Guest 000 Posted October 28, 2015 Share Posted October 28, 2015 New windows time for the H28. I am using Sika 291 together with 3M 4991 double sided tape. When I did the same job in the Cav 39 a few years ago I don't remember being unduly distressed, but I am now. $300 for 30 metres of 19mm tape??? Is there any alternative (read cheaper) to the 3M product?. Or does anyone have any tape offcuts they would like to sell me? I need 15 metres. Quote Link to post Share on other sites
Dagwood 57 Posted October 28, 2015 Share Posted October 28, 2015 All for supporting local companies and that stuff but looks like someone might be taking the micky to me: http://www.amazon.com/dp/B007Y7H1WM/ref=biss_dp_t_asn Quote Link to post Share on other sites
Guest 000 Posted October 28, 2015 Share Posted October 28, 2015 Panic over. 4991 tape is for special applications and difficult plastics. Apparently what I need is 5962 tape - high strength flexible bond suitable for acrylics and GRP. $106 for 30m. Still a lot of money for an up market sellotape, but I can live with that price. Quote Link to post Share on other sites
Guest 000 Posted October 29, 2015 Share Posted October 29, 2015 Yes, tape only, no mechanical fastenings at all. The cabin sides on the H28 have 7mm deep X 19mm rebates that the old windows used to fit into. The old windows were 6mm thick which left 1mm for the old style sealant so they needed screws as well to hold them in place. The new windows are 8mm. I rounded the edge on my spindle moulder and will use the tape to affix them to the cabin sides, overlapping the rebate. Then go down below and squirt the rebate full with sikaflex 295uv and tool it off. I find this method the easiest and cleanest, if you can ever keep things clean with that horrible black goo. Adhesion of the window to the cabin is via the tape and the sikaflex. I used this method on my Cav39 years ago and also on a 37 foot catamaran I recently built for my son. Performed well in both instances. Have you got your acrylic? I have quite a bit of 8mm clear due to not being very good at measuring when I ordered it. Doh! Quote Link to post Share on other sites
Kevin McCready 83 Posted October 29, 2015 Share Posted October 29, 2015 Two quick questions: 1. If you take a knockdown, then pop back up, without mechanical fastening what's to stop the window being sucked out as it comes back up? 2. Would this tape solve my problem of water ingress in a couple of places where my toe rails are breaking down. If my last repairs don't hold, I'm thinking of removing the rails entirely and sealing somehow so that no water comes into the cabin or gets down into the balsa core. Quote Link to post Share on other sites
Guest 000 Posted October 29, 2015 Share Posted October 29, 2015 I couldn't say regarding your toe rails, but if you go to the 3M NZ site, you will find screeds of info as well as technical specs for all their products. I prefer tape/sikaflex fixing over mechanical fastening for acrylic. Tape provides even adhesion all around the perimeter of the window whereas mechanical fastenings create stress points - something acrylic doesn't like too much. Quote Link to post Share on other sites
ScottiE 174 Posted October 29, 2015 Share Posted October 29, 2015 we had a not dissimlar discussion on this a few weeks ago over at tech talk: - http://crew.org.nz/forum/index.php/topic/12332-rubber-seals-for-window/ Paul kindly offered me the oportunity to look at his windows and I "popped over" on my way up to Russell! Paul allowed the sealant to fill the screw holes of his original window and actually it looks fine and not really noticeable. Certainly won't be a problem for the T9's eybrow windows. (does a knock down generate significant negative pressure on a window? Would have thought it would be positive while submerged hard to believe that this would go significantly negative as the window travels through the water. You could always buy a boat that doesn't suffer knockdownism!) Quote Link to post Share on other sites
Battleship 100 Posted October 29, 2015 Share Posted October 29, 2015 We used the tape used to hold spoilers on for the SR26 along with simpson glazing mastic works a treat. I wouldn't be too worried about them falling off the old ones were also glued on with mastic and we had to hammer a chisel all the way around the window to get them off, took hours if they popped off they would be taking the side of the boat with them. Quote Link to post Share on other sites
ScottiE 174 Posted October 29, 2015 Share Posted October 29, 2015 Or indeed the whole boat! Oh wait . . . Quote Link to post Share on other sites
Chewing Gum 17 Posted October 30, 2015 Share Posted October 30, 2015 You don't need tape or expensive sealant. Our boat is 12metre Lidgard with timber rebates and windows are glass. All that holds them in is Black Sika Silaflex MS (a modified silicone that is nothing like ordinary silicone sealant which is a no no). I think it is about $25 a cartridge from Placemakers. We just use wooden sticks propped against the safety lines to hold the glass for a couple of days until the sealant goes off. This boat has done trans tasman, around the pacific and a NZ crcumnavigation and twice down the west coast. Approx every say 5 years you need to replace the sealant as the UV gets to it. In the meantime they never leak. We use the same sealant (white) for all above water fittings, hatches etc. It is much better than the Sikaflex type sealants as it stays more flexible and you can remove fittings without wrecking your boat. Cleanup with meths but I like to use heaps of masking tape to avoid the mess. Usually I seal the wood with epoxy resin before fitting the windows. Quote Link to post Share on other sites
Guest 000 Posted October 30, 2015 Share Posted October 30, 2015 There are two points Chewing Gum, firstly, your windows are glass, and secondly I would guess not too big, so the sealant you are using is very suitable. Acrylic on the other hand presents difficulties with adhesion, hence the need for Sika 209 primer which then needs the 295UV sealant for comparability reasons. Also, expansion and contraction of acrylic is huge compared to glass so it really needs a purpose designed tape/primer/sealant system at huge expense - unfortunately. Quote Link to post Share on other sites
Battleship 100 Posted October 30, 2015 Share Posted October 30, 2015 If you get the right sealant it will come with a primer to put around the edge which protects it from UV, pretty much essential. Quote Link to post Share on other sites
Chewing Gum 17 Posted October 30, 2015 Share Posted October 30, 2015 There are two points Chewing Gum, firstly, your windows are glass, and secondly I would guess not too big, so the sealant you are using is very suitable. Acrylic on the other hand presents difficulties with adhesion, hence the need for Sika 209 primer which then needs the 295UV sealant for comparability reasons. Also, expansion and contraction of acrylic is huge compared to glass so it really needs a purpose designed tape/primer/sealant system at huge expense - unfortunately. No I our windows are actually quite large, would easily be bigger than a H28 and the sealant is very flexible. Not sure about the adhesion to Acrylic but I would be surprised if it didn't stick - would be easy to test it. It is not easy to remove the glass I can assure you. Quote Link to post Share on other sites
Guest 000 Posted October 30, 2015 Share Posted October 30, 2015 It's good that you have a solution that works for you. I am a little reluctant to depart from Sika's recommended methods given the complexities of working with acrylic - I'm trusting them that it's not just money making advertising hype. Plus, I've already shelled out on all the expensive gunk. Two points: Cutting acrylic is pretty easy on a bench saw with a fine toothed blade if all you want is straight cuts. The majority of boat windows are curved and need a jig saw and the problem here is overheating of the blade which causes the acrylic to fuse back in the cut behind the blade. Edge chipping can also be a problem. I've tried all sorts of blades and have had great success with Sutton Tools 8005-5 blades. They are a non-wavey blade and don't seem to heat up. If you get the feed speed right then you get a nice cut with no edge chipping and in all probability won't even need sanding. Secondly, Willow is correct that you should overcoat the outside of the acrylic over the sealant/primer to protect them from UV. Sika recommend paint and not their primer for this. I suspect there are many people who don't know what paint to use on acrylic and unfortunately I happen to be one of them, so if anyone can advise... Quote Link to post Share on other sites
wheels 543 Posted October 31, 2015 Share Posted October 31, 2015 Chris is spot on. Sika or any of those adhesives, won't stick well to acrylic without the primer. Eventually they will let go and leak and if not mechanically held in, will come right out.Glass is a different story and MS and Silicons will adhere well. Quote Link to post Share on other sites
Chewing Gum 17 Posted October 31, 2015 Share Posted October 31, 2015 From Dow Corning: Q: Can Dow Corning silicone sealant/adhesives be used underwater? We do not recommend our silicone sealants/adhesives for continuous underwater use. Q: Will your sealants adhere to hard to bond to plastics such as polyethylene, polypropylene, urethane, acrylic or PTFE? Normally, no, silicone sealants generally will not adhere to these substrates; however utilizing one or more of the following adhesion improvement techniques (chemical treatment, roughing the surface, corona treating the surface) may help. Always keep in mind, that even though they may not have great adhesive strength to these substrates, there might be enough adhesion for a particular application. Test the silicone sealant in your application prior to use. Q: Will silicones break down from UV light and ozone? Silicones in general demonstrate great UV and ozone stability. Quote Link to post Share on other sites
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