Ever stared at a half‑finished frame and wondered why the timber looks “off” even though you’ve measured twice?
The missing piece is often something so simple it gets skipped: the blank that sits on the timbers or is cribbed in place. It’s the quiet hero that keeps everything level, dry, and square. Skip it, and you’re courting squeaks, rot, and a lot of re‑work later No workaround needed..
What Is a Blank on Timbers or Cribbed?
In plain English, a blank is just a piece of material—usually a strip of lumber, a metal plate, or a composite shim—inserted between a structural member (like a beam or post) and the surface it rests on. Think of it as the “cushion” that takes the weight, spreads the load, and protects the wood from direct contact with concrete, soil, or another timber.
Types of Blanks
- Wooden shims – often pine or hardwood, cut to the exact thickness you need.
- Metal plates – galvanized steel or stainless, used when you need extra durability or fire resistance.
- Composite pads – plastic or rubber, great for vibration damping and moisture barriers.
Where They Show Up
- Foundations – a metal plate or timber blank under a sill plate to keep moisture out.
- Floor joists – a shim between joist and ledger when the ledger sits on a concrete wall.
- Roof trusses – a cribbed block of timber that levels the truss on uneven rafters.
In practice, the blank is the unsung middle‑man that makes the whole assembly behave the way engineers expect.
Why It Matters / Why People Care
If you’ve ever walked on a floor that creaks like an old rocking chair, chances are the blanks (or lack thereof) are to blame. Here’s why they’re worth paying attention to:
- Load distribution – A blank spreads the weight of the structure over a larger area, preventing “point loading” that can crush a timber or crack concrete.
- Moisture protection – Direct contact between wood and concrete invites rot. A waterproof blank acts as a barrier.
- Leveling – Cribbed blanks let you adjust for uneven ground without cutting the main timber.
- Vibration dampening – Rubber or composite blanks absorb footfall and wind‑induced movement, cutting down on squeaks.
When you get the blank right, the whole building behaves better. When you skip it, you’re setting yourself up for costly fixes down the line Practical, not theoretical..
How It Works (or How to Do It)
Below is the step‑by‑step rundown for installing blanks on timbers or cribbing them correctly. The process is the same whether you’re working on a basement floor, a deck, or a roof truss.
1. Assess the Surface
- Check for flatness – Use a straightedge or a laser level. If the surface deviates more than 1/8 in over a 4‑ft span, you’ll need a cribbed solution.
- Look for moisture – Tap the concrete; if it feels cold or damp, plan for a waterproof metal or composite blank.
2. Choose the Right Blank
| Situation | Recommended Blank | Why |
|---|---|---|
| Direct wood‑to‑concrete contact | Galvanized steel plate with a polyethylene liner | Stops rot, resists corrosion |
| Small height adjustments (≤ ¼ in) | Pine shims, pre‑cut to 1‑in width | Easy to trim on‑site |
| Vibration concerns (floors, decks) | Rubber composite pads | Damps noise and movement |
| Heavy loads (post‑foundation) | 2‑in thick hardwood block | Bears the pressure without crushing |
3. Prepare the Blank
- Cut to size – Leave at least a 1‑in overhang on all sides of the timber.
- Treat the wood – If you’re using pine shims, apply a coat of preservative.
- Drill pilot holes (for metal plates) – Prevents splitting when you screw them down later.
4. Position the Blank
- Lay it flat on the surface.
- Tap it gently with a rubber mallet to seat it fully.
- Check level again; the blank should be flush with the surrounding surface.
5. Secure the Blank
- Fasten with appropriate hardware – For wood blanks, use corrosion‑resistant nails or screws every 12 in. For metal, use self‑tapping screws with washers.
- Don’t over‑tighten – You want the blank to stay in place, not crush the timber underneath.
6. Install the Timber
- Set the timber on the blank – If you’re cribbing, you may need to stack multiple blanks to reach the desired height.
- Use a level to confirm the timber is truly horizontal or vertical as required.
- Anchor the timber – Follow your project’s anchoring specs (e.g., anchor bolts for posts, joist hangers for floor joists).
7. Final Inspection
- Look for gaps – Any space between timber and blank can allow moisture in. Fill with construction adhesive if needed.
- Re‑check load paths – Make sure the load flows through the blank into the supporting surface, not sideways.
Common Mistakes / What Most People Get Wrong
- Skipping the blank altogether – “It’s just a small gap, right?” Wrong. Even a thin sliver of moisture can start rot in a few years.
- Using the wrong material – Cheap plastic shims melt under sun‑exposed decks. Metal plates rust if not galvanized.
- Oversizing the blank – A huge block can trap moisture under it, creating a pocket that never dries.
- Failing to level – Placing a timber on an uneven blank leads to structural twist, and you’ll hear it at the first footstep.
- Not securing the blank – A loose blank slides, and the timber shifts—hello, squeaky floor and cracked walls.
Avoid these pitfalls and you’ll save yourself a lot of headaches.
Practical Tips / What Actually Works
- Pre‑cut a kit – Keep a small stash of pre‑cut shims (¼‑in, ½‑in, ¾‑in) on site. When you spot an uneven spot, you’re ready.
- Use a moisture barrier – Slip a thin sheet of polyethylene under metal plates when working over concrete. It’s cheap and adds years of life.
- Mark your blanks – Write the thickness on the side with a permanent marker. Later, you’ll know exactly what you used without measuring again.
- Double‑check with a spirit level after each blank is installed, not just after the timber is in place.
- Consider a “sandwich” – For heavy loads, sandwich a thin metal plate between two wood blanks. The metal spreads the load, the wood provides a soft interface.
- Don’t forget the edges – Seal the perimeter of the blank with a bead of silicone or a waterproof tape if you’re in a damp climate.
FAQ
Q: Can I use a piece of scrap lumber as a blank, or does it have to be new?
A: Scrap works fine as long as it’s free of rot, cracks, or insect damage. Treat it with preservative before installation Simple, but easy to overlook. That alone is useful..
Q: How thick should a blank be for a standard 2‑×4 wall stud on a concrete slab?
A: A ½‑in galvanized steel plate with a polyethylene liner is typical. If you’re using wood, a ¾‑in hardwood shim does the job.
Q: Do I need a blank under a deck joist that sits on a concrete beam?
A: Yes. A metal plate or composite pad will keep moisture out and distribute the load evenly, preventing the joist from sagging.
Q: What’s the best way to attach a metal blank to a wooden post?
A: Use stainless‑steel self‑tapping screws with washers. Pre‑drill pilot holes to avoid splitting the wood.
Q: If my floor is still squeaking after installing blanks, what should I check?
A: Look for any loose blanks, missed fasteners, or gaps where the timber can move. Tighten or replace as needed, and consider adding a rubber pad for extra damping Small thing, real impact..
That’s the short version: a blank isn’t just a piece of wood you toss under a beam. That said, next time you’re framing, pause for a moment, grab the right blank, and set it in place. It’s a purposeful, often overlooked component that protects, levels, and prolongs the life of your structure. Your future self (and your floor) will thank you.
