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Another problem with seams

  • John Kelly
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21 May 2009 18:18 #20508 by John Kelly
Another problem with seams was created by John Kelly
I posted a query in March and thanks for all the help. I now have a new problem. Having prepared everything for varnishing internally, I had scraped the old varnish off the seams and so these are of a whitish appearance, in some cases showing the top of the fabric weave. I bought some epoxy resin as suggested and hoped that this would soak into the fabric and so the seams would then become clear again. Sadly this does not seem to be happening, and I am worried now that it will just be locking in an awful appearance. I have for the moment abandoned the epoxy after just a couple of inches. Maybe in a few hours it will have change but it's not looking good. Can anyone help?
Many thanks

John Kelly

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  • cjyardley
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24 May 2009 20:18 #16506 by cjyardley
Replied by cjyardley on topic Another problem with seams
John

This does sound tricky. Its a bit difficult to assess the problem without seeing it but my feeling is that the bond between the fibres and the resin has parted not just on the surface but possibly deeper. I think that I would try a additional abraision in a very small section to try to assess where the problem is in the laminate. I would use a good 180 grit (or sim medium) wet or dry paper used wet with lots of water and try to grind off the top a bit more. This will show you whether you can 'wet out' the fibres (with the water)- if it still shows white with water on it, then its unlikely to wet out with epoxy (but still worth a try possibly with a little gentle heat to get the viscosity down - hair dryer does nicely) - or whether its deeper and there has been some poor wetting out or possibly later delamination of the bond between the resin and glass. If its really bad and you find that you cant rid yourself of the problem, all is not lost - a hot air gun will remove the entire tape and resin in one go (assuming its polyester - although epoxy will probably similarly respond to warming - My boats have always been old and used poly - can others advise on this??) and you can gently pull off the offending bits and clean up the wood and then replace the tape run in the conventional manner. The knack is to use a pallet type scraper (I like a 3" wide one of the type used for lifting paint), warm this with the gun and then, reasonably gently, warm and then hot the area of an end of a tape, gently work the pallet under the edge of the tape without digging into the wood and lift it. Wear thick gardening gloves and pick up the end of the tape whilst playing the hot air gun on the bit of tape just near the lift and pull. Keep the gun moving as much as possible to distribute heat (watch out as you can easily burn the wood with a hot air gun). clean up any poly gunge with the scraper and a bit more heat when teh tape is off and there you are (or should be). Dont be tempted to do too much in one go or the boat could go out of shape or a seam open, you need to keep an eye on the matter and use common sense - however I have taken all the tapes out of the inside of a boat including the keel and c/b case in one go and its still been rigid - except where it sat on the keel - so I supported the ends of the boat and not the bit in the cockpit. The main thing is to try not to cook the seams to much as this will loosen the tape on the outside as well....

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25 May 2009 10:43 #16507 by John Kelly
Replied by John Kelly on topic Another problem with seams
Thanks for the advice. I have some photos pf the problem but canot see that i can upload to the forum?

I tried the wet and dry approach on a very small area, but to get it did not become transparent until I had abraided right through the tape.

The boat number is 67656 so I do not know whether it is likely to have been epoxy or polyester and whether that is important. For example, if polyester would I now need a polyester resin to soak back into the tapes?

I stripped the varnish off using paint stripper in case that is relevant.

Even where the tape is fully exposed I cannot find anything that will wet the fibres -i have tried water, white sprit, number 9 thinners (for the varnish) and acetone.

Would you be able to say more about the "conventional manner" of tape replacement. I am afraid I have no experience of this sort of work.

Many thanks





John Kelly - "Storm"

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26 May 2009 10:49 #16508 by Martin Egan
John,

as abrading the tape as Chris suggested has not worked, I can't see any way you will be able to fix the problem (i.e. whitish appearance of tape as it was not wetted out correctly) without removing the tape and putting new tape on the join. It's really not that difficult, do a bit of practice, take your time, and the result should be a "proper job" as we say in Cornwall. I agree with all the advise from Chris. Once you have removed all the old resin and cleaned up the plywood, it is just a matter of applying fresh tape as you would if you were building a boat. I recommend you use epoxy resin, you should be able to buy 50mm wide open weave or close weave tape by the metre to match the rest of the boat. Mask off the area outside the join to keep things neat - so with 50mm wide tape, mask off, say, a 60 or 70mm wide strip (i.e. 30-35mm each side of the centreline of the join). You need something to help work or stipple the resin into the tape - an old brush, a spatula, I use a stick with a bit of cloth wrapped around the end and held on with an elastic band (you won't be able to get the resin off, so will end up throwing it away). Use resin with no thickening additives. I'm assuming you've not done this before, so don't try and do too long a length until you get better at it. Don't mix up too much resin as it has a short pot life and once it starts to go off, it will start to thicken, it won't wet out properly and you won't be able to use it. Put a generous coating of resin on the wood, apply the tape and position it. Work the resin into the tape, try not to add more resin at this stage, but instead work the resin on the wood into the weave. Use a hairdryer to help heat the resin which will make it flow better. You should be able to get the tape to go almost transparant (which shows the air trapped in the weave has been displaced by resin). If you didn't put enough resin on the wood and it really won't wet out, you can add some resin, but I find resin added on top of the tape is not as effective at wetting out as the resin on the wood. This is how I do it, there are probably other ways. I suggest you practice this a couple of times on some scrap wood joins before you try it on the boat.

A top tip for mixing up epoxy is to buy (or borrow) some cheap digital scales which will measure 1g or better. You can put your mixing pot on the scales, zero them, then add 5g of resin and 1g of hardener or 10g resin and 2g hardener etc (or whatever ratio you resin needs).

I think one way you can tell if resin is polyester or epoxy by how well things like paint and varnish will stick to it. With polyester I find paint will flake off readily if you scrape if off. With epoxy, paint sticks much better. In terms of doing your repair, I don't think it matters as epoxy resin won't react with polyester, so you won't get a problem where your new taped join ends and the old polyster join starts.

Heat will soften epoxy resin joins in the same way as it does on polyester resin joins.

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  • John Kelly
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29 May 2009 05:39 #16509 by John Kelly
Replied by John Kelly on topic Another problem with seams
Martin

Thanks for your advice abut this. Obviously my kids are disappointed as they were looking forward to getting their boat onto the water. I know it would look awful, but is it practical to epoxy over the current tapes perhaps using using a pigment or coat of brown paint to hide them. Or would you think that the boat is weakened by this problem. What I can't understand is why the tapes were completely transparent before I started, or is that possible with insufficient wetting?

There seem to be two kind of tape- one (most of the boat) that look fibrous; the other on the front deck section only that looks like muslin cloth. Is that what you meant by open and closed weave?

All of the tapes on the boat are affected so I will have to remove everything. Two problems arise. First, just how much should I remove before replacing some? Chris warns about not taking all off, but presumably when being built there would be none? Any guidance here would be great.

The other is that having sanded everything ready to varnish, worry that I may mark or damage the wood and then have to sand it down again. I notice that masking tape lifts the fibres in the wood surface and of course the laminate is pretty thin. Do you think there is any merit in getting a primer coat of varnish on before I start this work? Or is that going to lead to other consequences?

Last thought - is there a guide to building a mirror available?









John Kelly - "Storm"

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29 May 2009 10:35 #16510 by Martin Egan
Hi John,

Now I'm confused - tapes were transparent before you removed the varnish and they have now gone cloudy ? I've never come across that. If the problem was that they were not wetted out, that would have been visible through the varnish. Just wondering if the paint stripper has reacted with the resin ? I don't use paint stripper, so don't know what happens if it goes on resin (probably not good). If the existing resin/tape is still hard and adhearing resonably to the plywood, I would be inclined to do a temporary fix, go sailing and do a long term fix in the winter. Retaping every join will be a major job.

As a temporary fix I suggest you either;
1) just put on the varnish.
or
2) put some epoxy on the tapes as you had started to do, then varnish. I don't think adding epoxy an existing taped joint will add much strength, it's the glass & resin acting together which give the strength. Can't see any point trying to hide the cloudy tapes for one season.

If the resin is soft, or tapes are not adhering to the plywood, then that will have weakened the boat, but it may still be OK for a season. Alarmed that every tape on the boat has this problem. Please e-mail photos to martin.j.egan@tesco.net so I can have a look.

Yes, that's what I meant by open and close weave tape.

When the boat is built the hull panels are held together with copper wire, then taped on the inside. When the bulkheads and side tank panels are added they are glued onto small wood blocks then taped. As Chris said, you need to use a bit of common sense. In general if there is taping both sides of a joint, you should be OK to remove the tape on one side if the tape on the other side is sound, in which case it should hold it. I would be less worried about taking the tape off joins involving the bulkheads, side tank panels and deck panels as these are not as structural as the ones between the hull panels.

Do not varnish the area of the join before taping - the epoxy needs to soak into the wood, it won't be able to do that if the wood is varnished. But it's OK to varnish other areas to stop epoxy spills soaking in and masking tape pulling up wood fibres.

I don't think there a building guide online, but there should be and it's something I am working on. In the meanwhile, you might find something here http://mirror70407.com/aboutus.aspx of use







Edited by - MartinEgan on 29 May 2009 11:43:59

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  • John Kelly
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29 May 2009 13:23 #16511 by John Kelly
Replied by John Kelly on topic Another problem with seams
Hi Martin

Thanks for all this. Yes, the seams were transparent when I started.
I used stripper all over the boat, including all the seams. On <u>all</u> the seams, in many (but not all) places I have revealed the tape and that is white. I cannot seem to wet the fibres. Where I have not revealed the fibres the epoxy is rock hard and indeed scraping off the last bits of varnish was very hard, even using paint stripper. I am now wondering whether there was no epoxy over the tapes in many areas.
The seams are very firmly fixed down and are not soft. I cannot lift the edges of any of the tapes.

I will send you some pictures as suggested and once again thanks for all your help with this.

I have been advised to put 8 coats of 2 pack varnish on. If I am going to have to do a major repair job by replacing all the tapes next winter, which will then need mean a lot of varnishing, what do you suggest as the minimum for this year?

Thanks very much

John Kelly - "Storm"

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02 Jun 2009 10:19 #16514 by Tim Cushion
John,

Sounds as though the stripper has bleached the resin. I had a similar problem when I re-taped my old mirror completely after stripping all the old varnish off. Before re-varnishing I decided to bleach the black mouldy stains in the wood with oxalic acid. This was a great success completely removing the stains. Unfortunately it also left all my new tapes, which were previously invisible, glaringly white.

I’m going to redo them next winter. It surprisingly easy. No need to mask anything off. Any epoxy over spill can be easily wiped off the wood with an acetone soaked rag as you go.

I don’t know about using two-pack varnish – but I wish I had expoxied all the bare wood work before varnishing as I’m starting to get some staining again after a couple of years of hard use.

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02 Jun 2009 10:51 #16516 by Martin Egan
John has sent me pictures and the problem looks to me like "over enthusiastic" sanding of the taped joints has exposed the glass tape in places (which is what John said in his first post). In other places the glass tape has not been reached (because there was more resin on top of it, or less sanding,..), and it remains clear. I'm now corresponding with John by e-mail suggesting he applies resin and tries to get it to wet out the fibres, then varnish, then go sailing.

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05 Jun 2009 09:02 #16524 by Martin Egan
Correction to my post above. The kit specification is for 40mm tape, not 50mm as I said above, so that's what I would recommend for repairs and so on.

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06 Jun 2009 16:27 #16527 by John Kelly
Replied by John Kelly on topic Another problem with seams
Cush, thanks for your ideas and reassurance that doing the tapes is easy. It look horribly difficult but I have just bought a hot air stripper to give it a go

Can anyone comment else on Cush's point about epoxying before varnishing? I am just about to put on a primer coat! I can say that when I stripped off all the varnish the wood beneath was like new (but there was a really thick lot of varnish) so I wasn't going to use epoxy first, but if it will help preserve the finish I will.

Thanks

John Kelly - "Storm"

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06 Jun 2009 17:06 #16528 by huxley
Replied by huxley on topic Another problem with seams
I stripped just my rear tank down to bare wood 2 years ago and laid new tape. I then gave the wood a coating of SP 106 and then two coats of varnish on that. It saved the hassle of re-priming the wood with a thinned down varnish coat.

Looks mint - although there is a slight differential in colouring.

Wish I had the time and patience to do the rest of the boat <img src=icon_smile.gif border=0 align=middle>

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