The most common reason a new floor fails in an older Newcastle terrace is not the flooring itself. It is the surface underneath. Skip subfloor prep and you get bounce, hollow clicking, cracked tiles, or planks that never sit flat. This guide shows you how to assess and prepare the two subfloors you will meet in a typical Tyneside home: suspended timber and solid concrete.

First, know what you are standing on

Most terraces built before the mid twentieth century have suspended timber floors on the ground level: floorboards on joists over a ventilated void. Later builds and rear extensions often have solid concrete. Many houses have both, room to room. The prep is different for each, so identify it before you buy anything.

Suspended timber

The floor gives slightly when you walk on it and you may see or feel airflow near skirting. Under the boards is a void that must stay ventilated through the air bricks. This void is why timber floors are dry, and why blocking it causes trouble.

Solid concrete

The floor feels dead and solid. In older homes the concrete may have no damp-proof membrane, or an old one that has failed. That single fact drives most of your decisions.

Levelling a timber subfloor

Old boards cup, spring and sit at different heights. Laying a hard floor straight over them transfers every ridge and gap upward.

• Screw down loose boards to stop squeaks and movement. Locate joists and use screws, not just nails.
• Plane or sand down high board edges where they have lifted.
• Overboard with plywood or a proprietary flooring-grade board to create a flat, stable base. Fix it at close, regular centres so it does not drum.
• Never block the air bricks. Ventilation to the void must stay clear.

Watch the bounce

If the whole floor deflects when you walk across it, the problem is the joists, not the surface. Overboarding will not cure a springy structure and rigid tiles will crack. Sister or support the joists first.

Levelling and sealing concrete

Concrete brings two jobs: flatness and moisture control.

• Check for damp before anything else. A cold, older slab with no membrane can pass moisture up into wood and adhesives.
• If damp is present, treat it with a surface damp-proof membrane suited to the slab before levelling. Trapping moisture under vinyl or wood leads to lifting and mould.
• Fill low spots and cracks, then apply a self-levelling compound to get a smooth, even plane.
• Let levelling compound and any membrane fully cure to the maker’s timescale before flooring.

A real scenario

A couple in Wallsend laid LVT over a bare concrete kitchen floor in a rear extension. Within months the edges lifted and the adhesive stayed tacky. The slab had no working damp-proof membrane, so moisture rose steadily into the glue. The fix was to lift the floor, apply a surface damp-proof membrane, skim with levelling compound, and relay once cured. It has stayed down since. The lesson: the flooring was never the problem, the missing membrane was.

Common mistakes and how to fix them

• Blocking air bricks with a new floor or insulation. The timber void dries by ventilation. Keep every air brick clear, or you invite rot.
• Levelling compound over a damp slab. It will not cure properly and traps moisture. Sort damp first.
• Overboarding with thin, flexible sheet. Too thin and it drums and telegraphs the boards below. Use flooring-grade board fixed at close centres.
• Ignoring bounce. Fix the joists before the surface, or hard floors will crack.
• Rushing curing times. Fitting over green compound causes bond failure. Wait the full time stated.

Action steps

• Identify each room as timber or concrete before buying flooring.
• For timber: screw down, plane high spots, overboard, keep air bricks clear.
• For concrete: test for damp, treat if needed, fill and self-level.
• Address any structural bounce in joists first.
• Confirm the base is flat with a long straightedge across the room.
• Respect curing and drying times before laying the finished floor.

Conclusion

A good floor starts below the surface. Match your prep to the subfloor you actually have, deal with damp and bounce before cosmetics, and check flatness with a straightedge. Your next step: get down on the floor, identify timber versus concrete room by room, and note any damp, movement or dips before you order materials.

FAQ

How flat does the subfloor need to be?

Most flooring makers state a tolerance, often measured over a set length with a straightedge. Check your product, but the practical aim is no visible rocking or dips under the board.

Can I put insulation in a timber void?

You can, but it must be done in a way that keeps the ventilation path working. Sealing the void completely risks trapping moisture and rotting joists.

Do I always need a damp-proof membrane on concrete?

Not always. Newer slabs usually have a working one built in. Older slabs may not, so test first and only add a surface membrane if moisture is present.

Is overboarding always necessary on timber?

For thin, hard or click floors, usually yes, to give a flat stable base. Thick solid wood fixed across joists can sometimes go direct, but check the maker’s guidance.

References

• The National Institute of Carpet and Floorlayers Association (NICF) – subfloor preparation guidance.
• Manufacturer instructions for your flooring, levelling compound and damp-proof membrane products.