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Floor temperature BENEATH stove

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by roscolo, Sep 27, 2006.

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  1. roscolo

    roscolo New Member

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    Hi. I should be getting my stove in the next day or two (Osburne 2400). I'll be putting it near the center of a room (i.e., no established hearth) with a concrete floor that has been acid-stained and coated with epoxy.

    Apparently, putting the stove on the floor could create a problem with the epoxy under and around the stove. The heat can pull moisture up through the slab, causing the epoxy to fail. The epoxy manufacturer says "The temperature under the stove must be below 100 degrees F to sustain
    any coating. It is the heat that draws moisture in the concrete to the
    surface and causes delamination."

    The stove is a pedestal stove. How hot can I expect the area under the stove to get? Is heat going to be conducted down through the pedestal and / or radiated to the floor to make it hot (above 100)?

    I guess I can build a platform for it if so. Any suggestions? Slate? Thought about dressing up one of those concrete pads you put under a heat pump. Suggestions?

    Thanks. I haven't had a wood stove in any house since I was a kid. Looking forward to it.

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  2. elkimmeg

    elkimmeg Guest

    If the epoxy is combustiable you need to follow the owners manual about floor protercion including 18" of non combustiables in front of the laoding door
  3. roscolo

    roscolo New Member

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    Their MSDS says flashpoint is over 200 degrees Fahrenheit (non-flammable).
  4. KP Matt

    KP Matt New Member

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    Assuming this is the basement, you also don't want to be warming up the floor at the expense of the house. What does the manual say?
  5. roscolo

    roscolo New Member

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    Thanks...the stove is not in a basement. It's in a 1,400 square foot great room. The manual addresses wall clearances, and clearances to combustibles. The epoxy on the floor is not combustible. It's just that heat from the stove can pull moisture up through the slab. Moisture under an expoxy coating on a concrete floor = problems with appearance and adhesion. Flammability is not the issue here.

    I don't know if anyone wants to put a thermometer under their stove, but I'm guessing that the temp under the stove is probably warmer than 100 F. However, the stove is a pedestal stove, so the pedestal may solve the problem. Or it may make it worse. I don't know if heat will be conducted through the pedestal to the floor to make it hot or not. Also not sure if radiant heat from the stove will make the floor warmer than 100 F. Hoping someone can chime in on this.

    Basically I'm wondering if the pedestal may solve the problem or if it may make the problem worse via heat conduction.
  6. Roospike

    Roospike New Member

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    Why no hearth ? Why no hearth pad?
  7. begreen

    begreen Mooderator Staff Member

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    I would think with a pedestal stove that the heat would be minimal on the floor. If you're concerned, buy or build an insulated hearthpad for it.
  8. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    That 2400 is a bunch of woodstove. I would definately put a hearth pad under it that extends the recommended distance for non-combustibles out in front and back of it of it.

    Cleaning up the mess and fixing that epoxy job would not be fun or pretty.
  9. brian_in_idaho

    brian_in_idaho New Member

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    I doubt that you will have issues with conduction of heat through the pedestal, convection along the surface will keep it cool. Radiant heat from the "body" is a bigger concern. I agree with BB, for piece of mind with your epoxy finish, a hearth pad sounds like a good investment. Odds are pretty good that you wouldn't have problems, but why risk it? You can always sit it on a piece of wonderboard for a few fires and maybe put a thermometer on it and check your temp, if less than 100F you can remove it, if over replace with a pad, if you want to know and don't mind the extra work.
  10. roscolo

    roscolo New Member

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    Much thanks for the help, guys! I'll put something or build something under there.
  11. restorer

    restorer New Member

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    Let's go back to the main concern. Moisture being pulled up through the concrete at temps over 100 degrees. If you have a slab floor, was a vapor barrier layed before the concrete was poured? Where is the moisture coming from? Well set concrete has no moisture. Where did you get the informatin that the floor is good to only 100 degrees without deteriorating? If that were here it would go bad about the 5th of June (First day we usually exceed 100 degrees). Most epoxy has a much higher temperature tolerance. Even conversion varnishes and catalized lacquers have a much greater tolerance, in my experience. Last, if you want to go without a hearth pad, and you feel the floor covering may fail, why not remove the epoxy in the area you would normally put the hearth and recoat with a high temp clear coat, one used in industrial plants and warehouses. May have a slight different appearance, but would solve your concerns.
  12. roscolo

    roscolo New Member

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    The info. about moisture in the slab being pulled up by heat in the stove and causing problems for epoxy (and urethane for that matter) has been confirmed by several concrete / coating contractors. I got the "100 F" figure from the manufacturer of my particular Epoxy, Epmar. The Epoxy I am using is Epmar 3700 and I plan to do a topcoat of Epmar 2700 urethane.

    I also professionally applied an Epoxy clearcoat in a restaurant, in the area where people are seated. You'll rarely see Epoxy coating in the kitchen, or if you do, it will look terrible soon, because the Epoxy simply can't take the heat from the ovens and splashed hot grease is known as the real killer. You're correct, there are some high-temp epoxy coatings but the problem here with my wood stove in my house is not the HEAT affecting the EPOXY, the problem is the heat drawing moisture up through the slab, and then the MOISTURE is actually what will cause the problems with the epoxy coating around the stove. I'm not aware of any epoxies or urethanes that tolerate moisture underneath.

    Set concrete does contain moisture. If it doesn't contain it, it transmits it. From a manual on humidity testing a concrete slab:
    "All concrete is porous and transmits moisture through its capillary system. This moisture turns into vapor that is not visible to the eye."

    So I suppose under normal atmospheric conditions, this isn't a problem once the slab has "set." On a couple of concrete forums, numerous contractors have warned me about heat from the wood stove pulling up moisture. On another forum, I got this response regarding heat from the stove pulling moisture out of the slab: "that is exactly right, and that is your biggest problem. the heat from the stove will create a vapor drive of moisture from the slab outward. and because epoxies, and this one in particular, are NOT breatheable, it will likely result in blisters." This is exactly what my epoxy manufacturer also warned me about.

    Just want to clarify so someone reading this in a similar circumstance doesn't think a high-temp epoxy will solve the problem. I don't believe it will. I think the idea is to protect the concrete slab around the stove from reaching a high temp. thereby avoiding the moisture vapor problem under the epoxy.

    I appreciate your suggestions. Using a hi-temp epoxy seemed like a good idea to me as well until I understood the nature of the problem. I think I'll be making a hearth or pad of some sort just to be on the safe side. I have stripped epoxy off a floor ONCE, and I NEVER want to do it again!
  13. DonCT

    DonCT Minister of Fire

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    I think the pad is your easiest, cheapest bet. There are lots of styles out there or you could even try and make your own.
  14. elkimmeg

    elkimmeg Guest

    So whats you are saying your slab was poured without insulation and vapor barrier? Why is concerete used for drainage pipes or to build dams because water weeps threw? Why would you not have sealed that slab in the first place before putting epoxy on?

    I don't think you are getting accurate info or to many things went without propper application prior, with the slab prep and pouring
  15. Rhone

    Rhone Minister of Fire

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    Well, since he can't do anything about the epoxy or slab/moisture condition BB nailed it, the Osburn 2400 is huge and there's little doubt the floor will reach over 100F underneath. I'd definetely go with a hearth pad, you certainly don't want to risk having to deal with that mess otherwise.
  16. wahoowad

    wahoowad Minister of Fire

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    Since you are already working with a 'bare' concrete floor it would take very little effort to establish a functional hearthpad...and I personally would be excited by the options available to me with minimal effort! You could buy some large slabs of bluestone or slate or whatever rocks your boat.
  17. Corie

    Corie Minister of Fire

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    I agree.

    Plus, even though the combustion temp of the epoxy coating is over 200 degrees and the floor shouldn't reach that temp from radiant heating, what about hot coals? Wouldn't a hot coal hitting the epoxy leave an ugly burn mark if the flashpoint of the epoxy is only 200 degrees?
  18. begreen

    begreen Mooderator Staff Member

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    I may be in error, but would think that the flashpoint refers to the vapors of the raw product and not the finished product after it's cured.
  19. roscolo

    roscolo New Member

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    I'm no expert in concrete. I do know that even fully cured concrete is extremely porous. Of course my slab has insulation and a vapor barrier in the form of plastic sheeting, more accurately referred to as a vapor retarder, as this sheeting will not stop all soil moisture, especially gases. And it's common knowlege that the plastic sheeting doesn't last and often gets penetrated in the pour. Also, no one is saying water is going to "weep" through. Again, the problem is vapor drive in a section of the floor being subjected to a very high temp. We aren't talking about large quantities of water here...on the contrary, it's hardly detectable and certainly not visible. It's just that the stove will result in a higher pressurized area of vapor drive caused by the floor around the stove getting much hotter than the rest of the slab. The pressure will be enough to compromise the epoxy coating in this area appearing in the form of blisters. If I understand the phenomena correctly, moisture in the slab in the form of condensation from the hot / cold fluctuation of this part of the floor plays a roll here as well. And dams and drainage pipes aren't subjected to having a wood stove sitting on them. Actually, the porosity of concrete may be why concrete pipes are used for drainage and not for, say, petroleum pipelines.

    Again, I'm no expert, but this problem of a stove drawing enough humidity through a slab to cause problems under a floor coating has been confirmed not just by the epoxy manufacturer, but by numerous concrete floor pros. That's good enough for me at this point. Certainly good enough for me to not want to put my stove directly onto my epoxy coated concrete floor.
  20. DavidV

    DavidV New Member

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    Sounds like an excuse to sharpen up your masonry skills. I'd make a pad our of brick and morter or slate as you mentioned.
  21. restorer

    restorer New Member

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    This seems to be the best solution. You have already researched the concrete and the finish. What did you want from the forum? Don't put the stove on the bare floor, especially since you are using a poly- top coat. I will predict a problem in the finish you are using. One but not both. I have seen this combination peel in sheets. Salts and alcalies will be your worst enemy. Heat radiated from a stove will be absorbed by the mass of the concrete.
  22. roscolo

    roscolo New Member

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    Thanks for the suggestions. Read the first post - was just looking for hearth suggestions from the forum. Some other well-meaning folk took this down another path, questioning the slab, vapor barrier, etc. Maybe the thread will help someone else realize that one shouldn't put a stove on the floor if it's coated with epoxy or urethane and it will save them from a real floor repair nightmare.

    Might give slate a go for the hearth. Or granite, since I live near many major granite quarries.
  23. DonCT

    DonCT Minister of Fire

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    I think that would look sharp!!! Good luck with the project and don't forget to give us pictures when your done :)
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