Henry 345 Premix Floor Patch: Ready-to-Use Subfloor Solution

Henry’s 345 Premix Floor Patch delivers what contractors need most — a grab-and-go solution that sets in 2-3 hours. No mixing buckets. No powder clouds. No guessing about water ratios. Just open the pail and start patching.

This isn’t a miracle worker for major structural issues. It’s a practical patch for the everyday repairs that eat up time on job sites — smoothing rough plywood subfloors, filling cracks in concrete before flooring goes down, and patching non-moving joints. At 4-5 square feet per quart at 1/8” thickness, you’ll burn through material on large areas. But for typical subfloor prep and small repairs, it gets you moving faster than mixing powder patches.

Coverage and Application Reality

The numbers that matter for estimating:

Specification	Value
Coverage	4-5 sq ft/quart at 1/8”
Per Layer	1/4” maximum
Total Depth	1” maximum (multiple layers)
Set Time	2-3 hours
Color	Gray

Apply in 1/4” layers, allowing 2-3 hours dry time between each. That’s the catch with deep repairs — multiple layers needed for deep holes. If you’re filling a 1” depression, you’re looking at four separate applications with dry time between. Sometimes powder mixes that you can pour thick make more sense.

The patch is ready when it cannot be indented with a tool handle. Don’t trust the clock alone — test it. Montana’s humidity swings can throw off dry times.

Where It Works (And Where It Doesn’t)

Henry 345 bonds to concrete, plywood, OSB, and masonry. It does not bond to plastic — don’t waste material trying. Ensure substrate is clean, dry, and free of oil/wax. Dampen concrete/masonry surfaces before application (no standing water).

Once patched and dried, the surface accepts vinyl, tile, wood, or carpet flooring. The sandable finish means you can knock down high spots after it cures. Interior and exterior use gives flexibility — patch that concrete stoop or smooth interior subfloor with the same bucket.

Montana Considerations

The mold and mildew resistant formula matters here. Montana’s temperature swings create condensation in unexpected places. Spring melt saturates everything. A patch that won’t support mold growth saves callbacks.

Fast-setting formula with 2-3 hour dry time keeps projects moving during Montana’s short construction season. You can patch in the morning and install flooring after lunch — if the patch is thin enough and conditions are right.

Store in a cool, dry place; keep from freezing. That’s critical for job site storage. A frozen bucket is trash. One year shelf life if unopened — date your inventory and rotate stock.

The Bottom Line

Henry 345 is premixed and water-based, offering more convenience for small jobs compared to powder-based patches like Henry 549 which require manual mixing. Faster setup for small repairs; less mess.

Is it the cheapest patch? No. Will it handle every repair? Also no. But for contractors who value time over material cost, who need to knock out small repairs without hauling out mixing equipment, it delivers. Users praise the ease of use and adhesion, especially good adhesion to plywood.

Skip it for large areas or deep pours where powder mixes cost less per square foot. Use it when speed matters more than pennies — small patches, quick subfloor fixes, and anywhere you need predictable results without the mixing drill.

Frequently Asked Questions

Q: Can Henry 345 be used on wet surfaces?

Surfaces must be clean and dry, though concrete/masonry should be dampened before application with no standing water. The substrate needs to be dry to the touch but can be slightly damp for concrete and masonry applications.

Q: How thick can Henry 345 be applied in one coat?

Maximum 1/4” per layer. For depths up to 1” total thickness, multiple layers are required with 2-3 hours dry time between each layer.

Q: Does Henry 345 need to be sanded before flooring installation?

The product has a sandable finish, but sanding is only necessary if you have high spots or need a perfectly smooth surface. The patch is ready when it cannot be indented with a tool handle.

Q: What’s the warranty on Henry 345?

Henry provides a 1-Year Limited Warranty that covers manufacturer defects when instructions are followed.