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aluprr · 02-08-2013, 08:56 AM

New to the thread, so apologize if this is a repeat. I'm interested in tiling over my existing ceramic tile in the kitchen/hearthroom. Tile is in good shape, although it does have a slight gloss. I know the right thing to do would be to rip it out, but we're talking approx. 600 sqft of tile with thinset both above and below 1/2" cement board. I hoping to do anything to avoid the tearout, so is tiling over this tile an option? I've heard mixed reviews from different sources. My plan, if I move forward would be to clean the surface with TSP and let dry. I'd plan on using a polymer modified thinset to secure 12x12 inch tiles over existing 12x12...careful not to match grout lines. What issues am I not considering? I've done the load calculations using various forumulas and come up with about 50lbs/sqft based on my 2x10 joists 16" OC and max span of 15ft. Do I need to be worried about the extra weight? In my mind, I'm only adding about 5lbs per sqft with the new tile, so it shouldn't be an issue. Please let me know what you'all think. Thanks in advance.

Jaz · 02-08-2013, 02:14 PM

Yes, removing 600 ft. of CBU and tiles would be a big job, I'd rather move.

You can absolutely tile over tile if everything is done right. But the main thing is to make sure your joists are not over-spanned.

I'm not an engineer, but you may be over-spanned. I think you're wrong with the calculations of 50 lbs. per sq. ft. The #50 is probably the "live load" calculation, but the tiles become the "dead-load". Standard construction usually says 40/10 specs for regular floor coverings. I like to go 50/20 for tile, min. So, you need to add up all the dead load you have and plan to have and see where your framing rates.

You may need to stiffen the joists at the min. You're probably over #20 dead load already.

Jaz

aluprr · 02-09-2013, 08:25 AM

Thanks so much for taking the time to reply. Well you've certainly given more to think about and research in terms of potential load issues. I may have been too quick to plug in numbers when I came to the 50# result...so I'm not sure if the formula I used even addressed the live/dead load differences. I used FBd^2/9L to estimate the load capacity of each joist, then used a couple other calculations to arrive at the load per sqft. I know, amateur at best.

Assuming a get professional guidance on the load issue, anything else I should consider when attempting to tile over tile? I'd appreciate any additional do's/don'ts you're able to share. I've done a number of tile jobs, but never over existing ceramic. Thanks again for time!

Jaz · 02-09-2013, 09:57 AM

OK, I'll continue with no regards to the framing at all.

I'd make sure all the tiles are stuck well by taping them with the handle of a screwdriver to listen for hollow sounds. Especially around the perimeter. Even tiles that are loose will still lay there nice and pretty and no one will notice.

Clean and rinse as you described. It's best at this stage to scruff the glazed to create bit. (I've done it without doing this, but you really should.) At minimum run a belt sander with the most coarse paper you can get, or better yet, a diamond cup on a side grinder or similar. This can get dusty so have help with a good vac. The rise etc. of course.

Use a good quality modified thinset per directions. But Mapei makes a primer for just this purpose, be safe, find some. Eco Prim Grip.http://www.mapei.com/us-en/products-line.asp?IDMacroLinea=0&IDTipo=6737&IDLinea=102

Plan ahead how you're gonna finish doorways. Be sure to leave the proper expansion space at the perimeter and all solid objects. Be sure to include expansion joints within the field at strategic points and every 20-24 ft. +-.

There's many other thing, but can't write a book here.

Jaz

reubenbanks · 03-16-2013, 04:26 AM

You can tile over tiles with the right preparation. but I would never do this, the proper way is to strip right back to original wall finish. Don't worry if you do pull a bit of plaster when stripping the tiles, as its easy enough to replace. Tiling over tiles can make it awkward, i.e. extra thickness when tiling around shower fittings.