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Unread 10-17-2020, 06:39 AM   #2
Tool Guy - Kg
Moderator -- Wisconsin Kitchen & Bath Remodeler
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Join Date: Feb 2005
Location: Oak Creek, WI
Posts: 22,339
Welcome to the forum, Jack.

First thing to ask about is moisture. Do you have any moisture issues going on?

Second thing to understand is if your slab is porous or not. You want open pores for the mortar to stick. Pour a few ounces of water on the slab and wait 5-10 minutes...then wipe off all the excess. Hopefully, some moisture has sunk in and has temporarily darkened the slab. If so, you’ve got open pores and a surface that’s really to be stuck to. If the slab remains visibly unchanged, you may need to run a diamond cup grinder wheel (rentable) over the surface to rectify the sealed pores.

As far as the divots, they aren’t a big deal. Whatever setting material you’re going to use can very likely be used to fill them ahead of time. Just mix up some mortar and patch them with a little putty knife.

Assuming you don’t have moisture issues, you want to use a crack isolation membrane (rather than an uncoupling membrane that doesn’t have a rating for crack isolation properties). For an easy crack isolation membrane, you may want to consider using Custom Building Product’s RedGard or Laticrete’s Hydroban. These are both paint-on liquid membranes. While they don’t go on as easy as paint, they aren’t hard to apply with a roller and afford decent crack isolation properties. If you need a high-performance crack isolation membrane, Noble makes a sheet membrane called NobleSeal CIS that is the best of the best.

If you do have slab moisture issues, let us know.

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