Epoxy application - can epoxies be applied over tiles?

Contractors working in the residential, retail and commercial fields are almost guaranteed to hear one question from your customers:  “Can you go over tiles?”

It’s a very important question to be able to answer and I think it will only become more important as the resin flooring market continues to grow. While tiles have always been a popular flooring choice, I believe more and more people are falling in love with the seamless finish epoxy floors provide and they’re starting to look into their options more seriously.

With so many tiled floors already out there, a big part of this process from the customer’s point of view is trying to understand how to make the switch painlessly. Most people realise that removing tiles can be a messy, time consuming job - not to mention costly if it involves raising the floor by up to 15mm/6” afterwards - and they’re naturally drawn to the idea of simply going over the top; hence the popular question.

So, can epoxies go over floor tiles? I think many contractors will know the simple answer is yes, however it doesn’t always mean they should. There are some conditions and additional thoughts I always consider before jumping in. Here are a few of them.

Sticking to tiles

When going over the top of a tiled floor, the main concern is adhesion - with epoxy onto the tile and tile onto concrete.

Some floor tiles have a glossy finish from the glazing process, which can make them tricky to bond to. If the tiles are glazed, the gloss will need to be removed by grinding to allow the epoxy to grab hold. You can look to micro-etch with acid-based etchers, but in my experience this kind of preparation can be hit and miss. Vitrified tiles are non-porous and extremely hard all the way through, so grinding alone may not be enough to get a strong bond. With these, a specialist primer is typically needed to make it stick.

A glossy finish can also be a result of a sealer on the tiles, e.g. lots of terracotta tiles aren’t glazed, but a sealer can sometimes be applied to prevent them from looking dirty or showing a spill. If the tile is sealed then you’ll also need to grind as these sealers often have hydrophobic properties and can be troublesome if you approach them like a normal coating.

In addition to glaze and gloss of the tile itself, I always pay close attention to the condition of the grout lines. The biggest concern here is contamination. Being a porous material, grout has a nasty habit of soaking up all sorts of grease and grime that can play havoc with epoxy adhesion. If the tiled floor is in a commercial kitchen or anywhere else exposed to heavy oil contamination, you may find yourself digging up the grout lines or removing everything just to be safe.

Finally, as already mentioned, the issue of adhesion must also be considered with respect to the quality of the bond between floor tile and concrete. Tiles can become “drummy” over time and that represents a weak point in the flooring. If more than a few tiles are found to be loose during inspection - or they start to shatter, crack or pop while grinding - it’s probably better to remove them all so the concrete underneath can be used instead. If they all feel fine and you end up going over them, I’d recommend just having a word to the client anyway to make it clear you can’t control what the tiles may do in the future.  

Getting the tiles flat

If you’re confident the tiled floor is clean and sound and you can stick to them with your epoxy, the next challenge is to get them flat. In my experience, there aren’t too many clients fond of protruding edges or visible grout lines in their new resin floor.

While a flat substrate can be achieve mechanically through grinding, it’s generally quicker and easier to apply a levelling compound to do the job. There are a few things I’ll say about this task.

Firstly, you may need to apply up to 5mm/2” to cover grout lines fully, which can add significant cost to the project and cause problems elsewhere with regards to heights around fixtures etc. These aren’t major problems for the contractor per se, however it can be if these things are communicated clearly to the client beforehand.  

Secondly, don’t fall into the trap of thinking all levelling compounds are the same. While they may produce a flat surface, different products can interfere with the flooring system on top in different ways and give some undesirable results. For instance, floor levellers heavily diluted with water can form a very porous surface that could lead to bubbles and variations in gloss, while some epoxy floor  levellers can expand and contract at different rates to the tiled floor and lead to grout lines becoming visible once again (so-called “ghosting”).

Lastly, ghosting in the form described above tends to happen gradually, however grout lines can also show through immediately in some cases. The biggest offenders here are metallic flooring systems. Metallic pigments typically flow and settle freely in low-viscosity resins and consequently are excellent at finding any low spots. Even if you can’t feel the grout lines anymore you can still end up with a visible grid pattern, so you have to be very careful when applying these types of floors over tiles.

Grout lines showing through under a metallic floor applied over floor tiles.

Tile removal

Often the condition of a tiled floor will simply offer no alternative other than to remove what’s there and get back to clean, sound concrete. The actual lifting of the floor tiles is done relatively easily in most cases; it’s the glue underneath that can catch contractors out by being very stubborn and time consuming to remove/flatten. Another thing that can slip through the cracks with tile removal, so to speak, is the damage done to the concrete during this process. If you’re not planning to use a floor leveller, you’ll generally need to allow for a fair bit of patching to repair divots and chips before the resin floor goes down.

Overall, my opinion is that you should aim to get back to concrete whenever possible when it comes to resin floors. The path you take at the end of the day, however, will often come down to the preferences of the client and how they feel about the extra costs, time and risks associated with either option.

How do you approach floor tiles? Do you insist on removal or are you confident enough to go over the top?

Take care and keep smiling,