On tilt 0 Posted April 17, 2014 Share Posted April 17, 2014 I'm re-sheathing my cockpit, when removing the old glass it came off in sheets? Is this normal for possibly the original sheathing to come away like this. As I'm redoing it any tips on making sure this problem doesn't happen again?? Cheers Link to post Share on other sites
sow1ld 2 Posted April 17, 2014 Share Posted April 17, 2014 Hi there sometimes this can happen if they laid the glass up with a higher than normal humidity but looking at the pic the main problem seems to be the timber underneath. Check is dry before u reglass it and give any timber ur about to glass a quick flick with the grinder just to help th resin key in. Sometimes the timer can be so thirsty it absorbs all the resin leaving the glass starved of resin. Hope this helps Link to post Share on other sites
On tilt 0 Posted April 17, 2014 Author Share Posted April 17, 2014 The ply underneath is pretty sound. I was thinking, that when I've finished all the prep sanding to go over the timber with a wire brush to help key the resin to the timber?? Most of the glass lifted fairly easy with two small parts that stuck like crazy. Thanks for your input Link to post Share on other sites
Guest Posted April 18, 2014 Share Posted April 18, 2014 Might have used polyester resin Epoxy ought to be better. Link to post Share on other sites
wheels 543 Posted April 18, 2014 Share Posted April 18, 2014 It can be a common problem on old Glass over ply. There are several possible reasons, no one culprit. Such as.... If it is really old, some early Epoxy was not quite as good as it is today and did not penetrate the Ply well. They did not sand the Ply with a coarse grit before applying the Resin. This technique opens the Ply fibres to allow penetration and keying. Sand across the grain with 40grit before you lay the new glass. They did not wet the ply enough with Resin, so not enough penetration. A tip I learned from FNG, make sure you use a 360g glass cloth as minimum. That allows a decent amount of Resin to allow good wetting and stop shear when the ply and glass move in the heat and stops cracking of the glass. I have recently reglassed my decks because of exactly the same reason. When I first discovered I had a problem, I lifted the glass in sheets just like you, but it was soaking wet with water underneath. Make sure the ply is nice an dry before you reglass. If it is soft ply, make a mix of Epoxy and thinners and brush it over to allow a good soak in. That can harden up the soft ply. Or you can use the Evidure or similar products if you want. Check all nails as if water has got in under it, the nails rust and you will see those areas as black spots. Make sure none have rotted the ply. If they have, just dig it out and a bit of filler works wonders. Link to post Share on other sites
On tilt 0 Posted April 18, 2014 Author Share Posted April 18, 2014 Might have used polyester resin Epoxy ought to be better. Yeah I was going to use epoxy, like wheels says the old glass is just that, old and old technology. Link to post Share on other sites
On tilt 0 Posted April 18, 2014 Author Share Posted April 18, 2014 It can be a common problem on old Glass over ply. There are several possible reasons, no one culprit. Such as....If it is really old, some early Epoxy was not quite as good as it is today and did not penetrate the Ply well. They did not sand the Ply with a coarse grit before applying the Resin. This technique opens the Ply fibres to allow penetration and keying. Sand across the grain with 40grit before you lay the new glass. They did not wet the ply enough with Resin, so not enough penetration. A tip I learned from FNG, make sure you use a 360g glass cloth as minimum. That allows a decent amount of Resin to allow good wetting and stop shear when the ply and glass move in the heat and stops cracking of the glass. I have recently reglassed my decks because of exactly the same reason. When I first discovered I had a problem, I lifted the glass in sheets just like you, but it was soaking wet with water underneath. Make sure the ply is nice an dry before you reglass. If it is soft ply, make a mix of Epoxy and thinners and brush it over to allow a good soak in. That can harden up the soft ply. Or you can use the Evidure or similar products if you want. Check all nails as if water has got in under it, the nails rust and you will see those areas as black spots. Make sure none have rotted the ply. If they have, just dig it out and a bit of filler works wonders. Thanks Wheels Keying the ply sounds like the go for sure, the ply is in condition apart from where it meets the transom, still fairly sound but quite wet, so there I'll probably use everdure. The other thing is the screw heads, I have a problem on the boat with screw heads popping and being visible.... they are small brass slot head screws that aren't below the surface very far. Would I be best to remove them and replace them with bigger gauge stainless screws and counter sink deeper with a decent radius counter sink above the screw and then fill with epoxy then glass over? Cheers Link to post Share on other sites
wheels 543 Posted April 18, 2014 Share Posted April 18, 2014 Keep the Brass screws. I would expect they are Silicon Bronze. The best way to go. If you really have to, remove, countersink and screw back in. Don't use SST. Encapsulated SST in wood will rust if it ever gets wet. The Damp wood becomes slightly acidic and the SST can't get enough oxygen to remain SST and so it rusts away very quickly. Silicon bronze will last forever. Link to post Share on other sites
On tilt 0 Posted April 18, 2014 Author Share Posted April 18, 2014 Awesome! Thanks so much for that, your a true asset to this forum Cheers Andy Link to post Share on other sites
Dusty 0 Posted May 17, 2014 Share Posted May 17, 2014 I wouldn't recommend using Everdure under an area that you plan to glass. Whle Everdure does have penetration it doesn't have strength so would be the weakest link in the bonding of the new sheathing to the ply, this may also explain what has contributed to the original sheathing coming adrift. I have seen over enthusiastic amateurs get carried away with Everdure on area's that were about to be glassed and many times this has created the same problem as yours and exactly the same result has happened. If it were me I would make sure the ply was completely dry and prep it then thin the new resin down 25% with epoxy thinners and coat the plywood, allow this to go tacky and then recoat with more full Strength epoxy and then lay the new cloth in and coat with epoxy again on top, Link to post Share on other sites
Guest Posted May 17, 2014 Share Posted May 17, 2014 Are you glassing the existing ply.? Is so it will be a problem. The black marks "scream" water ingress and issues. Dry it until moisture content is below 15% the hard "cross hatch" sand (40 grit) timber The rougher the surface the better key. But do not sand thru the first layer to the glue line... well not to much. Low viscosity epoxies like Everdure will penetrate ply, that is not sanded very hard, and it will "densify timber but it can hinder resin adhesion on surface sanded too smoothly. Dust off then apply epoxy resin with glass cloth. If ply appear soft or weak then replace. The failure you have is either the result if moisture, contaminants (dust...)or inadequate keying of resin to timber. High viscosity resins and paints need more "keying" ( coarse sand) than water thin products that can absorb/soak into the substrate. Applying to smooth or dusty surfaces will result in failure. Remember a surface sanded in two directions will have 4 x the surface/bond area than a surface sanded lightly in one direction Link to post Share on other sites
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