Building an Outdoor Concrete Block Fireplace

1. Identify and Prepare the Location

We identified this corner of the yard as the prime location for our future fireplace. We previously had a metal fire pit there and it seemed like the perfect location to make a permanent fireplace. The space was prepped by removing the plant that previously lived in that location and scraping the rock out of the way. 

2. Pouring the Foundation

We used some leftover 2x4's from another project to make a frame to go 3 ways around the future foundation to go against the existing pavers. We then poured gravel into the bottom of the frame and covered it with several bags of Quick Crete before wetting it down and evening the concrete with a spade. This process was repeated until the concrete slab was level with the pavers. The slab was left to dry and then the wood frame was removed. 

3. Building the Box

Next, we used a variety of different sized concrete blocks to build the foundation and then then the sides and back of the fireplace around the firebox that we purchased from a local used construction supply. After settling on the pattern, we disassembled it layer by layer, and then used Liquid Nails Construction Adhesive to cement each layer in place. Be sure to leave space around the firebox around the sides and back for venting.

4. Chimney and Facing

After waiting 72 hours for the adhesive to set, a concrete sheet was cut to fit the top of the fireplace and holes were cut in it to allow for the chimney. We then used additional concrete blocks to build the chimney over the vent holes and used a stacked stone and the concrete adhesive to face the front of the fireplace. The sides and back of the fireplace were skim-coated with concrete to cover the block.

5. Hearth and Mantle

After the 72 hour drying period had passed for the adhesive, large pavers were set into place on the top and hearth of the fireplace using adhesive. The chimney was then faced with coordinating brick and topped with a paver. We then covered the gap between the mantle and the top of the box with a wood beam that had been stained and then screwed into place.