Can you put epoxy concrete sealer over acrylic sealer?

Answer 1

Of course you can. You can also scribble a mustache under the nose of a Picasso painting and use dirt as a condiment for your hotdog but none of these are good ideas. The question isn't one of whether or not it can be done but, what the chances of long-term adhesion are between the acrylic sealer and the epoxy coating.

As far as the two materials are concerned, it's really a pretty generic question because both epoxy coatings and acrylic sealers come in a multitude of different varieties and formulations. So, the answer will have to be equally generic.

First and foremost, any run-of-the-mill epoxy (bis-A, bis-F, novolac, water, solvent or 100% solids, etc.) will adhere, to one degree or another, to a clean, contaminant-free polymer treated surface as long as the formulation, mixing and application are done correctly. The chances of a higher rate of adhesion increase when a profiled surface (increased surface area) is available.

However, in the same way that a concrete foundation designed and poured to support a single-story residential home isn't well suited to support the weight and movement dynamics of a ten story building, a single-component acrylic sealer isn't well suited to act as the foundation for a two-component crosslinking epoxy. The long and the short of why this is true is simple:

1. Acrylic sealers typically have a solids content of between 20-30%.
2. This means that once the carrier (which is usually water or solvent), that makes up the counterpart to the solids content (70-80%) has evaporated, the solids are what remain on the surface as the dried sealer.
3. When examined microscopically, the solid particles appear as individual and independent specks.
4. Conversely, all two-component epoxies crosslink forming carbon chains, which make the epoxy coating a single sheet (like a roll of plastic) once it's cured.
5. When exposed to enough stress (think foot or wheeled traffic) the individual solid acrylic particles can act as an epoxy bond breaker because they inhibit the epoxy coating from making full contact with the surface that it's intended to protect.

In summary, although it's not recommended and assuming the sealer is in tact, if an epoxy is going to be used to coat an existing acrylic sealer (for whatever reason), it would be best to use either a 100% solids or a water-based epoxy to avoid any possible attack from an epoxy containing solvent.

With all this said, the best approach is to fully strip and eliminate the sealer so that the epoxy coating can have access to a well prepared, open and porous surface.