Hello Theo. That is correct on both points. PEI 4 or 5 is required in a garage for the proper wear characteristics. You need to refer to the DCOF (dynamic coefficient of friction) rating of an individual tile to determine its slip resistance. However, the original question had to do with the thickness. Most PEI 4 and 5 tiles are floor tiles that average 5/16″ – 3/8″ thick. These tiles typically have a compressive strength of well over 20,000 PSI. This is not to be confused with “breaking strength” which is how much weight an unsupported tile will withstand over an unsupported span of a particular length.

After some research I did, it seems that PEI (Porcelain Enamel Institute) rating has nothing to do with compressive strength of the tile. It is only about the hardness of the surface.

“It should be noted that the PEI rating involves testing of only the surface wear layer of a tile’s enamel glazing; it does not measure the fracture strength of the entire tile, nor does it offer any rating of the slip-resistance of the tile.”

Hi John. The thickness does not matter as much as the PEI rating. You need a 4 or 5. Most PEI 4 or 5 rated tile is 5/16 – 3/8″ thick. It’s the compressive strength of tile that matters, not the breaking strength. Most PEI 4 or 5 tiles have a compressive strength of greater than 20,000 lbs per square inch.

Hello Alex. At a minimum, it’s going to require an aggressive sanding and chemical wipe with denatured alcohol. We suggest that you contact customer service at Laticrete or Custom Building Products and discuss the situation with a tech. Paint definitely has to be removed, but quality coatings can be adhered to the concrete much better. They usually have a required thinset and prep requirements for actual coatings. We recommend a type of epoxy grout. KeraPoxy is an example. It does not require sealing (sealers will not adhere) and resists staining extremely well.

What needs to be done to an epoxy floor to prep for tile? It’s good industrial epoxy and very well bonded everywhere so I’d really like to not have to remove it.

What’s the best grout to withstand spilled oils, etc?

Thanks!
Alex