Proper burning after the construction of your masonry fireplace is essential to the longevity of your outdoor fireplace. Some may assume that you can crank up a fire in a newly built fireplace the day after construction. Doing so may permanently damage the smoke chamber and clay liner. There is nothing worse than spending your hard earned money on a beautiful masonry outdoor fireplace to have it crack the first time you fire it up. Masonry generally takes 28 days to cure properly. It is best to wait the 28 days to ensure that all the masonry is cured properly. Is there still risk? Absolutely! Here are some tips to follow when burning a fire in a masonry outdoor fireplace.
1. When you burn in your fireplace for the first time it is best to start a low fire and let it burn for about 4 to 6 hours or longer if possible. Not a scorching fire but a modest two log fire. Why so long? The reason you want to burn a modest long burning fire is to slowly dry out all the water that is trapped in the masonry and concrete. Concrete by nature keeps a certain amount of water so by burning a slow long fire allows the fireplace to dry out properly, curing the fireplace.
2. Gradually build up your fire on a masonry built fireplace. You want to gradually build up your fire, especially if you burn in your outdoor fireplace in the winter, if you start a blazing fire right away and the fireplace is cold you get what's called 'Thermal Shock' this may crack the flue liner and possibly the structure of the fireplace. It's best to warm up the fireplace slowly. Once you build the fire up slowly and warm up the fireplace you are OK to burn a larger fire.
3. Never use accelerators to start your fire in a masonry outdoor fireplace. Masonry is naturally porous so if you put gas on it or lighter fluid, the masonry will soak up the accelerator and could ignore the masonry. Accelerants burn too hot and could cause serious damage to the masonry structure and possibly you.
4. The most important thing to remember in caring for your masonry outdoor fireplace is to never extinguish the fire with water, unless absolutely necessary. Masonry retains heat and will get quite hot when you burn a fire for long periods. If you spray a stream of cold water from your garden hose onto the hot masonry fireplace it will crack. It's best to have a metal bucket and shovel handy and let the fire burn down, then shovel out the coals into the bucket.
After 18 years of building and using outdoor fireplaces I have found that these are essential tips to ensure your outdoor fireplace's longevity and ensure that you can enjoy extended years next to the warmth of your fireplace as you entertain in your backyard paradise.