Prep needed for laminate over old slab

Discussion in 'Laminate Flooring Q&A' started by KevinPo, Feb 12, 2020.

  1. KevinPo

    KevinPo Member

    Hey guys,
    I have a 71 years old slab. Due to the overtime settling i have a hump close to one end of the room. The floor slightly slopes over 30ft. The hump is close to 8 ft of one end which is the higher end. This high section is 1/2 to 5/8 higher than the lowest. I can say the permiter of room is lower for sure but it fluctuates between 1/4 to 5/8. Needless to say wavy but low around the permiter (foundation and middle of basement. This room is separated by a wall with the unfurnished side)
    To make matters worse, we used to have asbestos tile and cutback. I had an abatement company remove it since most tiles were popping off.
    They wet grinded the cutback and removed the residue with chemicals. I see that some manufacturers mention chemical remover create a layer similar to a sealer which can mess with bonding.
    SLC can be too much. Im not looking to level the room. Just flat. Would something like feather finish with screeding work? As said before high spot is a not small bunp but more of a gradual bump which is 6x6 ish.

    I attached pics. High point is where the laser is. We have grinded some high spots already

    Attached Files:

  2. Daris Mulkin

    Daris Mulkin The One and Only Charter Member I Support TFP Senior Member

    You don't say what you are putting down. That may help with the answers you get.


  3. KevinPo

    KevinPo Member

    Oh my bad. I left in the title. Laminate flooring. We have cats so carpet is not a good option with all of the hair/scratching. We have friends who have allergies and carpets make it very hard to manage. Tile is a no for us since sab is not insulated and I am in MN so winters will be very clod. Also tile is not that forgiving with what I have
  4. Chris 45

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

    You can screed out Feather Finish. Prolly a little easier to pull off than self leveler too. Just work it in bite size chunks. Have you done any moisture testing on your slab? It’s cheap compared to a flooring job gone south.
  5. KevinPo

    KevinPo Member

    We have never had any moisture issue but i rather not skip it.
    Would feather edge require concerte grinding in my case?
  6. Chris 45

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

    The more grinding of the high spots, the less filling of the low spots. I’d do a combination of both to achieve an acceptably flat floor but you can certainly skip the grinding and just screed out the low spots.
    • Agree Agree x 1
  7. Incognito

    Incognito No more Mr. Nice Guy! I Support TFP Senior Member

    It's a lot easier to FILL the low spots with patch than it is to scabble/bush/grind the high spots of a concrete slab.

    scrabble/bush/grind concrete - Google Search

    Get a 10' piece of metal or wood or pipe that has near zero flex------a STRAIGHT EDGE. You can also use mason line (string) with duct tape. From the HIGHEST POINT in the area swing the string or straight edge around to see how worse/worser/worsest your concrete slab REALLY is with an accurate measure of what is the EXTREME problem areas over a 10 foot span. Manifacturer's want no more than 3/16". I wouldn't allow more than a 1/4"

    Whether to grind or fill/float/screed depends on what happens when you try to raise the floor height when you get to fixed thresholds like exterior doors, windows, cabinets, appliances and such.
  8. KevinPo

    KevinPo Member

    I measured all low and high spots with my laser. Funny thing is I went to HD and grabbed a 10ft 2x2 aluminum bar. Works pretty well. I can say in most areas in a 10 ft radius the lowes are within 3/16 but it can dip in some point close to 5/8.
    So let me ask this. I know my high point. When i set my straight edge that is my center and point of start. How far do i need to move out for new point of reference? At the end of the 10ft or moving every few inches to find all low spots. Do you know what i mean?
  9. KevinPo

    KevinPo Member

    Also as mentioned before the mastic was wet sanded and then chemical remover and scrapper was used to lift us the mastic. At this point we can asbestos is gone and all is left is staining. But the chemical remover will leave residue on the surface. Does that need to be grinded down in order for any patch to work? If yes, do you think there are any risks with sanding it?
  10. Chris 45

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

    You will want to meet the 3/16” in 10’ anywhere you place your straight edge. Whether you move your straight edge 5” or 5’, you’ll need to conform to the flatness requirements. Just move it all around and any low spots you find will need to be filled in.

    As far as grinding, I hope you have HEPA dust containment and an appropriate dust mask. Feather finish will stick well enough to what you have going on right now if you choose not to grind any more. I’m not even grinding concrete and I have this baby rolling all day long.

  11. KevinPo

    KevinPo Member

    Thank you! I prefer not to grind anymore. I dont have a HEPA containment air filter. I have a p100 mask and HEPA filter on my shop vac.

    So here is the crazy thing. My tile guy grinded those spots down last year. They are good but some young guys are crazy and won't listen. I put sheets up to contain the area and opened up the windows. I came down an hour later and watch them both grinding concerete with no mask or shop vac/shroud. Room was filled with dust so im like 'WTH...thats not good for you'
    I handed them some n95 i had and they said nope to them. One wrapped his shirt around his face and the other didnt use anything... i hope they have a long life but man lung cancer is not fun.
    I can say that they put thinset in some areas to fill low spots but there are tons left. So i guess if thinset sticks, feather finish should be fine as well.
  12. Chris 45

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

    OSHA would eat those young guys alive right after I called them.
  13. KevinPo

    KevinPo Member glad i put sheets up. Just imagine how much dust would have gotten into the rest of the house, ducts, and...
    I just dont get it. Im not a contractor but if I was, i would never let my subs do it that way. As a homeowner all i can do is to make sure im safe...
    I also spray foamed the basement and one of the guys in his early 20s refuses to wear mask during any insulation work...people dont make sense most times
  14. Chris 45

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

    I could care less what those guys choose to put in their lungs but that could get real expensive when they have to pay to have your house and ducts cleaned. Some years ago we had a couple morons set up their table saw in the customers living room. I believe they owed more than they made that day.
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