using self leveling mortar?

stevescivicMarch 1, 2008

Hi everyone, I need some advice b/c I'm stumped as to what I should do with my basement tile job.

Right now I'm in the process of finishing off my newly developed basement and one of the things that I installed is tile heating wires over my subfloor. I've never laid tile before but I was told that I could use self leveling mortar to make the base on which the tiles will sit on but what I'm concerned about is how do I keep the self leveling mortar from spilling out to areas that aren't being tiled?

Right now my basement consists of a concrete slab, then a layer of dri-core and then over the dri core a thin layer of plywood. On top of the plywood I have installed the heating wires for the tiled area and now I want to bury the heating wires using self leveling mortar.

How on earth can I keep the mortar in the places that I want to and prevent it from seeping into the cracks between the subflooring and the walls? How do prevent the mortar from spilling over to the areas where the carpet will eventually meet the tile?

I was told to build a mortar bed frame but in my case its not the easiest thing to do and its costly. I was told to tape all the edges where the walls are and then remove/cut the excess tape off when its done setting.

Do I have to prime the plywood subfloor as the mortar bag says so?

Hoping someone can help....


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i didn't think you could lay tile over dri-core. even with that thin plywood on top, i wouldn't think it would be a rigid enough base and the tiles and/or grout seams would crack.

have you considered using a mortar base applied to the concrete and then tiling over that? If you need to make a thick base to match up to the dricore you could use cement board (maybe even 2 layers with 1/2 inch and 1/4 inch cement board) on top of the concrete, attach your heat mats to that and then mortar over the top. That would give you a very rigid base that you could easily build to the correct height so that when the tile is applied it is at the proper height in relation to the carpet and you don't have to wory about the issues you wrote about.

    Bookmark   March 2, 2008 at 7:59AM
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No way!!! Tiling a basement should be done directly on the concrete floor, no exceptions.

Lay your wires, then SLC, than thinset and tile. You can thinset the tile and wires in one step without the SLC if you have experience in tiling and have a level floor. But still, the SLC is a recommended step to make the tile install easier, especially for an unexperienced tiler. SLC is definitely a recommended step. In regards to keeping the SLC in the area, you need to take some wood strips and create a barrier. This is not expensive, the SLC will be a very thin layer. What is expensive is the bags of SLC.

    Bookmark   March 2, 2008 at 8:26AM
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Wow, that's doing it the hard way. I agree that the tile should go directly on the floor. How solid is your dri-core floor, anyway? Do you feel any "give" in any areas, or are all those "feet" resting perfectly on the floor? Hope so, if that tile grout is going to last.

Anyway, to answer your question of how to keep that stuff from running everywhere, you would tape or caulk all the seams. For the edges, install border pieces of wood, again caulking or taping all gaps and corners, including along the edge where it meets the floor (otherwise the SLC will ooze under it.)

If you do go this route, yes, prime the wood.

    Bookmark   March 2, 2008 at 11:57PM
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I am using dri-core over the floor for the sake of keeping things nice and warm. The issue I had was that I installed all the dri-core throughout the basement and then found out I couldn't put mortar over dri-core. I contacted the heating wire company and they said to install plywood over the dricore and then I'd be good to go. The problem I have now is that my entire basement is finished in dri-core and plywood and for me to rip that all out would be murder. I just finished installing all the wire holding strips to the ground and am pretty much ready to start mortaring. I do feel confident enough that the dricore and plywood is stiff enough to prevent any noticeable flexing. Does everyone here really advise against putting tile on plywood/dricore?


    Bookmark   March 3, 2008 at 12:46AM
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i recommend cross posting this on the flooring forum if you haven't done so already. You should seek advise from a tile expert - and there are a few over there.

I don't think tiling over dricore is a good idea even with the plywood on top. However - given that you have all this work invested in laying the dricore - maybe there is something you can do to minimize the cracking which is what I think is going to happen.

One thing that popped into mind are the new tile products that they make that come in sheets that snap together - requires no mortar. The tiles are set onto a vinyl or pastic frame - and these frames interlock. For the grout, it comes in tubes and is a latex product that might minimize cracking. I do not know if this will work - but it's worth asking the question. The selection of tile is limited - but the nice thing is that it is easy to pull up if you ever need to get to the subfloor. I do not know how (or if) these products would work with a heat mat.

I hope you can find a solution.

    Bookmark   March 3, 2008 at 7:54AM
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Tile guys will probably say "no way". (google john bridge tile forums and do a search). Since the dri-core is down, I wonder if you have considered another floor altogether. Might be the best, and many folks would consider this one advantage.

With the dri-core you can now do carpet or sheet goods (vinyl, etc, even those that look like tile, wood or anything else). Then you'll have a warm floor to the touch. The downside of tile in the basement is how cold it is, and frankly, I'm not a big fan of keeping grout clean down the road. Tile will also take away extra ceiling height by the time you're through.

So just in case you're thinking about pulling out the dri-core, think instead of ditching the tile and going with different heat. Just a thought. (Not easy to do after all the work you've put into it, I know.)

...and after you think about all this, maybe just pulling the dri-core out, and doing the heat + tile won't look like such a bad alternative afterall. (Think about the extra height you will get.)

Good luck.

    Bookmark   March 3, 2008 at 8:29AM
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This job CANNOT go as planned. You SHOULD NEVER install tile on plywood. Plywood is unstable and expands and contracts and your tile will literally pop off. Grout will crack and pop out. You need a STABLE surface (not just firm). You have a very very very unstable base as it is with the dricore and a thin layer of plywood will not help it at all.

You need cut your loses, and make a decision here based upon financial loss and your desired finish. I see two routes...1)Go with the dricore and use another finishing product such as carpet or pergo, etc. or 2)Remove the dricore and install your heating mat and tile.

I do not understand why you thought you needed dricore with heating wires. The heating wires will give you that warm feeling. Do you have a leaky basement?

You must have spent a fortune...dricore is very expensive, and the heating wires even more so.

I am sure you can sell either product on ebay depending on how you proceed.

In my opinion, I would prefer tile and the heating mat. Tile is nice in a basement due to lasting ability with kids and pets. I did mine in tile but could not afford the heating mats. I instead lay out some area rugs in the winter, than roll them up in the summer.

    Bookmark   March 4, 2008 at 12:42PM
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