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Rust around mushroom vents - do they need to be removed?


Lizzy

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In my opinion brass set screws with brass nuts inside is much better than tapping threads in the roof where the thread is likely to rust corroding and jamming the screws never to be got out in future without drilling them out. With the grills removed from the ceiling inside I've never had great difficulty removing or refitting the nuts, either with third hand holding a cranked spanner on them or on me lonesome with a small pair of Mole grips on the nuts.

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5 minutes ago, bizzard said:

In my opinion brass set screws with brass nuts inside is much better than tapping threads in the roof where the thread is likely to rust corroding and jamming the screws never to be got out in future without drilling them out. With the grills removed from the ceiling inside I've never had great difficulty removing or refitting the nuts, either with third hand holding a cranked spanner on them or on me lonesome with a small pair of Mole grips on the nuts.

 

I don't like the sound of that...

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Just taken my mushrooms off and as said before there was considerably more rust and pitting hidden underneath than on the rim.  I've rubbed down and treated with Vactan (good stuff) and another primer coat although I'm not sure the last coat was really necessary.

I'm top coating next week but am unsure whether to fill the pitting with filler or just let the paint fill the holes - any thoughts?

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8 minutes ago, Eldog said:

Just taken my mushrooms off and as said before there was considerably more rust and pitting hidden underneath than on the rim.  I've rubbed down and treated with Vactan (good stuff) and another primer coat although I'm not sure the last coat was really necessary.

I'm top coating next week but am unsure whether to fill the pitting with filler or just let the paint fill the holes - any thoughts?

No filler,,will become a moisture trap. The tape will cover and fill the small pits. Just make sure there is wodges of paint ☺

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1 hour ago, Mike the Boilerman said:

 

I don't like the sound of that...

:clapping:

Yeah, the thought of even a small mole gripping your nuts is not good. I guess the answer is to be wary when sunbathing on the lawn at this time of year, the moles are very active.

Sorry, totally OT but needed to lighten up. Just discovered two weeping glands on the bathroom heated towel rail whilst getting the boat ready to cruise on Monday.

There's always something...

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2 minutes ago, BruceinSanity said:

Yeah, the thought of even a small mole gripping your nuts is not good. I guess the answer is to be wary when sunbathing on the lawn at this time of year, the moles are very active.

One would be bad enough, but bizz is suggesting a pair! 

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There is nothing wrong with using silicone to my mind. It makes a good seal. It is a case of a film of silicone getting smeared over the adjacent paintwork - it gets on your hands and is transferred to everything you then touch - that then prevents the new paint sticking properly. I think it is called sissing.

 

 

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I am beginning to get seriously worried about this whole project. From the inside it looks like this. Wonder what's lurking under there! (I am waiting for this vactan stuff to arrive. Don't want to start opening up stuff before I can actually tackle it).

never tapped a screw. I don't even know what that means :(

 

IMG_0034.JPG

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7 minutes ago, Lizzy said:

I am beginning to get seriously worried about this whole project. From the inside it looks like this. Wonder what's lurking under there! (I am waiting for this vactan stuff to arrive. Don't want to start opening up stuff before I can actually tackle it).

never tapped a screw. I don't even know what that means :(

 

IMG_0034.JPG

If you worry whats hidden behind every lining you will never get any sleep. 

Tapping involves  putting a thread in a hole so it will accept a machine screw or bolt. 

If all your vents have a internal cover like the photo, you may already have a nut and bolt arrangement as bizz suggests. 

Edited by rusty69
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2 hours ago, Lizzy said:

I am beginning to get seriously worried about this whole project. From the inside it looks like this. Wonder what's lurking under there! (I am waiting for this vactan stuff to arrive. Don't want to start opening up stuff before I can actually tackle it).

never tapped a screw. I don't even know what that means :(

 

IMG_0034.JPG

A tool bit of hardened steel, called a 'tap', and looking like a tapered bolt with flutes, is used to cut a thread in a pre-drilled hole in the metal to take a matching machine screw (a bolt with a thread for the whole length). Tapping is a delicate operation that needs to be tackled with care, and if you have not done it before you won't be aware how easy it is to break a tap in the hole. Then you are in trouble.

But it seems there is no need to tap holes -  from the pic of the vent plate, it looks as though there is plenty of room to gain access to the underside of the mushroom, in which case it would be easier to use nuts and bolts  - as suggested by others; viz bizz.

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On 31/03/2017 at 11:07, Horace42 said:

Yes! drill and tap holes and use SS machine screws. That's what I did with mine (flat dish type). So it makes it easy to do next time. It makes it so much  easier to roller paint the roof without vents in the way. I made a rubber gasket to seal the gap. But cleaned of all rust and treated the bare metal first.

There is a slight possibility of galvanic corrosion using stainless fixings with mild steel.Bob

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1 hour ago, Hawkmoth said:

There is a slight possibility of galvanic corrosion using stainless fixings with mild steel.Bob

That's interesting - how does it manifest itself at a later date? It could be useful to know, although in my case it is a bit academic, the whole dish is SS.

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On 02/04/2017 at 13:57, Horace42 said:

That's interesting - how does it manifest itself at a later date? It could be useful to know, although in my case it is a bit academic, the whole dish is SS.

The mild steel will corrode quicker due to the minute currents set up between two dissimilar metals that are close to each other on the periodic table. I'm sure someone with more knowledge than me can come along and either elucidate or correct me.

Bob 

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Bear in mind that electrolytic corrosion requires an electrolyte i.e. a body of fluid in contact with both surfaces. Obviously for an external fitting this would be rain and condensation but the promotion of rust can be suppressed by controlling the environment.

In a stable environment i.e. one with consistently low levels of moisture and a lack of catalysts such as dirt or chemicals steel rusts very slowly and in itself forms a barrier to further corrosion. Therefore it is equally if not more important to change the environment than it is to directly treat the rust (you can't bring back the lost capacity of the steel).

I have just repainted my roof and I didn't remove the mushroom vents but they still have intact seals and no evidence of rusting around them although I don't doubt there will be a layer of surface corrosion on the top of the roof beneath them. However I have four brass eyes for attaching fenders and they did have bubbles of rust around them and a clear air gap visible around the perimeter. I didn't remove them but having wire brushed, rust treated, primed, undercoated and top coated around them I now intend to paint a small black square around them and seal the gap with a black sealant. My wooden pigeon box is sealed against the steel roof in a similar manner. It won't do anything for the rust underneath but it will comtrol further progression by stopping moisture from getting to the area.

JP

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  • 2 weeks later...

I finally got round to investigating what's under those mushrooms. From the top they are screwed down. Looking from the bottom, there is the insulation sort of glued (I think) to the inside of the roof. I can't see any nuts or any way those screws are tightened as the insulation seems to be over it. The insulation is level with the hole in the roof. From the brown colouring of the insulation it does look like rusty water has seeped into it. I hesitate to simply rip out the insulation around the hole. I can see no other way to get at this though. What do you think?

IMG_3454.JPG.553f36758cf72e700f747497124cc62b.JPGIMG_3453.JPG.860d404d439fb39276baad31e3f18110.JPG

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27 minutes ago, Lizzy said:

I finally got round to investigating what's under those mushrooms. From the top they are screwed down. Looking from the bottom, there is the insulation sort of glued (I think) to the inside of the roof. I can't see any nuts or any way those screws are tightened as the insulation seems to be over it. The insulation is level with the hole in the roof. From the brown colouring of the insulation it does look like rusty water has seeped into it. I hesitate to simply rip out the insulation around the hole. I can see no other way to get at this though. What do you think?

 

1.  spin off the mushroom top (may need some WD40 on the thread where the big nut is)

2. from outside mark where each of the flange screws are by reaching in and scratching a mark on the insulation.

3. carve out a little insulation under the steel deck at each screw location.

4. if there is a nut then use a bit more WD40 and remove the nut and bolt.

5 if there is no nut then use a bit of WD40 and screw out the bolt.

 

job done

 

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14 minutes ago, Murflynn said:

1.  spin off the mushroom top (may need some WD40 on the thread where the big nut is)

2. from outside mark where each of the flange screws are by reaching in and scratching a mark on the insulation.

3. carve out a little insulation under the steel deck at each screw location.

4. if there is a nut then use a bit more WD40 and remove the nut and bolt.

5 if there is no nut then use a bit of WD40 and screw out the bolt.

 

job done

 

I hope it proves as easy as you make it sound. If the bolts have been there for years, they will probably have rusted too. 

Good luck Lizzy, I would leave the wd40 on for a while before you try and remove the bolts. PlusGas is also good for this job. 

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39 minutes ago, MHS said:

Good luck Lizzy, I would leave the wd40 on for a while before you try and remove the bolts. PlusGas is also good for this job. 

Personally I think that PlusGas is superior. 

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