DIY Overgrouted Stone Fireplace

When we thought about the cozy lived-in feel we wanted to create for our living room, I immediately knew I wanted to do a DIY overgrouted stone fireplace.

There’s something about the look that, to me, feels modern and like an old cottage at the same time. Plus, as a DIYer learning how to overgrout a stone fireplace, I liked the idea that it’s supposed to look a little bit messy and organic (read: it’s forgiving if you aren’t perfect at it).

I already recapped the how to build the fireplace surround and how to add the stone veneer, and there are a few more reveal photos here, but let’s get down to the nitty gritty of how we made the overgrouted part of the DIY overgrouted stone fireplace.

Note: We obviously had made the fireplace ourselves in the lead-up to the overgrouting process, but most of the other DIYers I’ve seen take on this project do it as an update to their existing fireplace. So, this tutorial is applicable to a new build or to update an existing stone fireplace!

Tools & Materials

• Mortar (we used a Type N mortar for large tile and stone)
• Grout piping bag (this is found in the tiling section of the hardware store and looks like a cake icing bag)
• Cement dye (optional, but we used the colors Buff and Charcoal)
• 5-gallon bucket
• Drill
• Paddle mixer attachment
• Jointing tool, shim, putty knife, or other tool to work the mortar into the grooves
• Stiff masonry brush
• Grout sponge

Mixing the grout

This process is messy and makes you feel like there’s absolutely no way you’re doing it right, but I watched approximately every YouTube videos of how to overgrout a stone fireplace before I got going and being that the finished result is exactly like I wanted, I think maybe that self doubt in the middle is just part of it.

Here’s what it looked like pre-grouting:

I started by mixing up about half of the bag of mortar with the paddle attachment on my drill, and I added roughly 12 drops each of Buff and Charcoal cement dye. This color combo was the same as what Chris Loves Julia used in their overgrouted stone fireplace, but I used more of a 50/50 ratio for a slightly darker grout color.

Note: I tend to use the words ‘grout’ and ‘mortar’ interchangeably throughout this post, but to clarify: the process is called overgrouting, even though the actual material used is mortar.

Once the mortar was mixed well (it should be a quite thick, peanut butter-type consistency), I used a sacrificial wooden spoon and added spoonfuls of it to a grout piping bag until it was about ⅔ full.

I cut the tip of the bag so the opening was about an inch wide, then gathered the back opening of the bag so it was closed and pushed the mortar toward the open tip. Once all the air was out of the piping bag, I tightly twisted the back end of the bag and kept going until there was a steady stream of the grout coming out.

This is a surprisingly intense forearm workout to keep twisting and pushing, but the process is essentially just filling it into all the gaps between the stone until it’s just protruding out beyond the stone face. It honestly feels like piping a cake.

Where I went wrong

The piping took about an hour for me to get the whole way through the fireplace, and I was so anxious the whole time. I started this project at like 8 pm once my kids were asleep, and I absolutely should’ve waited for a Saturday morning so I’d have all day to mess with it afterwards. Learn from my mistake.

What’s supposed to happen is that you wait an hour or so after piping to begin ‘tooling.’ This is when you use a tool like a brick jointer (or a shim or similar) and indent the grout to flatten it out once it’s a bit more workable and give it that final look you’re wanting.

The mortar should not be fully set or it’ll be too hard to work with, but it also can’t be too sloppy still, so it’s meant to be a bit of a Goldilocks of a crumbly texture in between.

But what happened to me was a different story.

Once I had finished piping and waited an hour, it was about 10 pm when I should’ve been able to start working on it but this thing was still like cake batter up in those joints. Nowhere near set.

I waited up until midnight and it was still way too wet – when I tried pushing it into the joints, it was just ending up all over my jointing tool like when you try to check a cake’s doneness in the oven and the batter comes out on your knife.

I went to bed and set an alarm for another two hours later and when I woke up it was better, so I started working, but even then only about half the fireplace was at the level I needed it to be, so I went to bed and woke up AGAIN at 4am to do the other half.

After doing some researching and honestly just guessing, I think it could be the crazy humidity we had in Florida that week that caused it to take so long to cure (plus the quite thick gaps I had between the stones for my cottagey look) so I think my situation might be an anomaly.

Anyway, onto what you actually care about: how to overgrout a stone fireplace.

When and how to tool the mortar

Once the mortar was (eventually) at the crumbly stage, I used the jointing tool to just lightly push the mortar in at the gaps to make it flush with the stone. Around the stone face, I blended the mortar over the edges just a little bit for the more organic, old world look.

Tip: Using a stiff brush (like a craft brush or a grout cleaning brush) makes it a lot easier to blend over the edge of the face of the stones.

Cleaning it up

At this point, it still looked pretty messy. I posted a progress update about how to overgrout a stone fireplace on social media which ended up being seen by millions on multiple platforms and got a ton of hate messages (including death threats, which is wild), but it wasn’t done yet.

To soften the edges of the stones, I went back in the next morning with the stiff brush and some soapy water (probably about 12-16 hours after piping the mortar), and went lightly over the stone face to remove extra mortar. On the grout lines, I used soapy water and a grout sponge to soften those lines for the smoother look that I wanted. I also switched out with a wire brush on the really stubborn areas.

There was still some grout haze on my stone faces, though, so after another day I put some vinegar in a spray bottle then sprayed it onto the face of the stone and wiped off with a clean sponge after a minute or so.

I’ve read that some people use muriatic acid (which is often used as a swimming pool chemical), to get really stuck mortar off the face of the stone, but it’s very strong and I didn’t want to damage my stone veneer so I stuck mostly with the vinegar and the scrubbing.

The result

I am so happy with how it turned out!

It’s a little hard to explain just through photos but it just feels so cozy and like this overgrouted stone fireplace was always meant to be here. Also, since finishing this project I’m noticing overgrouted stone everywhere. There was an overgrouted stone wall in one of the fancy Italian villas in Succession recently, and if it’s good enough for the Roys then it’s good enough for me!

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