In our garden stands a very beautiful old acacia tree of about 8 metres tall. There is a wound on the trunk (maybe 10 centimetres across and 18 cm high) which has at some time been filled with concrete (no it wasn't us). The tree has been fine for the 8 years or so that we have been here but this spring a trickle of sap came out of the wound, which has left a pool of sap on the ground. It was fine during the summer but after recent heavy rain the same thing happened again.
In a nearby park I have seen trees with wounds which have been filled with expanding foam, (the sort you use for DIY work to fill holes / gaps).
So, does anyone know if I should I clean out the old concrete and the wound and fill it with expanding foam? Do I need to treat the area first? Or should I leave it alone?
I hope someone can help