filling control joints in concrete

Discussion in 'Floor Preparation' started by Mike Biedenharn, Dec 7, 2017.

  1. Hi all. I was sent here by @Kman on the John Bridge forum. they turned me into a pretty good tile guy and said you guys know your stuff on the vinyl. So.....
    I am finishing a basement. Glue down LVT over concrete (11 year old concrete)that is in like new condition. My question is; what is the best product to fill the designed expansion joints. The tile instructions say a Latex fortified Portland cement product, but if I use that, the joints are no longer expansion joints. My thoughts are a product like Silka, but I wonder if I will have problems with the vinyl cracking over those joints if a chair rolls over it or a load like high heels were placed on it.

    I don't think the slabs are moving anymore (after 11 years) but the earth moves.

    The joints are about 3/4" wide and 1/2" deep. I have almost 100' of joint total (2600 sq.ft basement) If I go with the silka, I will install backer rod to fill the cracks. I'm looking for advice from guys who know. I would rather not have to do any warranty work since I'm not paying myself to install it in the first place.

    Thanks for your help! Mike Biedenharn

    Hilliard, Ohio
    Last edited: Dec 7, 2017
  2. Here is picture of one of the joints. Hope it helps.

    Attached Files:

  3. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    Strange dimensions 3/4 wide, 1/2” deep.

    #1 reason for failure, Flooring is not supposed to bridge expansion joints. You have a close up shot?
  4. I can get one in the morning.
  5. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    Expansion joints are all the way through. Maybe control joints? There will always be movement. I prefer Feather Finish by Ardex. Joint may show down the road by movement, nothing you can do. So, hardness/softness of fill material, I still do not think it will change the aesthetics of fill material bulging out. (Wasted money on the filler)

    I think World of Concrete in a month has some seminars about concrete not needing any joints. I’m not going but dam there’s S-loads of info there, basically new methods though plenty of old slab technology.
    Last edited: Dec 7, 2017
  6. Here they are 20171207_201159.jpg crack2.jpg
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  7. And control joints - not expansion. (good catch)
  8. Jim McClain

    Jim McClain Owner/Founder Administrator

    I would grind down the sides of those joints to comply with the standard flatness of 3/16" in 10'. Then I would fill only the crack at the bottom of those joints with a small bead of silicone (not forcing it deep into the crack). Then I would fill the rest of the joint with Ardex Feather Finish (mixed with an additive for flexibility), followed up with skim coating the entire floor with the same. Two or 3 coats of FF over the floor might give you a smooth, flat surface to install your LVT.

    That isn't how I would do it in a commercial setting, but in a residential application, it would probably do well.
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  9. so when can you come over?

    Sounds good. I don't like the suggestion of floating the whole floor, but you are the expert. That is going to be a lot of work.

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  10. Jim McClain

    Jim McClain Owner/Founder Administrator

    I don't think you want me to come over to do your floor prep. ;)
  11. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    I wouldn’t separate the FF. I would press FF down into the separated slab and skim the top. It would somewhat help the patch stay together/ hold better. I think the separation is too small for backer rod. The patch will not sink like self leveling joint filler.

    I can’t see the slab too well but Jim says it needs skimcoat, I see from one pic some shady surface separation spalling where the corners of control joints are. What does the sharpie markings represent? So, grinding and skimcoating, doesn’t look like the concrete finishers were planning on a Finish Floor.
  12. Chris 45

    Chris 45 Director of P.R. on some deserted island. I Support TFP

    If glue down LVP/T is going to be installed, I’d say the skim coating is necessary if you don’t want to see what you didn’t prep over after the floor is laid. Floating LVP, I’d just deal with the joints and any obvious pits, divots or holes.

    I would plan on a whole day, and a unit of Ardex, for just prepping the joints and a couple skim coats. Would be worth renting a floor buffer and a sanding plate with some 12 and 16 grit discs to make that floor smooth.
  13. epoxyman

    epoxyman Pro Member

    That joint looks like more of a cold joint
    Then a cut joint with a saw
    Was it were they stopped and started pouring the slab at
  14. - You can just drink beer and point your finger. That is how I help people learn when I am the expert.
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  15. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    The shape of the joint bothers me too. Looks like a masons sled runner for dressing horizontal block joints.
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  16. The marker is where there are spots I need to hit with the grinder. I don't think they are cold joints (picture doesn't do it justice) the concrete guys just put in a giant control joint. It seemed like #1 they forgot the right tool and #2 they weren't going to come back and saw the joints so they might have used a trowel handle to make the control joints.

    Lastly; it is a glue down, not a floating floor. Most of it looks great, and I could probably live with it without the skim coat. But, if I don't do the skim coat and it looks bad I won't know who to blame (cause it won't be my fault- it's always someone else's fault)

    I would rather spend $200 on 6 bags of FF and put the time in. How thick do you put Feather Finish on for the skim coat? Is it truly just a skim (1/16" or less) to fill low spots and imperfections?
  17. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member


    I didn’t finish reading the article. But to date I haven’t seen a successful filler yet.

    I wonder if artists work with feather finish, the stuff is that good once you know it’s characteristics. At my local pool store the floor isn’t too flat. I took the picture because I saw the adhesive swirls though it didn’t show too good in the pic.

    Attached Files:

  18. Update on my job. Thank you for all the advice. It took 4 bags of Feather Finish and lots of grinding and sanding. I was too cheap to rent a big sander, and I have a couple hundred packs of 110 grit for my palm sander so I did it all by hand. (not recommended by the way)

    Floor 3.jpg Floor 2.jpg Floor 5.jpg Floor 4.jpg
    Last edited by a moderator: Feb 14, 2018
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  19. Chris 45

    Chris 45 Director of P.R. on some deserted island. I Support TFP

    Looks good. When I’m sanding prep with my palm sander I’m usually using 40 or 60 grit. 110 must have been painfully slow. You were almost polishing the patch ;)
  20. Saving $100 cost HOURS of my life. And it wasn't very dust frindly. A floor buffer with the sanding adapter would have been a much better choice.
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