Need product/method recommendation for plaster on a fireplace mantel

Hey all, new to the forum, but have done research here before. Thank you in advance for any assistance.

I have an extremely un-even, stone fireplace. I needed to build a mantel for it and the only real option was to use wood and then put a plaster or stucco coat over it. I have built the wooden box to be used for the mantel and installed diamond lath over the top. I was wondering if someone could recommend what type of product to use to make a decent smooth surface that won't crack too much given it will be exposed to heat. The the bottom of the mantel is 6" above the opening of the fireplace and will need 1/2" of coverage to be up to code. I will be attempting to put a "rough sawn wood" texture on the front face which will be painted. I don't need to blend it much as I have room to push the plaster right up against the rock and then use a sealer and paint.

Initially, I am thinking I will be using 5:1:1 sand:lime:crete for the first two coats (making them as wet as possible and wetting them throughout the drying process). Then Victas for the top coat. That said, I worry that the victas will be too difficult to work with for a finished look. I have never done this (although I have a lot of experience with concrete and some experience with stucco). I'm good at finish troweling and have little worry about that when doing crete, mud/taping, floor leveling, etc.

Again, thanks for any assistance or suggestions.

Any photo's available.

Here is a photo of the mantel in it's current state, ready for coating.

Not wishing to denigrate your hard work, I'm wondering if you're going about this the wrong way. You've got the pseudo lintel a bit too close to the fire opening, and that's why you're having to make it pretty much fireproof. I'd have used a green oak beam (easy to cut and work) and set it a little higher up. You could use a 125mm angle grinder with a diamond blade to cut out the stone facing, then drop the beam in on a couple of studs, and bed it in with resin. the drawback to this method, is you need to leave the oak to dry and shrink before it can gonon the wall.

The sand lime crete mixture will make the mix more flexible for the heat, but I wouldn't make it too wet, or it'll just drop off. As the Victas is heat resistant, why didn't you screw plasterboard to the wooden box, and the just use the victas.

Well, I hear you... but the stone is not just a face.. It's 5" thick solid stone, cutting it out was not an option unless I were to bring in a diamond blade demo saw, and even then, I don't know that it would have been realistic. So, I had to go this rout. I have 5 1/2" clearance from the top of the fireplace opening (definitely looks like less) so that should be ok.

As for the plasterboard, I have no answer... I am an amateur at plaster, so maybe I should have gone that route. The last fireplace I had was a kiva style that was completely made out of metal tubing and diamond lath. So I figured I would use lath again because I had success with it before.

I am wondering if the Victas is as difficult to finish as I have read. Any input about the product is appreciated.

Boy you've taken on a job there. I can now see where you're coming from, and I think you've done quite well under the circumstances.

Unfortunately, I don't have any experience of using Victas yet, but I'm building a pizza over later this year, hence my interest in this thread.

Having looked at the installation instructions, I wonder if it's necessary to use the sand and cement mixture, and just go straight for the Victus.