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Unread 09-09-2020, 01:05 PM   #1
Scott12345
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Backer Rod for 1/8" movement joint

Hi, I've just finished grouting a 16' by 25' space with Mapei Flexcolor CQ. 12" by 24" tiles over Ditra with 1/8 inch grout lines. Schluter recommends a surface joint to break up spaces over 20'. I did not install a Schluter movement profile but left a grout line mid-field ungrouted and will caulk with Mapesil-T.

I have seen that the caulk is only supposed to make contact with the edges of the tiles and not with the bottom of the grout line. I cannot find backer rod this small at local shops. 3/8" is the smallest available and given that a 1/8" movement joint is the bare minimum I want whatever I use to be flexible as possible and not to be jammed in tight.

Grainger carries several types of 1/8" rubber cord: Buna-N Rubber cord, Neoprene Rubber cord, Silicone Rubber cord, EPDM Rubber cord. Will one of these work? Or is there a source for backer rod that I'm missing?

Thanks! Scott
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Unread 09-09-2020, 02:04 PM   #2
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Hi Scott,

I usually don't use backer rod for tile floor joints. I don't know how thick your tiles are or how much thinset is in the bottom of the joint, but I would just caulk it.
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Unread 09-09-2020, 02:52 PM   #3
Scott12345
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Hi John,
Thanks for the quick reply! It's porcelain about 3/8" thick and the grout line is about 1/2 inch deep.

I was looking at the liberry post on expansion joints which is why I was asking about backer rod. In the post however the author mentions having sealant be at a depth that is equal to half the width of the joint which in my case would end up being 1/16" of silicone. That doesn't seen right... I'll poke around the internet a bit longer to see if can find small backer rod as I only have two tubes of Mapesil T.

Scott
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Unread 09-09-2020, 03:43 PM   #4
Dave Gobis
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Been a long time but we used to order a roll of pencil rod, which is 3/16 at the local masonry shop. Never was able to find small amounts.
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Unread 09-09-2020, 04:11 PM   #5
Radas
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Right, wrong, or indifferent, I've used screen spline for 1/8" movement joints under silicone with successful results.

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Unread 09-09-2020, 06:03 PM   #6
cx
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Quote:
Originally Posted by Scott
In the post however the author mentions having sealant be at a depth that is equal to half the width of the joint...
Yeah, Scott, technically this is what the ideal caulked joint should look like:

Name:  Caulking Bead.jpg
Views: 98
Size:  33.3 KB

Commonly a fella just tries to get as close to this as he can.

Ali is going straight to Hell for using screen spline as backer rod! Primarily that's because I never thought of it. If it'll fit in the joint and if your chosen grout won't stick to it, I can't think of any reason it wouldn't work, even being ridged like most of it seems to be. Possible if you're careful you could even get it down into your joint only far enough to approximate a "perfect" bead profile or at least you might get a lot closer than just caulking the joint full.

My opinion; worth price charged.
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Unread 09-09-2020, 11:12 PM   #7
Radas
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Hahaha CX, definitely not my first choice but the only damn thing at Home Depot that was flexible and fit a .12" joint. The stuff I bought was $3 and also had a hollow center with some decent "give" to it. Figured it'd do just fine between Schluter Schiene and hardwood flooring.

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Unread 09-10-2020, 09:03 AM   #8
Scott12345
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Thanks everybody! I'll give the screen spline a shot. As the gap is 1/2" deep I figure I can get two or three layers of of screen spline in before the silicone. Or perhaps like CX mentioned just one will have enough friction to hold in place.

I did find an online source for backer rod although the smallest they carry is 1/4". https://www.bestmaterials.com/Backer_Rod.aspx
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Unread 09-10-2020, 01:08 PM   #9
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Get some sill plate gasket at home depot and cut narrow ribbons of it to fit in the joints. It's about 1/8 in thick.
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Unread 09-10-2020, 03:34 PM   #10
jadnashua
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Quote:
Originally Posted by Paul
Get some sill plate gasket at home depot and cut narrow ribbons of it to fit in the joints.
You want the profile to be round to get the hour glass shape to the caulked joint. Cutting strips from a flat sheet would be flat...not ideal.
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Unread 09-11-2020, 07:16 AM   #11
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I had zero luck finding small diameter foam backer that didn't come in a 500 foot roll.

The screen spline is genius.
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Unread 09-11-2020, 07:58 AM   #12
speed51133
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https://www.zoro.com/e-james-rubber-...YaAhHJEALw_wcB

Here is 1/8in neoprene.

Will the 1/4in backer not compress? I have used it in saw cuts in concrete no problem. Those are about 1/8in. Just press it in with a flat screwdriver.

I also found EDPM foam (closed cell) here in 1/8in. That should be a home run: https://www.mscdirect.com/browse/tnp...caAuD-EALw_wcB
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Unread 09-11-2020, 09:48 AM   #13
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That first link sounds much like Ali's screen spline material, Mike, but maybe even harder. At a Shore A hardness of 70 I don't think it's gonna have much give when putting it in a grout joint. But if the size were right for the application, I can see it working fine.

The second link sounds like exactly what most of us have not been able to find. At thirty-something cents per foot it's a lot more expensive than the hard stuff in the first link, but would certainly be easier to get into joints that were a bit tight.

Good information.
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Unread 09-11-2020, 10:06 AM   #14
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https://www.mcmaster.com/epdm-cords/...dm-foam-cords/

half the price
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