How can the Weather affect my Wood Fired Oven?

The weather, especially rainwater, can affect the performance of your Oven. 

To understand this fully, you need to understand what happens to an oven that’s been built outdoors, exposed to the weather. It’s going to get rain driven at it from every direction, and despite your best efforts in sealing the dome with our roll-on render coating and fitting the water barrier system, if the firebrick front of the oven is exposed to rain then the firebricks will absorb that rain and draw it into the oven.

For your Wood Fired Oven to work perfectly every time, you need to keep the oven dry!

HOW CAN WATER GET INTO THE OVEN?

If you followed our building instructions and sealed the oven dome with the roll-on render coating, there is only one way that water can get into the oven. This is from rainwater soaking through the firebricks at the mouth of the oven, which then soaks into the Calcium Silicate (CalSil) Insulation board. Firebricks and all other refractory materials are very porous, so your exposed firebrick Vent Arch and Oven Floor will soak up water and hold it for a long time, even through subsequent periods of hot, dry weather. 

There are two ways that rainwater can make its way onto the firebrick Vent Arch and Oven Floor. The first is simply driving rain, falling directly on these porous firebrick surfaces. The second is rainwater that runs down the outside of the flue, which can make its way through the expansion joint in the top of the Flue Gallery, and down onto the Oven Floor. We would love this expansion joint to be watertight, however there is no waterproof sealant capable of withstanding the high temperature of the flue while remaining soft and compressible, which is necessary to protect the Flue Gallery from splitting in half due to the expansion of the flue as it heats up.

Please note that high humidity will not cause the oven to hold water, it’s only caused by rain or dissolved snow.

I’M IN THE PLANNING STAGE, WHAT SHOULD I DO?

If you’re in the planning stages of building your Oven then consider installing it so that at least the mouth of the oven is undercover with the flue sealed against the roof, as shown in the images below. This will make a signifant difference in keeping water out of your oven. It also means that you can use the oven regardless of the weather, as you will also be protected from the weather while you’re cooking. 

MY OVEN IS BUILT OUTDOORS

Many of you reading this will already have your Wood Fired Oven built outdoors as the centerpiece of your entertaining area, like the stunning ovens below. There is nothing wrong with building an oven outdoors like this, you just need to understand the effects that water can have on your Oven and how to deal with it. 

DEALING WITH WATER

So, to repeat – if your oven is built outdoors, unprotected from the rain, the firebrick vent and floor tiles at the mouth of your will absorb the rain that falls on them and draw it into the oven. This moisture finds it way into the Calsil board under the oven floor tiles and the only way to dry out is with a series of gentle firings. 

You – “OK, we get it, if the oven is out in the rain it will absorb water. Is that a problem?”

This really depends on where you live.

If you’re in a relatively warm climate that doesn’t experience really cold weather (ie. it never snows where you live), then the oven getting mildly damp is annoying, but not a disaster. A damp oven will take a long time to heat up, and will cool down much more quickly than it should because the insulation is damp and thermally conductive, transferring heat out of the oven rather than holding it in. If you’ve been wondering why your oven is taking a long time to heat up, we can guarantee that this is the cause.

If your oven gets really soaked (where leftover ash in the oven feels wet and muddy), it means that you will need to go back to Day 3 of the Curing Fires to gently dry it out. If you were to get a big fire going in a really wet oven there is a chance of a steam explosion in the oven floor.  This would only happen if you got a big fire going in a very wet oven, but is something we want to be very careful to avoid. 

You – “I’m pretty sure my oven has some water in it, but how do I know if my oven is really soaked, or just a bit damp? I don’t want a steam explosion!”

Great question! There are two things you can look for.

  1. If the ash and old embers in your oven are wet and muddy, your oven is definitely wet and needs to be carefully dried out again following the Curing Fires video (see below) starting at Day 3.
  2. If you want a more definitive test, take a tissue and lay it on the oven floor, where the Oven Door would normally sit. Put something flat on top of the tissue to weigh it down. Leave it there for ten minutes, then check on it. If the tissue has absorbed some water, the oven is likely wet. If the tissue is almost dry, then your oven is probably just damp and you’re safe to go straight to the major firings detailed in the next section. 

If you know the oven has absorbed some water and you’re not quite sure if it’s really wet or just damp, it’s not going to hurt to be cautious and assume that the oven is really wet, and to go back through those gentle Curing fires. It’s always better to be safe than sorry, and we want your oven to last for many years to come!

GETTING YOUR OVEN FULLY DRY

When you’re confident that your oven is ready for major firings, we recommend doing at least four full firings to ensure that you’ve driven all of the moisture out of the oven. The ‘Fire and Forget’ method shown below is a great one for this purpose, because the hot coals tend to spread out across the oven floor. 

For the first and second major firings just follow the Fire and Forget method shown in the video below. This will concentrate most of the heat in the back half of the oven, gently driving out the moisture in the front half.

For the third major firing, follow the same method. When the fire has burned down to hot coals, rake the coals forward until they’re covering the circular section of the oven floor (but not into the Vent area).

On the fourth major firing, repeat the process above but rake the coals all the way into the Vent area, almost to the landing (please use your oven door to protect your stone landing, as the direct heat from the coals could damage it). See the Oven Cleaning video below for a demonstration of raking the coals forward. This will heat the floor tiles in the Vent area and dry out the last section of the oven floor.

You’re done! Your oven will now be bone dry and back to good as new.
From here, the goal is to keep it that way – this is the best thing you can do for your oven in the long run.

RE-SEALING THE OVEN DOME

Once you’ve dried the oven out completely, we suggest giving it a fresh coat of roll-on render to ensure that any small cracks in the outside surface of the dome are properly sealed. It’s important to use the roll-on render to form a good seal around the base, where the dome render meets the benchtop. This is also a good opportunity to give your oven a fresh new colour if you want! Watch the video below to learn how to apply the roll-on render.

You may have run out of the roll-on that came with your kit – worry not! There is a great product in the USA called Behr Premium Elastomeric Masonry, Stucco & Brick Paint which is available at most hardware stores.

COVERING YOUR OVEN

If your oven is exposed to the weather you should consider getting a cover to put over the oven when you’re not using it, to keep the oven dry. For ovens in warm climates (where freeze-thaw cracking is not an issue), covering the mouth of the oven will keep most of the rain out. If water is getting into the oven through the flue, you could take the flue pipe off and place the cowling directly onto the flue sleeve as shown below. This setup should keep the majority of the rain out, but we would need to fully cover the entire oven to keep it 100% dry.

Remember, in warm climates getting a little bit of moisture in your oven is just an inconvenience. Providing it’s not getting really wet, any absorbed water will be driven out in your next firing. This means that the next best thing you can do for your oven besides keeping it covered is to use it regularly! 

 In the short term, keeping your oven dry could be as simple as lifting the flue off and covering the oven with a tarpaulin.  This is not particularly attractive, so we are working very hard on getting oven covers developed – it has been a real challenge finding options that are both functional and aesthetically pleasing, but we are making progress (see the images below). 

Let us know if you would like us to add you to our Oven Cover Waiting List!

If you’re handy you could make your own cover to suit the style of your build – it doesn’t have to be made of high temperature materials as you can wait until the oven cools to put the cover on.

You could make a cover for the oven mouth using any waterproof material – Michael in Pennsylvania made a very clever cover by using his Vent Arch formwork and some perspex. In Washington State, Robert made up a template of the canvas cover that he wanted using a cheap blue tarp and had a local uphostery company make the cover for him – the one change we would have suggested to his design is to remove the flue and have that section sealed, to make the cover more watertight.

COLD CLIMATES

If you’re in a region that experiences ‘freeze-thaw’ conditions, where the frost is so severe that it penetrates into the ground, it’s a very different story. In this climate if your oven has gotten wet and experiences a deep frost, the water held in the fire bricks and insulation may freeze and expand, causing serious damage to the oven. Water freezing on the outside of the oven dome can also damage the roll-on render coating.

Most freeze-thaw damage like the examples shown below can be repaired, but you would be better off to avoid this happening in the first place. Prevention beats repair every single time. If your oven has experienced some kind of freeze-thaw damage please Contact Us and we will do everything we can to assist you.

PROTECTING YOUR OVEN IN A COLD CLIMATE

The only sure way to prevent freeze-thaw damage is to build the oven into an enclosure that keeps it completely dry all year round, so that when the cold weather comes, it will have no adverse effect on the oven at all, as your oven is always kept dry. No rain ever falls on it, so there’s no problem! 
See examples of enclosures below. 

If building an enclosure around the oven is not possible, an alternative is to fire the oven throroughly before the end of Autumn to ensure that it is completely dry (using the process detailed earlier), then remove the flue and protect the oven with a suitable weatherproof cover for the winter. This method would require you to do at least 4 major firings (keeping the oven covered between firings), raking the coals forward into the mouth of the oven toward the end of each firing to ensure that the oven is bone dry from front to back, and top to bottom. The cover would need to extend over the edges of the stand to ensure that no water can possibly get to the oven.

The key to caring for a Wood Fired Oven in Cold Climates is to keep it completely dry during winter. 

For those of you living in a Cold Climate, who are in the process of building your oven – please make sure you finish building it and get it fully cured before Winter arrives! Part of the building process is soaking the firebricks in water to lay them, so your oven will be holding water until it’s been cured and fully fired. Please make sure you get this done before the cold weather sets in!