sealing where chimney enters the wall thimble

I test fit a piece of the Class A chimney into the wall thimble and I can see a gap; inside I can see light through the wall. How does one seal where the chimney passes through the thimble.

 

Roxul. High temp rtv.....

 

I pulled my installation instruction manual that came with my Supervent chimney. It said to use this insulation: http://www.menards.com/main/heating...0C75469CEA80A34A.eklka-prodapp5-external-mcom

 

That seems expensive for such a small amount of insulation.

 

Anything that's fire retardant is going to be pricey.

 

I think it said it was class 2 fibre glass.

 

This is not an area you want to cheap out on. Safety usually isn't cheap. Use the recommended stuff.

Fwiw, I put up a wtb ad in the classifieds for a small amount of roxul and a nice member gave me what I needed for free. Try that first.