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Heat resistant mortar
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Posted by
rudysmallfry (
My Page) on
Tue, Oct 25, 05 at 21:30
| Okay, I just spent 2 hours getting absoultely nowhere on this one at HD and Lowes. I am building a hearth pad for my wood stove that is coming on Friday. According to the instructions I have, I am supposed to use 3/4 inch plywood with 1x3 or 2x4 supports or backers. That part's done. The next step is to secure wonderboard onto the plywood using "heat resistant mortar". After that is regular thinset, tiles and grout. The reason I have heat resisitant mortar in quotes is because every store I have gone into looking for it looks at me like I have two heads. So now I ask the garden web class, what is heat resistant mortar?
Please don't tell me to check with my town. Their response to all of my wood stove questions so far has been, "just follow the manufacturer specs". I called the company that makes the flexibond products and was told that they don't rate their products for heat. I looked at the cement products in the masonry section, but none of their products mention heat either. Does anyone know what I should be using for the wonderboard step and where I can find it? |
Follow-Up Postings:
RE: Heat resistant mortar
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| As far as I know all mortar is heat resistance . it don't burn . You can screw the wonderboard in don't think that a few screws would transfer enough degrees to start a fire also your tile on top with the grout will act as a barrier Imho that is ..Im a retired mason and never heard of heat resistance mortar.. just screw it it to the plywood or use a non combustable adhesive. But sure someone else out there will tell you somthing else.. but thats what I would do... Read on here that if you put brick agaist a wood wall it would not be fireproof .. thats bs Ive built many fireplaces and they all worked fine and no fires .. but thats another story |
RE: Heat resistant mortar
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| You want to look for refractory mortar. Yes, all mortar is heat resistant, but refractory mortar is a lot more durable than simple portland cement or other types of mortar. You can actually buy the stuff in tubes that you can put in a caulking gun, or you can get it in tubs, bags that you mix yourself, etc. Here's an example of the different types: http://heating-and-cooling.hardwarestore.com/32-163-heat-proof-cements
-and-gaskets.aspx If you have a stove or fireplace store in your area, chances are you can find it there, or even a heating contractor. If not, try back at the big box home center, |
RE: Heat resistant mortar
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| refractory mortar is used on firebrick and the proper way to use is is mix it like a surly and dip the brick edge in and shove them on to one another .. that will not work on the wood and wonderboard.. Like I said just screw the wonderboard to the plywood.. When you build fireplaces they say to use refractory mortar but if you look in your fireplace you would find 99 and 9/10 are built with reg mortar mix.. Including the old Rumford fireplaces that last a 100 yrs.. with beams right in across the fire opening.. But if you want to I guess you can.. use the refractory mortar.. if it will make you have peace of mind.. that's the important thing.. I've built sewer disposal plants and that is the only time we used the refractory cement on the furnaces that burn the waste.. also on the old coal chimney's.. because of the high temperature. What I sugest is that when you grout the tile on top of the wonderboard use the sand mix grout with the additive in it that way the joints will hold up tight and not move on you.good luck with your project |
RE: Heat resistant mortar
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| You want to make sure you have at least 1" of non-combustible material over the plwood including the tile and mortar. If necessary put down two layers of wonderboard. You can mix "heat resistant" mortar yourself. Buy a bag of mortar clay (sometimes called fire clay) and mix that into the mortar mix. The bag will usually have a suggested ratio of cement, sand and clay. All mortar is "heat resistant", the addition of the clay makes this mix less prone to cracking and crumbling due to the temperature swings. |
RE: Heat resistant mortar
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| Sort of sounds like the company is covering itself for insurance purposes. |
RE: Heat resistant mortar
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| "refractory mortar is used on firebrick" Yes, yes it is. But there's more than one way to mix the mortar. You don't have to mix it to slurry consistency if you're not setting brick with it. 100 years ago fireplaces were constructed with the material that they had at the time. That doesn't necessarily mean it's the best choice for the application today. And yes, a lot of fireplaces have been built recently using standard bricking mortar (against code in many areas, I understand). That's very likely why a lot of fireboxes I see have badly degraded mortar. |
RE: Heat resistant mortar
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I don't know much about this but was curious. I had a patio contractor build in a fire pit - I was shocked they used regular mortar and bricks and was scared to use it. I believe regular cement can crack strongly enough for bits to shoot out. Of course they didn't know what they were doing and it turned out it smoked too much to use anyway.
Back to the point.....my dad worked in a factory that made glass tv tubes so he used to install these big furnaces and always used fire brick. They let him bring the bad looking and used bricks home and he would use them for other stuff. I can't imagine him not using fire brick and fire motar in a heated situation. But a wood stove with some clearance from the actual bottom of the stove may not really need it. Guess it depends on how paranoid about fire you are, how much you plan to keep the stove cranked at max for long periods of time etc.
Mary |
RE: Heat resistant mortar
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| I was able to get refractory mortar where I bought my firebricks, at a masonry supply house, should be one in your yellow pages |
RE: Heat resistant mortar
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Here is a link that might be useful: Refractory mortar
RE: Heat resistant mortar
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| I bought refractory cement for kiln repair. It exists. I think the local fireplace dealer sells it. I don't remember where I got mine, but I experiemented creating molds with it in my kiln- to 1500 degrees farenheit-it didn't crack and maintained form. Leslie
soon to be wood burner, glass artist and potter |
RE: Heat resistant mortar
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| 100 years ago they likely had some awesome asbestos mixed in their mortar too. |
RE: Heat resistant mortar
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| Could this refractory mortar be used as a cast for smelting glass? Would it hold its shape in the heat or crumble apart. I want to make glass bricks and the mortar would stay and hold the shape and give a little extra strength to the brick so it wouldn't matter that I couldn't get the glass out of the mortar shape, I just don't want the mortar to crumble apart and have the glass spill everywhere. |
RE: Heat resistant mortar
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| Stovo made by Rudland, Fireplace mortar comes in 1 Qt. Tub is good up to 2000 Deg F. You should be able to find it at Ace Hardware and it runs about 59.00 USD for a 6 pac. |
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