Henry 345 Premix Floor Patch: The 2-Hour Turnaround Solution

Henry 345 delivers what busy contractors need most — a premixed patch that’s ready straight from the container and dry enough to work over in 2-3 hours. No mixing, no measuring water ratios, no guessing at consistency. The gray compound works on concrete, plywood, OSB, and masonry surfaces, making it the single patch product that handles most subfloor repair scenarios.

Coverage and Application Reality

The numbers contractors care about: 4-5 square feet per quart at 1/8” thickness, with featheredge capability up to 1/4” per layer and 1” maximum total thickness. That translates to patching a typical 2x2 foot damaged area around a toilet flange with a single quart, or smoothing minor variations across a 16-20 square foot section with a gallon.

The 1/4” per layer limitation matters. Deep repairs require multiple applications with 2-3 hour dry time between each layer. A contractor fixing a 3/4” depression needs three passes minimum — that’s a full day’s project when you factor in drying time. Plan accordingly.

Specification	Value
Coverage	4-5 sq ft/quart @ 1/8”
Per Layer Thickness	Featheredge to 1/4”
Maximum Total	1”
Dry Time	2-3 hours
Shelf Life	1 year (keep from freezing)

The patch is ready when it cannot be indented with a tool handle — a practical field test that beats checking your watch. Montana’s varying humidity affects dry time. Expect the full 3 hours in basements or during spring thaw conditions.

Multi-Substrate Performance

Henry 345 bonds to concrete, plywood, OSB, and masonry — the four surfaces that make up 95% of subfloor repairs. Users report good adhesion to plywood specifically, which matters when patching water-damaged subfloor around fixtures.

The interior and exterior rating opens up applications beyond just subfloor work. Contractors use it for patching exterior concrete steps, filling masonry cracks before painting, and smoothing rough spots on garage floors. The mold and mildew resistance adds value in Montana’s moisture-prone areas — crawl spaces, basements subject to spring flooding, and bathrooms with marginal ventilation.

Compatible flooring includes vinyl, tile, wood, and carpet. That versatility means one product handles prep work regardless of what finish floor goes down. No switching between different patches for different flooring types.

Installation Process

Start with a clean, dry substrate free of oil and wax. Dampen concrete or masonry surfaces before application — moist but no standing water. This step prevents the dry substrate from pulling moisture out of the patch too quickly, which would compromise the cure.

Application uses standard tools — putty knife or trowel. The premixed consistency stays workable long enough for feathering edges but sets fast enough to minimize downtime. The sandable finish lets you fine-tune the surface after drying if needed.

Multiple layers are needed for deep holes — not a limitation unique to this product, but worth planning for. The patch doesn’t bond to plastic, so skip it for repairs involving plastic vapor barriers or plumbing fixtures.

The Premixed Advantage

Compared to powder-based patches like Henry 549, the premixed formula offers faster setup for small repairs with less mess. No buckets, no drill mixer, no cleanup of mixing tools. Open the container, apply, close it up. The convenience factor matters on service calls where you’re patching one damaged spot, not prepping an entire floor.

Storage requires keeping the product from freezing — standard for water-based products in Montana. Store it inside the heated shop, not in the truck overnight during winter. The one-year shelf life means rotating stock matters. Date your containers.

Frequently Asked Questions

How long should I wait between coats when building up thick repairs? Allow 2-3 hours dry time between each 1/4” layer. Test readiness by pressing with a tool handle — if it leaves an indent, wait longer.

Does this work for exterior concrete cracks? Yes. The product is rated for both interior and exterior use and works on concrete substrates. Dampen the concrete first for best adhesion.

What’s the actual coverage I’ll get from a quart? 4-5 square feet at 1/8” thickness. Thicker applications reduce coverage proportionally — expect 2-2.5 square feet at 1/4” depth.

Can I use this over existing vinyl flooring? No. While compatible flooring can be installed over the dried patch, the patch itself needs to bond to the substrate — concrete, plywood, OSB, or masonry. Remove vinyl first.

How do I know when it’s ready for flooring installation? The patch is ready when it cannot be indented with a tool handle. This typically takes 2-3 hours but varies with temperature, humidity, and thickness.