As we transition into the autumn season, we see more and more fall decoration in the stores. I spotted an isle full of ghosts & candy the other day and it inspired me to talk to you about the phenomenon of “Ghosting” in Polished Concrete.
When concrete coatings contractors talk about “Ghosting”, they are referring to what happens when a patch or previous coating under what they are putting down “shadows” or “ghosts” through their next coating.
For example, sometimes when lots of repairs / cracks/joints are being filled with Quick Patch/Quick Fix/Flexible Joint Fill (or utilizing another repair method) and then a texture system is placed over top of it, you may see the repairs / cracks “shadowing” right through both of the grout coat and the texture coats.
The same thing may occur when something has been sitting on slab for years and years and now is removed and you coat over it with texture . . . the ghost of what was previously sitting on that spot may show through.
Tile Ghosting may not be an issue if your texture is varied and/or stain is on the dark side (+ the repairs in the floor are minimal), but you should be concerned about it happening when your polished concrete coloring is lighter and you have to do many repairs.
When coating over a slab with PermaFlex or colored epoxy, ghosting is not a concern but when a texture system is going down, it is definitely something to consider or be concerned about.
Why does concrete shadowing occur?
Well, to put it simply, polished concrete ghosting occurs because the texture is absorbing into the slab differently than it is in the patched/repaired areas . . . or absorbing / curing at different rates in one area compared to another. These slight differences cause a color shift that may be noticeable.
How to avoid concrete ghosting
The only sure-fire way to avoid ghosting all together is to put down some sort of solid non-breathable coat first and texture over that (recommended on interior – climate controlled areas ONLY). For example, if you add a bunch of patches in the floor and you want zero ghosting to happen, you may consider putting down a coat of our Base Coat Epoxy and broadcasting sand into that (to rejection). The next day, you would sweep up the loose sand and apply your grout coat of texture right to the sanded surface. Even better yet, you could do a prime coat of PermaFlex and then do a broadcast coat of PermaFlex and broadcast sand into that for a complete moisture vapor barrier (make sure you’re not using a very fine sand here . . . you want to have a rough enough textured surface to have the Texture Mix bite into the broadcast coat).
Other methods that have been known to reduce or eliminate concrete shadowing are:
- Doing 2 or more “grout” coats of the texture with higher than normal amounts of integral color.
- Rolling a layer of concentrated HD Resin over the surface first and letting it dry before proceeding to your grout coat.
Ghosting and Concrete Polishing
The other system where ghosting occurs is Concrete Polishing. When you remove old VCT tile and mastic and polish the floor, the typical look will usually be a checkerboard floor where shadows of the old tile will ghost through.
This is something that cannot be corrected and the tile ghosting is consistent throughout the entire depth of the concrete. The space in between the tiles have been “breathing” at a different rate compared to where the tile has been sitting for years and the color shift is permanent.
Your client must made be aware of concrete ghosting (& the many other variables that may be there) if they are wanting a polished floor where tiles currently are sitting.