Rot in Balsa core

[davidpbo]

With reference to a previous post of mine here and here regarding using a Goscut tool to cut fibreglass and fibreglass repairs.

I have now started, delays caused by visitors, work and need to have slightly more than 3X2.5" posts across 15m of fencing to keep stock out of our garden and a disinclination to get involved in what may be a major long running repair when I would like to be sailing.

To recap, I had some cracking of the deck where the shrouds had lifted it, the reason the deck lifted was sorted at the time and the cracked of the gel coat was filled (2004) I thought all was OK but decided to repair the gel coat this year and found rotten wood underneath.

Yesterday I did some more excavating from on top and have opened up an area approximatley 400mm by 300mm around the shrouds on the port side.

I am begining to get back to what may be wet but not rotten balsa (it does incidently appear to have the grain running vertically. I bought a cheap moisture meter. What readings should I be looking for?

For comparison I am getting 12% on firewood that has been inside for a while and 17% on wood outside.

The area I have opened is the maximum I want to repair from the top. I intend to core cut some holes to the depth of the fibreglass inside and see what the situation is further along and on both sides of the boat. I may then review how to effect a repair.

The blade supplied with the Aldi Multitool did not last long as expected.

I will post pictures when I can.

 

[davidpbo]

For information. The bit of sound wet balsa core adjacent to the rot which I removed dried out to a moisture content of 12%. I am pleased with the moisture meter.

 

[smth448]

I had a similar problem with the balsa core on the cabin top on my boat where the previous owner had attached some new fittings without sealing the holes properly and wate had got in and spread through the core making it soft and useless. I approached it from underneath and ended up cutting away a similar sized piece of the inner moulding to you before we found dry balsa.
I did not use a moisture meter but stopped cutting when the core stopped dripping! Dry end grain balsa core is a pale brown / beige colour whereas the wet areas were almost black. So I suppose the thing I would do is cut it back until you reach the right colour. You may end up going further than you expect. Now you have started from the top it may be difficult to switch to underneath.

Once the area was opened we removed the wet balsa and left what remained for a couple of weeks to dry out as best it could. The balsa removed was replaced with plywood stuck in with epoxy mixed with a low density gap filling powder. Finally the whole lot was glassed in using epoxy and woven glass cloth.
We then re-fitted the fittings, having sealed the bolt holes properly. Surprisingly for one of my repairs it is still looking good.

 

[davidpbo]

That is what I am doing. I opened the area on top that I was happy to repair there were cracks anyway, and have opened the same amount on the starboard side which incidently was dry but nevertehless there was a smaller crack in the deck fibreglass. The rot extended further back on the bad side. I drilled 25mm holes in the fibreglass (non cosmetic) cabin headlining until I got past the rot, used a multi tool to cut out the fibreglass back to dry wood and will replace the small section of core with epoxy coated ply then glass it all in.