I notice the brick mortar on my outside window sill is crumbling in certain joints. It’s only on one window sill as shown in the pictures below. I would like to repair it. My plan is in the steps below. I’ve never done this before. Is there anything I’m missing or should be careful about? The joints are 3/8” wide. Thanks

Steps:
-clean out the old mortar using a hammer and flat chisel (not sure if I will need to use my angle grinder with a concrete blade or not)

-dust out the brick joint using compressed air

-mix some mortar and fill the joints using a pointing trowel

-finish the joint with a flat profile for better drainage since the window sill is flat

-mist the mortar twice a day for two days to help it harden

 

I'm no pro, but last summer I dabbled with repointing some brick. Sounds like you've got the right idea. You don't have to chip out all of the mortar, just about 1/2"-3/4" deep and anything that is crumbling. The verticals are the hardest part to make look nice. I've seen people put the mortar in grout bags or even a strong ziploc with the corner cut so you can pipe it in like decorating a cake.

Looks like a tight area so the grinder won't get all the way into the corners but it will get the face of the sill (vertical joints) pretty well. You gotta be careful to only grind the mortar and not the brick - it can get away from you fast.

Before you put the new mortar in, mist the bricks to get them wet so that they don't try to suck all the water out of the new mortar.

I have brick sills as well and I installed a drip edge above the window so that the rain doesn't drip directly onto the sill, but rather just beyond it so it helps to keep from eroding the bricks. Your bricks look like they might be spalling - hopefully someone with more masonry knowledge will chime in about that.

 

If you've never done brick work wear gloves. Many new people find it hard to not use their hands.

Also, make EVERY effort to not let the mortar touch the face of the bricks. Mortar will leave a white stain wherever it touches and it's much easier to not make the mess in the first place than to use acid and clean it off later.

 

As I remove the old mortar I notice that usually the 1/2" of mortar before I reach the window caulk is in good condition. Do I have to remove this 1/2" of old mortar right up to the window caulking or can the new mortar dry against the old mortar here? I'm just wondering about water penetration. Thanks

 

No you only need to remove the loose material!

And mortar is not waterproof.

Ive also never heard the misting part, mortar will set up in a couple hours so that is not going to do anything.

Also, if you get small amounts on the brick an old tooth brush and water will usually take it off!

 

Mortar, just like any cement product cures via a chemical process. It doesn't dry. It will cure and get stronger and stronger the longer it remains moist/wet. If it dries out the curing process stops so concrete or mortar can be covered with plastic or sprayed with water to allow more curing time and greater strength. Generally 28 days is considered a full cure when it has reached it's full potential strength though it can actually continue to get even stronger with time.