Tiling project [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-17-2011, 12:02 AM
I am trying to find what is the best product to bond backerboard to the subfloor and for the installation of porcelain tiles 13x13. I am looking for a thinset easily found at Lowes. They sell the pre-mix stuff, but everyone on this board advises against it.

Lowes carries the LATICRETE products. What would you advise me to use for a solid tile and backerboard installation? I am planing to live in my home for a very long time.


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07-17-2011, 08:04 AM
Hi Peter, welcome! You can use an unmodified thinset to put the CBU down and a good modified to stick the tile to it. Or make it simple and just use modified for everything. :)

07-17-2011, 10:40 AM
Thanks for the recommendation. I want to use one product for both the BB and tiles. I just looked into the data sheet of Lowes's Laticrete Multipurpose Pro. It specifically says not to use directly over OSB as part of its limitations :shrug:. Which modified thinset that you know of that would work on both? or should I just use different thin-set for the BB and the porcelain tiles?

07-17-2011, 11:23 AM
You dont need your backer to bond to the OSB. The thinset is mainly to fill voids or as one of the guys on here put it "to hold the backer up" your anchors hold the backer down. You just dont want flexible pocket between backer and subfloor. So that multi purpose thinset will work for both. You are right NO premix!

07-17-2011, 09:44 PM
Hi Peter, the Multipurpose pro will be fine for under the CBU and for setting the tiles. :)

07-17-2011, 10:45 PM
Thanks everyone for the recommendations.

Custom Building Products FlexBond thin-set claims flexibility up to 1/16" movement. Is there any truth to this marketing hype? HD wants $30 for a 50lbs bag.

07-17-2011, 11:08 PM
Peter, you gotta believe whomsoever you wanna believe. Why ever would you be more inclined to believe people not known to you on an Internet site than you would the manufacturer of a particular product? :)

It would be my guess, completely uninformed, mind you, that CBP had that particular product tested in hopes of meeting the requirements of ANSI A118.12 for Crack Isolation products, but it didn't qualify. But it did apparently offer some resistance to cracking so they, quite fairly, included the applicable test results in their advertising.

What's that mean to you? I dunno.

If you're interested in using a crack isolation product, I'd suggest you use something that says it meets the requirements of A118.12. Flex Bond indicates it meets A118.11. That means it's a modified thinset mortar capable of bonding to materials up to and including exterior glue plywood.

It'll work for everything you've indicated you want to do. Is it more than you need? I think probably so, but that's up to you.

Homer also sells VersaBond, also made by CBP. Will it also do everything you've indicated you want your thinset mortar to do? Yes, it will.

Or the Laticrete Multipurpose Pro that MMike has recommended.

My opinion; worth price charged.

07-17-2011, 11:17 PM
I will probably go with Laticrete. I just found interesting what they claim the product can do. I did not know that the thin-set has to meet ANSI A118.12 to be qualified as a Crack Isolation product.

07-17-2011, 11:26 PM
Any material that wants to be called a Crack Isolation product in the tile industry must meet that standard, Peter.

My opinion; worth price charged.

07-28-2011, 08:42 PM
I have an area that will be tiled it's sitting on 13.5'-14' joists (2x8) spaced about 16" . The ends of the Joists are sitting on cinder block walls, they are fully supported by two cinder walls (crawl Space). Now If I use the deflecto, it says not to use tile. The house was built early 2000.

Is there any exception to the rule? The floors are solid no squeaks whatsoever.

07-28-2011, 09:08 PM
The ends of the Joists are sitting on cinder block walls, they are fully supported by two cinder walls (crawl Space). I can't tell what you're saying there, Peter. Are the joist supported only at the ends and nowhere else? You need to know the longest unsupported span.

07-28-2011, 09:30 PM
The longest unsupported span is 12-13 feet. I forgot to mention that the joists are tied together by two pieces of wood (Cross bridging).

Two installer so far did not see any problem tiling that area

07-28-2011, 09:36 PM
The cross bracing doesn't help the design deflection rating, Peter, but it does help you benefit from what you have.

Can you find any sort of grade stamp on one of those joists?

Was this house built within a code compliance jurisdiction?

07-28-2011, 09:40 PM
Can you find any sort of grade stamp on one of those joists?

I will try to find the grade stamp.

Was this house built within a code compliance jurisdiction?


07-28-2011, 09:46 PM
Now, we've gone from"13.5 to 14 feet," to "13 feet," and now I see it's changed to "12-13 feet." That makes a difference. We gotta have a specific unsupported span to work with, eh? :)

07-28-2011, 09:49 PM
I will get the exact measurement and report back.

07-29-2011, 09:14 PM
Joists 2"X8" (1.5"x 7") 16 oc spanning 13.5 '. The area has 15 joists. The builder decided to reinforce 1/3 of the joists. They sistered 5 of the 15 joists. There wasn't any stamp on the joist that I could see.

07-29-2011, 10:01 PM
Pure guessing here, Peter.

Your builder framed that structure and the inspector told him it wouldn't fly. Builder told the inspector he could sister every third joist and it should average out to the required L/360. Inspector figgered the math would cover his ass and put a green tag on it.

Our Deflectometer is a pretty conservative creature, by design. Our visitors are seldom dealing with new structures and are nearly always adding a good bit of dead load. We use the full 50lb/sq/ft dead and live load in the calculation, rather than the customary 40lb. Makes for a more secure feeling, eh?

But if your house passed a code compliance inspection for the framing, any pro who elected to tile it would have industry backing. You don't even need that if you wanna tile what you've got for joist structure.

Which brings us to the subflooring, which I can't find any reference to. That's actually more likely to be your point of failure than the joists, and given how little material was put into the joists, I'd be concerned with your subflooring, too. What'cha got?

My opinion; worth price charged.

07-29-2011, 10:12 PM
They used 23/32 x 4 x 8. There is also 1/4 inch plywood on top of the sheathing.

07-29-2011, 10:29 PM
Boy, Peter, you just can't catch you a break at all, here.

The quarter-inch ply, most likely Luan, has gotta be removed. Non-structural and you don't want it anywhere in your tile package.

Is the 3/4" subflooring of the tongue & groove variety? Can you see any grade stamps on it from below?

My opinion; worth price charged.

07-29-2011, 10:39 PM
It's marked T&G 24oc Crossbands under Face Exposure 1 PS1-95 undelayment. Do I need to beef up the joists? I can get few 1.5"x7"x8' and sister them to the existing joists. How many will I need? Will it help?

07-30-2011, 10:07 AM
Any ideas?

07-30-2011, 02:27 PM
If you can't sister all the joists under the tiled area, then don't sister any of them. If it helps, the sisters need only span the middle 2/3's of the joist span, so that may resolve some interference issues. You'll need longer 2x8s to sister the middle 2/3s.

The plywood is good.

07-30-2011, 04:17 PM
If I understood you right I will need 2/3 of 13.5'. About 9 feet of 2x8. I need to run them from one wall. So 4.5 feet can stay unsupported. I may be able to sister 6 more but not all because of the electrical wires running through the 2x8. Some ducts and plumbing make it impossible to sister 4 of them.

Can I still tile that area with what I have without sistering any of them? is that an option?

Thanks for the help

07-30-2011, 04:22 PM
Nope, doesn't work that way, Peter. Read again:the sisters need only span the middle 2/3's of the joist span...[Emphasis mine]If you can't sister at least the center 2/3rds of the joist, save your time and money and don't bother.

07-30-2011, 04:29 PM
I am not in the construction business. This will be the first time for me doing it. Can you explain to me what you mean by center 2/3rds of the joist. I don't understand it. If you have a picture or a drawing, that will help me understand it.


07-30-2011, 05:00 PM

When you said.
save your time and money and don't bother

Were you referring to the sistering of the joists or the whole project?

07-30-2011, 05:02 PM
Peter, your joist is 13.5 feet long, or 162 inches. Half that is 81 inches. Measure from either end of your joist 81 inches and you are at the center. Make a mark.

You must sister 2/3rds the total length. That's 9 feet, or 108 inches. Half that is 54 inches.

Go back to your center mark and measure 54 inches in each direction from the mark and make two other marks.

The span between those two distant marks is the minimum space where you must install your sister joist with construction adhesive and mechanical fasteners for it to be effective in reducing your joist deflection.

I was referring to the sistering of the joists.

My opinion; worth price charged.

07-30-2011, 05:29 PM
Thanks Cx and Bob. I don't think it's feasible to sister all of them. I am not going to bother then. But I will proceed with the tiling of that area.