Roxul RHT80 Hearth Floor

[thebigt]

Hi,

Has anyone used Roxul RHT 80 for the hearth floor? I was looking for Cal-Sil but the hardware place recommended this instead. I ended up getting the 3 inch stuff...Will this work or will it compress too much? Thanks

[Gulf]

Re: Roxul RHT80 Hearth Floor

Hi,

Has anyone used Roxul RHT 80 for the hearth floor? I was looking for Cal-Sil but the hardware place recommended this instead. I ended up getting the 3 inch stuff...Will this work or will it compress too much? Thanks

I haven't used it but, the little search that I just did tells me that it is not what you want. I think that it will compress "too much" under the loads of a WFO.

[shuboyje]

Re: Roxul RHT80 Hearth Floor

The compressive strength looks pretty low in their technical data. They give two ratings, but even the better of them is in the range a 2.5 psi. That number is at 25%. For comparison I've found data for Cal Sil putting it at 100 PSI at 5% in the same test, ASTM C165. I can't find enough on ASTM C165 to tell you the exact meaning behind the percentages, but can tell you that in the same material the rating goes down as the percentage goes down, so this really does not bear well for the Roxul.

[thebigt]

Re: Roxul RHT80 Hearth Floor

Thanks guys i really appreciate the advice...I will have to try and source out some Cal-Sil here...tougher to find in Canada as it mostly ships out of the US and the costs get pretty high

[thebigt]

Re: Roxul RHT80 Hearth Floor

I believe that I can source this locally will this work http://www.brockwhite.com/files/Reso..._Prod_Data.pdf

[Gulf]

Re: Roxul RHT80 Hearth Floor

I believe that I can source this locally will this work http://www.brockwhite.com/files/Reso..._Prod_Data.pdf

Thermagold 12 from Johns Manville is what I used for my oven. I think you will be fine. I hope you can get it for a decent price.

[thebigt]

Re: Roxul RHT80 Hearth Floor

Thermagold 12 from Johns Manville is what I used for my oven. I think you will be fine. I hope you can get it for a decent price.

Yeah I found it locally unfortunately it would cost me 250 bucks since I'd have to buy a case. I'm looking at trying to locate it cheaper.

[Gulf]

Re: Roxul RHT80 Hearth Floor

Yeah I found it locally unfortunately it would cost me 250 bucks since I'd have to buy a case. I'm looking at trying to locate it cheaper.

Ouch! that is high. I think the 2" thick has 7 pieces to a case. My oven is a little big, so that was a good number for me to insulate under the oven and entry. I used the extra for an insulated, though heavy, door.

Good luck on the search. There should be some "industial insulation supply" within driving distance that is cheaper than that price.

[vtsteve]

Re: Roxul RHT80 Hearth Floor

If you can get Foamglas, the insulation value is better (and no water can wick through from below). I capped mine with cal/sil, but I believe other members have put their bricks right on the Foamglas.

[pizzaobsessed]

Re: Roxul RHT80 Hearth Floor

If I can jump in, Im having the same dilema roxul is readily availible and inexpensive and says it can withstand temps of 1200F for my dome is that enough?

[adm]

Re: Roxul RHT80 Hearth Floor

If you can get Foamglas, the insulation value is better (and no water can wick through from below). I capped mine with cal/sil, but I believe other members have put their bricks right on the Foamglas.

I am very interested in this....currently trying to figure out whether a 4" layer of Foamglas on top of a 6" reinforced concrete slab will work to sit my firebrick hearth directly on, or whether I should add a 2" layer of CalSil board as you did....

(I want to use the Foamglas instead of Thermalite/Cecon blocks due to the resistivity to water)

[UtahBeehiver]

Re: Roxul RHT80 Hearth Floor

adm,

I used 2" of FoamGlas with 1.5" of Ca Sil, my logic was Foamglas does not absorb water but is is fragile and does not take abrasion well. So you have to careful when laying the floor, Ca Sil was more forgiving. All Foamglas or a combo works, up to you. One thing I would do if you use FoamGlas is slather the edge with leftover mortar which acts as protection buffer from your toes as you build your dome or work on your oven. Good luck

[adm]

Re: Roxul RHT80 Hearth Floor

Thanks for the swift reply Russell,

Good point on the fragility of the Foamglas. I think I will plan to use 2" Foamglas and 2" CalSil under my firebricks.

I am just reading through your build diary now - very inspirational as I am pretty much set on a corner build like yours.

Cheers,

Alasdair

[vtsteve]

Re: Roxul RHT80 Hearth Floor

Yes, I also parged the exposed edges of the Foamglas with left-over mortar, leaving a gap so it couldn't wick water through the parging. Before I did, every time I brushed it there was a stink of sulfur and a dusting of powdered glass (it's foamed with carbon monoxide and hydrogen sulfide - don't cut a lot of it in a confined space!).