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I have a tongue-and-groove laminate floor, laid on 3mm foam underlay on concrete slab. After around 10 years of use, the long edge of one floorboard now drops around 1mm when stepped on. I think there was a slight step or ridge in the concrete slab here, the floorboard was supported by being locked to its neighbour, but now the tongue has snapped off. (Photo below shows pushing down hard on the broken edge.) under load

The floorboard is right in the middle of a large open plan space and lifting the surrounding floor is not really an option. There is also no clearance between the board and its neighbour to insert any tool.

My plan so far is:

  • drill some small holes (say 2mm) through the board close to the sunken edge;
  • insert screws in some of the holes, and turn until the board is lifted level with its neighbour;
  • inject some kind of liquid resin through the other holes using a syringe, and plug the holes with more screws;
  • once resin has set, remove screws and fill the holes with matching filler.

Does this sound like it would work?

What could I use as the liquid? It needs to be very thin, but probably not water-based. I have no experience with resins and no idea what to use.

Thanks in advance.

  • You have a picture? – J D Apr 7 at 5:25
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    My instint tells me that any liquid that's too thin will want to seep to the surface in between the tongue-and-groove which are, likely, not water-tight. Maybe larger holes and self-levelling compound through a funnel MAY do the trick? – FrK Apr 7 at 6:46
  • @JD added a photo. No wide angle but the total length that sinks under pressure is about a foot long. Either side of that there's no movement, so I expect those parts are better supported. – Roofus Apr 9 at 1:39
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    @FrK I was hoping I could add just enough to liquid to fill the space, so I would stop as soon as it starts overflowing. I planned to use something that did not expand. Self levelling compound worries me a little as the boards are MDF and easily damaged by water and may absorb water from the self levelling mixture. – Roofus Apr 9 at 1:43
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I had something similar done on two different floors (solid wood herringbone parquet and more recently on an engineered wood floor). I assume the same trick will work for laminate flooring (given that it's pretty similar to my engineered wood example).

The trick was to use low expansion polyurethane foam to fill in the voids underneath the flooring. The foam comes in a can ending with a ~2 mm diameter pipe, so all you need is to drill suitably sized holes into the floor, stick the pipe in and carefully inject foam until everything is level again. Of course you can't do this with ordinary PU foam as that expands a whole lot and would rip your floor out.

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  • That is a very good idea, I'm just worried about how much to add, once it's there it would be very hard to do anything if it swells up more than expected. I guess I could make up a test bed using some spare materials and a spare floorboard and see what happens! – Roofus Apr 9 at 1:45
  • I wonder if molten wax would work? -- it doesn't expand! – Roofus Apr 9 at 1:49
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    Foam MIGHT work, although it cracks easily under pressure (at the end of the day, the structure once cured is made of air bubbles). The key thing to watch out for during installation, as Roofus mentioned, is how much it expands. – FrK Apr 9 at 6:53
  • @FrK I had a specialized floor renovation contractor do it on both occasions, so I don't really know how they get the expansion right. Either way, they were injecting the foam really really slowly (and I guess they know the stuff they're working with). Cracking doesn't seem to be a problem (after 8 years), even though the repair was done in a doorway. – TooTea Apr 9 at 7:04
  • @Roofus Whatever you pick, you'll have to use a whole lot of pressure to inject it if it's something as thick as molten wax. I guess that's why foam works, it's a thin liquid until it cures and it's under pressure in the can. – TooTea Apr 9 at 7:06
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Well, if that's a typical laminate like Pergo, and not an engineered wood, then the stuff is relatively flexible. I'd take a broad (maybe 4" or 6"), thin mudding knife (the thinner the better), and try to shim it in between the boards vertically, and the bend the handle towards the highboard to lever it up enough to lift and flex the lower over the higher. Then, if you place a few thin door jamb shims or a even better some popsicle sticks (although anything on par will do) to keep the separation, you might consider using some shims with adhesive on top (to affix the shim to the bottom of the low plank) to level the edge so the two planks are even.

If you're looking for a precise match, you can mark the offset and use a micrometer to know exactly how thick your shim should be on the thick end. Might even be a good idea to give yourself a tad extra to account for a depression in the foam depending on how wide your shim(s) is/are. The core of laminate is practically cardboard, so breaking more of the edge should be a primary concern, and I'd proceed very slowly starting in the dead center of the blank where you'll have the most play.

The other issue may be that the lip isn't fully broken off between the p planks. Then scoring with a utility knife ideally without cutting the foam/plastic barrier might have to occur. Let us know if you solve it!

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  • Unfortunately I can't fit even a sheet of paper down the gap between the board and its neighbour, let alone a tool. I'm still favouring the drilling method, and I might try screwing a screw into one of the holes and seeing if it can lift the board far enough to push something under. I'd hate the screw to pull out though as it would make a pretty messy hole. Anyway will definitely post the result. – Roofus Apr 10 at 7:01
  • Man, I hate laminate. I suspect a coarse threaded screw is going to rip through the pressed board and that surface always cracks and fractures. Another strategy might be to take a drill right near the edge, and drill a hole large enough to accomodate a hooked pick to pull up the end. When you're done, fill it with some putty. – J D Apr 10 at 21:06

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