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I am planning to build a workbench and want to use layered plywood for the bench top. To keep costs down, I am considering using 3/4" OSB for the base and glueing 1/4" plywood on top instead of layering 3/4" plywood (I'm fine with the slight difference in sizes).

With OSB being more textured than regular plywood, will I have problems with the glue not covering evenly and ending up with a weak glue job?

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  • I don't see why glue would be any problem here. You have so much surface area, it would be fine, even without a perfectly smooth contact. However, have you considered the advantages of screwing the top down instead of gluing it? That way, it could be a sacrificial top. You could easily replace it when it gets beat up. That's what I've done on one of my workbenches. Cheap 3/4" plywood as a base, with another 3/4" nicer grade plywood as the sacrificial top. Jul 18 '15 at 3:45
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With OSB being more textured than regular plywood, will I have problems with the glue not covering evenly and ending up with a weak glue job?

Weaker yes, but it shouldn't be a problem as there is still ample surface area. Some additional care would be advisable to ensure a successful bond forms.

Firstly, in case you're unaware wood surfaces to be glued should be freshly worked — that is, they should have been planed, cut, scraped or sanded recently — for a proper glue joint to form. And with sheet goods some sanding is considered a good idea anyway to remove any minor surface contamination it may have accrued during storage and from handling with bare hands.

So lightly sand both surfaces to be glued, spread a thin even layer of glue over both boards (a hard rubber or plastic roller can work well here if you have one) and then bring the boards together and 'clamp' using heavy objects. Use plenty of weight spread around the boards, you can use paint tins (full), stacks of books and even bottles of water to supply the clamping force.

Wood glue is very lubricative, so watch out for some slippage as weight is applied.

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My application is OSB to SPF (2x BORG lumber), and I could not find definitive data about appropriate glues for OSB and other resin-based engineered wood materials, so I called Titebond / Franklin International, and spoke with one of their engineers. His first recommendation was to use their polyurethane construction adhesive, noting that its gap-filling properties would be helpful to overcome the rough surface of OSB. While PVA glues (Titebond II, III etc.) can reach strengths approaching 4000 psi on normal wood, he noted that OSB tends to fail around 700 psi.

Therefore, regular PVA wood glue is actually fine in this application, because OSB itself is the limiting factor. He cautioned their PVA glues do not fill gaps well, so the surfaces should fit together well (i.e. flat), and said to not over-clamp. I asked about the 100-150 psi clamping recommendation for softwoods on their chart and he said that number is actually for pieces that may not fit perfectly, so very flat, well-fitting pieces need even less clamping force.

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    Hi Scott, welcome to Woodworking. I have to be honest here, I'm not sure if the engineer you spoke with is actually repeating his company's actual info. The warning not to over-clamp set my alarm bells going for sure, because this is basically impossible in the home workshop! So in actual fact "over clamping" isn't even really a thing, not as far as we are concerned. I've tested this myself by clamping small pieces with a ridiculous number of C-clamps — by far the strongest clamps I own — and couldn't get a joint that failed due to glue starvation (the supposed consequence of overclamping).
    – Graphus
    Dec 12 '20 at 8:33
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    Hi @Graphus, thank you. Clamping pressure is a bit of a separate topic from the OP but based on this Fine Woodworking article, recommended clamping pressures vary by an order of magnitude depending on the wood and grain: finewoodworking.com/2010/05/11/… Matthias Wandel's tests here woodgears.ca/joint_strength/glue_methods.html also found that the surface texture makes a difference-- too smooth, and too high of pressure did weaken his joints somewhat.
    – Scott
    Dec 14 '20 at 14:07
  • As I've cautioned many many times over the years, please don't pay much attention to Matthias's tests, they're fundamentally flawed in many ways. He even acknowledged a problem at the time, and has never in all the years since bothered to repeat the testing to get a proper data set. And really, there's no such thing as too smooth for a joint surface as long as the wood hasn't been burnished. You can confirm this easily in the home workshop by comparing edge-joint strength between planed edges and those achieved by other means.
    – Graphus
    Dec 14 '20 at 21:26

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