Millboard?

[Michael6268]

Im working on a hearth related project and the spec's call for a non-combustible protector equivilant to 3/8" millboard. How can I find out what is equivilant to this. I believe a ceramic tile floor is approx. equal to that isnt it? I was thinking of using one continuous piece of 1" thick slate. Any info would be great!

 

[elkimmeg]

Mo said to leave no post un answered so, I'm going to take a stab at this. The millboard has an r value to insulate combustiables from underneath your stove. It prevents thermal transfere of the radaint heat to thoses combustiables . Tile r value is .02 or something like that. Most stoves require 1.0 to 1.5 R-values under there. common 1/2 " cement board .42. Your stove manufacturer will list what thermal resistance has to be met in either R or U values. Thats what is required. I doubt 1" stone granite meets the requirements without additional help or spacing of millboard. There is a lot more involved that just being non combustiable.

Hopefully others who have recently built their own floor protection will ring into this post

Mike what does your installation manual state for requirement R or U values? Knowing this we can better advise a proper solution.

 

[Shane]

milboard has an R value of 2.13 per inch . Slate has an R value per inch of .05 per inch. So you'd need about 15" of slate to meet the appropriate R value.

 

[KP Matt]

According to the above, you need some with an R value of 0.8 - assuming you need 3/8" of millboard or equivalent, and given that millboard has a an R value of 2.13 per inch.

Elk, I'm pretty sure Durock or Wonderboard have an R value of approx. 0.25 for a half inch thick sheet.

Check out this page https://www.hearth.com/articles/64_0_1_0_M1.html for more details on the R values of various common materials; unfortunately doesn't mention millboard. What is millboard anyhow?

Does millboard mean thermal "millboard"? i.e. Micore or equivalent?

 

[Shane]

J-Therm 1401 Millboard® is a monolithic board made of ceramic fibers, clay, inert fillers and a small amount of organic binders used as a backup thermal insulation or parting media

I used the R value from a table in a Profile 30 install manual which called it "Kaowool M board". I assume it is the same. The J-Therm stuff has a higher K value (meaning a lower R value) And it is my understanding that the thermal resistance/thermal conductivity vary alot between different manufacturers of millboard. You could use the lowest R value for Millboard you find but personally I would go higher than lower. I don't mean total overkill or anything but if you match your hearth to the 2.13 your sure to be safe.

 

[webbie]

Im working on a hearth related project and the spec's call for a non-combustible protector equivilant to 3/8" millboard. How can I find out what is equivilant to this. I believe a ceramic tile floor is approx. equal to that isnt it? I was thinking of using one continuous piece of 1" thick slate. Any info would be great!

Millboard used to be called "asbestos millboard" and was available at lumber yards and elsewhere. Just the fact that it is mentioned shows how old some of this documentation is!

Elk and the others are in the ballpark when they say 2 to three thicknesses of Cement Board (1-1.5"). A really safe installation on wood floor would be a sheet of metal on the floor under the durarock. Certain wavelengths of radiant heat are stopped my metal....of course, the cement board won't let it get too hot anyway.

 

[Michael6268]

It is a small Century stove. FW240007 I tried for a few days to get the specs off the website but the link is shot. I called CFM today and asked the min. R value and the person I spoke with replied R value, whats that? I explained the manual stated 3/8 millboard or equivalent, but I needed to know min R-value. At this point you could smell the smoke pouring out of the phone as he struggled to figure out what R value was. He put me on hold, came back and stated "3/8 millboard or equivalent is acceptable" ! I asked again about the R value and he replied, "you would have to find that out from someone who deals with that stuff"... GOODBYE!! I hung the phone up and tinkered on their website and got at least the first page of the link to come up, luckily it was the one with the floor protection listed. It states .446 . Does anyone know for sure the R value of cementboard? The chart states .52 . If that is true then one layer should be ok if I am reading it correctly? I would probably use 3 or 4 to build up the thickness for aesthetic reasons anyhow. Also could I use screws on the first few layers or would heat transfer to the wood floor/framing be a problem?

 

[Michael6268]

That was the one I found but when I try to scroll to page two, I get this wacky error message... Maybe its my computer.... Thanks

 

[Jags]

DUROCK Brand Cement Board has an R value of 0.26 and a K value of 1.92.
Non-combustible - panel is fire safe and is used in fire resistant designs

This comes directly from their web site.

Elk - Do most prefab hearth pads take the insulation requirements into account when they are made?

 

[Michael6268]

Seems as though there is conflicting info on the R value of cementboard but .26 seems to be the actual for Durock, so I assume other cement boards would be close. I think I am going to go with the 3-4 layers and 1/4" tile or slate on top of that. Although with Coasters additional info found on the website, it sounds to me like if a ceramic tile job is ok, that the 1" of slate would work too. Does anyone have any sugestions on attaching the cement board? I just wonder about the heat and the screws.....

 

[Shane]

Just don't put the screws where they'll be directly underneath the stove and you won't have any worries.

 

[elkimmeg]

A word on codes if one digs deeper enough there are codes NFPA 211 codes that govern floor protection in relationship of the distance the actual stove or stove legs sit above combustibles. If need be I will cut and paste them It goes something like this 4 to 6” requires x r or u factor for thermal resistance 8 to 8” less and 12 and beyond even less
Again what is tested and listed takes precedence to NFPA code requirements either reduction or additions.

There is also language concerning combustibles in relationship to ambience temperatures up to 90 degrees. In this case it is hard to prove that ambient temps do not exceed 90 degrees at all times and all different stove operations. In lew of not being able to document ambient temperatures manufacture’s listed and tested specs are used. At times as an inspector I have to make judgments where I can call in these little known codes.

To mike 3 layers of ½” cement board dressed with a decent looking tile will work. Screwed ont directly under the appliance where most radiant heat exist

 

[Michael6268]

Thanks All ! If I ever get a digital camera I will post pics of it. Also of my Keystoker and Lopi Berkshire gas stove. Maybe even my mug shot! I guess I could get regular pictures developed/saved to CD, but usually the full rolls of film sit on the counter for like, 3years before I get them developed, so it could be a while! Thanks again!