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Slate Install & Grout Release

dfkirk | Posted in Construction Techniques on December 17, 2007 06:41am

I’m about to install a slate floor and need advice or any special tips concerning the use of grout release before grouting and the effect on the stone.  With other porous tiles or glazed porcelin I’ve used grout sealer/ release with good results.  Any ideas regarding the special differences I could expect with slate??

 Any ideas on the effect these products will have on finished level of sheen? 

I’m well prepped with a solid 1/2″ of durrock over 3/4″ of plywood over rock solid framing.   I’m ready to deal with the varying thicknesses of the individual pieces.  Sage wisdom requested…

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  1. Tuneman | Dec 17, 2007 03:57pm | #1

    DIYer and first time with slate.  Everyone said "seal first, then grout".  I didn't. Used a grout bag with black grout. No Problem.  I used the grout bag to fill 3/8" spaces, and then worked in with the float.  When shaping the grout, if your tiles are of uneven thickness, shape from the low edge to the high edge to "ramp" the grout to prevent a proud edge on a tile.  The grout cleaned off of the unsealed slate ... no problem.  Good Luck!

  2. rlrefalo | Dec 17, 2007 05:11pm | #2

    3/4 subfloor is insufficient. Tile council rec's minimum 1 1/4 structural, cement board is not structural. Slate does not need sealing as it is very dense. If in doubt mix a small amount of grout and apply it to a slate and see how well it cleans up.

    Rich

     

  3. User avater
    lindenboy | Dec 17, 2007 06:08pm | #3

    Your sub-floor should work fine under normal circumstances.  Mine's been holding up for several years now, where I put slate over the old 1x plank with a layer of the thinner (5/16"?) durrock cement board.

    Also, while it is a pain to grout natural slate, I just used a float and tried to be fairly precise with where I put the grout.  In addition, I've used the same technique for both a floor and a wall, and it turned out great each time, with a minimum of clean up and virtually no staining or retainage of grout.  You do have to wash more than normal, which may weaken the grout, but so far it still looks like it did the day it was completed.  Oh, and I put a sealer over the tile after the grout cured, because it was a walk-off and gets a lot of salty water in the winter time.

    My parents, who donated the tile in the first place, tried the grout bag technique on their kitchen back splash and conceded that it's as much a pain (possibly more so) as the float technique, with little increase in quality of the finished look.

    GL.

    "It depends on the situation..."
  4. Waters | Dec 18, 2007 03:50am | #4

    If your subfloor is over 16" centers on adequate joist depth--I also think you're fine.  The 1/2 in durock is not structural however.  And my belief is it's better to put the durock joints in the field of the subfloor--meaning not on the joists.  As well, don't nail into the joists, and use thinset under the durock.  Then the whole unit will 'move' independently of the joist/subfloor system and you won't get problems.

    Regarding the grout release--I wouldn't think of not applying a basic polymer sealer as a grout release first before grouting slate.

    Some slate is indeed smooth and not very porous.  Some is very rough on the face, and very very porous, which could be a grouting nightmare!

    If you're after the wet look--or sheen--you can apply an enhancer type sealer.  But I don't know much about the application of said product before grouting--or how it would go on after grouting, having used a basic polymer sealer.

  5. Waters | Dec 18, 2007 03:52am | #5

    Oh, and ixne on the grout bag.  If you can get your sanded floor grout through a grout bag, its' mixed far too loose (IMHO).

    You want less water in the mix you know.  Grouting is a tough job when it's mixed right.  Easy when it's too loose. (wet)

  6. User avater
    JeffBuck | Dec 18, 2007 03:55am | #6

    if I can I make the room to lay alot of the tiles spread out flat ...

     

    then mist them over and over with the sealer in a garden sprayer.

    do them in batches and stack them.

    Jeff

        Buck Construction

     Artistry In Carpentry

         Pittsburgh Pa

  7. TBone | Dec 18, 2007 04:02am | #7

    Always seal the slate. I've got horror stories about non-sealed. I do it twice. Yeah, it adds to the time...but clean-up sure is easier. And I'd not use the grout bag either. The grout needs to be stiffer than that.

    Get the matte sheen. It deepens the color a bit but doesn't make it particularly shiny.

    I'd beef the subfloor up to meet standards...but have never had a problem with 1/2" Durock over Advantech.

    Always set the tile and deal with height differences later. That way you have a solid setting bed. I've had good luck with a chisel and grinder after the fact to level things up and straighten grout lines.

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