Recommended sealant for boat roof

[robtheplod]

Hi All

I'm going to be repairing/de-rusting and painting parts of my roof (in prep for solar), and one bit is the roof 'rack' that holds the poles/plank - bubbling rust around the screw holes. No worries re treatment and removal etc but I just wanted to check with how to reseal this back. I'm assuming it needs a sealant due to the screw holes but the one often discussed (Sikaflex) seems to come in lots of flavours so wanted to be sure I got the most suitable one:

 

is this it??  https://www.ebay.co.uk/itm/Sikaflex-221-White-Adhesive-Sealant-High-Strength-Car-Van-Boat-Home-Sika/312705796684?epid=1105593821&_trkparms=ispr%3D1&hash=item48ceb7ca4c:g:Rf4AAOSwJ~hd86BS&enc=AQAFAAACYBaobrjLl8XobRIiIML1V4Imu%2Fn%2BzU5L90Z278x5ickkRjLZq23gAR%2BKma9gM2Z1hl7BU0pcDT0JWrUO6DXblDBQOu2dzh%2BR0RzSyoyzSZUhkrcicqcLM4QHxPkXktGgo%2FL%2B8gLXbRimj2RyYyzrA3%2B5GqDz8kqGpJVZ8h6Y1EBlcQI4mI2bHmWK6K2xOJgj28lwmjtc8VAP5eBWeJPpOU%2B7l0b2Apftl8OTy0WufKXNJW3c81W%2BgdKhPLe1AYD2lIwF3QvUbhcLdWqF%2BAAU0q%2BckConr%2BlsSBZovudTUFjuRNSj%2FOEaDuN28Ux172gEgfznt1oylM1DOzohcIMmJ31LN2CFX%2Fu5qRX3VWELsvdOMta%2BBud93%2B5hPga9XrZ%2BDL9o%2Fg1Jv7z%2FHuFCAbEc%2FjAOiwBIHk8UhjCCkPW7fxj1C6wQbHsr%2F%2BaipAczdS7b19DSfuvQYxVNmWjUMiMM6cQO1ZjmiEYSH02X1wSD5mJUvVkFQzhhb7h%2Fhu%2BX2PXbVaxCKyZ8qMslvfy3fUvtOP7d%2BGYB96J%2BHuOEho1M4XtzVDP3Eom2oknRX3qTeaknYnPn59UmGxKmUzEFZg1KZaf1jU%2F%2FrwM5b5QkYl80V6Nw3INEf9hgmQ7lcjC7x1hfjK07%2FPRSDpKMQlRA8jUufO3tBIHnkAYdMJsUebUYNE7DT4vcd8fchJ63ENppXsFT%2BkE6Lsmtnl8oXBctnrINqC6e4iz4%2BSt33J38MijNyc%2F8RRYau%2FRYvwVrjJzKLeeMPn%2B%2BYRDwfKqehxVWyLMuq10icQvsPwX4TftddxiaTc%2Ff&checksum=3127057966841e87e43546084b27881d66b61cbe7ff5

 

 

[BilgePump]

Sikaflex 291 is the one you'll see punted for marine stuff. You'll only need a tube but someone who needs a lot could consider Puraflex 40, about half the price and made by Sika.

[David Mack]

Or Stixall from tool station, available in black, white and clear.

[Sea Dog]

4 hours ago, David Mack said:

Or Stixall from tool station, available in black, white and clear.

Good stuff - which will accept paint, unlike silicone products.

[blackrose]

I just use stixall now. Clean the area and the fittings with a bit of white spirit to degrease first and clean off any excess with the same cloth afterwards. I'd use some of those thin latex gloves too because you've only got to look at these sealants and it's all over your hands.

[BilgePump]

Normally get Puraflex40 from Toolstation, but going to try Stixall considering comments.

 

And for gloves, that's why I had hundreds at lockdown. Varnish and sealants. Sticks like the proverbial to a blanket. 

[dmr]

I have had this problem. It might be due to standing water trapped in any tiny gap between the the roof and the feet of the plank rack, or water getting down between the screws and the plank rack. An additional problem is that water finds its way into the tiny spiral gap of the screw threads themselves.  I suggest a proper low strength thread sealant on the screws, then a blob of any silicone sealant on top of the screws and also between the roof and feet of the plank rack as you seat it into place.

 

.............Dave.

[WotEver]

2 hours ago, dmr said:

... then a blob of any silicone  sealant that isn’t silicone based...

Fixed that for you

[dmr]

6 minutes ago, WotEver said:

Fixed that for you

Silicone sealants have a lot of advantages. They are waterproof, last several years (but not forever) and come apart again when needed. Need quite a bit of cleaning before any repainting which is tedious but not impossible. Some of the "adhesive sealants" that boaters like to use are a right pain because they are adhesive, and when you try to take things apart they bring the paint off too. Silicone sealants are really good for sealing the tops of the screws holding down plank racks, you can use the neutral curing ones if the acidity concerns you. They are not a universal fix. Neoprene gaskets and plumbers mait are a better approach for things like portholes and mushroom vents.  

 

If you know of a good non adhesive sealant let me know, as I find silicone very messy and would love to try something else. It needs to be waterproof, not to turn brittle with age, able to fill gaps, and relatively easy to remove.,

 

................Dave

[Sea Dog]

12 hours ago, dmr said:

 

If you know of a good non adhesive sealant let me know, as I find silicone very messy and would love to try something else. It needs to be waterproof, not to turn brittle with age, able to fill gaps, and relatively easy to remove.,

You're no duck egg, so I expect you've already considered butyl tape?

[dmr]

17 minutes ago, Sea Dog said:

You're no duck egg, so I expect you've already considered butyl tape?

Yes, tried that a while ago, that's messy and tedious stuff to get off too but it does seal.  There was some rust poking out round the portholes so one of the lock down  projects has been to get them out, derust/bare metal behind them, 7 coats of paint and refit them. They had been fitted with adhesive sealant and they were a nightmare to get out, had to hammer a thin scraper in between them and the cabin side and slowly pry them off, and even where there was no rust the sealant pulled a lot of paint off. I've put them back in with neoprene gaskets as they will need to come out again in a year or two for a repaint. The neoprene looks to seal ok but has to be very well compressed to get a seal.

 

.............Dave

[Slim]

just don't use closed cell foam alone. The guy who last painted my roof did on the mushrooms, houdini hatches etc. On most of the roof fittings rust is now bubbling up from under them in the area of the screws. Obviously water ran down the screw threads into the tapped holes. When I strip and re-paint my roof (start tomorrow) I'll use some form of sealant.   

[dmr]

14 minutes ago, Slim said:

just don't use closed cell foam alone. The guy who last painted my roof did on the mushrooms, houdini hatches etc. On most of the roof fittings rust is now bubbling up from under them in the area of the screws. Obviously water ran down the screw threads into the tapped holes. When I strip and re-paint my roof (start tomorrow) I'll use some form of sealant.   

Looking at the porthole rust most had started at the fixing screws. Water really does find its way down the spiral gap between screw and threaded hole. A thread sealant will fix this, but water getting down past the screw and sitting on the steel surface is still a problem. You can not depend on a countersunk screw (bolt) to be watertight at the countersink especially if the holes were hand drilled and at a slight angle. A suitable sealant is required. I would not use silicon here.  If you have mushroom vents or even a bullseye on the roof then I like to seat them on plumbers mait but have not yet found a screw head sealing method that I am 100% happy with. Hex head bolts on a copper washer would be good but most people would not like the look of this ?.

 

The plank racks usually have the screws in recessed holes and I have found silicon is fine here.

 

I am working on the ultimate porthole bolting method right now. Stainless steel socket head screws (not countersunk) sitting in the countersunk hole on a copper washer is a bit punk but should be water tight. Currently trying to cut threads on the outside of the socket heads, not easy on stainless and broke a die yesterday. I will then put modified brass dome  nuts on the bolts to get a suitable appearance.

 

..........Dave

[Slim]

48 minutes ago, dmr said:

Looking at the porthole rust most had started at the fixing screws. Water really does find its way down the spiral gap between screw and threaded hole. A thread sealant will fix this, but water getting down past the screw and sitting on the steel surface is still a problem. You can not depend on a countersunk screw (bolt) to be watertight at the countersink especially if the holes were hand drilled and at a slight angle. A suitable sealant is required. I would not use silicon here.  If you have mushroom vents or even a bullseye on the roof then I like to seat them on plumbers mait but have not yet found a screw head sealing method that I am 100% happy with. Hex head bolts on a copper washer would be good but most people would not like the look of this ?.

 

The plank racks usually have the screws in recessed holes and I have found silicon is fine here.

 

I am working on the ultimate porthole bolting method right now. Stainless steel socket head screws (not countersunk) sitting in the countersunk hole on a copper washer is a bit punk but should be water tight. Currently trying to cut threads on the outside of the socket heads, not easy on stainless and broke a die yesterday. I will then put modified brass dome  nuts on the bolts to get a suitable appearance.

 

..........Dave

If you can't cut a thread on the head of the socket bolt why not drill out the thread in the brass domed nut and stick it on the socket head with a dab of suitable sealant/adhesive. Think of a crowned/capped tooth?(I am cos I've got one playing up) 

Edited June 23, 2020 by Slim

[dmr]

3 hours ago, Slim said:

If you can't cut a thread on the head of the socket bolt why not drill out the thread in the brass domed nut and stick it on the socket head with a dab of suitable sealant/adhesive. Think of a crowned/capped tooth?(I am cos I've got one playing up) 

 

Yes thought of that, its currently plan B. I think the cap heads are going to need a little chamfer putting on in a lathe, so doing than to 66 bolts, then cutting 66 threads is suggesting that plan B might well become plan A ?

 

...............Dave

 

 

[TheBiscuits]

Would LS-X not work well as a thread sealant?  It is silicone based but never sets hard.

[dmr]

11 minutes ago, TheBiscuits said:

Would LS-X not work well as a thread sealant?  It is silicone based but never sets hard.

That looks quite good, but it is silicone ?

As a CCer doing ongoing nomadic maintenance I have additional constraints of storage space and shelf life, so stuff that has multiple uses and does not go off too quickly is good. Something that comes in big pots, goes off once opened, and is only good for one specific job is bad.

When I worked we always got things in big pots and now I find buying a tiny tube of copperslip etc a bit wrong but it makes sense.

Silicon sealer does not keep for long once its opened (maybe a year or two) . I keep a tube on the boat and try to use it for several things to make use of it, though this does mean buying the very expensive anti-fungal stuff so it can do bathroom sealing as well as general boat jobs.

I have used a low strength thread locker as a thread sealant, because It doubles as a thread locker ?

 

.............Dave