Oven base keeps getting damp

[pgrambs]

This is my third summer with my Primavera Pizza oven, and up until now I've had no problems. But starting this spring, coming out of a mild winter here in CT., we have found the base of the pizza oven is damp. We've kept the chimney cap on and oven door closed all winter, and no apparent water got in. Am wondering if water could be seeping in under the base - it is sitting on a granite slabe. The result is that unless we do extra heating of the oven, the pizzas come up soggy. We grouted according to directions, and all was fine up until now. Any one have any similar experiences or suggestions?

[Gulf]

Pgrambs,

I'm betting that a few more firings will get your oven back in shape. I'm also guessing that "mild" means warmer temps and less frozen precipitation. What about rain? Most of us who own WFO's have problems after periods of unuse. I moved your topic to Forno Bravo Oven Installation. Also, I'm alerting Alex_FB at Forno Bravo. They are a great bunch that want everyone to get the most out of their ovens, wether built from scratch or one theirs.

[Guest]

Hello Pgrams,
Assuming you bought an oven kit you built yourself how did you finish your oven and what kind of stand did you build it on? Is there a seem at the base of the oven where it meets the slab/stand you built your oven on?
The firebrick floor tiles are porous so they will absorb a certain amount of moisture naturally through the air and like Gulf had mentioned after a few burns it should be act normal after a few long burns. If after this is done it still seems damp and not getting hot , you will want explore the possibility that water did indeed make it to the insulation board. Im not sure how difficult it would be for your particular oven to remove 1 floor tile piece and feel the board with your hand but that is the easiest way to check and be sure without disassembling your oven.

[dakzaag]

Zoolander, probably a good idea to start a separate thread for the moisture issue on a new build vs and existing oven. What board are you using and how mushy is it really? I have some exposed board that could be defined as soaking cardboard, and it is holding up just fine. (not recommended by any means, but the oven is exposed right now and hence the board is exposed) It is much better to keep it covered and protected for the life of the insulation. Of course that is really tough with extended build time and then extended time of inactivity in a completed oven.

A new Cal Sil insulation has been introduced to the insulation industry that is water resistant and I am looking forward to trying this out. As usual, the devil is in getting quantities less than a truckload.

Finally to answer your question, in general a lot of ovens are built on a high temp insulation board and they turn out fine and perform for a long time. If you cannot manage the moisture during the build, it is likely you won't be able to manage the moisture after your done, so tighten up the procedure of covering and protecting the build. A fire on top of the floor will do very little to dry out the board underneath. A long summer drought with high heat and winds will be your best friend, but I suspect the insulation is not that wet, so proceed unless you have additional information that is pertinent.

[jonv]

What is that insulation board made from? Doesn't look like calsil, which retains its structure rather well even when wet.

[agrasyuk]

Looks like what you have installed is not a rigid board. From the looks it will not support a floor even when dry. Replace it with proper insulating casil board.
or perhaps cast a layer of vermicrete over it - I didn't have casil in my budget so I Embedded a 2" sheet of rockwool into my insulating hearth .

[UtahBeehiver]

Zoolander,

Let's start with what type of build you are doing, is it going to be enclosed or will it be and igloo? What stage of the oven are you at, IE laying the floor, laying the solder courses or just fitting? Water migration comes from two main sources, your hearth pad channels water to CaSI soaking the insulation from below, or from above, exposure to rain or leaks in the enclosure if you are this far. To mitigate water soaking from below, several options may be possible if you have not gone to far with oven build. Raise the CaSi off the hearth, one builder placed the CaSi on a paver base, I used FoamGlas, which is will not absorb water as my base course. David S advocates drilling weep holes or sloping outward the hearth slab. If you are past the point of raising the CaSi, you could drill weep holes from the bottom. Key is to keep water from getting to the CaSi. This is harder to do with an igloo than an enclosure building. If you are enclosure, do what ever you can to min. exposure of CaSi until you get it enclosed. Just some suggestions.

[shanxk8]

I've just finished my hearth pour, and now reading this think I should put some drain holes in the concrete. Is there a suggested spacing/location for these holes? (probably good to do this in advance)

[david s]

I've just finished my hearth pour, and now reading this think I should put some drain holes in the concrete. Is there a suggested spacing/location for these holes? (probably good to do this in advance)

I do just one in the middle of the slab about 1/2" diam, but my ovens are very small you might prefer a few for a larger oven.

[dakzaag]

Zoo, Nice patio you got there. I agree, whatever that material is, it is not Cal Sil Board. The key word is Board. All of these products are high temp insulation, designed for many applications. Pipe being a common item insulated which often requires a flexible cal sil product. What I see in the pic is not something I think can support the oven wet or dry. Fiber board is another product that works because it is compressed. If I were you Zoo I would start over. I can source proper board for you, but it will probably be cheaper locally. Start at Harbison Walker and work from there. Try the pottery supply outlets near you.

[agrasyuk]

I have never worked with this material before I can't say for certain at this point.

you can be very certain - calsil board doesn't flex like what you have pictured, wet or dry.
with the fiberish look on the side this actually looks more like a blanket (FB sells those too), will make a good dome insulation so not a total loss at all.

[Guest]

Hello Zoolander,
The insulation board is indeed what you have and thats exactly what it looks like when it gets wet. It is the same insulation board that we use on our fully assembled ovens , commercial and residential. It is not meant to be exposed to water. At this point I would dispose of those boards , They are able to be saved if they have a little rain on them but that looks like more of a monsoon.
Send your invoice number and a photo of the boards to support@fornobravo.com and I will get you some new boards. We stand by our product and its performance. You can also take a look at our photo gallery and see the different ways we finish/enclose our oven to protect it. There is no comparison to oven with insulation board to one without it .

[Gulf]

Zoolander,

It sounds like that you are getting some new ceramic fiber board (CFB). CFB is a great insulation. It has an insulation factor slightly better than CalSil. Both need to remain as dry as possible during and after the build to be effective. Many of us took great pains to make sure of that during our builds. I used an EZ up shelter along with weighted tarps to insure against the blowing blowing rains. Later in the build I built a scissor truss roof over my igloo. Since my build, elevating the insulation above the concrete hearth has become a newly added idea. It is a good one. It just makes sense. All concrete floors in homes are at least one to two brick courses higher than the exterior brick. Any amount of elevation will help a bunch. Russell, has mentioned this extensively in some recent threads. I think that is a good practice for igloos or doggie houses. I really hope that this new start works out better for you.

[UtahBeehiver]

Getting the new insulation board off the hearth will help keep it from water that might find it's way into the hearth surface. FYI, Durock is not waterproof, they suggest a membrane if you require waterproofing. So it is possible that if the Durock get saturated enough it could move up into the insulation.