Pouring concrete chimney crown?

Question

i am going to pour a cconcrete chimney crown. i read to leave a void between teh flue and the concrete for expansion. How do I pour the cement around the 3 clay flues and leave a gap taht i can seal alter? what material do i stick in there that can be removed once the concrete has set up?

Answer 1

Use a piece of aluminum sprayed with WD 40 to act as a release agent

Answer 2

USA   Go to any builder supply store and buy expansion joint or joint filler.  How much of a gap do you need to leave?  The expansion joints and fillers are usually 1/2 or 3/4 inch.  Use the aluminum - or plastic - between the filler and concrete so you can remove the filler.