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Unread 07-09-2005, 08:53 PM   #1
ourzoo
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Repairable mortar base??

First off I just want to give a big "Thanks!" to the administrator and members of the Forum. I stumbled on your Forum looking for information on my floor tiling problem and it appears the true experts are here. Your advice is great!

I live in a house constructed in 1955. The current project bathroom, (all of 8 foot by 5 foot in size) is mostly original and it's time for an upgrade. I've taken the wallboard down and removed the original cast iron tub. I'm now working the floor and am unsure how to handle the situation I've created.

The floor was tiled with small (1"x2") thru-color tiles (not sure of the technical name for these tiles). The tiles were set on what appears to be a mortar base with concrete below. Here's how the floor was built... 1"x2"s were nailed to the sides of the floor joists, so that the top edge of the strips were 1.5" down from the top of the joists. 3/4" pine boards were laid between the joists, and rested on the strips. Concrete was then poured on top of the boards up to about 1/2" over the floor joists. A 1/2" layer of mortar was then applied over the concrete and used to level the floor. And finally, the tiles were on top. A neighbor re-did his bathrooms, completely removed the mortar and concrete, and found that the joists under the concrete were "hatcheted" to a wedge like shape. It looks like the concrete sits on this wedge and the 3/4" pine boards. I'd like to avoid removing the masonry base if possible. Looks like a pain to do.

Before finding the John Bridge website, I crossed another site that stated I could remove my tile by using a combination of hammer blows to the tile, and a chisel to pry up the loose pieces. I've done this, with a heck of a lot difficulty, time and vibration. Unfortunately, the mortar decking has fractured in spots and in other areas, the mortar sounds hollow, (but looks intact). Also, I see that small (less than 1/16th inch) cracks exist in the mortar along the tops of the joists. These cracks were not visible in the original tile floor.. I could have created them with all my pounding.

Another issue. It looks like the old cast iron tub was installed first, directly on the floor joists without any sub-floor, and then the concrete and mortar were poured. The tub had a unique shape on the side wall, an "in and out and back in" sort of look. I'd like to install an appropriate sub-floor for the new tub, up to the level of the mortar. However, the in and out shape, which does not match with the new tub, will leave an opening about 3" by 24" between the old and new sub floors. I could pour more concrete and mortar to fill the 3" x 24" area then install a conventional plywood/hardibacker floor under the tub. But the tile will need to straddle the joint between this new concrete patch and the original masonry work. I could also cut out the new sub-floor material to match the 3"x24" shape but then I'll have dissimilar materials joining together under the tile floor. Seems like this will be a prime spot for the tile to fracture.

Can I restore the concrete/mortar base to a point where it will be a solid enough for the new tile floor? Any suggestions on how should go about doing this? If I can do this, any thoughts on how to handle the 3" x 24" area?

The straightforward solution to all of this is to just break up the exiting masonry and install a new sub floor. If I need to do this is there any low impact way of removing the concrete?

I would greatly appreciate any thoughts any of you have.

Thanks!

Tom
Beltsville, Md.
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Unread 07-09-2005, 09:17 PM   #2
Davestone
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Well, Tom, ya got a real dinosaur tile job there.How's about checking your subfloor on the DEFLECTO above.I don't see any cracks in the concrete,but i would have a hard time recommending to go over it because of the other problems,unless the deflecto gives a good reading,unless you went over it with a membrane.If you did take it out, and use plywood, and backer you would eliminate the other problems.
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Unread 07-09-2005, 09:18 PM   #3
John Bridge
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Hi Tom, Welcome aboard.

The cracks running along the tops of the joists are probably not a problem seeing that the subfloor was depressed below the joist tops which would make those areas the weakest. Still, though, I think you should use a membrane on top of the mud before you install the new tile. Do the patch where the old tub was before installing the membrane. I recommend Schluter Ditra as the membrane. You could also use Nobleseal if you can get a small piece.

http://www.schluter.com (Small pieces of Ditra can be ordered through our store.)

http://www.noblecompany.com
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Unread 07-10-2005, 07:26 PM   #4
ourzoo
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Thanks for the Advice.

John, Dave - Thanks for the advice!

I'm not sure which way I'll go just yet. Sounds like the isolation membrane is a must if I decide to keep the original floor. I've already botched one tile job (in my basement) so I really want to make sure that this one is done right. Seems like the safest bet is to remove the concrete but man, this is going to be a mess.

Thanks again. - Tom
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Unread 07-18-2005, 08:21 PM   #5
ourzoo
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Plywood to plywood bonding necessary?

Thanks to all for the recommendations on my previous post! After accepting the reality of the situation, and the lousy condition of my original concrete and mud subfloor, I decided to start over. and pulled it all out. I now have 1.5" to build up to, using plywood, backer board, thinset and tile. At this point I'm thinking about using two layers of 1/2" plywood, 1/4" Hardibacker with tile on top. The floor area is only 5' x 5' and I don't think I'll need an isolation membrane.. the joists are all 2x10s, 16" oc. I am concerned about gaps between the layers of plywood. If this is a sound idea, do I need to put any adhesive between the plywood layers then screw the heck out of it to hold it all together and keep the flexing down??


Another option is to use 3/4" plywood and 1/2" fiber-cement board, but I haven't read much in recent postings on taking this approach. Seems like the 3/4" with the outer grain running perpendicular to the joists will give me the best strength but if 3/4" is good wouldn't 1" be better??

Thanks for your help and comments!

Tom
Beltsville, Md.
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Unread 07-18-2005, 08:37 PM   #6
cx
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I merged you with your previous thread, Tom, so's everyone can keep up with the history of the project. Keep all your questions here until we finish this one, eh? If you don't like the title, we can change that anytime - just PM moi.

The two sheets of half-inch properly glued together would, indeed, be better than one layer of 3/4 inch. Better still would be a layer of 3/4 and another layer of 3/8ths or half-inch. or you could get you a couple sheets of 1 1/8 SturdiFloor, but you'd have a lot of waste.

If you glue up two layers, do it with a full spread of wood glue. I favor Titebond II, but there are many other waterproof glues out there. Including Titebond III, which don't nobody hereabouts carry for me to try.

My opinion; worth price charged.
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Unread 07-18-2005, 08:51 PM   #7
ourzoo
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Thanks, CX!

No problem merging the posts. I would have continued the original thread but this newbie couldn't find his original post

Your suggestion sounds pretty good! I've done some woodworking but my mind was stuck in the house building and didn't even think about Titebond.

So the plan would be to screw down the first layer with the outer grain perpendicular to the joists, then apply glue, then the second layer with the outer grain running with the joists, screwed along the joists and in the open field in between to pull it all together. I hadn't thunk this through all the way but it looks like screw location management will be pretty important!

Thanks.

Tom
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Unread 07-18-2005, 09:04 PM   #8
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No, no, no, both layers must be oriented with the face grain perpendicular to the joists. All layers go that direction. All the time.

Lotsa screws to pull that second layer tight to the first. I always pre-drill the second layer.

My opinion; worth price charged.
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