Partial Ply Deck Replacement Technique

[darrenyorston]

Hello All (Or as my American partner would say Hello All Y'all!),

Just found your forum and am wrapped with the variety and quantity of information posted here. I am down here Down Under with a recently purchased 12m (40ft) wooden trawler designed vessel that was built in 1960 out of Australian Spotted Gum, an extremly dense native hardwood, that is in need of some work.

Nothing is so severe to require a shipwrights services however I would like to get onto the work before it does. I have a number of tasks on my "Jobs to do List" however the ones that are at the top are some wood rot issues. No rot in the Spotted Gum. It's in the ply wood decking, maple coamings and pine walls surrounding a window.

My reading on the forum over the last few days, as well as other research, as shown that the best option is removal of the rotten wood and replacement. So that's what I intend to do and I would appreciate some advice and techniques:

Problem 1. The deck is ply over spotted gum beams. There is an area where a a repair has been previously been made and the ply coating (non slip deck paint) has been breached allowing fresh water to enter and rot the underlying ply (it's all spongy and water wells up when pushed). The previous repair was carried out, I assume, by cutting out the affected damage, afixing a piece of ply greater than the size of the hole with screws and inserting a new piece of ply, filling the gaps and repainting. I can't say if the ply was coated with a sealent of some form however I can say that the bottom layer was not.

The Plan 1. My plan was to cut out the original repair, remove the support piece of ply that had been fitted, strip the surrounding ply back to bare wood to ensure I have got all the rot, coat with Bote Cote epoxy utilising TRPDA for absorbtion, coat a new piece of ply as a support with epoxy and attach below the deck, coat a new piece of ply deck with epoxy and epoxy glue to the ply support below. I will then fill the gaps with epoxy containing a sandable filler. I will then sand even, recoat with non slip deck paint and Robert's your mother's brother! How does my plan sound?

Problem 2. The seal around a window to the galley has been breached and water has leaked into the sourounding wood which I think is pine (may not be though as I have not stripped the paint back yet to good wood) which is mushy and visibly wet. The wood holding the window is around 2" thick and about 20' long. The wood on the outside of the boat where the internal rot is located is still solid (tapping with a hammer there is no difference in sound to others parts).

Plan 2. I have carried out a temporary seal on the window so no more water can enter. My original plan was to pull out all the rotten fibres, dry with a hair dryer or hot air gun and treat with CPRS. Once the area was fully soaked and dry I was going to fill the remaining gap with epoxy and a filler (micro beads I think), sand and the then repaint.

I am leaning away from that plan now towards removing the rotten fibres, drying with a hair dryer/hot air gun and treat with Bote Cote epoxy thinned with TRPDA. Once that was all done I was thinking about trying to epoxy glue in a piece of timber, of similar type that was removed, to the gap and fill the gaps with epoxy, sand and repaint. How does that sound?

I look forward to some feedback! I have some photos I will post ASAP.

[longliner45]

wellcome aboard darren , as we say here in sw ohio ,,,,jump in and hang on ,longliner

[waikikin]

Darren , dont be shy about removal of rotten timber- the "roots" (not scientific term) always extend further than the eye can perceive- cut out the rotten areas by a goodly margin of 12"+ or to some further convienient point(such as original joints), scabby little patches only lead to more trouble! Cut out rot & be happy its gone, all the best in your endeavours & regards from Jeff.

[hansp77]

Welcome Darren,

I have just replaced most of my deck and cabin roof on a 30 ft ply van de stadt.
Check out my gallery photos (I have more of the deck stuff I can upload if you want.)

The job itself got bigger and bigger the more we uncovered, but at one point, I originally planned to just replace the rotten sections, similarily to how you have described.
After I stripped all the paint, it became apparent that I was going to be cutting and fitting so many individual peices that replacement of the whole lot would be better and easier. This meant removing all of my deck gear, pushpit, staunchens, splashboards, traveller, winches and stay's. (hopefully yours will not have so much to remove.)
It is hard to know how far you need to go past the rot to remove all of the rot spore afected wood.

Often it makes sense to remove the ply past whatever safety zone you have decided upon to the nearest support beam, so that you do not have to resuport it with another.
You will need to scarf and dry fit every single peice with sufficient beam support underneath so that the join cannot move.
The sections on my deck that had only used "a new piece of ply as a support with epoxy and attach below the deck" were some of the ugliest rottenest bits. You really can't expect to to walk up and down on a join like that in the floor without the killing the join- letting water in and rotting all over again.

Depending on the condition, how bad your rot is, for all these reasons it may be easier and result in a better job to replace most, if not the lot (of your problem areas).
If you have a look at your areas of concern and you have more than two or three patches to do within an area that could be covered by one sheet of ply- then it could be easier to just fit a whole sheet.

Because I did it this way, it allowed me to get access to and repair/improve a lot of things that replacing in patches would not have allowed me to.

After I had removed the old decking, and started to dry fit the new, it became apparant that I was getting 'bounce' between supports. We then when along and added in substantial re-suporting for the whole new deck.
At the same time we clamped, glued and screwed every single joint, new and old. Some of the beams had even started to pull of the hull/rubrails. I know now that I could spend half the day jumping up and down on this new deck and not get ANY movement or (much) damage.

I also ended up replacing the back chainplate, which upon proper inspection needed to be done, but may not have been.

Post a few photo's.

Good luck

Hans.

[hansp77]

About the epoxy.

I used a lot of penetrating epoxy- epiglass wood preserving epoxy (with fungacide in it) on the old wood, and International Evidure on all the new wood.
For the real epoxy, and filler etc, I used West system.

There is a lot of debate on the value of penetrating epoxy.
You should probably read up on it.

Next time I am just going to make my own.
Here is a thread where we talked about this.
http://boatdesign.net/forums/showthread.php?t=12061
although it is debatable,
I reckon that laquer thinner seems to be one of the best off the shelf thinners.
Read through
http://www.westsystem.com/
they have a lot of advice, amongst which a good presentation of the 'to thin or not to thin' problem.

Penetrating epoxy, and then filler, sounds like it could be good for the window. Sikaflex also maybe.
You will really want to dry it out thoroughly though, as in hours and hours of hot air.
Epoxying it will just seal in any moisture.

Hans.

[D'ARTOIS]

The value of the penetrating epoxy is that it forms the basic bonding layer for the correct application of the final epoxy system. It will make sure that there is a maximum bonding between the old material and the added epoxy.
Secondly, you will have an almost impermeable layer that stops any further rotting.
It minimises cohesion between the old material and the added epoxy/repair system.

You may cut out the rotten layer(s) and glue in new ones (with epoxy or Aerodux).