leveling and backfilling FB insul board

[waynespizzaworld]

My FB board got a little beat up in shipping and some of the edges are bashed and some thickness irregularities as well. I will try my best to sink the thicker pieces into the structural hearth at the time of its pouring to level out the top surface of the FB Board somewhat. I am wondering about kind of back filling around the FB board with vermiculite mix to hold it in place and also to fill in under the vent landing and oven landing as part of my vent and oven landing will need some build up to support my bricks to the same level as the rest of the FB board.

So my questions are........

1. I understand the FB board has been treated to handle moisture better than other insulating boards, but what about the cut edges. I am guessing this coating or treatment is only on the surface so when I cut into this board is it still safe to back fill vermiculite and portland cement mix to its sides?

2. I have read in the instructions for the FB board to be dampened before laying brick on it. Because my board is a bit beat up and the corners that are smashed have gone a bit soft I just want to check if others have had to deal with this and if they were concerned about moisture in this part of the process with a softened and crushed product.

for what its worth if I was shipping something all the way to Canada I would double check it was in good condition before it was sent and that it had proper packaging to ensure a safe delivery. A cardboard box does not cut it in my opinion. I would have paid extra for it to arrive safely or else I would not have ordered it at all.

[splatgirl]

Re: leveling and backfilling FB insul board

#1. yes. It's going to all dry out eventually anyway, and the water it will absorb from the vermicrete is going to be the proverbial drop in a bucket vs. what it will see from your brick work. You can level the surface of the board with dry refractory sand or brick dust before you lay your hearth bricks.
"Backfilling" around it with vermicrete to hold it in place isn't at all necessary. I wouldn't and didn't bother. As far as having to have something to level out the height between your /hearth/vent and the landing in front of the vent, vermicrete is certainly a viable option, but I would wait until you're to that point. Decide on what you're going to use for a landing material BEFORE HAND, otherwise you're just guessing about the height. Unless you know the exact thickness of the finish material you want to use there, that is.
#2. no.

My boards arrived as you describe and not at all flat or of even thickness. Smush it back into shape and proceed. It's not going to make a lick of difference, but I do hear you on the complaint. It's annoying.

[Tman1]

Re: leveling and backfilling FB insul board

As an added bit of info/suggestion.. I wouldn't cover the FB board until it's dried out

[Neil2]

Re: leveling and backfilling FB insul board

"I will try my best to sink the thicker pieces into the structural hearth "

I would avoid this type of detail. You will be creating a "bathtub" that will hold moisture and water, both during the build and in the future if moisture enters your oven.

I suggest that the top of your structural slab be one even plane with a slight slope towards the front.

[sjmeff]

Re: leveling and backfilling FB insul board

I would contact FB about this. I recall other posts about them replacing boards damaged in transit.

[waynespizzaworld]

Re: leveling and backfilling FB insul board

"I will try my best to sink the thicker pieces into the structural hearth "

I would avoid this type of detail. You will be creating a "bathtub" that will hold moisture and water, both during the build and in the future if moisture enters your oven.

I suggest that the top of your structural slab be one even plane with a slight slope towards the front.

not sure if you understand what I meant here.....as one piece of board is 1/4" thincker than the rest that is the only piece I would kind of set a bit deeper into the hearth. Instructions say its ok to place these boards on hearth when the cement is still wet so I figures I would just squish the one board in a bit extra like 1/4" just so the tops of all board is somewhat level to each other. I will be setting my brick to insulating board with super 3000 mortar which does not like to be used in thicknesses greater that 1/8 th so I figure I need a level surface to the boards before setting my brick floor into the tops of the FB board......hope this makes sense and I am on the right track.

Has anyone else done this to make up for uneven thickness in the FB board?

[splatgirl]

Re: leveling and backfilling FB insul board

The variation in insulation board thickness would be better addressed with dry sand under your hearth bricks (or by rasping down the board if you are adverse to option a.). Your solution seems like the worst option, IMO. What Neil said is valid. If a portion of the surface of your hearth slab is lower, it's going to be the natural point where water would collect, vs. a flat, ever so slightly pitched slab that would drain water if it ever needed to.

Is there a reason why you want to mortar your hearth bricks down? It's not advised.

[waynespizzaworld]

Re: leveling and backfilling FB insul board

thanks Splatgirl for your help......because I was not sure about sanding down the top layer of the FB board as I thought it was treated with some kind of surface prep and did not know if it was ok to sand it down I did not consider that. If it is ok to sand it down then that is what I will do. Thanks for the tip!

I plan to have a gazebo roof structure over the oven so cant really see any water getting in but maybe you have a point. This is my second oven and the first one had the vermiculite treatment at 5 inches and that is what I think I will do for my third oven as well. At least its flat and cheap....My FB board was over 350.oo delivered to Canada and so far I am not impressed.

Regarding your question on setting the brick on fireclay and sand I think on my photo album for my first build I had mentioned that that was what I was going to do, but I instead used my super 3000 mortar when it came down to laying the floor. I just dont like the idea of the bricks not being locked in place during the build. My mind is still not made up for this build but at this time I would like this post to stay on the one topic or my questions will clouded with other issues............thanks for the help and I welcome more form others that can feel my pain............wayne

[splatgirl]

Re: leveling and backfilling FB insul board

I hear you on the FB board. Faster, though. Or not. In my case the latter.

I am not aware of the water resistance feature, but my build using the FB product was two years ago, so perhaps it has changed. If you are really worried about rasping but feel that is the route to take, you could set the rasped side down facing the hearth, so that the "finish" side would be the one seeing the moisture from setting brick. Just a thought...

[dmun]

Re: leveling and backfilling FB insul board

or by rasping down the board

and did not know if it was ok to sand it down I did not consider that. If it is ok to sand it down then that is what I will do. Thanks for the tip!

I'd really avoid any more airborne insulation particles than are absolutely necessary. I don't think this is a good idea at all. If you do this, use a respirator, protect your lungs.