I recently replaced the broken wood threshold at my door with a new oak one that I finished with Spar Varnish. The lumber store suggested using "Liquid Nails-Heavy Duty, LN-903" to secure it to the concrete floor. However, the original builders had used uneven small concrete blobs to support the old threshold, so I needed to apply the Liquid Nails quite thick, up to 1/2" in some spots. After weighing it down for 24 hours, I found that it hadn't set at all, and the threshold could still be moved easily. I removed it and reapplied more Liquid Nails, but I'm wondering if this adhesive will ever fully cure, or if I'm using the wrong type for this thickness. Would an epoxy be better, or should I just wait longer? The Liquid Nails worked fine on a thinner application earlier, but now I'm uncertain about the best approach. I've also considered nailing it down, but I'm worried about messing up the alignment or the concrete being too tough for screws.
3 Answers
Concrete often has a dusty surface that can make it difficult for adhesives to stick. It can also absorb moisture quickly, which may interfere with the bonding process of the Liquid Nails. Additionally, it sounds like you may be applying it too thick, which isn’t how it's meant to be used. I suggest cleaning up the concrete blobs and leveling the surface first, then adding a mix of cement mortar to fill gaps before using a thin layer of adhesive. Priming the concrete first can also help with adhesion; that might give you a more solid bond for the oak threshold.
From my experience, construction adhesive can struggle with concrete. I've had better luck with flooring glue, but that doesn’t fill gaps. Also, if your threshold is sealed, the Liquid Nails might cure slowly. I recommend using plastic shims to level it instead of relying on adhesive blobs. Once everything's secure with the shims, you can apply the construction adhesive and it should hold better. If the shims shift, try hot glue to keep them in place while you fit everything.
Give it a few days; sometimes it just takes time for heavy applications to set. You could also try using a heating pad to help with curing, although make sure it's not too hot that it damages the wood.
That's interesting! We had a freak rainstorm right after we installed, so I'm sure the concrete got damp. Maybe that's affecting the Liquid Nails.