Repairing Ply Decay Due To Water Ingress - Other Solutions?

[Deleted member 36384]

Hi,

Water has entered ply from the edge which has caused deterioration ranging from complete crumbling of the ply edge to just dampness.

The source of the water (rain) has been identified and corrected and all is now drying out. To pull the whole panel out and replace it would be a big job and before undertaking it I am investigating alternative methods.

The damaged edge of the panel is accessible and I can cut back to good ply where it crumbles away, which is just a very short length. The minor damage, which is the majority (some ply separation as well as the dampness), I would like to stabilise and then preserve, if suitable.

The panel is the interior lining of the saloon, running along the coach roof sides, surrounding the windows. A previous owner filled the gap between the frames and panel with brown sealant, meanwhile the water had still been entering from underneath the frame, behind the sealant.

Any ideas, or products to effect repair and preservation. The finish will be painted. A wooden motor boat I delivered was held together with Git Rot. I am not so sure this is a good idea but would like your opinions.

Regards,

BlowingOldBoots

 

[Tranona]

Epoxy with a filler such as microballoons. Can also use veneers or glass tape to build up thickness. Sounds like it is non-structural so you need to concentrate on stabilising by drying out and soaking in epoxy then building up the surface to be level and smooth to take your final finish. Actual material will depend on extent of damage and rigidity of what is left.

 

[oldharry]

The problem with end grain rot in ply is the distance it travels inside the laminations. Rain ingress tends to rot from the inside out, so that the middle laminations have rotted further down the exterior veneers which have remained dry. Even with BS1088 the interior sheets may be of inferior grade material which rots faster making water ingress damage worse than it appears from outside. However it is possible to make an 'invisible repair' to a ply sheet, although it requires a degree of skill.

I have seen end grain rot go right down one single internal lamination, effectively splitting the front from the back, although from outside the ply looked fine. It is not unusual where the outer veneers only show damage an inch or two back from the edge, to find the water has penetrated up to a foot down the inside laminations, even on BS1088. If the interior sheets are thicker than the external veneers then this is invariably softer wood, and although the skin veneers may look perfectly OK, the inside laminations will almost certainly be extensively damaged.

The 'invisible repair' is acheived by effectively creating a long scarph along the edge of the sheet where the new ply is going in. The scarph needs to be at least 4:1 to give a strong joint, glued with epoxy. In a structural component, 6:1 or more will be needed. On non structural trim, a narrower scarph will be suffice depending on the thickness of the ply.

Substituting with another material can be done, but it can be a lot more difficult to achieve a properly matching finish. The problem with substitutes like Git Rot is firstly it is extremely difficult to dry the damaged internal laminate sheets, because the glue is waterproof and traps the moisture, allowing it to continue to destroy the ply. Git Rot type compounds will not displace any moisture remaining, so just seal it in with disasterous results. secondly, it is extremely difficult to get any such materials to penetrate and fully impregnate the damaged timber right back to where it is sound. This is why sheathing an old boat so rarely works. New ply should have less than 15% moisture content, so will allows epoxies etc to take up. Epoxy suppliers often recommend even lower moisture content than that as a maximum permissible level for ply. Older ply which has been immersed or has been damp will take months of forced drying to get back to such a low moisture level, and this is rarely practical.

I have tried most of the 'patent repairs' over many years of owning elderly plywood boats, and found the hard way that the only material that really works on plywood is more plywood.

 

[Twister_Ken]

Might be easier to replace? See this blog, from here onwards for a few pages.

 

[Lakesailor]

Get it really dry and coat with epoxy, thin as you like, a few coats. It will soak well in and build up the adhesion between plies whilst actually adding structural integrity to the veneers.
I did it on some compound curved sections at the bow when restoring my Heron. It worked an absolute treat. Also stabilised the transom on another boat the same way.

 

[oldsaltoz]

As others have indicated the first and most important point is to ensure it is a dry as possible, no amount of work or money will fix your problem if moistuire is still inside.

I use heat lamps and a moisture meter befor even contemplating this type of repair.

Once dry, expose the edge and use thinned epoxy resin, you can thin it by adding up to 35% Methylated Spirits by weight to a mixed batch or epoxy resin.

Make small batches and add slowly allowing the resin to get wall inside the laminated layers.

When it will take no more mix in some Micro-fibres, this will add strength but clean up as you go because it's hard work sanding any excess off.

You could Micro-balloons (Closed cell only) if structural strength is not critical, it's very easy to sand.

Good luck and fair winds.

 

[johnlilley]

One successful method of repairing plywood if not fitting a complete new panel is firstly as others have said, eradicate the existing decay & cut the area out into the parent panel with straight edges.
Scarfing plywood in situ is extremely difficult & not easy to fit. Better to scribe a straight line about 2" back from each straight edge & cut half thickness away to leave a clean step. The new panel is cut precisely to fit with similar step. This can then be offered up & finally made a perfect fit with no gaps, quite easy generally.
Now glue & screw the panel into position. You can use a permanent batten on the reverse side for extra strength overlapping the whole joint, or simply a temporary one to screw into to hold the glue join together whilst setting.

There are one or two photos of this type of repair on my website http://www.turbolink.co.uk/seasurveys2011/example2.html

John Lilley

 

[rob2]

Although you say that replacement is a big job, you'll have noticed that the repair is not exactly a minor affair either! I've spent hours or even days taking rotten pieces out of a ply deck and trying to achieve a good edge to fit new panels in. Even then, the new metric ply was slightly thinner than the original imperial size so had to be faired up to the old level. When the boat was sold on, the new owner took the whole deck off and replaced it in total, in less time than it took us to patch it. This had the added advantage that he could seal the whole panel, edges included with epoxy before it was fitted.

Total replacement may seem like a brave decision, but may well save an awful lot of time and achieve a far better result.

Rob.

 

[oldharry]

Agree with Johnlilley, a stepped scarph faired along one of the internal veneers will do just as well, and is probably easier.

 

[LittleShip]

This is a product which is known as CPES (clear penetrating epoxy sealer) in the States and is epoxy based but very thin.

http://www.mbfg.co.uk/epoxy-resins/eposeal-300-epoxy-primer.html

It will soak into the ply and seal it from any future water ingress. you will however need to replace the rotted ply first by cutting back to good wood and then coat with this. It wont do anything for the rotted ply but is much better at getting into the wood than normal epoxy. Three or four coats will completly seal the wood.

Tom

 

[Deleted member 36384]

Thanks everyone for the very useful replies. I now have some tips and guidance which will help me to make the decision to repair or replace. I am now of the opinion that the panel will have to come off. At the bottom of the panel is a shelf, which runs from the lower edge of the panel and under the side deck; below the shelf are lockers. Hence, its worth knowing if this shelf is suffering water damage.

You know what its like, the panel will come off and then its headlining, trim, hidden wire etc etc. But one must do the correct job on a boat!

Hopefully the panel can be salvaged, if not, it should at least make a good enough template.

I appreciate your advice and insights.

Cheers,

BlowingOldBoots

 

[electrosys]

I see this repair as being a 2-stage process: stabilise what you already have, and then effect a repair.

Stabilising isn't as easy as it might first appear. Cutting-back to good, dry wood is the theoretical answer, but as someone has already said, moisture creep along the inner laminations may continue further-in than you might appreciate.

Heat lamps and a dehumidifier is one approach - but you'll need to completely 'mask off' an area with polyethylene sheeting and tape so that you don't dehumidify the whole boat plus a fair few cubic metres of atmosphere every time you open the hatch to see how things are progressing ...
If you can get the wood thoroughly dry by such means, then a lick of general purpose epoxy resin diluted with c. 10% acetone or thinners applied to the end grain should do the trick.

Another approach would be to accept that some moisture will remain after cutting-back, and then use that moisture to cure polyurethane sealant brushed onto the end-grain. That sealant can then be used as a base for an epoxy-based repair. The only real disadvantage to this approach is that you'll have a helluva lot of polyurethane sealant left over afterwards.

G.P. epoxy resin and G4 sealant can both be obtained from:
http://www.resin-supplies.co.uk (no connection, just a very satisfied customer over many years).

I won't comment of the actual repair process - there's been some good suggestions so far - a stepped repair sounds good to me.


Ok - ignore all of the above - I've just seen the above post which arrived whilst I was typing mine ...

 

[SHUG]

Many resin based glues rely on water to cure so it would seem reasonable to work this kind of adhesive into slightly dam ply and then clamp up to cure.

 

[oldharry]

Many resin based glues rely on water to cure so it would seem reasonable to work this kind of adhesive into slightly dam ply and then clamp up to cure.

Yes but they don't displace water in the timber - again they just seal it in.

 

[rbcoomer]

I'd second the 'replace' option as it will last longer and you get the satisfaction of knowing it's done well and will ultimately be a better job. I'd certainly resin-coat the new plywood however - unless it will be a varnished/caulked finish etc or otherwise sealed.

I'm facing a similar dilemma with the Fletcher Arrowbolt I'm restoring. The ply floor was rotted away, but the stringers, whilst sopping wet have only rotted at the exposed ends - the majority still being solid. However I have decided that although more work & cost, the best method is probably to replace completely - it's the only way to be certain it won't come back to bite you later! Thus that's what I'm doing even though it will almost certainly push the project well into next year. Never having done any boat restoration before it's proving an interesting and enlightening experience rolleyes, but as all hardwood and plywood will be resin coated before fitting, I will at least have faith in the finished article not rotting again for a very long time.

Thread over on the Mobo forum if you want a good laugh at the scale of the task in hand! http://www.ybw.com/forums/showthread.php?t=285958