Replacing basement windows in cinder blocks.

This polyurethane based masonry caulk is amazing

Loctite PL 10 fl. oz. Polyurethane Concrete Crack and Masonry Sealant-1618522 at The Home Depot

so I want to use this as the main sealant and then mortar over it for a nice finish.


Can I brush on a masonry bonder slurry to the cured poly caulk and then mortar (mixed with water plus more bonder) over it and not worry about the bonder/mortar eating away at the poly caulk?

 

You can try tossing some dry mortar onto the wet sealant after you have troweled the sealant to a watertight finish. That will cause some of the mortar/sand to stick and give you texture to the joint without having to fiddle with one over the top of the other. Blend the repaired sealant with paint once it had sufficiently set up. My fear is that the thin mortar joint will not hold up to the weather over time and fall out.

 

well I heard back from loctite, and they said they don't recommend putting mortar or sealant over the Loctite PL S10 Polyurethane Concrete Crack & Masonry Sealant.
So it's either just caulk, or composite trim after caulk, or caulk then tool and dust with sand that matches existing finish, and/or paint the s10 which it says is okay.
I don't trust mortar not cracking from settling, harsh weather etc.

 

chimney separating from house, chimney settling separation repirs - YouTube
this stucco guy posted a video of the exact same scenario (stucco/mortar over bonding agent over polyurethane masonry caulking over great stuff), and addresses the questions of if they're all chemically compatible, and answers yes, but sort of rhetorically and sarcastically. So he has probably made this same repair years ago and it's holding up fine in case anyone's wondering if each chemical won't like eat away at the other and ruin the seal, although loctite told me something like 'it's not suggested' , they might have just not wanted to answer something they didn't test.

 

I like Z's suggestion of embedding some mortar into the wet caulking. That should hold up ok. I doubt that mortar applied to caulking will hold up long term! It may bond ok to the masonry on the side but not to the caulk.

Not sure I understand the aversion to just caulking. I've caulked 100s of windows to block and never felt that the caulking looked bad provided it was done neatly.