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I have one curved staircase riser I need to veneer or otherwise match with hardwood floor. All the other risers are going to be done with thin plywood and clear coated (treads will be assembled from hardwood planks and nosing).

There was carpet installed on those stairs, so the wood underneath is fairly rough, splits, cavities, etc. My first attempt with liquid contact cement (solvent based) failed miserably, there are bubbles and splits, etc.

There is no way I can think of clamping it over whole area (especially the curved part), so whatever is used should stay put with minimal support.

For the next attempt I'm looking at sanding failed veneer down to base wood and applying new layer with polyurethane construction adhesive (PL Premium, or one of the variants). The idea is to heat it up a bit so it flows better, spread it evenly on the vertical riser with a trowel or a roller, then apply paper-backed veneer, roll it out to get an even surface (small waves are ok), then support it with a few boards (might actually sit fine as is).

The idea is that PL will fill the cavities and act as a bodyfiller under veneer, and if I manage to get a fairly smooth surface, it will stay like that forever.

The floor and stair are in natural maple, so any kind of light wood look should blend well.

The question is: will this work? Does anybody use polyurethane glues for veneering? What problems should I anticipate?

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    Kudos for putting together a well-worded, comprehensive Question; we don't get those here as much as we should. Unfortunately I have nothing for you other than to suggest you try a test and see how it goes! You might get one or more suggestions for this to be a better fit on DIY but I don't think that'll help in this case. I think this is one of those things where you have to try a test yourself — even if someone(s) say they've done the same thing their situation won't exactly match yours and any, or all, of the variables may have an effect. [contd] – Graphus Nov 26 '19 at 9:41
  • You can take it as a given that their veneer will not exactly match yours, they might have used an adhesive with different properties, temp/humidity are certain to be different and so forth. So any successes (or failures) don't necessarily inform what you can do. Best of luck! – Graphus Nov 26 '19 at 9:42
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    If you can't clamp it, will heavy weights applied across the tread surface work. I once glued down a thin plywood sheet with quite a few concrete blocks. – Ashlar Nov 27 '19 at 0:50
  • @Ashlar, yes weight as clamps can be a good solution sometimes. But you need to go really heavy, like with the concrete blocks you mention, for it to work well IME. A few half-empty paint tins won't cut it :-) – Graphus Nov 27 '19 at 9:10
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    The normal way to do this is to cut kerfs every 1/2" or so in the backside of the riser material. They should come to within 1/16" of the show surface. Then the riser can be bent to match the blocking without any DIY veneering. – SaSSafraS1232 Dec 3 '19 at 0:52
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Ok, so I ended up gluing felt-backed flexible birch veneer with PL Premium, the 3X stuff. I also had a tube of 8X, but I could barely manage to get it out of the tube, forget spreading.

Some notes:

  • Takes a lot of adhesive -- surface area slightly smaller than two standard risers took more than 2 tubes of PL, so have a few extra on hand.
  • V-notch tile trowel works great, plastic adhesive trowel would have had too-small notches.
  • PL sticks to vertical surfaces very well and doesn't seem to run.
  • Use a lot of painter's tape, and cover decorative side of the veneer completely.
  • Veneer will mostly stick to the surface, but some support is needed, or it could peel off under its own natural tension.
  • Have lots of paper towels on hand.
  • Don't roll it out like contact cement, this will push out too much adhesive and telegraph all surface defects, a flat board at moderate pressure should work fine.
  • Bubbles (I got a few after applying water based polyurethane a day after) can be pressed down and clamped a day after application (depending on humidity/temp/surface permeability affecting curing speed I guess) -- I left it clamped for another day and they were gone.
  • PL will expand slightly and ooze from the sides a bit while curing
  • I clamped the flat side using 2 1x4s brad-nailed boards on the sides and some staples through a piece of plywood at one edge of the curved surface. A melamine board would do better here.

Overall this worked out nicely, much easier to work with than contact cement in this configuration. I got a few bubbles, and I rolled out too hard, so got some depressions manifesting that I could have avoided. But overall it feels solid.

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  • Excellent, well done for trying it for yourself and documenting some of the ins and outs. – Graphus Dec 5 '19 at 9:07

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