Calcium (?) leaking between base and hearth

[carioca]

Hi guys,

I used to put a tarp over my oven but eventually tired of the expense of replacing the tarps...

Now I notice white stuff leaking out/crystallizing from the transition of the hearth insulation to the concrete dome support proper (see photos).

The upper part of the plate is made using insulation mixed into the concrete, the lower part is pure armoured concrete (construction details av. in my G+ album, Forno del Gallo)...

What is happening, and what should I do to stop this disfiguring leakage?

Thanks for any ideas!


Edit: caption from another photo which I can't seem to be able to upload:

After spending two days casting a 1.2 m diameter pad on the hearth slab from a mix of LaFarge ciment fondu and two bags of No. 3 vermicuilte - as recommended by a Forno Bravo forum expert, I spent today chipping off the outer portion that would have extended under the dome wall.

[deejayoh]

Re: Calcium (?) leaking between base and hearth

It's probably efflorescense. If you want to stop it, you'll need to keep the oven dry (which is probably a good idea anyway!)

Efflorescence - Wikipedia, the free encyclopedia

[stonecutter]

Re: Calcium (?) leaking between base and hearth

Not probably, it's definitely efflorescence.

You've got water penetration above that midslab crack. Find it and seal it off. My guess is that your slab isn't pitched away from the oven enough and your getting water seepage into the slab from around the perimeter.

[carioca]

Re: Calcium (?) leaking between base and hearth

Thanks guys! So that's what it is...
Not only will I now protect the dome with a painted-on permeable membrane, but I'll also try to cut a V-groove into the blue plate and fill it with suitable grout, then repaint it.

Since the excrescences are all between the semi-insulated hearth plate and the concrete slap beneath, I don't think I need to worry about static failure in my structure LOL

Ciao, e buona fortuna!

[cobblerdave]

Re: Calcium (?) leaking between base and hearth

G'day Carioca
Its great to see an oven from 2006
I've tracked back in your user CP and found you Picasso pics. Must say that's a nice oven. I do like your stand, very unique. I also am taken with the gothic style arch entrance , it certainly sets your oven apart from most.
Sounds like your on your way to stopping the water from getting in. I'll add some more possible causes you might want to check out. As stonecutter pointed out you got stop the water from getting in first but there can be more than one cause.
I read about your fly screen windbreak sounds like your oven faces the local wheather. You might consider an external plug style entrance cover to stop the rain from getting to the hearth brick where it's easily taken into the oven insulation through the cracks between each brick.
The entrance appears from the pics to be firebrick. Firebrick is not water resistant like a house brick and soak up water fast. A clear brick sealer regularly applied might help.
Cracks around the flue pipe. A high temp automotive sealer, the one I'm thinking of is rated to 650 C only problem is that its red in colour.
Cracks in render or where render meets the entrance brick . Clear paintable silastic could help. Even fine cracks can soak up water , capillary action really sucks. Fine cracks can be scrapped bigger to squeeze the sealant in.
Hope something here might help.
Include a pic of your oven I'm sure others would like to see
Regards dave

[david s]

Re: Calcium (?) leaking between base and hearth

Another entry point is where the base of the dome meets the top of the hearth. A crack can often appear here so inspect it carefully. It is also a good idea to make sure this slopes slightly down and away from the oven dome so water is not encouraged to gather in this spot.

[carioca]

Re: Calcium (?) leaking between base and hearth

G'day Carioca
Its great to see an oven from 2006 ...
Include a pic of your oven I'm sure others would like to see
Regards dave

Hello Dave! Thanks for your kind words! The full album of our Forno del Gallo che canta is now on Google Plus (https://plus.google.com/photos/+LutzHuesch/Albums etc) but I'll post an older snap here now for your instant enjoyment!

The oven opening actually faces north, away from the prevailing wet southerlies. But I definitely need to plug that door opening - haven't still got around to it...

The firebrick arch is already painted with clear water-repellent film but perhaps I need to reapply some... Flue is well sealed in with ciment fondu-based mortar but like all the other possible points of entry you mention I'd better check it all out once again and try to make good any faults.

Trouble is, I'm nearing 80 and often run out of energy, particularly with so many jobs around our house still to do! And now all the fruit trees need their bird-netting placed over them, and they've grown so big LOL

Cheers, and best regards to Brizzieland!

Luis

[carioca]

Re: Calcium (?) leaking between base and hearth

Another entry point is where the base of the dome meets the top of the hearth. A crack can often appear here so inspect it carefully. It is also a good idea to make sure this slopes slightly down and away from the oven dome so water is not encouraged to gather in this spot.

Good points, David! I left the surround flat because it serves as a 'bar' when we have visitors - people can park their plates or glasses there, out of reach of the free-ranging poultry LOL

Cheers,

Luis

[david s]

Re: Calcium (?) leaking between base and hearth

Good points, David! I left the surround flat because it serves as a 'bar' when we have visitors - people can park their plates or glasses there, out of reach of the free-ranging poultry LOL

Cheers,

Luis

You only need a tiny slope