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  • New Oven and need help with Finish

    Hello community, I am a brand new member with a brand new forno delivered this week. It was made in Portugal and needs to be finished in mosaic or anything else you can suggest that would be waterproof and protect it from the elements.

    My oven is exposed to the elements and currently has a layer of cement render over the outside. It sits in a metal frame which, the guy who sold it to me, said that i would also need to mosaic over so that it does not rust.

    My questions are as follows:
    1- is there an option to apply a waterproof render?? i like the look of the render and want a black render finish.
    2- what tile glue do i use? is it just a normal tile glue?? and normal grout?

  • #2
    1. There are two schools of thought here and both solutions depend somewhat on your weather conditions. The first is not to seal the outside at all, so the oven can breathe. Because sealing from water entering also seals from water escaping. This is the traditional Italian method for ovens either indoors or outdoors. The second method is to either make the outer stucco impermeable or apply a waterproof coating over the top. A good method for doing this is to use an acrylic render. Use the 100% acrylic that is wet and comes in a bucket, not the less expensive dry stuff in a bag which may be called acrylic but is in fact a cement based acrylic modified render. The 100% acrylic has some elasticity which as well as being waterproof, allows it to cover cracks in the cement layer under it. I find it easier to apply by watering down 20% and painting it on in about 3-4 layers.A third and probably the best solution is to have a roof over your oven so it can't get wet in the first place, but this is the most expensive option.

    2.Assuming your oven is insulated then the outer shell should not get hot enough to worry tile adhesive. Use a good quality outdoor tile adhesive. I use Monoflex, but that may not be available to you.
    Last edited by david s; 12-26-2017, 02:07 PM.
    Kindled with zeal and fired with passion.

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    • #3
      Originally posted by david s View Post
      1. There are two schools of thought here and both solutions depend somewhat on your weather conditions. The first is not to seal the outside at all, so the oven can breathe. Because sealing from water entering also seals from water escaping. This is the traditional Italian method for ovens either indoors or outdoors. The second method is to either make the outer stucco impermeable or apply a waterproof coating over the top. A good method for doing this is to use an acrylic render. Use the 100% acrylic that is wet and comes in a bucket, not the less expensive dry stuff in a bag which may be called acrylic but is in fact a cement based acrylic modified render. The 100% acrylic has some elasticity which as well as being waterproof, allows it to cover cracks in the cement layer under it. I find it easier to apply by watering down 20% and painting it on in about 3-4 layers.A third and probably the best solution is to have a roof over your oven so it can't get wet in the first place, but this is the most expensive option.

      2.Assuming your oven is insulated then the outer shell should not get hot enough to worry tile adhesive. Use a good quality outdoor tile adhesive. I use Monoflex, but that may not be available to you.
      Thank you so much! I think the rendered look will be great. Ill go to bunnings and see what they have in an acrylic render. Im assuming if i use sikaflex or some kind of heat resistant silicone around the chimney and joins from the render to the metal base, this will help with sealing. As i cracked the cement render in the install, ill patch that up first with a heat ok cement render then go with the acrylic render. Your information has helped so much.
      I tried to upload a photo but it wouldn't work. https://brendastajcic.shootproof.com/gallery/forno/ i have attached two photos here at this link
      Last edited by Bstajcic; 12-27-2017, 03:44 PM.

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      • #4
        Normal silicon won’t stand up to the heat from the ss pipe in that location. Sikafireate will but it goes hard when heated. I’ve found the only thing that remains flexible and can tolerate the heat (just) in that position is high temperature silicon. (There may be other products that work, but I’ve not found them.) The highest rated silicon that I can find is Permatex Ultra Copper. You need to wrap some cardboard around the flue pipe before rendering up to it. After 24 hrs remove the cardboard and fill the space with the sealant. Because the conductive pipe will expand rapidly on heating it is important IMO, to fill this gap with something that will remain flexible, otherwise the expanding pipe can create stress and cracks in the cement surrounding it. The gap needs to be approx 6 mm. If not sealed properly this is a common entry point for water as it easily runs down the outside of the pipe.
        Looking at that damaged area, if it were mine I’d just go over it with the acrylic render. But if you want to fix it with a cement render first then you will need to make the area damp before working over it and try to keep it moist for at least 24 hrs after. If the cement render is thin and it dries out too fast it won’t be successful.
        Last edited by david s; 12-27-2017, 08:27 PM.
        Kindled with zeal and fired with passion.

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        • #5
          I am almost at the end of the curing process and about to acrylic render the oven. The outside temp of the cement render is approx 40-50 degrees- the internal dome was at about 400degrees. Is that temp ok to start the waterproofing temp? I believe the oven was quite dry when we bought it as it wasn't made on site but we were told to cure it

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          • #6
            All the black soot should have burnt off the inside of the oven if all the moisture has been purged and you”ve got the temperature up. It won’t hurt to use the oven normally a few more times before adding the outer waterproofing. If there’s significant moisture left in the oven theacrylic waterproofing can blister as the moisture is trying to escape.
            Kindled with zeal and fired with passion.

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            • #7
              Originally posted by david s View Post
              All the black soot should have burnt off the inside of the oven if all the moisture has been purged and you”ve got the temperature up. It won’t hurt to use the oven normally a few more times before adding the outer waterproofing. If there’s significant moisture left in the oven theacrylic waterproofing can blister as the moisture is trying to escape.
              thank you i did this based on your advice and as you said, the black soot did burn off. Turns out it was a great suggestion also as a few hairline cracks appeared in the cement render (not waterproofed as yet) so I'm guessing, although they are small (long but hairline width) this needs to be fixed
              Do you think this is a concern or is this normal? Im going to fire it up again this weekend then waterproof after.
              many thanks for your advice.

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