serious delamination - how many layers should I put back

[corto-armitage]

Thanks a lot for your input. I had though 3 layers of 300 g because we removed 3 of 450 g mat on the rationale that they usually say biaxial is "much stronger" than mat. One of my 3 partners insists on 2 (and tends towards the theory which also is common that the old boat is thick and would be fine even if we didn't do anything). What you're saying makes me think maybe 2 layers of 300 g and 1 600 g, or 4 of 300 g, plus reinforcing the stress points.

I'd certainly like to get back to you when I have had other readings, have had the boat sounded for delamination and figured out more precisely the thickness of the boat in the various areas before and at the woven roving. In the meantime I was wondering if you could help me with the following:
1. Did you do the work yourself or the boatyard? How did you / they go about doing it? (West System suggests laying the sheet flat, soak it, roll it on a plastic tube, unroll it on the surface of the boat)
2. The reason I was thinking 300 g is that they've told me that above that (one said 200 one said 400, so I averaged it out) it is more likely to fall of when you attach it overhead. How did the 600 g work out?

 

[keesvugts]

Corto-armitage,
I think that with a heavier layer of biaxial glass rather than several thinner layers, you will achieve a better glass to resin ratio and you will end up with fewer adhesion challenges between layers. I found it impractical to apply several layers wet on wet over such a large surface. (you will use lots of peel ply )
I did the work myself for two reason: the labour costs would be horrendous if done by a professional company, and secondly there is so much rubbish being talked about osmosis and osmosis treatment, even by so called professionals, that I ended up not trusting anyone.
The method does vary with type and weight of cloth, for example 200 gr woven cloth wets out easily and can be applied dry on a pre wetted underground followed by further epoxy application from the top, where as 450 gr and 600 gr biaxials have a very closed structure and need to be thoroughly pre wetted before applying the glass to the work. Be prepared to waste a fair bit of epoxy that is squeezed out of the glass after application. Rolling the saturated glass on a plastic former and unrolling onto the hull does work. However you will need to construct some clamps to hold the glass in place as you work it. Even the heavy glass does not fall off or lift once the excess epoxy has been squeezed out however peeling back whilst you work it around the complex shape of the hull is a challenge, hence the need for clamps (you will run out of hands). In practice for the heavier cloths I ended up folding them back on themselves a number of times so that I ended up with a manageable package that could be carried to the hull between two people (my wife still hasn't forgiven me). The end of this was fitted into the clamps that pushed this against the hull. Following this the cloth was gradually unfolded as it was worked onto the hull. However we can talk about what worked and what did not when you are at that stage, for now concentrate on the remaining substrate to make sure that this is as sound as practicable (any damaged glass. / polyester must be removed), fair with a good key and scrupulously clean (mechanical and chemical). There is no point in sticking good material to a poor substrate. Get in touch to exchange ideas about the cleaning and preparation process once all rotten material has been removed.

Regards,
Kees.

 

[corto-armitage]

Thanks, when the time finally comes there should be all four of us. I was thinking two layering, one preparing and one for whatever is needed. We were aiming for wet on wet, doing one layer every 12 hours for 2-3 days in a row.

Do you have a picture of the clamps you were using?

 

[keesvugts]

Corto-armitage, unfortunately I don't have any pictures but I will sent you a sketch of how it worked. However if there are four of you working together you probably have enough hands to hold the top of the cloth against the hull whist it is being worked. Wet on wet is a good ambition, I tried but could not sustain the workload that was required for this.

 

[corto-armitage]

Thanks, that would be great. One question, did you fair the hull before you did the layering? Some said we should only fill in the craters. If you did, did you use the light epoxy filler or the one they call "structural" (at least in Italy), which is basically epoxy with glass powder, which is what they recommend for small craters?

As for wet on wet, I was thinking of the possibility of beginning with a smaller portion of the boat e.g. half one side and layering all the sheets, leaving them stepped with the inner ones protruding under the successive ones. This way we would be sure we could keep a schedule of two layers per day and would half to sand only the edges of the sheets if it cured. If we realized we could work faster then we could do more, e.g. half a boat or more all at once. I would also pre-cut all the sheets to size and shape.

 

[keesvugts]

Corto-armitage,

Yes I faired the hull beforehand after sanding to the appropriate grade to ensure a good key and coating with epoxy, but before the epoxy coat had cured. I used epoxy with colloidal silica as a filler. The way of working you propose could work. I used very large overlaps (50 cm) and a very shallow fairing angle. Wet on wet you have no fairing angle and perhaps a 10 - 20 cm overlap is ok. I do suggest that you leave a larger protrusion for those sheets where you don't work wet on wet so that you can crease a very small fairing angle before further sheets are added after sanding. Do make sure that all exposed work is covered with peel ply before you let it cure, this saves an incredible amount of sanding work. Be aware that epoxy with a high colloidal silica load is hard to sand. Definitely plan your sheets and pieces out before hand and cut them ready before you start. To make it easy mask off the top sides for a considerable distance above the highest point where you want to apply the glass cloth. This allows you to put a somewhat larger piece on and gives space as you shape the cloth to the hull shape as this will result in the edges no longer being straight. Cut the cloth to size after the epoxy has started to gell but before it completely sets.

 

[keesvugts]

Corto-armitage,
My fairing was constrained to several small dents, in your case if you have removed significant pieces of roving, patch these up with pieces of glass cloth, don't apply thick layers air large lumps of filler / filled epoxy.
I'm interested to hear how you decide that all damaged glass is removed as sanding and especially grinding does not leave a transparent surface that allows you to inspect the underlying polyester.

 

[corto-armitage]

Just a little update: we've been working weekends during the summer, mostly a friend and I, and dug out all the places were we had high humidity readings going beyond the first layer of roving and on some occasions beyond the second and third and digging a hole in the boat, but there was little choice because the liquid was very close to the last layer. I suspect in many cases this was because water had come from the inside, given that the worst parts were near the bilge and in the bow where the water tank was (originally of fiberglass). We ended up with 89 (yes... 89) craters mostly 10 cm but 4 or 5 30 cms.
The moisture meter proved fairly reliable, when it gave high readings we found liquid. When we dug where the readings weren't so high just to make sure we found none. After we did this the readings fell to acceptable levels more or less everywhere. In a few parts it did not although we had dug a lot but I think the meter was reading the wooden parts: bulkhead or some wood that was deep in the bilge in a section that is not accessible. We patched up everything with cloth and epoxy, each crater requiring between 10 and 20 small layers of 300 grams cloth. We have now just begun layering with two layers of 300 grams cloth and ready-made epoxy fairing. We are doing it in sections so we reduce the amount of sanding to the minimum. We've also filled the rudder and the skeg which were full of water with closed cell polyurethane foam (Espak 90 from Prochima) and sealed the holes we found with epoxy, finally wrapping up with two layers of 300 gram biaxal cloth. To attach the cloth we're not prewetting the cloth. We wet the Surface of course than lay it and use rollers and brushes. two or three people working together. I would have try pre-wetting and rolling on a tube, but since I have become a bit allergic to epoxy I am confined to the cloth cutting and let the other guys do what works for them.
We've also changed the seal on the saildrive and on the propeller axle; re-attached a chainplate to the side with epoxy and cloth, and fixed one of the bulkheads which was partly rotten digging out the rot and replacing it with epoxy filler and cloth. Fixed the seals on all the portholes etc. and now the boat seems finally water tight. Also repaired the Navman instruments with this "elastomer" I got from the US. It's a lot of work but at least now we have begun reconstructing . A lot of it was actually fun, though the sanding and the layering wearing a plastic suit and mask with 30 degrees Celsius for 8 hours in a row I could have done without. The other part I didn't like was when I got epoxy allergy and couldn't sleep because of the itching. I used the time to watch all the war movies on Netflix my girlfriend refuses to watch, so it was ok I guess.

 

[corto-armitage]

We finished fairing the boat with two layers of filler. Then epoxy layers then epoxy primer layers for about 400 microns (I think). As of last month, the boat is finally in the water and doing ok. It is very hard to tell with these things I imagine how the job went. I'll get other readings in December when I pull it out for a month but other than that, I imagine only time will tell. Hopefully a very long time. Thanks again for all your help
Gabriele