Stone Enclosure - Moisture

[pizza_bob]

I am about ready to add the insulation blankets around my my dome. My enclosure around the dome will be stone as shown below. The stone will NOT be a veneer mounted to cement board. It'll basically be stacked and mortared stone. The space between the stacked stone and ceramic blanket over the dome will be filled with loose popcorn size vermiculite. My concern is that moisture will get through to ceramic insulation and/or the dome. Tscarborough suggested a moisture barrier.

What can be used for the moisture barrier?

Will I need cement board betwen there?

Will I need some sort of vent to drive moisture out?

Thanks,
Bob

[SCChris]

Re: Stone Enclosure - Moisture

Bob,
Someone must have done about the same sort of exterior that has more direct feedback for you, but.

I'd do everything that can be done to waterproof under the stone and over the insulation.

"What can be used for the moisture barrier?"
After you identify what the outside temp of the insulation during hard saturating burns then you'll have some better direction as to what materials can be used. In most modern building a layer of high tech building fabric would be used. Heat would be my concern here.

"Will I need cement board betwen there?"
Hardie backer easy to work with and moderately water tight, so you might be able to build up an enclosure that your stonework would hide and also keep the insulation dry. Joints can be taped with fiberglass tape and thinset. I think this might be what you want to do. If you go this way, keep the roof moderately slanted rather than flat just in case water gets that far.

"Will I need some sort of vent to drive moisture out?"
A small water tight vent hidden somewhere on top wouldn't be a bad thing. I'm in an area where we just don't get a hard freeze, but you'll be getting a few a year. Cracks, freezes and water don't mix, this could tear things up in a hurry. Remember that even though the dome is covered over and under with insulation cold will creep in through the door area and it could get below freezing in there.

If you were a wealthy sort you could have a copper jacket built.

Chris

[Tscarborough]

Re: Stone Enclosure - Moisture

There are basically 2 types of wall systems you could use. One is a barrier wall, the other is a weeped wall.

A barrier wall is just that: A barrier to any water penetration through to the inside surface. An example of this type is a three hundred year old rock wall that is 12" thick. Moisture does penetrate, but over the cycle of the seasons, it seldom or never reaches the interior. As you may have guessed, a 12" thick wall is probably not practical for your application.

The other method is a weeped or veneer system. This is the most common method of wall construction today. It assumes that moisture will make it to the inner surface of the veneer, but allows for that moisture to be stopped there and is provided a way to exit the wall via weep holes. The problem for you here is that you have to build 2 walls, the stone outer one and an inner one that is waterproofed and flashed, plus the two walls are normally tied together in some fashion. Also not real practical for your application.

The best compromise is to build the rock veneer, then before you roof it or fill it, you waterproof the inner surface with a liquid membrane waterproofer, AND provide weep holes just in case. Here is the type of product I am talking about and it is not cheap.

MEL-ROL LM Liquid Waterproofing Membrane

The poor-boy solution would be to use a cementious product like Thoroseal which would also work fine, but takes a little more effort to apply.

[Tscarborough]

Re: Stone Enclosure - Moisture

If you are going to build one like that (with the stone roof), then that area is treated differently.
The sequence would be:

Build the walls to top of the vertical section and waterproof them as noted above.
Fill the building, build the frame work for that type roof out of wood or steel.
Sheath, felt, and flash the roof.
Lay the stone roof

Seal the entire exterior with a penetrating sealer like Prime-a-Pel 200.

Edit-But I can tell you with about 95% certainty that that is not real stone on that fireplace, it is an adhered veneer (like the brand Cultured Stone, which is what it looks like). It is stuck to either a stucco or cement board structure.

[SCChris]

Re: Stone Enclosure - Moisture

When I remodeled a bathroom bath enclosure I used hardie backer and once it was all tight and taped I rolled on a product called "RedGard" before applying the tile. The tile is still tight after many years and the product creates a waterproof membrane. I don't know how it would hold up outside but it might help give you somewhere to start to look. The waterproofing materials for foundations could also work given that the interior in this area doesn't get too warm. Tscarborogh sounds like he's done a fair bit of research along these lines so I'd bounce ideas his direction as you get further.

Chris

[Tscarborough]

Re: Stone Enclosure - Moisture

RedGard is about the same thing but is consumer grade (which mainly means it is packaged in smaller quantities and has better labeling) and would work just fine.

[pizza_bob]

Re: Stone Enclosure - Moisture

Tscarborough/Chris,
Thanks for all your help with this. It seems as if my best might be to build the sheetmetal studded/cement board enclosure and use a thin stone veneer. This was my first approach but the mason who is building a retaining wall running up to my oven suggested that he can enclose the entire dome with stacked stone. It sounded like a good idea and the price was right but we didn't discuss moisture concerns. I know nothing about framing with sheetmetal studs so I'll have to have someone come out and do that for me. Will it be difficult to tape and seal off the intersection of the tapered roof to the vertical walls? It sounds like cement board or hardibacker should keep the moisture out. The sheetmetal/cement board enclosure should help me create supports for the chimney system. The chimney will be class-A stainless steel pipe (DuraTech) which is 8 inches inside diameter and 10 inches outside diameter. It's double walled 430 stainless steel which should out last me. In order to get the vent to the center of this style roof I need to add 30 degree elbows and about 48" of this pipe. The double walled pipe makes this set-up quite heavy. I'll post pictures next week sometime.

Thanks again!

~Bob