I have a "rustic" river rock chimney / fireplace setup. My mortar is getting pretty bad in certain spots with cracking. What product can I use to patch it up, how do I go about color-matching it, and is there something I can use with a needle to inject the patch into crevices?
Any pics? Is the mortar loose and crumbly or just cracked and separated from the stones? The cracking is usually a result of freeze/thaw cycles in cold climates. Very common problem here in Southern New England. Long life clear silicone caulk (GE silicone 2 is really good) works well and lasts vs trying to tuck point cracks with mortar. A good water repellant (not sealer) should be applied prior to caulking. I've successfully repaired many chimneys with similar issues over the years as a professional roofer. There are "color matched" caulks that stick out badly to my trained eye. My late father (whose roofing business I took over in 1988) did this to repair leaks on chimneys after discovering it on his own house in the 1960's. Chimneysaver clear water repellant is a great product I've been using for nearly 30 years.
It’s cracking for one of only a couple reasons. Either the footing is moving or you’re getting water down through the top of the cap and it is freezing/thawing and pushing the stones around. Usually it’s the cap allowing water inside.
Another reason masonry can crack. Flues that are motared in solid and burning creosote expanding rapidly. Along that same line a large rapid increase in temperature can crack masonry. You'll want to figure out why it's cracking. Caulking can work if it's structurely sound enough to be safe. Matching color begins for me with trying to match the color sand that was used. That's a big determiner. Then the type cement used to create the mortar. Whitish is Portland type 1. Greyish is Portland type 2. A bath with muriatic acid a few days later will bring out the sand color and age it more like the original. They make mortar bags with nozzles for tight crevasses. I've used one just once in 40 years. Chances are you don't need one.
