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

[Lizzy]

So ... I'm up to step 3 now. There are no nuts, so no parts to lose in the void. Hoping for the best that I can get these screws off. For the moment everything is still stuck. What I'd like to know is what to do with regards to treating the rust on the inside. As you can see the insulation is rusty at the top. Is it better to remove the insulation as far as I can reach and treat it with the Vactan stuff? I can't reach that far on the inside so might not get to all of it. Will removing the insulation make it worse in the long run? Or should I rather keep the insulation intact?

Edit: there seems to be a problem with image upload at the moment. So you can't actually see. Will add when this is working again. 

[Lizzy]

Wooo got the screws off intact! Another pic with mushroom off that I can't show you. It's not looking as bad as I had thought. (I know you are probably all going to tell me that it's AWFUL and needs to be fully stripped back etc.)

[Murflynn]

any rust between the insulation and the steel is likely to be the result of moisture leaking through the vent.

I don't think it will spread, and I wouldn't remove any insulation if you don't need to for access to the screws.

I would slap some vactan or jenolite on any exposed rusty steel, and then some metal primer (aerosol spray would be easiest in that location).

if you have removed a significant amount of insulation you can replace it using a PU foam aerosol (B&Q, Wickes) but be careful because it will drip everywhere, although if it does it's best to leave it for a day to harden, when it can be scraped off hard surfaces (but not fabrics!).  it will expand and needs trimming back after a day.

[Lizzy]

So .... this is taking longer than expected as some of the screws didn't come off in the end. They had to be drilled out with a 4mm drill and I was hopeful to fit stainless bolts and nuts instead. But it is impossible to actually reach so that the nuts can be put on properly, so I suppose tapping new screws it is. Again something I haven't done before. From a bit of research there seem to be two options, self-tapping screws (in metal?) and taps and matching screws. I'd like to go the easy way obviously, and it seems self-tapping screws are less faff. Is there any reason why I wouldn't want them?

[WotEver]

21 minutes ago, Lizzy said:

it seems self-tapping screws are less faff. Is there any reason why I wouldn't want them?

Yep, several. Firstly, 4mm plate (as your roof is likely to be) is a bit too thick to get a self-tapper into. Secondly, self tappers are also known as self-unlooseners in some circles. Thirdly, any Corrosion will likely make the screws let go as opposed to becoming more solid. 

The best solution is bolts with nuts. The second-best is tapped holes. 

Edited April 18, 2017 by WotEver
Autocorrect decided that bolts should be boots - it was wrong.

[Murflynn]

using a thread tap is easy peasy, just go carefully and gently, a bit at a time, back and forward, lots of lubricant WD40 or thin oil.

if the hole is only 4mm then a 5mm tap should do fine, buy your new stainless machine screws on ebay; use a bit of threadlok liquid (also from ebay) when tightening the new screws.

[WotEver]

5 minutes ago, Murflynn said:

use a bit of threadlok liquid (also from ebay) when tightening the new screws.

Or Sikaflex. 

[Horace42]

4 hours ago, Lizzy said:

So .... this is taking longer than expected as some of the screws didn't come off in the end. They had to be drilled out with a 4mm drill and I was hopeful to fit stainless bolts and nuts instead. But it is impossible to actually reach so that the nuts can be put on properly, so I suppose tapping new screws it is. Again something I haven't done before. From a bit of research there seem to be two options, self-tapping screws (in metal?) and taps and matching screws. I'd like to go the easy way obviously, and it seems self-tapping screws are less faff. Is there any reason why I wouldn't want them?

Tapping a thread seems the best option, as others have said. But care is needed, especially if you try to tap the old holes with bits of the rusty screw still in them.  Might be better to drill them out to a larger size to give completely clean holes then use a matching tap and screws., and it should be easier using a larger tap - they are not quite so fragile.

[WotEver]

1 hour ago, Horace42 said:

Tapping a thread seems the best option, as others have said. But care is needed, especially if you try to tap the old holes with bits of the rusty screw still in them.  Might be better to drill them out to a larger size to give completely clean holes then use a matching tap and screws., and it should be easier using a larger tap - they are not quite so fragile.

Or just fill the old holes with Sikaflex, rotate the vent slightly and drill new holes. 

[bizzard]

I wouldn't go gooing up the treads with lock-tite if you ever want to remove them again, perhaps a bit of copper grease. What with the thick circle bead of goo between the mounting and roof all thats needed is a drop of goo just under the countersunk screw heads to stop rain wiring through. To be honest if that insulation was pared away with a sharp knife or old wood chisel a bit I'm sure nuts could be fit.  The crumbles of insulation can always be stuck back up there.

Edited April 18, 2017 by bizzard

[WotEver]

7 minutes ago, bizzard said:

To be honest if that insulation was pared away with a sharp knife or old wood chisel a bit I'm sure nuts could be fit.

That was my thought too. Perhaps not all the mushrooms have the same access below as the photo?