How do I expose the stones in this section of wall that I'm repointing?

Hello guys,

Fledging DYI'er here. Happy to be on board. Will post any results back here in case it's helpful to someone else in the future.

I'm repointing an old stone wall that used to be a kitchen firepit in this old farmhouse.

It was going great... until I got to the lower third of the wall. The stone here is covered with some kind of tough layer of sand/soot/old mortar/something and I can't figure out how to expose where the stones are without damaging them in the process.

In the attached photo, I've highlighted the regular area in green and the lower area in red.

I have a power chisel, but if I use it here, I could just be chewing into stone and don't want to damage them.
I have a pressure washer, but this is indoors and well... I don't know how good an idea is.

Could it just be one large stone?

Is there some method of cleaning, some chemical or product I could try to see if I could figure out what I'm dealing with here?

Thanks for any help or insights. I'm stumped with this.

Hi Mark. Looks like one big stone to me. Could it  be the bedrock? Very neatly chisseled off?
If it isn’t then joints have to walk through the highlighted bit on your pic.
Could be some old cement mixed in with bits of the same stone your wall consists off. Then just try to get in there from the upper joints down. Using a chissle and hammer. Place the chissle right there where you expecr the joint. Place it standing up and hit down. If a crack appears hit it from another angle into the empty space so to say.
If there is no joints and it’s bedrock you have three options. Leave it be in it’s glory and be done with it. Or render over the whole thing. Then you come more into the room. Or three break it with the hammerdrill and then render over it. Respecting the level of your wall.
Depends on time and money, and if you have more to do than just this.
Hope this helps.
Ps i’ll be off rendering in a minute.

Hugo Morvan wrote:Hi Mark. Looks like one big stone to me. Could it  be the bedrock? Very neatly chisseled off?
If it isn’t then joints have to walk through the highlighted bit on your pic.
Could be some old cement mixed in with bits of the same stone your wall consists off. Then just try to get in there from the upper joints down. Using a chissle and hammer. Place the chissle right there where you expecr the joint. Place it standing up and hit down.

Thanks! That was helpful. Not sure why I didn't think to just determine the edges of that big piece to verify it was actually a single piece. Here are the photos of a couple of new joins I found.

If someone knows a way to expose these joints through a cleaning process, I'd love to hear it. Otherwise it's gonna take me forever to figure out what is stone and what isn't and I'd love for there to be an easier way.

If there is indeed a layer of mortar or something of the like over those stones, it appears to me to be in sound condition which makes me think that the mortar holding the stones together is good and doesn't need point tucking.

James Freyr wrote:If there is indeed a layer of mortar or something of the like over those stones, it appears to me to be in sound condition which makes me think that the mortar holding the stones together is good and doesn't need point tucking.

Hi James, thanks for the reply.

I wish you were right. Sadly, although the outer layer of whatever-the-hell-it-is is has been baked tough by the old fire pit, underneath it's basically just wet sand that absorbs moisture from the ground and brings it into the house. The drainage on the outside is also being fixed. This mortar though is around 150 years old, soft as manure, a little moldy, and in need of repair.

Someone recommended I try a bushing tool on my SDS drill. Gonna give that shot. Will post results.

All suggestions welcome in the meantime. Thanks.

A question on mortar... What kind of mortar are you thinking of using?

Old stonework is all done with lime mortar, which is generally softer than the stone and self-heals to a degree if cracked. Much recent repair of old stone/brickwork uses modern cement mortar which is totally rigid, may be stronger than the stone/brick, and leads to damage.

What is the chance that the lower part of this fireplace wall was repointed/rendered with cement mortar?

Glenn Herbert wrote:A question on mortar... What kind of mortar are you thinking of using?

Old stonework is all done with lime mortar, which is generally softer than the stone and self-heals to a degree if cracked. Much recent repair of old stone/brickwork uses modern cement mortar which is totally rigid, may be stronger than the stone/brick, and leads to damage.

What is the chance that the lower part of this fireplace wall was repointed/rendered with cement mortar?

Hi Glenn!

Under the black surface, it's like a fine brown/beige powder, darker brown and denser at the surface (apart from the black soot top later) then turning slowly into dryer, looser beige powdery material the deeper in the wall you get. Makes me think of lime a bit now you mention it, because it's so pale. Although definitely not white.

I'll use whatever mortar is on the other stone walls in the house. Will need to ask a family member what mortar they used on them. Not sure atm.

Lime can often mix up as a light grey colour.

Just to update this, after trying many things, turns out I need a screwdriver, a dense wire brush, a crapload of time and a crapload of effort.

When the wall is done, I'll post here with the methods, tools and chemicals I tried, what worked and also some images of the finished wall. Looks like oven cleaner is good for taking soot off stone. But that thick layer of baked-solid mortar just requires a ton of work.