Sealing Roof vents

[DHutch]

The roof vents on emilyanne [5" brass dome vents] all all surrounded by rust which is blistering up from under the vents

 

- i beleve they where stuck on with domestic silicon, which containing acidc acid has been eating though the paint these last 15 years, and begun rusting the steel work

 

- so this summer i plan to take then all off, take off the rust, repaint the area and then reseat the vents, before we have the whole roof repainted.

 

- but i dont know what would be the best thing to use for using instead of the silicon???

 

- also someone say that they would paint over the whole base of the vent, so that you got a "paint seal" between the to (as well as the sealent) - and this soundnd like a good idea, i dont think it would look to bad, and i think that our paint would be upto not cracking - its very soft and doesnt ever crack, even when we bend the engine rook roof in half, and back again!!

 

 

thanks, daniel

Edited December 14, 2004 by dhutch

[Rick]

I don't think that the silicon would eat through the paint. It does contain acid, acetic, but I wouldn't think it strong enough to dissolve paint. I suspect that what happens, and it happens around windows as well is that the silicon allows water to seep under the edge and if this finds a weak spot in the paintwork rust commences and it's downhill from then on.

 

I think you will find that most mushrooms, windows and whatever are sealed with silicon. After cleaning the rust of it might be useful to clean the area where the mushroom sits with a degreasant such as cellulose thinners. This would provide a better surface for the seal.

 

Speaking from experience circle each bolthole with sealer when you apply it.

 

Richard

[DHutch]

ok, thanks

 

- it just seams weird because there is no rust around the "sky lights" which where stuck on with mastic (except one whoich was re stuck in a hurry last season)

 

 

daniel

[John Orentas]

Daniel.

 

I think you will find when you take the ventilators off you will find that little or no paint had been applied to the cabin roof before they were fitted. Even if that is not the case when the fixing holes were drilled no rust treatment was applied.

 

Rust spreads at a rapid rate in these circumstances. I am not aware of any corrosive effects associated with silicone sealent. You can use it with confidence on any materials.

 

John Squeers

[Guest]

I once had a data sheet for silicon, and from my memory I remember that it was acidic during curing process (there is a fancy term for this), but was neutral when cured. Hope this is true 'cause we have used a fair bit!

[John Orentas]

I won't hear a word against silicone sealent. I have been using it in work and play for 20 years. Never had any kind of trouble.

 

Temp. range.................+150 deg. C to -80 deg. C

Electrical insulator...................Excellent

Sealing...............................Totally waterproof. Oilproof

Adhesive.........................Quite good (done properly)

Cures nappy rash.

 

And loads of other things I can't remember

 

 

John Squeers

Edited December 15, 2004 by John Orentas

[DHutch]

ok, so i'll clean it down, paint it and then just sillicons it back down again, making sure there plenty every where, especially around the threads and head of the bolts.

 

- and should i paint over the base?

 

daniel

[ChrisPy]

I won't hear a word against silicone sealent.  Cures nappy rash.

 

<{POST_SNAPBACK}>

go on, tell me how, I'm fascinated...............

............. or are you just being naughty. I can imagine Mums up and down the country covered in goo trying to apply it to babies' bums.

[John Orentas]

Chris.

 

Perhaps I got a bit carried away.

 

John Squeers

[Yamanx]

You shouldnt use silicone as paint wont adhere to it.

 

Use polyurethene sealant.

 

We manufacture steel refuse bodies, which are never fully welded. The paintshop fully seal where the welds are'nt. They use a polyurethene sealant called Stickaflex that lasts for years and the paint does not come off.

[DHutch]

You shouldnt use silicone as paint wont adhere to it.

 

Use polyurethene sealant.

 

We manufacture steel refuse bodies, which are never fully welded. The paintshop fully seal where the welds are'nt. They use a polyurethene sealant called Stickaflex that lasts for years and the paint does not come off.

 

Sounds good, does it metter if i get a diffrent brand of polyurethene sealer, or are they diffrent?

 

daniel

[Rick]

You shouldnt use silicone as paint wont adhere to it.

<{POST_SNAPBACK}>

 

Ah well, that's where you sort the men from the boys. You have to keep the silicon only where you need it. No good covering the area around the job with an half inch of the stuff.

 

Richard

[John Orentas]

I think we are missing the point here, paint first, then fit the vents.

 

Thats what caused the problems in the first place.

 

John Squeers

[DHutch]

I think we are missing the point here, paint first, then fit the vents. 

 

Thats what caused the problems in the first place.

 

John Squeers

 

yeah, well like i sayed, i plan to remove the vents, paint under them, and replace them, then we'll get the whole roof done after that.

[Rick]

I think we are missing the point here, paint first, then fit the vents. 

 

Thats what caused the problems in the first place.

 

John Squeers

<{POST_SNAPBACK}>

 

Really. Leave thundering great holes in the roof since September 2003 when the shell went in the water. I primed the roof with two coats of primer then used a weathering primer. Then fitted the mushrooms.

 

In point of fact silicon used to be and probably still is permeated by air which could be moist. This then can start corrosion at the edges and so it starts. The reason I know that it is air permeable, to a small but definate degree, is that a number of people have tried to make double glazing sealed units using silicon as an edge sealant. They broke down.

 

Richard

[John Orentas]

Rick.

 

I think you are a little confused, the reply was to the original thread by Daniel but since you mention it you should always apply gloss paint, primers and undercoats are not waterproof. Why do you want to leave holes in your roof for so long, the first priority is to weatherproof it.

 

By the way silicone sealent is used extensively with double glazed units, I used to make them.

 

John Squeers

[dor]

Part of the problem here may be what is meant by "silicon sealant" There seem to be dozens of different varieties on the diy market, start looking at trade suppliers and professional applications and it becomes a minefield.

 

So I think it is likely that some are vapour-permeable; but maybe others are not. Some may stick better than others. Some are high-modulus, some are low modulus - what is that supposed to mean (I presume it is something to do with its flexibility but...).

 

So talking about "silicon sealant" as though it was one single product is bound to lead to conflicts of experience.

[John Orentas]

The best specification is SILICON R T V.

 

Dor is correct there are a lot of poor products with labels like 'contains silicon' made for sealing baths etc. and not much good for that.

 

John Squeers

[Rick]

By the way silicone sealent is used extensively with double glazed units, I used to make them.

 

John Squeers

<{POST_SNAPBACK}>

 

Is there any trade you haven't become involved in, truly a man of many parts.

 

When you say silicon sealant is used extensively with double glazed units are you refering to their use as sealants between the unit and the frame or between the two panes of glass and outside of the spacer bar.

 

I too used to make sealed units for use in the windows and doors I made. I have come a significant number of people who have used silicon and had them fail. I was old-fashioned and used two pack sealant made for the job, mostly because I didn't want customers phoning up and complaining that their units had broken down.

 

Richard

[John Orentas]

Richard.

 

Yes we used to manufacture 'viewing windows' for use in pharmacuetical clean rooms, our business was recessed lighting but we made the windows to be compatible with them.

 

"Between the two panes of glass and outside of the spacer bar". They were not required for insulation and did not even need to be waterproof, but formed a barrier against micro-organisms of various kinds.

 

We did occasionally have problems with misting but we found that as long as we bonded them when the factory was warm and dry (not in the morning) we had no further problems.

 

John Squeers

[maffi mushkila]

The best specification is SILICON R T V.

 

Dor is correct there are a lot of poor products with labels like 'contains silicon' made for sealing baths etc. and not much good for that.

 

John Squeers

 

Well if we are talking about sealing to keep out moisture what about the silicone sealant used to manufacture aquariums? That should keep the rain out.

[DHutch]

i was talking to a feind of my dads yesterday and he sayed the ONLY thing to use was this stuff called Stick-o-flex (i think) - which i think somone was talking about on another thread here

 

 

daniel

[DHutch]

It was "sikaflex" [datasheet]

 

- and he gave us a tube of the stuff, so i guess we'll have a go at that once its go a bit dryer out!

 

Also, i was thinking, when i paint the rusted area, before i but the vents back on, should i use a two-part paint/primer, like we will be using for the whole roof after the vents have been replace, or is there somthink i can undercoat it with that isnt two part, to save mixing up a load of paint just for doing a 12inch round area.

 

daniel

[John Orentas]

Daniel.

 

Just paint the area which will be covered by the vent plus a bit, grind off all the rust, primer, undercoat and ordinary gloss. The colour doesn't matter too much as you will paint over the visible bits when you paint the roof.

[Alastair]

Sikaflex can be painted over, it is a polyeurothane, AFAIK. sillycone can't.