UV Window Adhesive Protection

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long_ben

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Hi everyone,

I'm new to this forum and also new to boat ownership having just purchased myself a Trident Voyager 35 to live aboard and - once I've done enough work to it to satisfy myself - go cruising in. My most pressing issue at present relates to the replacement of some irritatingly leaky windows. My plan is to replace the current aluminium framed windows with some surface mounted acrylic. I've been looking at Sika's range and I'm comfortable with everything apart from one issue... UV protection. Whilst it appears that the 295UV is (as the name suggests) UV resistant, the primers aren't. I know Sika produce a UV tape but that seems like a fairly untidy solution. My windows aren't neat squares and I don't want to have to start faffing about trying to make tapes look tidy. What I'm hoping is that someone has some experience of this and might be able to recommend a UV resistant paint that will work on acrylic. I'd like to cut a neat border from the sticky protection film on the acrylic and then spray a UV protecting border. Is this a viable way forward?

Many thanks in advance for your knowledge... hope you're all keeping well in these crazy times...

Ben
 
Unless the ally frames are badly corroded the usual fix for this is to take out ally frames and take apart,
take out and re-bed glass in butyl mastic,
replace frames in butyl mastic.

Plank
 
Polyurethanes are inherently vulnerable to UV in the bond area. You can try to block it with primers, but that's just a patch.

Dow 795. It's pretty much the standard here. I've used both, and 795 is easier and more reliable over time.

(Not just any silicone. This specific product only.)
 
Our windows were 'simple' curved acrylic, no frames, attached to the coachroof with Dow 795. The adhesive has survived the UV in Sydney for 20 years. The acrylic itself, 10mm, has fared less well and we replaced 5 of the windows last year. We used a local adhesive, which will not be available in the UK but competitive with 795. 795 was used in the glass windows in the Petronas Towers in KL.

Use of these adhesives is relatively easy and easier with 2 people if the windows are large. You may need to shade the windows and you will need to devise a means to keep the windows under pressure as the adhesive sets off. Mask off the area, with masking tape, and clean up following the instructions meticulously.

The most difficult part was removing the old windows and removing the remnant adhesive - we used a filleting knife and colourful language.

People in the UK use a product called CT1 as a sealant adhesive. I'm not suggesting it is suitable. But CT1 has a very high reputation, or is used by many, and I cannot believe they are a 'one product' company. They may produce something that is suitable, maybe someone will post - or use CT1 in the forum search engine - and then use the telephone and speak to them! Again I cannot believe that Dow 795 is the only suitable product in the UK.

Jonathan

Ben - and welcome to the Forum!
 
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I tried everything to stop my ally framed windows leaking. In the end, I got a slightly thicker perspex to fit the outside shape of the frame . I cut the inside part of the old channel from the frames and used them as a trim with a bit of neoprene tape between the trim and the perspex. Bolts through the ally, neoprene, perspex, butyl tape and an internal 3mm ply trim hold everything together. Interscrews would probably have been best, but I'm a tightwad, so I used machine screws with Allen key heads and dome nuts on the onside The windows look good and, best of all, no leaks.

Perspex has reasonable UV resistance. I've a feeling that polycarbonate may be slightly better, but scratches more easily. I'm not aware of anyone who bothers with UV protection for either. The only thing that will last forever is glass.
 
Thanks for your suggestions. Unfortunately, simply refitting the windows won't be an option. At some point in the boats life, someone saw fit to replace the mineral glass with polycarbonate of dubious thickness. It was clearly done 'on the cheap' and hasn't faired well. Given that its a pilothouse design, the cost of having new glass made up would be prohibitively expensive. Plus, I doubt very much if the frames will accept anything near a thickness I would consider acceptable. There are sloping windows on the front of the pilothouse which are just begging for someone to put a foot through them.

Since I posted this, I've found a company called Kolorbond who produce a paint which molecularly bonds with hard plastic. I do appreciate that the UV issue might not be as huge as I think (thanks Neeves for your input on that one) but I'm working on the basis of doing the job as well as I can and the documentation from Sika suggests a UV barrier would be 'best practice'. I'm hoping I can work out if there is a suitable primer that would enable me to paint a UV border on the inside face of the windows which would make the job even neater. Ultimately, a solution much like Stemar - but minus the bolts - is where I'm aiming. Gonna get some hardwood to make up some nice trims on the interior but the first priority is to get rid of the drips.

Thanks all again for your input. I will be replacing the glass in the fore and midships port-lights so I suspect some Dow 795 will be being deployed to that end. I'll report back if I get any useful developments on the paint front.
 
Where I used to work, we made such windows out of acrylic, designed to be directly bonded into sometimes quite heavily curved sections of coachroof.

For those, there used to be a very slight rebate machined in the rear (inwards facing in the boat) face of the acrylic, all around the edge. This aided in masking off the main part of the window, the outside edge, an inch or so, was then painted black..this protects the eventual adhesive from UV damage.

However, your priming/painting procedure has to be bullet-proof...as rather than an acrylic/adhesive bond being what holds the window in place, you're adding 2 extra interface layers/potential areas of failure. Adhesive->paint and paint>acrylic.

Therefore, if your paint fails over time, the window will fall out, or you'll have leaks.

Most builders now using glass instead, with a frit-print edge to achieve the same...advantages being the fret-print cannot fail, and glass->grp bonding is very reliable.
 
@thinwater Thank you for the clarification.

And, @sailorbenji, bulletproof is what I'm aiming for... hence my concern with UV protection. I'm confident that I can get a decent GRP bond and also the bond to the acrylic sorted... I'm just very keen to ensure that my hard work doesn't decide to fall to pieces because I neglected a part of the process. I think maybe the idea of painting the inside bonding area is best left. After all, my concern is having leak free, high strength windows. Aesthetics, although somewhat important, have to take second step - and the potential for the paint being the weak link is far too high. I have emailed Sika. They may come back to me with some neat solution.
 
In terms of the primer on the acrylic - you don't need this if you have a properly compresssed seal.
I assume that you will have screw or interscrew fixings and not trying to simply bond the window.Keeping the sealant tidy is another matter.It is recommended that you apply polish to acrylic anyway to prevent early crazing from the UV.The Greygate polish obtainable from Hadlow Windows and others has a particular pedigree here in that It wa first employed on the windshields of Spitfires.
 
I did a bunch of testing of adhesives for sailcloth for a sailing mag (Practical Sailor). What I leaned is that polyurethane sealants let go after 1-year of UV exposure on the cloth side, but this ONLY happens on fabrics, such as sailcloth, that are relatively transparent in the UV. This did not happen with Sunbrella and it did not happen with most other adhesives. It did not happen when the sun hit the glue side of the sailcloth, only when it hit the underside. I then repeated the tests with acrylic. What seems to happen is that the UV penetrates and hits the bond area, which makes it release. Silicones are more resistant. Some epoxies, unsurprisingly, are also quite vulnerable.

This is why SIKA requires a paint-like primer. To block the UV from the bond area.

Hitting the bond area with UV is different from hitting the topside of the sealant with UV. This degradation will happen even if the seal is compressed, with the Polyurethane releasing, although it might not leak. Or it might.

This is just not the best use of polyurethanes. I like them, but not for this.
 
@bluerm166 That's exactly what I'm trying to do... dispense with screws altogether. Modern structural bonding adhesives should be up to the job. I fitted a window on the sliding door of my van about a year back. Nothing but a line of PU adhesive holding it on and its been over some fairly bumpy ground (and our wonderful pot-holed British roads)... still there. As far as avoiding primer... perhaps if I was using screws then this would be viable... but as I'm relying on bond strength then I'll be using the correct primers/activators.

@thinwater That's useful info. Thank you.
 
Ben,

I forgot (and its fairly important).

I don't know how big your windows are but ours needed two of us and we only managed one window per day and installed at least a complete day apart (to allow the adhesive to set sufficiently). We replaced 5 windows and left each window as long as possible with battens and weights, see below.

Our windows are huge, some dimensions are over 1m. The actual window hole is quite small as we have a roughly 100mm edge to which to apply the adhesive all round each window. Our windows are a quite dark acrylic. The first one we applied was a disaster as in following the instruction we had 'combed' the adhesive, over that 100mm border, and applied with care and then found you could see the adhesive, black, through the adhesive and see the underlying gelcoat, which is white. It was a real mess as we had to take the window off and clean up all the 'wet' adhesive.

We had pre-sanded the area where the adhesive would be applied.

We discovered the original windows had been painted to over come this issue, reference made above from others on pre-painting. I don't recall which paint we used but it was advised by the supplier of the adhesive.

So check!!

We had to sand each edge, mask up and paint each edge, then apply adhesive then stick windows. Most of our windows are slightly curved and I had pre- checked that we could apply that level of curvature. Our windows are 10mm acrylic. The curves were in one dimension only (for the windows we have replaced). The windows have a gap between them and we simply used heavy battens of wood and simply screwed through the gap (between the windows). We then back filled the hole made by the screws. To increase pressure on the adhesive, our windows 'slope', they are not vertical, we slung 20l water containers hung on ropes (you will need to device a way to hang them) so that the weight of water applied even pressure to the windows, usually 40l per window. We applied one window every other day.

We finished off each window, smoothed the adhesive, roughly when we had applied the each window and then neatened up after 24 hours by applying extra adhesive round each edge. It proved impossible to obtain perfection with the top and bottom battens and 40l of water all in the way - so needs must.

The other thing to watch - you need quite a thickness of adhesive to allow the windows to expand in the sun. If the adhesive is too thin it will not 'stretch' sufficiently. Again this detail will be in the application instructions.

Our windows have no screws - they are held in/on with the adhesive.

We are confident of the adhesive - we sailed back from Tasmania on one memorable passage with 50 knots minimum over 11 hours and seas breaking straight over the cabin roof. The windows and yacht coped well - the crew (wife and I) were slightly apprehensive. The forecast missed a small low pressure cell in which we sailed and that moved at roughly the same speed and direction we were sailing.

Jonathan
 
"That's exactly what I'm trying to do... dispense with screws altogether" Don't even think about it. You don't need screws you need bolts!
If you get a leak in o window that's annoying. If you get a hole where the window was that's a catastrophe.

Plank
 
long_ben said:
And, @sailorbenjiI think maybe the idea of painting the inside bonding area is best left. After all, my concern is having leak free, high strength windows. Aesthetics, although somewhat important, have to take second step - and the potential for the paint being the weak link is far too high.
Click to expand...

Hi Ben, glad the info was of some use....don't misunderstand the purpose of the painted inside perimeter of the panel...whilst it is of an aesthetic use (in that it covers up the bonding area...see Neeves' nightmare first application above) its primary purpose is to protect the adhesive/perspex bond from UV damage.

Believe me, we spent many, many months, also working with the adhesive manufacturers, to make sure a bond-only system (no fixings) for one of the largest boat-builders in the world was safe, repeatable and long-lasting, so at least in this respect I consider myself quite well versed!
 
Having been through the process and having had long conversations with Fix Tech in Oz

This the background to the adhesive we used

https://s3-ap-southeast-2.amazonaws...Acrylic-and-Polycarbonate-Window-Guide-16.pdf

Our original windows were bonded with the Dow product and our builder now (and ourselves) used the Fix Tech product. The windows we replaced, 5 from 13, actually cracked the acrylic (and the Dow was a devil to allow removal of the cracked windows).

I cannot imagine Fix tech is available in the UK (but I might be surprised) but I am sure the technology is not unique.

I suspect that the film thickness, the surface area to which the bond is attached and the size of the window are fairly critical dimensions - a small bond surely cannot be 'so' strong - something to look at - and maybe Benji can comment - as he seems to have had some in depth exposure.

Jonathan
 
The particular window I remember was about 1.5m length...we had a 8mm bonding width, and appropriate gap up to any GRP rebate around the outside (though interestingly this wasn't filled in as the Fix-Tech documents suggests). Recommended sealant thickness, from memory was 6mm.

Interestingly, we similarly looked at losing the fixing screws and bolts from hatches (up to 700x700)...bonding the aluminium lower frame direct to the GRP. The bonding strengths we could achieve, and on a lower frame like that you got maybe 5-6mm width of bond, and only 2mm maybe in height once compressed down whilst curing, was quite exceptional.....nobody quite had the cojones to put it into production though.

Modern adhesives really are phenomenal, the mind-set that mechanical fixings are 100% required is very much old school thinking. That said, adhesives are very reliant on preparation, application and so on, and in that respect a mechanical fixing is relatively idiot proof by comparison.
 
Thanks so much guys. I've been having quite an interesting day (blocked toilet which resulted in dismantling of pump.... got through a whole toolbox worth of colourful language in the process...) so it's a relief to sit down now and get back to planning a job I'm actually going to enjoy doing (although whether that remains the case after fitting 9 pilothouse windows and rebuilding 4 aluminium framed portlights remains to be seen...).

@PlankWalker I do get that people are still a little reluctant to go 'screw free' and I can see how it might seem counter-intuitive. However, given that bonded windows form part of the structural integrity of most cars and some buildings these days, the technology is out there to achieve something at least as strong as a mechanical fixing.

@Neeves I don't think we have fix tech I the UK. At least I haven't found them. I'm rolling with Sika as they seem to produce a range of marine sealants/adhesives which meet my requirements. I also have some fairly large windows to deal with as I have a pilothouse so I'll be employing the services of my partner (although I may not have explained this to her yet) to help with the lifting and shifting. Interesting that it took you a while to do all your windows. I'd banked on doing it in maybe four days. Might have to rethink that time frame. I've been around and applied some sealant on the current windows which - although it stands zero chance of being a long term fix - I'm hoping will stop me getting dripped on in the night until I manage to work my way to a permanent fix.

@sailorbenji As far as the paint goes... I will definitely be including a UV barrier. I haven't quite worked out how yet though. My least favourite choice is the Sika UV Shield Tape as I think it'll look unnecessarily untidy, second is an exterior paint (molecularly bonded - i.e. Kolorbond), and my first choice would be a paint on the 'back side' of the window. However, I think where I've got to in my head is that the idea of a DIY application of paint to a bonding surface holds too many unknowns. Hopefully, I can manage a coat of matt black on the exterior surface which won't look disastrous... we'll see.

Just as a further point... It has been touched on here by others, but in case anyone else is planning this as a glazing solution. In the case of the adhesive/sealant choices I've made, there are some pretty stringent parameters to work to. The bond depth needs to be between 4mm and 6mm for the sizes of windows I'm fitting (4mm on the smaller ones and 6mm on the larger) and there needs to be a bonded area at least 15mm wide... with a further backfill around the edges of between 15mm and 25mm. There are also specs for gaps between windows should this arise in your case. I'm having to use two different primers and an activator... I'm throwing this all in as a caveat. Adhesive technology is remarkable - but only when used correctly... hence my seeking advice here (as well as direct from manufacturers)... so my windows don't fall out at some point when I really would rather they hadn't...
 
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