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slader99 08-15-2011 12:50 PM

Tile over Shiplap Floor
About to lay some tile in a bathroom project and wanted some advise. Right now there is shiplap (3/4" finished) and I've got 1/2" treated plywood cut out and ready to lay on top. I was then going to put down 1/4" concrete board followed by the tile. Below is an unfinished peagravel crawlspace.

I've replaced questionable pc's of shiplap and driven all the nails home with additional screws into the joists. My original plan was to put tar paper between the shiplap and 1/2" ply but I'm second guessing myself. As there is some minor crowning to the shiplap I'm wondering if using thinset between the shiplap and ply would result in a stronger, stiffer surface for tiling. Will this be a problem as I'll now be missing the vapor barrier properties the tar paper would offer?



slader99 08-17-2011 02:11 AM

As far as I can tell the only purpose tar paper would serve between my shiplap subfloor and 1/2" ply underlay would be a moisture barrier. After I'm done my tiling job I will put poly in the crawlspace.

Hoping someone can confirm the rest of my attack plan. I have screwed the 1/2" treated ply thru the shiplap to all the floor joists. I am now planning on laying my 1/4" concrete board on top of the treated ply and screwing it down 6" in the field, 4" on the edge. Do I need to put thinset between the ply and concrete board?



oh'mike 08-17-2011 06:50 AM

Yes! Set the backer board into a bed of thinset and nail or screw every 8 inches---

The thinset is there to fill any void so the board can not flex.

slader99 08-17-2011 09:42 AM


Thanks for the reply. Should I have bedded the 1/2 ply in thinset as well? It certainly seems rock solid right now....

When I do my skim of thinset before laying the backer board how thin should it be and should I groove it like I would if I were laying tile?

After the concrete board has been glued and screwed and set do I need to caulk outside edges or is the thinset bedding sufficent?



oh'mike 08-17-2011 09:52 AM

You did the plywood correctly--

Trowel the thinset for the rock just like a tile---1/4x 1/4x 1/4 or 3/8x1/4 are fine---

I use galvanized roofing nails for the floors and save the screws for the walls--but screws for a floor are fine if you wish.

slader99 08-19-2011 12:01 PM

Thanks for the advise so far!

Laid the tile last night - finished at around 2 in the morning. Looks pretty damn amazing if I don't say so myself. Is there any tricks to get thinset off the top of a tile? I'm not aware of any that I left but I'm sure upon closer inspection I will find a tile or two with some thinset on it....

I'm wondering how quickly I can stand on the tiles - I've got to do an additional coat of paint on the walls and time is a factor =). I was hoping to walk on them after the thinset has only cured for 14-16 hours. Is this a bad idea? What if I was to lay down something like blue insulation foam or ply wood to spread the load?

I was going to wait a full 20-24 hours to grout....

Also how long between grouting and sealing?



Bud Cline 08-19-2011 05:03 PM


1. The reason one would wait twenty-four hours to grout is so that the bond of the tile is not compromised from having someone on the tile prematurely before the bond had set properly. The need to paint is not a free-pass to get on a fresh tile installation prematurely.

2. For the benefit of those reading and watching and not participating...

Your sub floor IS NOT SHIP-LAP. Ship-lap is an entirely different thing. Ship-lap is the horizontal placement and lapping of boards on a vertical surface so as to promote water-shed and run-off, as in siding, or old wooden ships for that matter.:)

slader99 08-19-2011 05:50 PM

Thanks for the feedback regarding walking on the floor early. Thought there might be some sort of way I could get on it quicker if need be - its the only bathroom in our house and it's been out of service for several days already. I guess I will just have to wait it out.

What would the correct term be for lumber with rabbits on opposing ends? The profile I have is shown on this wikipedia link:

This is what my subfloor is made of. It is layed diagonally to the joists. It had 1/2" ply underlay on top of that. I went to a local demolition yard and he gave me replacement 'shiplap' boards which matched the material I removed. I wouldn't think the name of the board profile would change when the application is on the floor vs on the wall.



Bud Cline 08-19-2011 06:00 PM

My bad...I was thinking tongue and groove all this time. Never gave the rabbeted style any thought. All my minds-eye was seeing was lap siding style (ship-lap.)

There are different names in different parts of the country. Here, the product you describe is know and lap-slat.

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