Joe's 42" Corner Build

[UtahBeehiver]

Mullins,

Great question, I did not place a vapor barrier under my insulation per se but I did raise my CaSi board up from the hearth floor by installing 2" of FoamGlas insulation under the CaSi. FoamGlas is made by expanding molten glass with an inert gas. Bottom line it will not absorb water and it positioned the CaSi above any water that might migrate along the hearth floor. CaSi board will absorb water like a sponge. Like I mentioned lots of ways to skin the cat but since I did not use I will defer to others. I just wanted to point out that it is important to keep the CaSi board dry.

[david s]

Can someone explain the logic behind having vapour barrier under the insulation? I have seen some ppl have drilled a couple of hole to let water run off, but would a vapour barrier not act the opposite to that and trap water?

It depends on what kind of material you use to build the stand, and your weather conditions, but if you use cement blocks they can wick moisture up from ground level to accumulate in the porous under floor insulation.
Should the insulation get wet either from water wicking up from below or rain entry from above, the drilling of a few holes through the slab near the centre provides an exit for water to escape from the insulation, driven out by the fire from above.

[joeykramer]

so after all this talk, i somehow neglected to put the vapor barrier underneath the insulation, i have two options... 1. i redo it, 2. you guys convince me not to redo it because ________. 3. some other option/combo of the above.

i wasnt planning on covering it with a 'dog house' or a roof over it. i put down the 4 inches of insulation, fireclay/sand, and laid the brick floor and completed most of the first course. not a terrible amount of work done, but i dont want to regret it in the future if i cant get the oven to get hot or hold temps.

what should i do?

thx

[Gulf]

Can someone explain the logic behind having vapour barrier under the insulation? I have seen some ppl have drilled a couple of hole to let water run off, but would a vapour barrier not act the opposite to that and trap water?

Mullins,

This my two cents: I believe that a vapor barrier is a little insurance on moisture wicking upward from the concrete hearth. And yes, a moisture barrier could trap water in the insulation, not giving it a a gravity fed means of escape. I agree that holes will aid in gravity feeding massive amounts of water. Buckets of water from a flood may, but the insulation has to exceed it's water abosrption capabilty before that will happen. You can hold a full sponge in your hand and it wont spill a drop. Most oven insulations act the same as a sponge. But, where is that moisture going if it does not have a mosture barrier installed. If you have a wet oven, some of that moisture will be driven down into the concrete hearth. When the oven cools, that moisture will wick back up into the insulation. Imo, that will take even more firings to eventually drive all the moisture out. Maybe, strategically placing a hole in the moisture barrier directly over a hole in the concrete hearth will help against a catosropic event.

I agree with Russell on the idea of elevating the insulation layer from the concrete hearth. Along with the moisture barrier, that is my new mantra .

[Gulf]

[ATTACH=CONFIG]n386412[/ATTACH] so after all this talk, i somehow neglected to put the vapor barrier underneath the insulation, i have two options... 1. i redo it, 2. you guys convince me not to redo it because ________. 3. some other option/combo of the above.

i wasnt planning on covering it with a 'dog house' or a roof over it. i put down the 4 inches of insulation, fireclay/sand, and laid the brick floor and completed most of the first course. not a terrible amount of work done, but i dont want to regret it in the future if i cant get the oven to get hot or hold temps.

what should i do?

thx

You've have probably gone too far to turn back now imo. Moisture barriers and holes in the oven floor, are relatively new ideas. Although, they are great ideas. Sealing the dome render from the elements is one. Sealing where the dome render meets the hearth is another. Waterprooofing/sealing the entry/ dome connection is also another one to think about. Leaving a reveal on the exterior of the outer entry arch with the render will allow for a storm door. If all else fails, most can figure something out for a "roof over". In my humble opinion, a roof over the oven will extend the number of days per year that your oven is useful and will negate most, if not all of your conserns.

just sayin'

[david s]

Mullins,

This my two cents: I believe that a vapor barrier is a little insurance on moisture wicking upward from the concrete hearth. And yes, a moisture barrier could trap water in the insulation, not giving it a a gravity fed means of escape. I agree that holes will aid in gravity feeding massive amounts of water. Buckets of water from a flood may, but the insulation has to exceed it's water abosrption capabilty before that will happen. You can hold a full sponge in your hand and it wont spill a drop. Most oven insulations act the same as a sponge.
.

I've been casting a hole in the centre of my supporting slabs for seven years now, not really new. In my design I have a recess in the supporting slab so a drain is even more important. I only use a single hole because my ovens are only 21" internal diam. For a larger oven I'd suggest three. You really need to over the hole with insect screen to prevent insulation (vermicrete) falling through the hole, or insects entering from underneath. In regard to your excellent sponge analogy Joe, I'd agree, but it actually works better than that, because as you heat the wet insulation steam pressure builds up and forces the moisture out the hole. I can't remember who it was (maybe cobbler dave) but someone reported that after getting their oven really wet, on firing it up hot water began dripping and streaming out the hole. I've also experienced the same thing firing a new empty kiln when the internal temperature reached around 400 C water started dripping at a pretty fast rate from the bottom of the kiln. Yes you do need to make holes in any plastic sheeting over the drain holes obviously. In my case I use an additive called Xypex, instead of a mechanical barrier, in the concrete mix, which apart from enhancing the concrete strength also makes the whole slab waterproof.

[joeykramer]

here's what i have done this weekend. i dont think that i have gone too far to start over. i am still trying to 'wrap' my head around the vapor barrier idea. let me see if i understand this correctly. The VB prevents moisture from coming up from the slab, but if i waterproof seal the final coat of the igloo all the way down to the floating slab, will that do justice from regular rain? i plan on putting some sort of counter top down,(not sure which). if the slab gets wet, i am assuming that even though the outside is sealed, water will still saturate the insulation from the pad when it gets wet, right?

and even if i don't redo it and just waterproof the outside, once the insulation gets wet, when firing up, the water needs to go somewhere, so does it take longer to heat up? or will i struggle to get high temps if the insulation is wet and can never really get it dry? what if i just drill three holes from underneath the slab to the top and carefully stop once i hit the insulation, will that do anything?

if i put the VB down, drill a hole in the center of the floating slab and barrier so the water, if it gets in through the door, has a place to go.

i figure i can break it down and put it back to where it is today in a couple of hours, i didn't get that far mortaring, my slab was level so only minimal leveling was needs under the brick. I am laying the first course on top of the floor and all the outside cuts are done with a chisel. didn't want to waste time making the outside perfect if it was going to be covered up.

[Gulf]

If you are going to go to all that trouble, you might want to also think about elevating the insulation off of the concrete hearth.

[joeykramer]

Ok i just called a supplier near me that sells FoamGlas. $145 for 36 sq feet, 2 inches thick. i think i might feel better about that at the end of the day...

Having not done much research on this product, do i just lay it down under the fiber board and thats it? no other VB needed? thanks guys/gals

on a side note, can someone teach me the right way to upload pics? i am hitting the paper clip button and attaching from url. pics are housed on google+ and i am copying the url from there and i hit Thumbnail.

[Mullins]

Camera button on bottom left is also an option, see attached photo

[admin]

Hi Joeykramer,

To upload an image into your post that shows as a thumbnail, you'll need to upload the actual jpg and use the camera icon on the left side. If you use the paper clip on the right side, it will upload as an attachment and you won't get a thumbnail. I am not aware of a way you can use the URL for a picture from Google+. You may want to create a picture album on the Forum and then use photos from the album in your posts.

Thanks,
Mitch

[joeykramer]

Lets try this....

[Gulf]

Ok i just called a supplier near me that sells FoamGlas. $145 for 36 sq feet, 2 inches thick. i think i might feel better about that at the end of the day...

Having not done much research on this product, do i just lay it down under the fiber board and thats it? no other VB needed? thanks guys/gals

on a side note, can someone teach me the right way to upload pics? i am hitting the paper clip button and attaching from url. pics are housed on google+ and i am copying the url from there and i hit Thumbnail.

Sorry for the late reply. I poured a foundation for an outdoor fireplace today (insert Dawg Tired emoticon here) . Foam glass is a great idea for someone who wants to both elevate and have that layer for extra insulation. I know that it is said that "you can't have too much insulation" but, you already have 4" of CalSil. If you have problems getting the foam glass, about 40 bucks worth of paver blocks and a piece of plastic film will work just fine. Place the plastic directly between the paver block layer and the CalSil. If you get the foam glass, you can skip the moisture barrier.

[RandyJ]

I would agree with Gulf. More insulation is never a bad thing, but unless price is no object you do need to make cuts sometimes and this could be one. You already have great insulation under the floor. I know that I doubled my budget I had set. None of witch happened till I started the enclosure and veneer. I knew all of the pricing up till the dome was done. The rest was unknown. With that said if you can swing it then go for the foam glass.

Randy

[UtahBeehiver]

Joey,

Since you already have 4" of CaSi, adding FoamGlas may be overkill. Even though I did the combo FoamGlas and CaSi IMHO, I think you would be better off raising your existing CaSi with pavers and a VB. That said, if you do add the FoamGlas it cuts really easy, like styrofoam, caveat, it is brittle to impact or abrasion.