Located between patio slabs at a house in Southern California. Am looking to possibly replace it during the cosmetic repairs planned for the area. Even if I don't replace it, am wondering what this stuff is called and what it's supposed to do.
this post was submitted on 25 May 2026
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What is this thing?
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That looks like a hard plastic, which is weird.
Usually they use something flexible for "expansion joint filler", like flat foam https://www.bunnings.com.au/sika-10-x-100mm-x-25m-abelflex-expansion-joint-filler-foam_p1060067
Also there are types designed simply to reduce the volume of a flexible filler (black polyurethane?) needed to fill the gap with caulking guns. https://www.bunnings.com.au/sika-13mm-x-50m-abelrod-gap-filler_p1060406
Both of those suggestions seem to agree with the planned maintenance: grind down the "peaks", remove that zip strip, use filler materials (like those and caulk over the gap filler), then float in the "valleys". After all that, paint the entire thing to help cover up the minor imperfections.
Yeah, not the very best solution, but the house is going to be sold and the next owners might tear the whole patio out in order to build an ADU (Accessory Dwelling Unit, aka: Mother-in-law Apartment, aka: Dower/Dowager House).