What do you fill holes in oak trees with so they wont rot out? i.e. cement?

Question

we had to have some limbs cut off

Answer 1

Dear Cary, there is a coating that you can buy that is for tree "wounds". However, research has shown that this is not necessary, and the tree should be fine with the removal of the limbs. Now, I'm assuming you have a healthy tree, to start with. If you tree is sick, you would need to look into treating it.

If you want to in order to feel comfortable, get the tree wound coating, and put it on. After that if you do some research or speak to an expert, you will find that it is not necessary. But put it on if it makes you feel better if you are uncomfortable. There's nothing wrong with that. I'm just advising you that you don't need it, after working with trees for many years.  

Answer 2

I've seen trees with a tar-like substance on the area where limbs have been cut.  

Answer 3

Standard practice is to coat the wound with a tree wound dressing if its larger than about one inch.  This will help prevent the spread of Dutch Elm disease, or in your case Oak Wilt disease, caused by insects feeding on the sap that oozes from the wounds.  One popular brand is Treekote.  A cut smaller than one inch or so will callous over fairly quickly

by itself.  If you have really big holes there are several cement/asphalt products you can buy specifically for the purpose. Check with your garden supply store.