How to Install a Solid Wood Floor

Simon Nicholls

HOW TO FIT SOLID WOOD PLANKS

 

We strongly recommend that the installation of solid wood floors is carried out by trained wood floor fitters.

  1. Site Conditions

The building must be weather-tight, the heating system operable, and all wet trades (plastering, painting etc.) must have been completed.

 

Hardwood flooring is kiln dried to moisture content (MC) of 9% to 11% prior to despatch The MC of the subfloor, room temperature and relative humidity (RH) should be checked on site prior to the delivery of the materials. Room conditions at time of delivery and installation should be as close as possible to the expected in-service conditions – this usually means a room temperature of 18oC to 20oC and a RH of 50% to 65% (60% maximum for planks wider than 175mm). Once these conditions are achieved the delivery of the materials to site should be as close to the installation date as possible.  

Keep a record of moisture content and room condition measurements that exist at the time of installation.

 

  1. Sub-floors

Measure the moisture content of the sub-floor. Target MC should be 12% to 14% for wooden sub-floors; 3.5% (or 35% to 40% RH using the slab humidity test method as described in BS8201) for cementicious sub-floors. It is good practice to fit a damp proof membrane (DPM) over cementicious sub-floors; this could take the form of heavy duty polythene (200 microns minimum thickness) or a liquid DPM. Any joints in polythene DPM must be overlapped by 200 mm and be taped with polythene adhesive tape, take the DPM up the side walls by 25mm minimum. Use a breathable building paper on top of wooden sub-floors (any joints to be overlapped by minimum 100mm) e.g. bitumen impregnated craft paper. Contact your supplier for further advice.

 

Ensure that the sub-floor is hard, free from dust, and level; according to BS8201   the height deviation must be no more than 3mm measured over a 2m distance using a straight edge. Use a suitable levelling compound if necessary. De-nib the sub-floor to remove any sharp irregularities that could cause the new planks to pivot; even a 3mm nib could cause rocking. For wooden sub-floors make sure that all nail or screw heads are flush with the surface; for uneven wooden sub-floors fit 6mm (minimum) wood panels (plywood or similar) to provide a level surface, ensure joints between panels do not coincide with existing joints in the sub-floor.

 

Voids below wooden sub-floors must be adequately ventilated and where possible a DPM should be fitted at ground level; air bricks should be clear and the ventilation path should be clear of obstructions.

 

Clean the sub-floor and remove any contaminants such as mortar, plaster and mastic droppings.

 

  1. Expansion provision

It is essential that an expansion gap of at least 15mm or 2 mm per metre of span, whichever is greater,  is left around the perimeter of the room, any obstructions such as columns, radiator pipes, door casings, hearths etc. and in doorways between rooms. The approximate rate of expansion can be calculated. In larger rooms, above 10m x 8m, it may be necessary to provide additional expansion provision. Contact your supplier for advice. Expansion gaps can be covered with a variety of solid wood profiles or skirting, it is essential that any covers used do not impede or restrict the natural movement of the boards that will occur throughout the life of the floor e.g. do not force the skirting down on top of the boards, leave 1-2mm gap below the skirting and above the boards. Do not nail or glue covers to the boards.

 

  1. Installation

Take the boards out of the packs immediately before installation; draw from at least 3 packs to ensure a good colour/grade mix and to avoid banding. Carefully check each board for defects, liability will not be accepted for defective boards once they have been fitted. Decide on which direction to run the planks; usually with the light-fall from windows or along the length of the longest wall. Centre the rows of planks so that the perimeter rows are no smaller than 50mm width. Cut the first row of planks to size and shape to follow the wall whilst maintaining the required expansion gap along the edge and at the ends, use wedges to maintain the gaps during installation – remember to remove the wedges after completing the installation. Start with the tongue of the first row facing into the room then proceed with the rest of the floor, try and stagger header joints in adjoining rows by at least 200 mm and keep the length of the end planks in a row greater than 200mm.

 

 

  1. Fitting methods

Solid wood flooring should be mechanically fixed to the sub-floor by means of glue or nails/screws. Alternatively a proprietary installation underlay system such as Elastilon can be used, contact your supplier for further information.

 

  1. Nailing

Secret nailing to joists or battens at an angle of 45o obliquely through the shoulder of the tongue, use lost-head nails punched below the surface. Nail length should be 2.5 times the thickness of the planks. Use a specialist nailing device such as a Portanailer. The first and last rows should always be face nailed to prevent boards opening up in use.  If fixing to battens or joists apply nails at each intersection.  If nailing to plywood the nails should be at least as long as the combined thickness of the boards and the plywood and other wooden sub-floor elements e.g. existing floorboards. If nailing to plywood fixed directly to joists the plywood should be minimum 18mm thick. Nail the boards at 200 mm centres. If nailing directly to existing floorboards the new boards must be fitted across the run of the existing boards or at 45o to them otherwise gapping could occur in your new floor.

 

  1. Stick down

Use a permanently elastic glue system, there is a wide range of glues available including Solvent Based (single or two-component) or the more user friendly M S Polymer type. When sticking to cementicious sub-floors use a matched liquid DPM from the same manufacturer of the chosen glue; mixing products could result in compatibility issues which, in the event of problems, could make it difficult to apportion blame. The glue should be spread out using a notched trowel to the glue manufacturer’s specification. Only spread as much glue as you can cover within the curing time of the glue, usually about 30 minutes; always follow the glue manufacturer’s instructions. If in doubt contact your supplier for advice.

 

  1. Elastilon

Elastilon is a specially developed adhesive mat that allows wooden floors to be “floated”, however we do not recommend this system for installing solid wood floors over under-floor heating. Elastilon is 3mm thick dense foam with a nylon scrim contained within an adhesive bed. It is laid out in 1m wide rows set at 90o to the direction of the boards to be fitted, the protective layer must be facing upwards, and butt-joint the rows do not overlap them. Each row of Elastilon should be measured to allow an additional lap of material measuring one board width plus 100 mm. Peel back the piece of protective layer and cut off the exposed foam, this foam can be used at a later stage of the installation. Install the first row of boards on top of the peeled back protective layer; carefully pull the peeled back protective layer so that the row of boards comes into contact with the adhesive bed, press down on the boards. Now you can install more rows by repeating this process. Please go to www.elastilon.com where you can watch a demonstration video. Elastilon is not a DPM, separate provision must be made to protect against moisture ingress from the sub-floor – see paragraph 2. Ask your supplier for detailed fitting instructions.

            

      

 

  1. General

Wood is a natural product, each plank is unique and, depending on grade, may have knots, sapwood and colour variation. Natural defects can be cut out and the resultant cut boards can be used at the end of rows; due to their size. The dimensions of solid wood planks can vary slightly – this is a typical characteristic and not a cause for complaint. A professional installer would normally add an additional 5% of flooring to allow for wastage for defects and off-cuts.

All furniture should be fitted with felt pads to protect the surface of your new floor; if you need to move heavy furniture first place the item on top of soft pile up-turned carpet (make sure it is clean and free from grit) to carefully drag across the floor. Fit entrance mats adjacent to external doors. If you intend to put rugs on your new wood floor please make sure that the backing is non-abrasive, no liability will be accepted for any damage caused in this manner. Wood flooring can be damaged by dropping sharp or heavy objects, by walking on your floor in high heels, or by dragging heavy or sharp objects across it. Clean the floor using non-abrasive, lint-free, damp cloths (never use wet cloth or soak your floor); ask your supplier for a suitable cleaning agent – this will depend on the type of surface chosen. Solid wood flooring should not be fitted in bathrooms, wet rooms, saunas, or in basements/cellars.