Min. Distance to Combustibles, Micore 300, Durock, Ceramic Tile Questions

[Bill 700]

The stove is a Pacific Energy Fusion. With a double wall connector the distance to combustibles at the rear is 6-1/2". The combustible will be a sheet of 3/4" plywood. The distance to the sheet of plywood will be greater than 6-1/2".

The plywood will be covered with 1/2" Micore 300, then 1/2" Durock, then ceramic tile. The distance to the ceramic tile will be approx. 5". The Micore would, as far as code compliance was concerned, be just overkill.

1) Is this a code issue?

2) How do I keep the grout between the ceramic tile from cracking from thermal stress?

Regarding the grout cracking, I have thought about:

leaving a 1/2" air space between the Durock and the Micore;

installing the tile butted tight with no grout joint;

using a double layer of 3/8" Durock with the joints lapped, and the joints taped in both layers;

All feedback and ideas will be greatly appreciated.

Bill NC

 

[DougA]

I don't understand why you want/need the Micore since you are past the limits of the distance to combustibles.

 

[begreen]

Sounds like you are seriously overthinking this Bill. Skip the micore, you don't need it. The Durock will add some insulation alone and it will provide a stable tile base. Use latex modified thinset per directions and you should have no issues.

Do you even need the plywood? If this is going over a sheetrock wall I would just screw the Durock over it with a screw every 8".

 

[Bill 700]

Doug, the Micore would just be an extra safety margin. I always view building codes as minimum safety standards. I remember reading about the early rooftop solar hot water panels catching on fire after they had been in service for a number of years. The temps never got high enough to reach the combustion point for the wood used in the panels, but the temps did get high enough to cause pyrolysis (sp?) over time, which lowered the combustion point of the wood.

BeGreen,

This install is going into a new addition. The room behind the stove is a guest bedroom that is being built to double as a hurricane shelter. There will be a double layer of 3/4" plywood on the wall for projectile resistance. I have used Durock with a vented airspace behind it (open top and bottom) in an installation in a rental house that I own. I taped the joints per Durock instructions then basically trowelled on a very thin layer of sanded grout with one of the floats with the foam facing to get a light texture. The horizontal joint did crack, so I was trying to ensure that did not happen on this installation. I checked and Durock is available in 1/4" sheets, so I may go with a double layer, joints staggered, taping the joints in both layers, second layer fully adhered to first with mortar.

Thanks for the latex modified suggestion. I can't remember if I did that on the earlier install or not.

Bill NC

"Everything's your own fault if you're any damn good." Ernest Hemingway

 

[begreen]

Two layers of 1/4" Durock will add R=.39, two layers of 1/2" Durock NexGen will make an R=.78 insulation barrier and will nicely improve the projectile barrier.

 

[Bill 700]

BeGreen,

If I can fit it into the budget, there will be a layer of 12 ga steel, then a double layer of 3/4" plywood with joints and direction staggered. That will bring the bedroom pretty close to a cat 4 tornado level.

Cutting, drilling, handling sheets of 12 ga steel will be a pretty significant labor cost however, so I'm not optimistic that I'll be able to do the steel.

Bill NC

 

[mellow]

I am not linking to this to advocate gun use, but it was all I could find to see how concrete board stacks up to projectiles:

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[begreen]

We're talking 150-200mph wind drive projectiles not bullets here.

 

[mellow]

I thought the concrete board did a good job standing up to a shotgun blast, meaning it should do good for projectiles, but I could not find that info in a search. That was the only thing I could find, just thought it was interesting as I have not thought about using Durock for a hurricane shelter.

 

[begreen]

If I was making a tornado proof room it would be like a fallout shelter, 10 ft underground.

 

[Bill 700]

Many tornado deaths occur at night when people do not get the warnings, and so they do not get to a shelter. FEMA has plans online. One wood framed room has a double layer of 3/4" plywood and 12 ga sheet steel, which has been tested with a 2x4 fired from an air cannon.

 

[begreen]

I am so glad I don't live in a tornado zone. How many have struck your area?