Can you post a picture?

I've only ever been involved with tuckpointing as a means to replace mortar that eroded away which I'm assuming hasn't happed with your fireplace. Is the existing mortar flush with the stone now? If so, placing additional mortar might result in an overgrout look as below:

I hesitate to suggest this but you could consider painting the black grout. It would be tedious work but not that much more labor intensive than tuckpointing. Please post photos of your finished fireplace. Good luck!

I agree tuckpointing is not what you need that mortar will then be too prominant. Since the FP does not look functional painting the grout is probably the best solution but please not white so look for the new color from the stone.

It is a fully functional fireplace, equipped with gas logs.

what kind of paint should I use? Thanks for your advice.

In case anyone is following, I had a brick mason look at the FP and he suggested staining the grout gray. I bought the stain at S.W. and will see how it goes.

Hi, How's this looking now? I'm getting ready to change the mortar in my brick fireplace. I saved this discussion as a reference since yours turned out so beautifully!

@Joan Head I checked the SW site and looks like there are a few options for concrete stain. Do you recall which one you used? Thanks

I couldnt be happier

with it. it was tedious work but so rewarding.

Thanks so much, I found it. As soon as I finish painting the walls, I'm going to give it a try. Here's what I'm working with. Tedious indeed!

I have a huge fireplace and did it in one day......time well spent.

Sure it’s hard to find info on just changing the mortar color, so glad iI found this thread! @tozmo1 please share pics when done!!

I would suggest you start an area on the side where it won’t be noticed to get comfortable with the tedious painting. I guarantee you will be thrilled with the results. It gave such a updated feel to the entire room. I am SO glad I didn’t whitewash. That may be the right choice for those who don’t like the organic feel of rock but, in my case, I thought the stone was beautiful but the black mortar was the focus.

@ruehles Hope to get to it soon. Finally finished all the painting I could until the room's drywall ceiling is replaced, so maybe this weekend I'll get started on the fireplace. Too hot to trim my hedges. Thanks for the motivation to get started on it!

@Joan Head I'm with you on stone and I feel the same way about attractive brick. Why cover it up? I think my brick is very nice and will work well with the room. Just need to get rid of that black mortar. I snagged the SW stain during a 35% off sale, so nothing stopping me now.

I hope you’ll post a pic. Just get the music going, paint and enjoy watching the beauty unfold!