Caulk fi x wouldn’t be issue if mortar were classic lime
Q: My 10-year-old house developed some cosmetic cracks in the mortar. I got some bids to have tuckpointing work done and nearly gagged. I’m wondering about using a special caulk I found that’s made to repair mortar joints. It contains fine sand so it’s textured and the color matches my mortar. I did a test in a small area and am really satisfied with the appearance. It seems too good to be true. Is this the Holy Grail of mortar repair? What could go wrong? — Aaron W., Prosper, Texas
A: Before we discuss your magic caulk discovery, let’s talk about the permanence of brick mortar. What would you say if I told you that your bricklayers could have used a mortar that’s been in use for over 4,000 years and is still in great condition?
What would you say if this mortar had the ability to heal itself and repair tiny cracks in some cases? I knew you’d be interested. If your bricklayers had used hydrated lime mixed with the sand instead of regular mason’s mortar mix, you’d probably not need this caulk you discovered.
Hydrated lime is a building product that’s rapidly slipping from history to legend to myth, just like the golden ring in J.R.R. Tolkien’s “Lord of the Rings.” I’m doing my best to ensure the wonders of lime mortar live on.
Let’s contrast it to this caulk. I’ve not used it, but I know that no caulk, no matter what it contains, could equal the lifespan of lime mortar. When you mix hydrated lime with water, it transforms back into limestone. We all know how long-lasting limestone can be, as many of our federal buildings and monuments are faced with this durable stone. Sand, which is nothing more than tiny pieces of rock, makes up the rest of the mortar.
The chemicals used to make the caulk will succumb to the ultraviolet (UV) rays of the sun. It may take a decade or two, but the sun’s UV rays breaking apart a flexible caulk would be like you trying to tear apart a wet paper towel.
I’d also be concerned about the color fastness of the caulk. It may match your mortar now, but will the color pigments withstand the UV rays in two, four or 10 years? If the color does fade, what do you do?
What about long-term adhesion? The caulk may work really well now and develop a tenacious bond with the mortar. What kind of mess might you have on your hands five or 10 years from now if the bond fails?
In all fairness, I’ve seen some high-quality commercial-grade caulks used to fill expansion joints on large exterior brick walls. Some still look good after a decade.
There may be another solution. You may be able to spray onto the brick and mortar a clear water repellent that’s got a very high solids content. It’s possible the liquid may do a great job of repelling most of the water you should be worried about.
I’d spend hours and hours researching clear water repellents and doing due diligence to see what other users have experienced. Here’s hoping you’re able to locate that magic liquid, should it exist!