

Expanded polystyrene insulation or polythene film will not suddenly spontaneously combust and unless welding it taking place and ignition will be via the cabin lining so you would hopefully be out of the boat before the fire got through the lining to ignite the polythene.

 

It is, as always, a question of assessing the risk. I think the risk from the polythene catching fire on a boat to be so low as to all but negligible.

 

 

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1 hour ago, lxs602 said:

 

The vapour membranes available at stores nearby are polythene, flame resistance category E. Isn't that a fire risk?

 

 

 

I was told by someone that you shouldn't put waxoyl over a layer of paint? I would have to use a second layer of Hammerite.

My boat was waxoyl on bare steel. Have a look at the Waxoyl spec sheet for full info.

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I think I would go for Tectyl 506 rather than Waxoyl if I could get it (seems to be a shortage of stock). It forms a better dry wax film which is less likely to melt and run in summer when the cabin gets hot and it smells far less strongly once the solvent has evaporated.

 

Alec

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On 06/02/2023 at 13:24, Tony Brooks said:

 

So you painted your steel with Hammerire that is almost certainly combustible. Your cabin lining is what, plywood, hardboard, block board, OSB, match boarding, tongue and groove? All of which are combustible. Then how are you going to decorate it? Would it be with more combustible paint or varnish

 

It seems, even Kingspan/Celotex type insulation will burn if exposed to enough heat.

 

Expanded polystyrene insulation or polythene film will not suddenly spontaneously combust and unless welding it taking place and ignition will be via the cabin lining so you would hopefully be out of the boat before the fire got through the lining to ignite the polythene.

 

It is, as always, a question of assessing the risk. I think the risk from the polythene catching fire on a boat to be so low as to all but negligible.

 

 

Indeed so. I have just spent several days ripping out aged unhoused wiring running next to 1980s polystyrene sheets, so fire risk has been on my mind. 

On 06/02/2023 at 13:57, Ex Brummie said:

My boat was waxoyl on bare steel. Have a look at the Waxoyl spec sheet for full info.

 

23 hours ago, agg221 said:

I think I would go for Tectyl 506 rather than Waxoyl if I could get it (seems to be a shortage of stock). It forms a better dry wax film which is less likely to melt and run in summer when the cabin gets hot and it smells far less strongly once the solvent has evaporated.

 

Alec

Probably too late now. I'll have to go with a second coat of Hammerite direct-to-rust paint. Thanks again for the suggestions.

Edited by lxs602
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  • 2 months later...
On 03/02/2023 at 14:37, Tony Brooks said:

 

That is correct, but make sure it is not one of the high tec permeable membranes that are used under roof tiles.

 

It has been difficult getting a perfect continuous barrier with the vapour membrane on the warm surface of the rockwool. Water has condensed on the metal roof despite the membrane, and seem to be trapped in by it, and then also not be dried out by the fire.

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Boatbuilder advised against vapour membrane suggesting it would trap water, which seems to be happening, and that the stove and sunshine on the metal roof would dry out the rockwool if not used. I don't know if others who have used vapour membrane  may have just spent a lot of time to get a seal as required, as  otherwise it seems to be counterproductive.

 

Interestingly, a government paper from Sept 2021 titled Retrofit internal wall insulation: best practice says (emphasis added):

 

Quote

45. The risk of interstitial condensation with internal wall insulation can be high  due to warm internal air passing through or around the insulation and  airtightness layers and condensing on the cold wall, and/or from external moisture within the masonry. The addition of a vapour barrier inside internal  insulation (IWI) on solid walls used to be regarded as essential, partly due to  inappropriate moisture risk assessment methods. However, it is now agreed  that, in many cases, this may cause more harm than good. Therefore, a  moisture open internal wall insulation build-up is recommended in the  
insulation of solid walls, or alternatively a moisture closed system with a  ventilated cavity (of at least 25mm) on the cold side.

 

Edited by lxs602
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