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tink
12-05-2016, 09:53 AM
http://uploads.tapatalk-cdn.com/20161205/bba69b59ccd70ac77775a7c8e8b8310a.jpg

Two years ago there was some darkening of the plywood to one side of the hole for the mast in the foredeck. To fix it I did the following:
1. Locally remove varnish with Nitromors
2. Clean thoroughly with white spirit
3. Multiple applications of oxalic acid to bleach the wood
4. Good wash with fresh water
5. Good drying out time
6. Two coats of epoxy
7. Six coats of International Schooner Gold

Temperatures for all applications within manufacturers specifications

The repair looked fine when finished for one session. Progressively it started to darken this session and then in the last few months in rapidly became darker. The darkness is isolated to the area previously repaired.

I would be very grateful if anyone could advise me what I have done wrong and if there is a way of fixing it.

Thanks Tink



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David G
12-05-2016, 10:09 AM
At first glance - I'd say you have a common problem. Moisture instrustion stemming from unbedded, or poorly bedded, hardware. What was your bedding protocol?

Thorne
12-05-2016, 10:14 AM
Well I'm certainly no expert, but it sure looks as if the darkening is associated with holes in the ply. Are / were the holes cut oversize, filled with thickened epoxy, then re-drilled to size? Otherwise the edges are exposed and rot can flash along the plies quite rapidly, at least when compared to rot in solid wood.

I **suspect** that once it starts to rot / mold, the spores are in place and aren't completely killed by white spirits or oxalic bleach -- so they start breeding again.

Again depending on what process you try next, this **might** be a job for penetrating epoxy. If you can't replace the ply, try sanding it down as much as possible and treating with oxalic acid. Then a coating or two of CPES, hot-coated with the epoxy you put over it. The CPES will soak in along the wood fibers and plies, and hopefully (!) keep the mold from spreading in that area.

Let's see what the more experienced folks say...

tink
12-05-2016, 03:06 PM
Thanks a lot David and Thorne

My usual way of attaching fittings is to fill the hole with varnish by dipping a tooth pick in varnish and then poking into the hole and repeating.

Where the worse bit is there are no fixings but I chipped the side of the mast hole at the start of the season. CPES looks good stuff, but 0.95 of a litre is a lot more than a sheet of ply to replace the whole deck which is the long term plan. I will start be trying to remove what varnish and Epoxy is already there.

upchurchmr
12-05-2016, 05:51 PM
Think seriously about using epoxy to seal the fitting holes, like Thorne recommends when you do the full repair.
For something with load on the edge of the ply due to the fittings, use some powered fiberglass and / or shreads of cloth to reinforce the epoxy on the edge.

Epoxy is not really strong by itself, but varnish is much less strong.

Bob Cleek
12-05-2016, 05:59 PM
Odds are you didn't do anything wrong. The problem appears to be chafe or repetitive impact damage where the mast rubs on the edge of the hole it's in. It doesn't take much to skuff off enough material to open up an edge of plywood and once water hits the endgrain, it moves fast.

upchurchmr
12-05-2016, 06:23 PM
There must be something wrong with the damage shown.

Tink, I don't want to be poking you in the eye with a sharp stick, but that damage could certainly be avoided.

You might want to look here: http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook%20061205.pdf Page 129 about installing hardware.

Good luck with the repair, I'll shut up now.

Thomas.Nance
12-05-2016, 06:32 PM
I agree with the other posts.
Varnish isnt up to the job in sealing anything, especially plywood end grain, when in contact with other moving parts. Chafing etc.
It is possible with fastener holes to drill over size, fill with 403 thickened epoxy then redrill to final size.
With your mast hole it can be useful of again drill over size and use either similar method to fastener holes or insert a solid timber ring. Solid timber can hold up to the wear much better. When epoxied in, it also offers a glue join barrier between the water and plywood.
Plywood end grain is just too susceptible to wear and then sucking the water through.

tink
12-06-2016, 10:47 AM
Thanks again one and all, had a good look at the mast hole and its damage was much worse than I remembered and hidden by the mast and fittings so gone unnoticed.........

http://uploads.tapatalk-cdn.com/20161206/27ce2cbcbc4af38d783be7bdb2ab1eb8.jpg

There is some blackened wood where one of my attachments is, upchurchmr I don't mind a poke in the eye at all. My ego is much easier to repair than a wooden boat.

Anyway, have been considering how to fix and decided to remove all the fittings and strip back the wood and repair best I can. The mast hole and fittings all get a full Epoxy treatment. Cosmetically it will not be good looking but it will do for next year. I will probably replace the whole foredeck next winter and the stern deck the following year.

I think there is a case for some protection around the edge of the hole, under the ply is solid wood

Thanks again

Tink




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tink
12-07-2016, 12:23 PM
We things are looking worse but actually become a lot simpler. The main black bit was completely rotten and has be easily removed. By the mast hole there are two pieces of hard wood which are sound. I have cut back to good wood but may go an inch or so until I get to cosmetically good wood (green line). The fix is easy and I have materials and Epoxy to hand. The other black areas are sound and should bleach out easy.

http://uploads.tapatalk-cdn.com/20161207/2f096a914e0173e3b9412e5175223efe.jpg
http://uploads.tapatalk-cdn.com/20161207/a2759e97cdbd8149ec57b19823a21372.jpg


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the_gr8t_waldo
12-07-2016, 02:40 PM
I would suspect that all the blocks attached to the base or the mast, is flexing the deck ,when under strain. I would back up that area with a second peice of plywood, glued to the under side- just to spread out any load. Along with the previously mentioned stuff A shame to have to tear out the damaged area.....thinking out loud here, as a interim measure, painting the area white to mimic a pad might go a long way- all depends on you're desired level of Finnish.

tink
12-07-2016, 04:45 PM
I would suspect that all the blocks attached to the base or the mast, is flexing the deck ,when under strain. I would back up that area with a second peice of plywood, glued to the under side- just to spread out any load. Along with the previously mentioned stuff A shame to have to tear out the damaged area.....thinking out loud here, as a interim measure, painting the area white to mimic a pad might go a long way- all depends on you're desired level of Finnish.

Thanks, I haven't had time to fully evaluate what can be done but I certainly will be adding some strength to the repair. I have considered painting but it will be a fall back if I can't get the cosmetics right. Going to try even if just as a learning exercise. I had considered was paint effecting carbon fibre which looks quite easy.

One thing I will also be doing is removing about 5mm of the ply around the hole for the mast and infilling the removed ply with a ring of Tufnell. That way the mast will be rubbing against the hardwood and the Tufnell and not the ply endgrain.

Jamesh
12-08-2016, 01:31 PM
Or you could put a triangle of glass/epoxy over the affected area ad mount the hardware on that allowing the glass to wrap into the mast hole. If access is OK do the same from below and rotate the slits I the cloth down the mast hole?

upchurchmr
12-08-2016, 02:29 PM
Wrapping the glass over a sharp edged hole will be a problem.
You need at least 1/4" radius to get the glass to lay down over the edge, at least, usually.
Especially a circular hole.

tink
12-08-2016, 02:44 PM
Or you could put a triangle of glass/epoxy over the affected area ad mount the hardware on that allowing the glass to wrap into the mast hole. If access is OK do the same from below and rotate the slits I the cloth down the mast hole?

Thanks but I would worry that the glass would wear the anodising off the mast. The hole is about 25mm deep and only the top 4mm is ply. The rest is hardwood and in fine order. Providing I stop the end grain of the ply getting damaged I am sure everything will be fine. I believe the damage has been caused be me chipping the edge of the hole when putting the mast in and leaving in un repaired for eight months rather than sailing.

tink
01-22-2017, 01:05 PM
https://uploads.tapatalk-cdn.com/20170122/7afde463a6cd51751420ada06cd5c30a.jpg
https://uploads.tapatalk-cdn.com/20170122/87cd415eb1dacaa8e05d89de98cdac29.jpg
https://uploads.tapatalk-cdn.com/20170122/0b9cf263b8109f097e4e092ff03fb660.jpg
https://uploads.tapatalk-cdn.com/20170122/3f131cca82ab76b0882c08ddf1d25233.jpg
https://uploads.tapatalk-cdn.com/20170122/415d5251fb5db030ea1cd30114b6b7f2.jpg
Just to finish the story. I epoxied in a piece of Tufnell so there is no chance of damaging the end grain. Repaired the hole and carefully recessed 0.5mm of the damaged wood and re veneered with 0.6mm Sapele. Have put one coat of thinned varnish and will then fill I a few tiny bits as required.


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upchurchmr
01-22-2017, 01:18 PM
Looks quite good.
Good luck with it in service.