Replies

1. 
   Guest_ | Jul 27, 1999 07:55am | #1

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   Loose, cracked, or altogether missing grout is a sign of loose tiles. What caused them to loosen? Take a close look at the cleaned off concrete. Are there any cracks 1/8" or larger in width or change in elevation? If not, a repair is pretty straightforward. If there are large, active cracks in the concrete you should post again.

   For resetting the tiles, use a latex acrylic modified thinset mortar that complies with ANSI A118.1. Do not use more than 1/2" thickness of thinset below the tiles. If you need to go higher in elevation to match the rest of the floor you should use a 4:1 mix of 20 mesh sand and common cement.

   Actually, for your climate, I'd suggest not even going to the maximum 1/2" for thinset. I'd plan on using a mud mortar bed right off the start. Skimcoat the tile back with thinset and set in wet--not soupy or runny--mud. But since you are doing a repair you need to match the elevation of the other tiles.

   For grouting, use a 2:1 mix of silica sand and common cement. That gives a natural grey color. If the existing grout is colored you should use a sanded grout colored to match the existing.

   Were the tiles that you pried up broken or did they come up in one piece?

1. 
   Guest_ | Jul 27, 1999 08:29am | #2

   *I hate to pipe up again with our "crude" approach, but construction adhesive notch-troweled on will do a fine job of holding the tiles down too. We used an ordinary (HD) sanded grout that appears to be wearing fine; the installation is sheltered, however.

1. 
   Guest_ | Jul 28, 1999 05:13am | #3

   *Andrew, this is an exterior slate floor over concrete (slab on grade?) prone to frost and snow in the winter months. What adhesive do you have in mind? You aren't chirping about Liquid Nails again, are you?I don't use L.N. for much of anything--didn't say it's not a fine product--so perhaps you can say how well you think it'll do for the given task.

1. 
   Guest_ | Jul 28, 1999 06:03am | #4

   *"Chirping"? I have a ground-shaking baritone, I'll have you know. :)As I said, our porch is sheltered. I was VERY skeptical when the masonry supply yard recommended glue but figured what the heck. Did try some LN, hated it, last time I've touched the stuff. PL400 was easy to work with and did a nice job. (I've been using OSI more recently .. it doesn't ooze during the summer after you put the gun down like PL.) Troweled on (3/16" V-notch?), set up very quickly, perhaps provides some resilience in the bond. Subfloor is 3/4" plywood. Did not manage to grout the whole thing before it got too cold last winter, but the traffic-pattern part that I did do has not cracked. This is in Virginia, where winters are mild (by Northerner standards).My wife did the work and commented on how is easy it was. I didn't have to wonder whether she mixed anything wrong and she could start and stop as it was convenient.Just a different approach.

1. 
   Guest_ | Jul 28, 1999 09:50am | #5

   *I'm always on the look out for a different approach, at least, I'll contemplate using a different method/materials. But, would you use PL given the climate/site conditions mentioned in the original post? Besides, isn't using PL a tad bit more expensive than, say, thinset?

2. 
   JohnK | Jul 28, 1999 10:52pm | #6

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   Thanks for the info guys. The peices I'm working with vary in thickness from about 3/8" to 3/4", so thinset sounds like the way to go. I'm not sure if I could bring myself to use PL400 on tile, but it might be a good idea if the substrate flexes.
   Rich, The pieces came up easy. It looks like they're just sitting on fine sand, but there's grout in between. Have you ever heard of anything like that? The house was built in '57, for what it's worth. John

3. 
   Guest_ | Jul 29, 1999 12:48am | #7

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   John,

   I have heard of brick being set dry in a sand bed, but it is dependent on the thickness of the brick and a tight fit to lock it in place. A flat tile with a grout joint will not stay in place on sand. Perhaps this was a very poor mortar that has deterioriated over 40 years. You won't be able to make up 3/8" difference in thickness with thinset. You would either need a regular mortar bed, or to sort the tiles as to thickness so that there was no apparent difference in adjacent tiles.

1. 
   Guest_ | Jul 29, 1999 06:21am | #8

   *Great response; comprehensive, concise, and lucid.

1. 
   Guest_ | Jul 29, 1999 06:22am | #9

   *John, you're interrupting...Andrew hasn't answered the question.Actually John, the only think I can think of is that the fine sand you mention is whats left of the mud base they used when originally installing the slate. Only they didn't have enough cement in the mix...it became unconsolidated causing the tiles to become loose.Or, perhaps, they used a mud base, but is was really a minimum thickness--sort of like using it to gauge ungauged slate tiles--that it eventually succumbed to the weather. That's not to say all mud would give in over time, just that they probably used a too lean mixture of sand and cement.

1. 
   Guest_ | Jul 29, 1999 09:07am | #10

   *Hey, Rich is da man on this stuff.In response to his questions below, I'm watching the tiles with curiosity for durability of the glue. The substrate is quite rigid, but it is wood -- I didn't notice JohnK was working on a slab.My impression was that mortar sometimes had trouble maintaining adhesion even in this mild Virginia climate (winter feels like Hawaii after Chicago) -- hey I may as well ask, we have some of that fake veneer stone mortared to the cement block foundation that a contractor mortared back on. It fell off within a year. Any ideas before I do it again (or God forbid use glue)?Yes it's more expensive but the glue cost was pretty minor in relation to the slate (itself not bad at $2 sf). I think the main attraction is convenience, though demo'ing it later might be unpleasant.

1. 
   Guest_ | Jul 29, 1999 09:09am | #11

   *See above, Dad, I answered (honest, I'm not on this thing 24 hours!).Who does this John guy think he is, butting in on our conversation? :)

4. 
   JohnK | Jul 30, 1999 02:21am | #12

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   Excuse me Andrew while I butt in with another pesky question.(just kidding) I dug around a little more, and I think you guys hit it with the decayed mortar. I've only ever done tile in thinset before, so can you give me the run-down on a full mud install? What's the minimum thickness? What mix do like? etc. Thanks again, John

5. 
   JohnK | Aug 01, 1999 01:39am | #13

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   I have a slate floor on my front porch that's in need of repair. It's about 10' wide x 7' deep w/ more extending into the foyer. There are 2 steps and a couple feet that are not covered by the eaves and the mortar (grout?) between them is completely gone in places. I pried up a peice and it looks like they're set on fine sand on top of concrete. The grout width is about 1/4". What should I use to repair this without causing more damage later? This is near Chicago. TIA, John

6. 
   Guest_ | Aug 01, 1999 01:39am | #14

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   This resilience thing is interesting. My tile setter is pushing sheet cork as as an isolating and resilient barrier between tile and plywood underlayment. Haven't let him do it yet, so I'm not real sure of the particulars. I never thought about a good adhesive before. It would be waterproof and slighty resilient, so house movement wouldn't seem to effect it as much as thinset. Any thoughts?

   BB