QUESTION

Can we avoid scarifying the substrate if we use a polymer modified thin-set? - I'm working on a project where many thousands of square feet of slate tile is delaminating in spots from the cast-in-place concrete substrate. In an effort to save money on the re-install of the slate tile I was wondering if the new slate can be installed with a polymer modified thin-set mortar to avoid the labor costs associated with scarification of the substrate?

ANSWER

ANSWER - Absolutely you cannot avoid properly preparing the substrate regardless if you use a polymer modified thin-set mortar or a standard thin-set mortar or even an epoxy.  The installation is only as good as its bond to the substrate.  The cast-in-place concrete substrate should always be scarified to open up  the pores to a CSP3 profile finish.  Often form release residuals are on the surface and it isn't as absorbing as it should be.  There are many different types of polymer modified thin-sets that are used for different conditions and come in many different levels of performance.  So it is important to use an appropriate thin-set for the intended application