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Longmont, CO new WFO build - casted over sand - Forno Bravo Forum: The Wood-Fired Oven Community

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  • Originally posted by david s View Post
    I break with convention here and don't use lath. Primarily because it takes too long. Instead I use randomly mixed AR glass fibres in the render coat. Also because of the time factor I do the cement render in one single coat of around 12-15 mm thick, finished with a sponge. Then wrap the whole thing in cling wrap to keep the moisture in the outer layer, letting it cure for a week to enhance strength. After unwrapping it and some more fires to ensure the outer shell is thoroughly dry I then apply the acrylic coats.
    David - how do you apply the acrylic coats, in terms of a trowel? I've read that a plastic trowel is preferred?

    Also - on your single cement render coat, do you scratch it to better hold the acrylic layers to come?

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    • I water down the acrylic 20% so it can be painted on. Using a paintbrush. Around three coats gives a thickness of about 2 mm. I don't scratch the rendered coat it is applied on to.
      Kindled with zeal and fired with passion.

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      • Originally posted by david s View Post
        I water down the acrylic 20% so it can be painted on. Using a paintbrush. Around three coats gives a thickness of about 2 mm. I don't scratch the rendered coat it is applied on to.
        Do you use any sort of conditioner or primer between base coat and the acrylics? I'm going to do a base coat soon of cement based stucco (I've attached the lath to hardiebacker). I will wrap that in cling-wrap for the recommended cure time and once all water is out (I think I read 2 weeks) and it's good and dry, I plan to try your paint on stucco method of the colored acrylic I have on hand. I figure everything I've followed from you has worked out so far, so why not?

        By the way, we have really zeroed in on the right recipes and techniques, and the oven performs perfectly. I am still hoping to get a door fabricated here soon and also have a lot of finish work to do. Could use some more tools (for example I can in no way cook 2 pies at a time in my 32" ID oven). But maybe with a smaller peel and more practice?

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        • Do you use a small banjo peel for turning and unloading pizza? I use a large wood peel for loading but after that it is a small 8-9" diameter turning peel to turn, dome and unload. Click image for larger version

Name:	68B Banjo Peel  9.19.12.JPG
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          Russell
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          • Originally posted by cnegrelli View Post

            Do you use any sort of conditioner or primer between base coat and the acrylics? I'm going to do a base coat soon of cement based stucco (I've attached the lath to hardiebacker). I will wrap that in cling-wrap for the recommended cure time and once all water is out (I think I read 2 weeks) and it's good and dry, I plan to try your paint on stucco method of the colored acrylic I have on hand. I figure everything I've followed from you has worked out so far, so why not?

            By the way, we have really zeroed in on the right recipes and techniques, and the oven performs perfectly. I am still hoping to get a door fabricated here soon and also have a lot of finish work to do. Could use some more tools (for example I can in no way cook 2 pies at a time in my 32" ID oven). But maybe with a smaller peel and more practice?
            No I don't use any sort of conditioner. Just make sure that it's quite dry before painting on the acrylic or it can blister if applied over a damp surface.
            Kindled with zeal and fired with passion.

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            • Originally posted by UtahBeehiver View Post
              Do you use a small banjo peel for turning and unloading pizza? I use a large wood peel for loading but after that it is a small 8-9" diameter turning peel to turn, dome and unload. {"data-align":"none","data-size":"medium","data-attachmentid":400940}
              Definitely need to find a good 8" peel for that.

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              • Originally posted by david s View Post
                I water down the acrylic 20% so it can be painted on. Using a paintbrush. Around three coats gives a thickness of about 2 mm. I don't scratch the rendered coat it is applied on to.
                David,
                Is there a certain type you use in terms of how coarse of stucco you use for this method? I notice they have sand coats (finest) and then more coarse. The one I have seems like a medium one.

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                • I'm not sure whether your question refers to the acrylic coating over the cement render/stucco or whether you mean the sand in the actual cement render itself. I actually use flexible pointing which is a product designed for ridge caps on tiled roofs. It is a very flexible acrylic with sand for high build up. If you meant the sand in the cement render then it should have a variety of grain sizes.
                  Kindled with zeal and fired with passion.

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                  • Originally posted by david s View Post
                    I'm not sure whether your question refers to the acrylic coating over the cement render/stucco or whether you mean the sand in the actual cement render itself. I actually use flexible pointing which is a product designed for ridge caps on tiled roofs. It is a very flexible acrylic with sand for high build up. If you meant the sand in the cement render then it should have a variety of grain sizes.
                    I already did a base coat of cement stucco over lath covered hardiebacker board. I am looking to do an acrylic coating over that and assumed you were talking about an acrylic stucco. What is the flexible pointing product you use?

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                    • Flexible Pointing is an acrylic product designed to go over the mortar on the ridge cap on tiled roofs. It is extremely flexible to cope with the constant expansion and contraction of the roof and as such makes an ideal solution for a pizza oven. It has high build up because it contains a high proportion of sand. It is designed to be troweled on but I find it better to water it down 20% and apply by brush, around 3 coats gives a thickness of about 2 mm.
                      Kindled with zeal and fired with passion.

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                      • david s: It seems all google searches return products in Australia or videos of Australians fixing their roofs! It does not seem like this knowledge has hit the US yet! Anyone know of such a product used here?
                        Last edited by cnegrelli; 09-24-2017, 02:45 PM.

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                        • Does anyone know if such a product is available in the US? I wonder if it's not allowable per building codes at this time?

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                          • Look for "acrylic stucco and masonry coatings". Here is one made by Valspar that is supposed to be available at my local Lowes. Also google "synthetic stucco".
                            joe watson

                            "A year from now, you will wish that you had started today "

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                            • Originally posted by Gulf View Post
                              Look for "acrylic stucco and masonry coatings". Here is one made by Valspar that is supposed to be available at my local Lowes. Also google "synthetic stucco".
                              The product I have is an acrylic stucco, but no chance it can be painted on as is. That Valspar product you linked is actually paint, not stucco. Was that what you meant?

                              Edit: I went out and opened the bucket of acrylic stucco I bought on craigslist from a stucco supplier who had a pre-colored overrun. I got two buckets. It is a lot more workable than I was under the impression (maybe the first bucket had dried up?). I believe one bucket will be more than enough and I plan to proceed. I guess I have to find a stucco primer and then go at it. This is a finish coat only for over the cement stucco I already applied a week ago.
                              Last edited by cnegrelli; 09-24-2017, 04:49 PM.

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                              • Stucco has to be worked to get the desired finish. It comes in different blends for the different layers. You may be able to sieve (I use an old window screen) some of the larger aggregate out of what you have to get a smoother finish coat. (add the fiber back to the mix) You may also get a smoother finish by using a coarse damp sponge on the finish coat before it totally sets. The damp sponge will knock down the high spots and fill in the low spots.

                                The product that I linked is not just a paint. Going up a couple of posts, and referencing the product description, it has most of what David S recommends for the waterproof flexible acrylic coating.
                                Last edited by Gulf; 09-24-2017, 05:03 PM.
                                joe watson

                                "A year from now, you will wish that you had started today "

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