The difference between exterior & interior prep
Lately I’ve been noticing job pictures from contractors on social media with grinders sitting on exterior slabs during the preparation phase of the project. This has got me wondering how many guys are grinding before laying down texture or GraniFlex?
While grinding on an INTERIOR slab & vacuuming well is an acceptable form of concrete prep before laying TEXTURE MIX, I don’t feel comfortable doing that on an exterior slab & it’s not recommended.
The one and ONLY texture delamination failure I had in 14 years of installing concrete resurfacing systems was because I used grinding as my method of preparation on an exterior patio.
It’s a whole different world between interior / climate controlled projects and exterior projects. Extreme low temps on up to extreme high temps (plus all of the other weather related factors that exist outside) call for better prep on exterior slabs to achieve that forever bond.
Grinding pushes lots of dust into the concrete capillaries and many times just vacuuming alone is not going to cut it on exterior projects.
The only time you should be grinding on an exterior slab is to remove an existing coating or sealer (and 90+ % of the time, there is none outside) . . . which means you should be thinking straight up acid etch, neutralize, pressure wash, rinse as your #1 exterior concrete slab prep before texture systems and doing Graniflex.
Not only is etching faster than other prep methods, it’s less expensive and will give you a better profile to achieve a better bond.
As I pondered the reasons why I had a failure on that dry prepped patio a few years ago, here’s what was happening at the time of install:
Dry prep (grind).
Patio poorly blown “clean” w/ leaf blower.
Temps at 95 degrees Fahrenheit, direct sun + a hot, hot slab…
The grout coat baked on that slab (dried extremely fast) and when you combine that with with a dusty/dirty slab that was caused by grinding & poor cleaning . . . that coating didn’t have a chance.
If you have to grind outside to remove an existing coating or sealer . . . follow up with an acid etch, neutralize, pressure wash and rinse.
The same thing goes for putting down the Graniflex system. To get the full benefits of Permaflex, grinding is NOT an appropriate method of prep (inside or outside) . . . you need to acid etch or shotblast.