My patch was a 4x6 inch where the (insert many bad words) PO had added a cleat without bedding. Luckily it hadnt spread and I used a 1"x1" x4' carving chunk of the hardest balsa I could find cut into 1" cubes and bedded in epoxy with the grain vertical. Worked great on a small area but I see what you mean about large areas. And no the cleat is no longer there, I never could find a use for it besides smacking my toe.The balsa that you would use to build a model airplane is not what you would use in your deck. The coring material used in most if not all boats is made by a company called Baltek. It is high density end grain core balsa squares on a fibreglass mat. It is not expensive and is readily available.