The lime in concrete attacks the lignon which is the stuff that binds wood cells together. It desolves it and leaves a mass of seperate fibres which have no strength.
I found this problem with a 32 wooden cutter
I bought back in the 80s. The only external sign was a sprung garboard strake on one side. (no I didn't get it surveyed, it was back in my young and stupid days
) Apparently the owner filled the bilge
area with scrap steel
and sealed it in with cement or concrete.
Once I got possession, I spent a week with a couple of buddies chiseling out the mess, and once done found the entire top of the keel
disolved to a depth
of a couple of inches. The floors, Oak sided 3 inches thick were also almost completely disolved as were the botton 10 inches of 32 consecutive pairs of ribs.
Needless to say I started to try and repair it, this is where I developed a love affair with west system. After saturating the floors I took one up to Cold Creek to the rifle range and tried to shoot some .303 slugs through them. No success. The ribs I cut off and replace the damaged bits with stubs, and a 3foot long cap strip of 1x1/8 stainless steel
. Sadly I lost
my job and that boat shortly there after. I guess the old lady who owned it just let it rot