Renrut Sanding Block Review

Renrut sanding blocks are an Australian product with limited distribution. The underlying question — what makes a sanding block good — has a cheap and long-settled answer.

Hardness is the whole specification

Too hard (a wooden block, or a steel-backed one) and the abrasive cannot follow a surface at all. Every slight high spot gets cut and the block bridges the hollows, which is what you want for flattening and wrong for everything else. A hard block on a moulding cuts the crest off.

Too soft (a foam block, or worse, your fingers) and the abrasive wraps around every edge. Sand an arris with a soft block and you will round it. This is why hand-sanded work so often looks soft and slightly melted at the edges compared with a crisply machined piece.

Cork sits between the two and has for a hundred years. Firm enough to hold a flat and keep an edge crisp, compliant enough not to gouge. There is a reason it is still the default in cabinet shops.

Keeping it working

Flatten the block occasionally. Cork wears where you press hardest — usually under the heel of your hand — and a hollow block rounds everything. Rub it on a sheet of coarse abrasive laid on a flat surface until the face is even again.

Tap the paper out, do not sand through it. Abrasive clogs long before the grit is worn off. A tap on the bench, or a rub with a crepe stick, restores it.

Keep one block per grit. Loose coarse grit trapped in a cork face will scratch through a finer grit and leave a line you cannot see until finish goes on. That single scratch is the most common hand-sanding failure.

Sand with the grain, always

Across the grain, the scratches show under any film finish and no amount of finer paper hides them fully. If you have gone cross-grain, you have to work back up through the grits in the right direction.

What to buy

Cork sanding blocks, three-pack, linked below. Three is the right number — one coarse, one medium, one fine — and the cost is trivial.

For contours, wrap paper around a piece of the moulding itself, or a length of dowel. A block is for flats; the profile is its own best sanding form.