Matching wood flooring with the right adhesive for substrate bonding

A detailed guide designed for construction professionals, aiding in the selection of the ideal adhesive for securely bonding wood floors to various substrates.

Wood flooring: a universal favourite with unique characteristics.

Despite the range of alternative options available, wood remains a popular floor finish. Wood is aesthetically pleasing, robust, durable, easy to clean, and economical. It is a natural product, and there is something warm and appealing about that. Engineered wood flooring seeks to retain all the appealing characteristics of natural wood while improving some of its properties and reducing some of the variability that comes with an organic product.

Unlike other flooring systems such as carpet, vinyl, LVT, or linoleum, which are flexible, wood flooring is more rigid and, therefore, more sensitive to the flatness of the substrate to which it is fixed. Wood is also sensitive to moisture, relative humidity, and temperature. The moisture content of the substrate to which the flooring is bonded is an important factor. Under significant changes in conditions, elements in a wood floor can swell or shrink and warp and buckle if they are inadequately – or overly – restrained.

Thus, it is vitally important to select the most appropriate adhesive to ensure the year-round and long-term performance of a wood floor.

This article gives you a guide to the adhesive options for wood flooring; the considerations required to ensure compatibility with the substrate; application techniques; environmental considerations; and how to maintain wood floors and ensure their longevity.

Adhesive options for wood flooring.

Small-dimension wooden blocks and small engineered wood planks are not overly sensitive to sharp changes in temperature and humidity. Thus, their main requirement is that they be stuck down onto a smooth and flat substrate. In this situation, wood flooring adhesives such as polyurethane, resin alcohol, and modified silicone polymer can be used.

However, as the dimensions of the flooring increase – for example, as the planks get longer – the more important it becomes for the adhesive to meet high shear and bond strength requirements. This is particularly crucial for solid wood flooring. A polymer adhesive system is flexible enough to hold the planks in place while at the same time dissipating the stresses induced in the flooring into the substrate without causing separation.

The performance of an adhesive will depend on its polymer content. The higher the polymer content, the more expensive the adhesive – and the better its performance.

Subfloor compatibility.

You cannot simply bond a wood floor down to a substrate and expect robust long-term performance. Don’t leave it to chance.

It is crucial to consider the subfloor conditions when you assess a flooring job. Here are four points to address when you’re looking at the subfloor:

Assume nothing. Except that ground floors in old buildings were not constructed with a damp-proof membrane.

After you’ve lifted up the existing floor, you may notice clues that there is undue moisture in the ground slab. Or perhaps the moisture content of the flooring you’ve just pulled up is what led to its failure. But even if you see no obvious clues, it is far better to assume that either there is no DPM, or if there is one, it has deteriorated over the years and moisture can come up through the slab.

Test the moisture content of the subfloor.

Use a hygrometer calibrated to the standards applicable to the country in which you’re working. If the moisture content of a solid subfloor is more than 65%RH, you will need to apply a Bostik HYTEC moisture control barrier or surface DPM such as Bostik HYTEC E570 ONE COAT surface-applied epoxy DPM.

If the existing subfloor needs to be smoothed before applying a DPM, you need to apply a highly moisture-tolerant smoothing compound.

Once you’ve applied the smoothing compound and the DPM, then you can begin installing the flooring. The adhesive must be applied within 24 hours of a Bostik HYTEC DPM solution reaching cured status.

Choose a wood flooring system that works in tandem with the subfloor.

It’s much easier to select a compatible flooring system than it is to rebuild the subfloor. Work with what you’ve got. For example, under the humidity and temperature changes that are likely to be experienced, a thinner engineered floor whose elements are more stable may be more appropriate than a thicker, solid wood floor.

Application techniques.

Three Bostik products cover most applications of solid wood and engineered wood floors.

WOOD H110 ECO PARQUET

This is a hybrid adhesive for laying engineered parquet in all formats and solid parquet up to 110mm wide.

Apply only enough adhesive that you can work within 40 minutes, using a suitable trowel. Use a single application method, at a rate depending on the roughness of the surface and the type of parquet, as given below:

Mosaic parquet, cork/rubber underlayment: 800–900 g/m2; Notch type B5
Engineered parquet up to 110mm wide / 15mm thick: 900–1000 g/m2; Notch type B11
All format engineered parquet, solid parquet up to 110/15: 1000–1200 g/m2; Notch type B12

Pay attention to detail. Allow for sufficient gaps around the perimeter of the flooring area: 0.15% of each of the largest dimensions to be covered by the parquet floor, a minimum of 8mm.

Press firmly on the boards to ensure good adhesive coverage of at least 80%. Apply weights to any distorted floorboards until the adhesive is fully cured (24 hours).

WOOD H160 MULTI PARQUET

This hybrid adhesive is designed for laying engineered parquet in all formats and solid wood planks up to 160mm wide and 23mm thick.

Apply only enough adhesive that you can work within 40 minutes, using a suitable trowel. Use a single application method, at a rate depending on the roughness of the surface and the type of parquet, as given below:

Mosaic parquet, cork/rubber underlayment: 800–900 g/m2; Notch type B5
Engineered and solid parquet up to 110mm wide / 15mm thick: 900–1000 g/m2; Notch type B11
All format engineered parquet, solid parquet up to 160/23: 1000–1400 g/m2; Notch type B12

Pay attention to detail. Allow for sufficient gaps around the perimeter of the flooring area: 0.15% of each of the largest dimensions to be covered by the parquet floor, a minimum of 8mm.

Press firmly on the boards to ensure good adhesive coverage of at least 80%. Apply weights to any distorted floorboards until the adhesive is fully cured (24 hours).

WOOD H200 ELASTIC

This high-performance hybrid adhesive is suitable for all types of wood flooring up to 200mm width and engineered wood flooring.

Only apply enough adhesive to work within 30 minutes.

Spread the adhesive with a sweeping motion at a 60-degree angle with a suitable notched trowel over the floor.

Place the floor covering into the adhesive while it is still wet.

Press the flooring firmly into the adhesive to ensure full contact Is achieved.

The flooring can take foot traffic after 24 hours. Leave it for 48 hours before sanding and varnishing.

Environmental considerations.

Regardless of the type of flooring that your client eventually selects, the floor elements must be stored within the room where they will be installed. Doing this will ensure that the flooring is acclimatized to the likely in-service conditions by the time it comes to installation.

It is important to do this so that there is no immediate environmental shock to the planks when they are installed. Consider what might happen if your load of wood flooring is kept cool and dry inside a truck until it is installed in a humid, warm building. Or if the planks have been stored outside (hopefully, under shelter) in a hot and humid exterior environment and are then brought in and installed in a cool and dry air-conditioned building.

Maintenance and longevity.

The key considerations for the longevity of your client's wood floor are that (a) they select the most appropriate type of wood floor for the situation, (b) you select the most appropriate Bostik adhesive and other products as necessary, and (c) you install the flooring in strict accordance with the flooring manufacturer's instructions AND Bostik's instructions.

Make sure nobody walks on the floor for 24 hours, and don't do any sanding or varnishing until Bostik's instructions tell you it is okay to do so.

From then on, it is up to your client to protect the floor from significant point loads such as high-heeled shoes or stones brought into the house stuck to shoes.

Installing the floor well and then treating it well in use will ensure the longevity of the wood floor.

The beauty of wood floors is worth the effort.

As we have seen, installing a solid wood or engineered wood floor is not as simple as pulling any type of adhesive off the shelf and sticking the flooring into place. A certain level of pre-planning is required. You have to assess the existing subfloor conditions. Do you need to apply a smoothing compound? A DPM? Consider the likely environmental conditions and the overall dimensions of the floor.

The key is to select the type of flooring that is most appropriate for all the conditions that you have assessed. A wood floor that has been selected intelligently and installed according to all the manufacturer’s recommendations will give your client a long-lasting and high-performing asset.

And you will be satisfied with a job well done.

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