Dry Screed System Installation - Rigidur Floor Panels

The build-up is simple. A protective membrane goes onto the structural base. Dry levelling fill goes on top to even out irregularities, sometimes with a rigid insulation board instead of or on top of it. The floor panels go on last. An edge strip runs around the room and separates the floor from the walls.

A Rigidur floor panel is two gypsum fibre boards bonded together with an offset. This creates a rebate, a small step along the edges, where the next panel locks in. The joint gets glue and is then secured with screws or staples as the manufacturer specifies. The result is a solid, continuous surface.

Why not a conventional screed? A sand and cement or anhydrite screed brings a lot of water into the building and takes weeks to dry. It is also much heavier, and an older timber floor or loft may not carry that load. A dry screed is light. You can walk on it as soon as the glue in the joints has cured, and it does not bring moisture into a home people are living in.

1. Remove the old floor covering and any loose layers. Clean the base and check that it is sound and dry.
2. Lay the protective membrane with overlaps. On a timber floor it stops the fill trickling through gaps. On concrete it protects against rising moisture.
3. Fix the edge strip around the perimeter and around any fixed elements.
4. Pour the fill, level it with a straightedge along guide rails and compact it as the system requires.
5. Lay rigid insulation boards if the build-up calls for them.
6. Cut the rebate off the wall side of the first row of panels and start laying from a straight wall.
7. Apply glue to the joints, press the panels together and secure the joints with screws or staples.
8. Stagger the rows so the end joints do not line up.
9. Once the glue has cured, scrape off any squeezed-out residue. Trim the protruding edge strip only after the floor covering is down.

The panels come in several thicknesses, and some have insulation already bonded to them. A thinner panel is usually enough for flats and houses with normal domestic loads. A thicker panel suits areas with more foot traffic, heavy furniture or heavy appliances. Versions with polystyrene or mineral wool improve thermal insulation and reduce impact sound. Your downstairs neighbours in a block of flats will notice the difference.

For the fill you can use the manufacturer's own dry levelling fill or expanded clay granules. The manufacturer states which fill is allowed under the panels and how thick it may be. Thicker fill goes down in layers and needs thorough compaction, otherwise the floor will settle later.

A dry screed can take laminate, vinyl, timber, carpet and tiles. Floating floors usually go straight onto the panels. For glued coverings and tiles, the surface is normally primed and, depending on the covering, skimmed with a smoothing compound. Tiles need a flexible adhesive. A bathroom needs waterproofing, because gypsum fibre board on its own does not belong in a wet area. You can combine a dry screed with underfloor heating, but only with a system the manufacturer approves for that build-up.

The work goes fastest in an empty, square room with a solid, fairly level base. These make it take longer:

• Removing old layers, adhesives and bitumen felt
• A large height difference that needs a thicker layer of fill
• An irregular layout with alcoves, narrow hallways and thresholds into other rooms
• Pipes and cables in the floor, which need cutting around and careful filling
• Difficult access, such as carrying materials up several floors without a lift

In older houses with timber floors, check the condition of the joists first. If the floor is springy or the timber shows rot or insect damage, ask a structural engineer to assess it. In a flat, talk to the building management or owners' association before you start, mainly about noise and impact sound for the neighbours. Ask your local building authority whether replacing the floor needs any approval under local building regulations. Any new electrical wiring in the floor must be installed by a qualified electrician.

• No edge strip. The floor touches the walls, carries sound and the joints can crack as the materials move.
• Poorly compacted fill. It settles over time, and the floor sags or creaks in places.
• Non-system fill. Sand or untested materials may not be stable enough.
• No membrane. The fill trickles through gaps or draws in moisture from below.
• Loose cables in the fill. Cables belong in protective conduit and must not create high spots.
• Rebate left on at the wall. The panel edge is then unsupported and cracks or creaks along the wall.
• Too little glue in the joint. The panels move against each other and the joint opens over time.

If you have a sound base, an accurate spirit level or laser, and some patience, you can lay the panels yourself. If the timber floor's load capacity is uncertain or there are services in the floor, call a professional. Read the manufacturer's instructions first. They take priority over this guide.

1. Clear the room, remove the old covering and vacuum the base.
2. Find the highest point of the floor and set the finished floor height, including the covering and the thresholds at the doors.
3. Lay the membrane with overlaps and turn it up the walls.
4. Fix the edge strip around the whole perimeter.
5. Set the guide rails, pour the fill, level it with a straightedge and compact it.
6. Lay the panels gradually and step only on panels already laid, not on the fill.
7. Cut the rebate off the first row and lay it along a straight wall.
8. Apply two beads of glue to the rebate, press the next panel in place and secure the joint with screws or staples.
9. Offset each new row so the end joints do not repeat in one line.
10. Check flatness with a long straightedge as you go, not only at the end.
11. Once the glue has cured, scrape off the residue and vacuum the surface.

• The floor is flat, and a straightedge shows no noticeable gaps and does not rock
• Nothing creaks underfoot and the panels do not flex
• The edge strip runs around the whole perimeter and the floor touches the wall nowhere
• The joints are glued and secured, with no squeezed-out glue left
• End joints are staggered between neighbouring rows
• The floor height matches the thresholds and doors
• With underfloor heating, the build-up follows the manufacturer's instructions and no pipes or cables are damaged
• The installer has told you which system was used and which coverings and adhesives are suitable