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Hi, tiling newbie here,
I have recently removed the tiles from our fireplace hearth and I am wanting to retile. My current plan is to level the concrete slab with self levelling concrete to be flush with the hardwood, and then a layer of mortar, followed by Hardie concrete board over the top of both surfaces to even it out. Unless anyone has a better idea? Currently the concrete portion of the hearth sits about 10-20mm below the wood portion, and I think the previous tile job was done with just concrete and mortar directly onto the hardwood and concrete slab , but I have leftover board so I thought I’d use it.
My main question is, do I need to use a special type of grout or mortar? The fireplace is a standing box so the tiles probably won’t get that hot. But I worry about the grout if any embers fall on it. Ideally, I’d like to use Dunlop flexible coloured grout as I’ll be using that in the bathroom as well.
Any advice is appreciated 
Hi @kaitolin,
Dunlop Flexible Tile Grout is only designed to withstand up to 70 degrees Celsius, so in normal operation, that would likely be fine, but not in the event of combusted material falling out of the fireplace. Given the purpose of a hearth is to withstand higher temps than normal operating temps, this product would not be suitable. You'd need to use a refractory grout specifically designed for grouting hearth tiles, and unfortunately, I am unaware of any products that would suit your project.
I thought I'd double-check the requirements for the tiles. Our Decor8 brand can be used for hearths, and there are no safety concerns there.
The James Hardie board would need to be installed as per their installation instructions and only if it complied with the requirements for hearth construction from the fireplace manufacturer and construction codes. James Hardie cement sheet and board products were not designed to create hearths, so you'd need to rely on the testing and advice of the fireplace manufacturer.
Given the above, it might be best to enlist a professional tiler with experience with such projects. As mentioned, these products might be fine under normal use, but when something goes wrong, like a log rolling out of the door, they need to work.
Please let me know if you have any questions.
Mitchell
