Best UV resistant adhesive sealant?

[Ammonite]

Any recommendations for sealing around a fixed acrylic windscreen and the joint between a teak toerail and the hull? I used CT1 the season before last and it's totally degraded to the point it's falling apart. What I need is the stuff used for my teak faced plywood cockpit seats and sole (Moody from 1999), or something as good as this, albeit in white rather than black, as while the the wood itself has seen better days the sealant used between the teak strips and around the panels is as good as the day it was installed.

 

[Poignard]

Did you use clear CT1?

The reason I ask is because I was told a technical advisor at CT1 that the clear sealant degrades when exposed to UV light.

I had been in touch with them assking advice about sealing acrylic windows set into a wooden coach roof and, as a result of that advice, I used brown CT1. That was many years ago and the sealant is still in good condition.

I have just had a look on the CT1 website and found this, which claims CT1 clear is UV resistant.



Bit of a mystery, unless they changed the formulation since I contacted them.

 

[Ammonite]

Did you use clear CT1?

No, white

 

[geem]

Any recommendations for sealing around a fixed acrylic windscreen and the joint between a teak toerail and the hull? I used CT1 the season before last and it's totally degraded to the point it's falling apart. What I need is the stuff used for my teak faced plywood cockpit seats and sole (Moody from 1999), or something as good as this, albeit in white rather than black, as while the the wood itself has seen better days the sealant used between the teak strips and around the panels is as good as the day it was installed.

What about TDS? We used it to calk our teak decks in 2016. Boat in Carabbean and its still good

 

[Ammonite]

What about TDS? We used it to calk our teak decks in 2016. Boat in Carabbean and its still good

That looks like a good call. I've bought a load of Sabatack 750xl to stick my new synthetic cockpit teak down and was going to use this to seal the edges as well (the bit exposed to UV) but TDS suggests their product is longer lived than MS Polymers so I might go with this instead, as well as using it for the screen and toerail. The only downside seems to be the price although if lasts I can live with that.

 

[smithy]

I ran a bead of white OB1 between the top of the toe rail and hull and its started to degrade after a couple of years and that's in Scotland.

 

[thinwater]

Polyurethane adhesives, like CT1, Sika 295, and 3M products, are vulnerable to UV damage at the bond surface. They cannot be used for glazing unless the galzing is first coated with a UV opaque paint, because the UV goes through the glazing and atacks the bond. See the Sika 295 instructions. I have done panel testing on the subject. This CT1 failure is a classic example. Good product, but not for glazing.

Another solution is to use DOW 795 silicon, made for this sort of structural galzing. It does NOT have this UV vulnerability and many builders worldwide use it for the framless windows on boats and buildings. Not just any silicon. 3M 795. Pricey outside the US. Perhaps there is a similar UK glazing-specific silicone. Sika does not make one. You can always tell Sika mounted windows by the paint primer.

 

[Plum]

I could not find Dow 795 in the UK. Contacted Dow in the UK, told them I wanted to bond acrylic glazing to aluminium hatch frame and they said to use Dow Corning 791 silicone weatherproof sealant which is commonly available here. Still perfect after 6 years. They were very helpful. Sugest you get their advice.

Www.solocoastalsailing.co.uk

 

[thinwater]

I could not find Dow 795 in the UK. Contacted Dow in the UK, told them I wanted to bond acrylic glazing to aluminium hatch frame and they said to use Dow Corning 791 silicone weatherproof sealant which is commonly available here. Still perfect after 6 years. They were very helpful. Sugest you get their advice.

Www.solocoastalsailing.co.uk

They rate it for glass curtain walls, so I am sure it is very similar. I looked that the specs and they are just slight variations. Equivalent products, I would say. I'd use the Dow 791.

3M VHB tape is typically used to actually mount the window, with sealant filling the gaps.

 

[dankilb]

I could not find Dow 795 in the UK. Contacted Dow in the UK, told them I wanted to bond acrylic glazing to aluminium hatch frame and they said to use Dow Corning 791 silicone weatherproof sealant which is commonly available here. Still perfect after 6 years. They were very helpful. Sugest you get their advice.

Www.solocoastalsailing.co.uk

I did manage to get 895 here (it’s the grade of 795 certified for use in zones of seismic activity!). It isn’t cheap (£25 IIRC) and in the end I took took a case that was near use-by date to lower the cost.

I also bought some 791 (less than a tenner from toolstation!) for any shortfall and it was the same to tool/apply and had held us just as well (it’s excellent stuff in all respects).

Our windows are 100% bonded. No VHB tape and no fasteners!

 

[oldgit]

Used "Clear" CT1 in an attempt to seal a couple of large leaky MoBo windows.
Cleaned the glass aluminium joint very carefully with acetone removing any loose bits of the previous oil based ? sealant.
Masked up and applied a very small bead of clear CT1 which did stop all the leaks.
It worked for about a couple of seasons before degrading and losing its structure .
Removed and repeated the operation it again lasted about 2 years before failing.

 

[Fimacca]

I read that sika make 295uv for this application. Its exxy, as usual, and you need sika 209N to prep the surface first to do a proper job apparently.

Down to screwfix for my £8.99 Dow 791 then.......!

 

[geem]

I did a bit of research on this recently. It appears that the stuff we have been using for the last 15 years is a MS polymer. Geocel Works is one such version of this. It is used used by boat builders to fix windows in. By construction companies to joint rainscreen cladding panels and to joint concrete panels. It has a typical 10 year UV resistance.
We have used it successfully and would continue using it for all windows and deck fittings. The MS means modified silicon. It bears no resemblance to normal silicon in use.

 

[Plum]

I did a bit of research on this recently. It appears that the stuff we have been using for the last 15 years is a MS polymer. Geocel Works is one such version of this. It is used used by boat builders to fix windows in. By construction companies to joint rainscreen cladding panels and to joint concrete panels. It has a typical 10 year UV resistance.
We have used it successfully and would continue using it for all windows and deck fittings. The MS means modified silicon. It bears no resemblance to normal silicon in use.

In my experience the chosen polymer type is less important than the UV stabilization additives that are added to the polymer. The same generic sealant material in a product from one supplier may have a good UV stabilization additive and that from another may have no additive. If yours has lasted 15 years then it would be useful to know the specific brand/specification, please.

Www.solocoastalsailing.co.uk

 

[geem]

In my experience the chosen polymer type is less important than the UV stabilization additives that are added to the polymer. The same generic sealant material in a product from one supplier may have a good UV stabilization additive and that from another may have no additive. If yours has lasted 15 years then it would be useful to know the specific brand/specification, please.

Www.solocoastalsailing.co.uk

We have used it on two boats. We started using it 15 years ago on our old boat. The windows were sealed on the current boat when I replaced them in 2012. When we resprayed the boat in 2021, we removed the windows. They had been trouble free, mostly in thr Caribbean for thst period. We use Geocel Works.
There are lots of good MS polymer sealant/adhesives. A quick Google will tell you which ones have a good UV resistance.
Compared to polysulphides, they are generally far better

 

[Plum]

We have used it on two boats. We started using it 15 years ago on our old boat. The windows were sealed on the current boat when I replaced them in 2012. When we resprayed the boat in 2021, we removed the windows. They had been trouble free, mostly in thr Caribbean for thst period. We use Geocel Works.
There are lots of good MS polymer sealant/adhesives. A quick Google will tell you which ones have a good UV resistance.
Compared to polysulphides, they are generally far better

So is this the specific one you used 15 years ago? THE WORKS PRO Sealant & Adhesive | Geocel ?

Www.solocoastalsailing.co.uk

 

[geem]

So is this the specific one you used 15 years ago? THE WORKS PRO Sealant & Adhesive | Geocel ?

Www.solocoastalsailing.co.uk

Yes. Currently, every deck fitting, windows and our new toerails are bedded with this product.

 

[Ammonite]

I'm thinking about giving this sealant a try around my acrylic fixed windscreen and hatch garage. It's a fraction of the cost of Sika 295UV and would appear to have similar properties to glazing silicone without the drawbacks. Any thoughts?
CHEMFIX - Total Service

 

[thinwater]

I'm thinking about giving this sealant a try around my acrylic fixed windscreen and hatch garage. It's a fraction of the cost of Sika 295UV and would appear to have similar properties to glazing silicone without the drawbacks. Any thoughts?
CHEMFIX - Total Service

What are the drawbacks of silicon for glazing? And not the "nothing sticks to silicone" stuff, because properly removed, it is nonsense. Nearly all commercial glazing is silicone.

In the US DOW 795 is universal. I've used it on a number of boats and never had a re-do. I believe DOW 895 and 799 are more common in the UK, but I would ask the rep.

 

[Ammonite]

Not much, if you know where it's been used and can clean it up properly, however what I'd really like is a cost effective UV stable sealant that I can use more generally for the hatch garage, cap rail, acrylic screen and pretty much anything else where butyl isn’t suitable so I dont end up with a freezer full of half used tubes as I have now. This one looked like an interesting option and is half the price of the Dow products and a fraction of the cost of TDS and Sika 295UV. Its also cheaper than the Geocel product mentioned previously and is specifically designed for glazing but I have zero experience with it hence the question