Home Help and advice Installing wood flooring - it’s not the same as other floors!

Installing wood flooring – it’s not the same as other floors!

In this detailed column, Martin gets into the nitty-gritty of why the installation of wood flooring requires a specific skillset.

THE functionality and natural beauty of wood flooring has been established through centuries of use. A stroll through any National Trust property, church or other historic building will more often than not reveal very old, well-worn, yet intact timber flooring.

Along with stone, mosaic, and tiled floors, these were a staple design and it’s easy to understand why: they’re robust, natural products that were easy to cut, design and fit, and they could be refurbished. This combination meant long before timber flooring with specialist designs and features was to become a manufactured product, it was possible to create a warm, decorative, functional timber floor.

In those long ago days (I wasn’t there by the way) it would’ve been the job of a craftsman to install the flooring, though I can’t say whether it would be considered carpentry or joinery. Nails would have been the fixing method of choice and, nearer to the present day, rudimentary bituminous adhesive started to be used.

Nowadays, the installation of wood flooring seems to have moved away from the joinery skillset to a flooring installation skill. Indeed, there are training courses available in installing timber floors and relevant British standards (BS 8201:2011: Code of practice for installation of flooring of wood and wood-based panel).

However, it’s clear there are skills that are complementary to installing resilient flooring as well as ones that differ significantly, so it isn’t necessarily an easy transfer for installers to move from, for example, fitting vinyl to fitting solid timber flooring.

An old friend, who for the purpose of this article I’ll call Fitz (he fits flooring – get it?), is now quite prominent in the flooring game. He was generous with his time many years back and agreed to fit some flooring for me. Initially we had carpet in the hallway, but with young kids (yes, this was a while ago) the carpet didn’t really stand a chance. Vinyl didn’t appeal to Mrs Cummins, so we explored the option of a timber floor.

The following process and discussion served me well in going through the process of thought when looking to install a timber floor, and served us very well in achieving a fantastic floor without concerns or pitfalls. Bear in mind Fitz had been a flooring contractor in the field of resilient and textiles, so, other than his handyman skills, he too was learning on the job to some degree.

Stage 1. What sort of timber flooring did Mrs Cummins aspire to have? With all options initially available, a solid oak floor was our preferred choice. The plank size of 180mm long would be ideal and Fitz asked me to measure up so he could source a ‘good deal’.

Stage 2. The carpet was then lifted up to reveal a mosaic patterned floor, which at first glance looked like timber. This was bonded in a bituminous adhesive. However, the flooring looked dark and on testing it with my pin meter it was found to be very high in moisture. Why hadn’t this warped or cupped? In reality it wasn’t a timber product but something like a Granwood material, about 8mm thick with fibres and fillers. After this was left for a day or two, it started to dry out and began lifting in places. It had to be fully removed, which was arduous but necessary, and left a bituminous adhesive residue.

 *POINT ONE: Prepare your floor – otherwise you are relying on the success of previous installers, rather than trusting your own workmanship.

Stage 3. We now knew moisture was a potential issue (pretty obvious really for a ‘50s build, but I didn’t know if anyone had applied a surface DPM previously). The old black adhesive had performed well over the years, holding a relatively stable floor, but the adhesive does NOT block moisture. It isn’t affected by moisture; however, unless it is a continuous overall coating then moisture will pass into the flooring.
Any flooring contractor knows that moisture with resilient flooring is a problem, yet you may be surprised how few people think the process through with regard to timber. Timber itself can allow moisture to pass through, whereas resilient flooring generally doesn’t.

*POINT 2: Assume ground floors in old buildings will not have a DPM.

Stage 4. The floor needed to be smoothed BUT it also needed an application of a surface DPM. Fitz was prepared for this and recommended a moisture tolerant bag and bottle followed by a high quality epoxy surface DPM. The smoothing compound would bond to the bitumen and the DPM would control the moisture, which we all should know is a major issue for timber flooring (NB BS 8201 goes further in its demand for floor dryness in comparison to BS8203, with a requirement for 65%RH, which is a very dry floor).

*POINT 3: If pre-smoothing a floor before a DPM, you need to have a highly moisture tolerant smoothing compound. If bonding onto an old adhesive you need a high polymer, and subsequently a low-strength smoothing compound.

Stage 5. Fitz advised us against going for a large solid timber floor. This was based on the fact that any installation needs a degree of compatibility between layers. Solid wood flooring, if changing dimensionally with ambient conditions, will put stress on the materials below and a high strength compound should be considered.

Mrs Cummins heeded the advice, and a thinner engineered timber floor was selected. This was delivered and Fitz instructed that it should be stored in the property under the likely conditions it would experience in service – not in the garage or the back of the van until ready to install! The manufacturers of this particular flooring also instructed us how to store and acclimatise it, so we simply followed that advice.

*POINT 4: Choose your wood flooring to work in tandem with your subfloor. It’s much easier to change your timber choice than to rebuild a subfloor.

*POINT 5: Acclimatise your timber in the property under its likely in-service conditions. Follow the manufacturer’s acclimatisation instructions.

Stage 6. The smoothing compound and DPM were applied successfully. Normally, for resilient installations there would be a need to apply a smoothing compound over the DPM to both ensure an absorbent medium and also to give a spot on smooth floor. Vinyl and such only have a thin spread of adhesive (eg A2 trowel) and will be pressed against the subfloor when rolling, so they will mirror any undulation.

Timber on the other hand isn’t compressible or resilient (it will not return to its original shape), so it is much better to use an adhesive that can hold ridges and make contact with the underside of the timber, even where the substrate has slight variations. The best wood flooring adhesives have rheology that enables the ribs to stand up and, when using deeper notch trowels, you can ensure much more intimate adhesion.

*POINT 6: Timber isn’t resilient so a high rib adhesive and much higher consumption rates are needed.

Stage 7. In this instance we had recently brought out a new MS hybrid polymer adhesive for timber. I knew from my testing in the lab that this would bond very well directly to a recently applied epoxy DPM. It also resisted a great deal of movement of timber with its very high polymer content and tenacious elasticity/flexibility. Against Fitz’s wishes, I asked him to bond directly to the DPM and not apply a further smoothing compound.  

*POINT 7: Adhesives that can fully cure within themselves do not require an absorbent medium. High rib adhesives are preferred for timber flooring.

Stage 8: Adhesive applied and timber floor bonded, Fitz left a small expansion around the perimeter. I asked if this was really necessary because the adhesive we had used was flexible and strong and capable of dissipating the stresses and strains within the timber under fluctuating conditions. The hall wasn’t wide enough to need a mid-floor expansion strip putting in, so surely the risks were minimal. We agreed to disagree on this, but Fitz had a fair point to make: it’s not just the floor that can move – the building and skirting boards can too. It was okay though because the beading actually made an exceptionally good finish to the floor.

*POINT 8: Movement can occur in the flooring itself, in the substrates and in the building, so movement at perimeters, pillars and thresholds as well as changes in substrate need to be considered on timber installations. Allowances must be made, even with the modern high specification adhesives.

Stage 9. Avoid trafficking while the adhesive cures, which in our case was only six hours owing to the high spec adhesive selected. Of course, anyone with any sense would leave it longer before any significant loadings or movements took place, so our wine cabinet had to stay put for a while.

*POINT 8: Follow the guidelines for the adhesive before trafficking. Disturbing a bond that is still being developed will be a permanent issue.

Stage 10. Enjoy your floor. We have now had, for a very long time, an easy-to-clean, functional, warm, decorative floor in our hallway thanks to Fitz, but I wish he would have been more forceful. Initially he suggested a barrier mat to prevent stones etc. marking the floor as people entered. We both resisted this as it would have taken a lot of the aesthetic appeal away, yet it has clearly suffered some hammering over the years.  Luckily, we quite like the little marks and scratches – it makes it authentic – but I’m sure many people would not be happy with this.

*POINT 9: Timber can be damaged underfoot by point loads, stones in shoes etc. If this is a concern, introduce a barrier mat, then get the kids to take off their trainers and ensure high heels come off too.

The above is not totally inclusive of all points to consider, but hopefully the thought process carried out is something you can take away and use for each and every timber flooring project you come across.

Cheers, Fitz – the sawdust on the lawn and the noise of your cutting machine was all worthwhile in the long run.

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