Cracks in the cement before tiling.

[Baitball Blogger]

Is there a special tape we need to use to tape up those hairline cracks in the floor? How thorough do we need to be about this?

[tk2kewl]

1. if the cracks are "hairline" i wouldn't worry

use a good quality flexible thinset mortar and a square notched trowel - i always use Flexbond.

[OffWithTheirHeads]

2. Once you tile over the cracks you won't see them anymore.

Aside from that, no problem.

[Baitball Blogger]

3. No worries about vapors?

[OffWithTheirHeads]

4. Nope. People stopped having vapors with the demise of the Victorian age.

[Baitball Blogger]

5. Lordie me!

[Hassin Bin Sober]

6. You can apply a crack isolation membrane either liquid or mat.

Home Depot uses Custom Building Products as their tile products supplier for grout, thinset and liquid isolation membrane called "Redgard".

Redgard acts as a waterproofing membrane AND crack isolation membrane. It should be applied thicker for crack isolation - with a 3/16th trowel if I remember correctly. You can do the whole floor or there is a formula for width over the crack based on tile size. Read the directions AND call the mfg.

I like Redgard because it s relatively easy to apply, acts as a water proofing membrane AND has the extra added benefit of giving you extra working time when working over porous surfaces like concrete or cement board. It keeps the concrete from sucking the thinset dry before you set your tile - this helps the thinset cure slower and stronger. Make sure you dampen the concrete so the Redgard doesn't dry too quickly per mfg instructions. READ instructions!

As mentioned up thread, use a good quality modified/fortified with latex thinset like Custom's flexbond in the mid to high 20 dollar range for a 50 pound bag. Don't cheap out with 8 dollar a bag stuff.

This is all predicated on the fact your slab is suitable for tile and not subject to hydrostatic water pressure. Is it above grade? Or a basement below grade?

[Baitball Blogger]

7. Standard floor.

Not subject to hydrostatic water pressure.

Around here we usually do it to prevent termite access and radon vapors.

[Hassin Bin Sober]

8. You are in florida so I assume a slab foundation above grade?

As long as they are hairline cracks with no deflection upward, you should be OK. If there is movement up, you are kinda screwed.

You might try a roll crack isolation membrane like Ditra if you really want to make sure. I've never used it and I assume there is a tiny bit of learning curve but the pros really like it.

I don't like to skimp when it comes to tiling. It's too f-cking hard and the materials can add up. There are people like the Tile Council of North America and ANSI who test this stuff and write the standards.

I usually start a thread here to let some pros take a gander at my scheme:

http://www.johnbridge.com/vbulletin/forumdisplay.php?f=1

[Baitball Blogger]

9. They're just hairline cracks.

In fact, when we removed the tile the original tape was still on the hairlines, so it all came from natural settling.