Ceramic Tile on Cracked Concrete

[Tom]

I'll be laying 12" ceramic tiles on a concrete floor in my 1978 condo unit. The carpet and padding have been removed. The floor has a crack running the length of the room and is about a 16th of an inch wide for most of its run; the rest is even skinnier. The surfaces on either side of the crack are not quite flush --- a 16th or less difference.

On a couple of the TV fixit shows, there have references to using a membrane of some sort to bridge the crack to keep it from telegraphing through the tiles someday. I inquired about this membrane at Home Depot and might just as well have requested a dissertation on pre-Columbian art in the western hemisphere for all the help that I received.

My questions are: 1. Is such a member really required for that size of a crack? and 2. Where might I find such a product and how is it applied?

TIA. Tom

[Rick]

Home Depot sells a "RedGardT Waterproofing and Anti-Fracture Membrane, Custom® Building Products" SKU number 755504 - "Ready-to-use. Elastomeric, waterproofing and anti-fracture membrane for interior or exterior commercial and residential tile and stone installations. Can also be used as a slab-on-grade moisture barrier under resilient or wood flooring. Easily applied with roller, trowel or sprayer. Reduces crack transmission in ceramic tile and stone floors."

They also offer "FlexBond® Premium Flexible Bonding Mortar, Custom® Building Products" SKU number 839581 - "Utilizes Custom® Building Products' cross-linked cFlex3 Tri-Polymer Technology®. Provides maximum flexibility and the highest bond strength (twice industry standards). The best choice for tiling over surfaces subject to minor movement and hard-to-bond-to surfaces such as laminates, ceramic tile and plywood. Allows tiling over cracks up to 1/16 (2 mm) without repairs. Just add water and mix; no additives needed."

Rick

[William W. Plummer]

A long time ago I remember the standard fix was to use about 6" wide strip of roofing felt over the crack. The idea was to let the two sides of the cracked slab move a little and not try to make your tiles couple them together.

[Tom]

Thanks for the info. I looked up the products on Custom's website. Fortunately, there are three or four other HomeDepots in Las Vegas. I'll get to one of the others and see if they can help me find the RedGardT on their shelves.

[Tom]

Going to check out Rick's recommendations. Thanks.

[PJx]

I'm wondering if that crack has been there 26 years or if it started last year and will double in size every year? If you do nothing else, at least document the heck out of the crack.

PJ

[Ron Maggi]

Tom,

Yes, don't cut corners and use the underlayment. Otherwise, you run the risk of the tiles and grout cracking. Any tile store should be able to provide "felt" underlayment paper. It's specific purpose is to bridge small cracks. The cracks should be filled first and then the felt is glued down over the cracks. If the crack is confined to one area, the felt only must be applied to that section. If there are many cracks, it is best to cover the entire floor with the felt. Thinset cement is applied on top of the felt and the ceramic tiles are installed as normal.

Ron

[Dee]

For questions and products like this, find a local tile store. They will be able to help you out - some of them even give classes on tile laying. They will also have the membrane, if you need it.

Dee

[Tom]

We've been in the house for four years and don't know how long the crack has been there. We found it when we pulled the carpeting and pad.

Picked up Custom Products RedGardT membrane at a different Home Depot, laid it on and am more than half way through tiling now.