Repairing a balsa core deck

[Achillesheel]

We have an Achilles 24. Part of the coachroof is sagging slightly, and the core is black when viewed from underneath.

We intend to repair this over the winter. I understand the technique is to drill small holes in the affected area, use an Allen key in an electric drill to cut up the affected core, hoover the bits out, and fill the resulting space with resin. Finally filling the holes with epoxy filler.

I doubt it is as simple as it sounds; has anybody done this? what filler should I use, how big do the holes need to be, how long should I leave the holes open to dry, how do I get the filler in the holes, and above all, will it work?

At least I do not have to worry about what it will look like, because the repair will be covered by the decklining, but I want to stop the rot spreading, and ensure the strength of the deck.

Any hints, tips, and/or advice greatly appreciated.

 

[futurama]

The first step should be to find out how it got in that condition to start with and cure that problem.
Also I would start from the outer edge of the damage and work in towards the middle.

 

[30boat]

The balsa core is rotted and has to be replaced and at the same time the leak must be fixed.You can do the repair from underneath but it's not easy.I have done this before and found out that it is a lot easier to cut the deck out from above and apply new core.Plywood is very good.It should be bedded in epoxy putty and after smoothing everything down the laminate that was removed before can be glued back on .

 

[ningcompoop]

There's an article here covering the subject:Replacing damaged balsa core
- the chap did it from above, removing the deck. As 30boat says it can be done from below as well, but this does make it more difficult. Either way, it may turn out to be quite a big job!
If you google "replacing balsa core" you'll turn up quite a few articles about it.

 

[oldsaltoz]

G'day Rod,

As others have pointed out, you need to establish how the water got in to start the rot, or you may not fix the problem.

You also need to establish the extent of the rot / damage.

If the topside is in good condition it's best done from below, even though you plan to cover the area later, the covering may come off later in her life and expose a mess that will reduce her value.

Important: The area to be repaired MUST be DRY.

To check the extent of the damage a simple method is to drill small holes from below and check the drill bit waste for signs of wet or damp Balsa wood.

Start with a grid of holes about an inch apart and keep working out from the centre till you have a line of dry holes.

Then mark each dry hole to give you a profile of the area to be repaired. Cut the bottom sheet off and check all the way round to ensure no more moisture is left; also check the remaining Balsa id stuck to both top and bottom layers of glass.

Using an allen key in an electric drill, remove about half an inch of the remaining dry timber all the way round.

Sand any loose material off the underside of the topside and wipe the whole area with Acetone to remove any dust and contamination.

Apply a coat of epoxy resin over the whole area making sure you cover all the exposed Balsa.

Mix some epoxy resin and closed cell Balloons and apply a good dollop on the section you cut out and offer it up, use some tape to close off the holes and push it into position, secure it in the correct position with wedges or more tape, let it cure.

Then get a disposable serynge from your local chemists and inject more resin mixed with balloons through the remaining holes, tape up each hole when resin squeezes out till all are filled and taped.

After curing, remove the tape / wedges and add more balloons to fill and gaps or holes, cure, sand and paint. all done.

I hope this helps.

Avagoodweekend......

 

[PCUK]

How about semi-closed cell expanding foam, foam was often used instead of balsa for cored decks?

 

[oldsaltoz]

[ QUOTE ]
How about semi-closed cell expanding foam, foam was often used instead of balsa for cored decks?

[/ QUOTE ]

And failed.

Expanding foam was used to reduced cost, not maintenance.

Avagoodweekend......

 

[PCUK]

Hello Oldsalt. Was the problem water ingress the same as for balsa or just lack of strength? Thanks.

 

[exfinnsailor]

Had the same problem with my Finn sailing dingy .. It was where you always put your feet / knees while sailing .. Floor felt soft and you could push it in with your finger .. Bit the bullet and decided to have a look .. Unlike our Aussi friend did not have the luxury from getting underneath .. Used a router to cut round the soft spot and remover glass fibre panel .. Not a pretty site .. I then realised just how far the water had gone .. Biggest problem is that balsa is like a very good sponge .. You may have to go a very long way to find something that is not wet .. Finished up with a very large section of floor missing .. Used core mat to fill the hole .. Then glassed over the top .. Not pretty .. Sanded back to flat and painted with none slip .. Bit of a job .. Cannot see how you can do it from underneath as all the resin is very runny .. Hope you can formulate a repair from all the replies .. Remember that you must get back to dry balsa or you will get trouble later .. You cannot fill the hole with solid resin as it needs to flex .. The core adds strength glass on top glass underneath .. Core in the middle just like an RSJ in building ......

 

[oldsaltoz]

[ QUOTE ]
Hello Oldsalt. Was the problem water ingress the same as for balsa or just lack of strength? Thanks.

[/ QUOTE ]

The foam turned into mush when exposed to water, reducing strength and buoyancy.