Be Warned! This article is relatively detailed and lengthy. It encapsulates the installation of a fully bonded (adhered/glued down) herringbone oak solid block 22 mm wood floor. This article is NOT a how to guide, although you will gain some very useful information. There are many ways of installing this type of flooring and innumerable situations that will have an immediate impact on the method a particular herringbone is installed. Therefore, no installation is ever the same and can change subtly or greatly in the way it should be approached. Therefore, I ask if you’re reading this with the view to copying this particular method, please think again. The dynamics of each installation do require a professional eye and sense of what is best. Hire a professional! With that said, let’s get started…
The herringbone was to be installed on the ground floor over a 60 square metre area in a completely renovated detached home in Sale, Manchester, UK. As well as the renovation, there were several extensions to the property which obviously changed the floor plan. A large section of the original concrete slab was to be kept with the additional sections of the concrete sub-floor in relation to the extended areas of the property added on.
This presented us with several considerations. When new concrete is laid next to an existing and well established concrete slab there is always potential for movement as the new concrete settles and cures. Indeed, the intersection of where the two meet is classed as a movement joint, which in the world of flooring means this joint should be taken through to the finished floor covering. As this herringbone floor was to be installed across the entire ground floor (excluding the kitchen area) and the movement joints/extension sections intersected several rooms, this was of particular concern. My client was understandably adamant that there was to be no movement joints across his new herringbone floor. Our solution or I should say our method of greatly decreasing the probability of problems in the future is concluded below in the sub-heading ‘Mesh’.
Our next consideration was that this project was essentially a build in progress. Therefore, we had to closely monitor the progress of the build prior to allowing the herringbone wood flooring from being delivered to the property. With any wood floor project, the property must be up to living conditions in relation to the in-home climate. Therefore, as the build was coming to the latter stages, I made several visits to monitor the temperature and air humidity as well as communicate with the project manager in relation to other trades working on the build and making sure the heating system was commissioned and working to keep the conditions in the property stable. A hugely important aspect of the entire project as installing any wood floor in conditions not aligned with normal living, will often lead to costly problems further down the line.
I’ve structured this article in sub sections to describe each stage of the project. The materials used for the preparation were largely a complete Ardex system. For a closer look at the pictures, please use the zoom option in your browser (if available).
Firstly, it’s well worth talking about the acclimatisation process. All timber floors need to have a consistent moisture content in direct relation to the climate around it. We call this ‘Equilibrium’. A natural state of harmony. Nature will always strive for harmony, although it may not always appear that way as friction is a requirement of harmony. I’ll leave the philosophy out of this article. Anyway, we want the timber to be in harmony with its environment, equilibrium. If this isn’t the case when the flooring is installed, it will be the case after. To explain, nothing will stop the equilibrium process.
Therefore, if the moisture in the timber is lower than it should be or will be when it gains equilibrium, the timber will expand, once more moisture is taken on board as part of this process. This expansion will dramatically affect the floor as there is a co-efficient expansion ratio to consider. In other words (only as an example – not to be taken as exact), if you have 50 blocks of flooring in a row and each block expands by 1 mm, there will be a co-efficient sum of 50 mm. You could say, the co-efficient is like a domino effect. This is why you hear the phrase ‘acclimation’ or ‘acclimitisation’. It’s not just a buzz word. The aim of acclimation is to prevent excessive expansion or contraction after the floor has been installed. If the acclimation process isn’t carried out and carried out well, in the famous words ‘there may be trouble ahead’!
Again, part of this installation was being carried out in site conditions. To expand, the property was sealed with windows and doors fitted, however, the heating system had not been commissioned. To a wood floor installer this equates to sleepless nights! To add to my stress levels, the wood blocks had already been delivered. You really do have to keep on your toes when it comes to wood flooring as any slight change in the entire schedule can mean the approach needs to be altered to create a positive outcome. Lack of experience can soon see the walls crumble around you, as unexpected corners are cut!
There was going to be a period before the installation of the herringbone that the main sub-floor preparation was going to take place. During the start of the preparation, the heating would be commissioned. Therefore, my approach to keeping the herringbone unaffected by the current climate conditions was to keep it wrapped in its packaging and moved upstairs where the conditions were more favourable and stable i.e. the first phase of decorating had been carried out some weeks before as was the tiling and plumbing etc. Here is where the herringbone would stay until several days prior to the installation. The picture to the right shows yours truly inspecting the herringbone.
All the way through the preparation and installation, air relative humidity moisture readings where taken. As expected these readings would spike for a few days after self levelling layers were applied. Remembering there was between 90 and 120 litres of water that needed to come out of each self levelling layer.
Nearer the time of the installation the ground floor air humidity and temperature was monitored with a requirement of between 45% – 55% RH at around 18 Degrees Centigrade. Once the atmospheric conditions where stable, the herringbone was brought to ground level and left to acclimatise. With this particular installation, I opted to keep the herringbone packaged apart from a cut in its wrapping to allow air in. At the above conditions, Oak blocks should have an equalibrium moisture content of between 7 and 9%. We took a reading from several blocks throughout the bundles of timber during the installation. Indeed, the ECM readings showed an average 9%. Be aware, depending on your location and species of wood, the ECM can be different.
Grinding and Cleaning
The very first step of preparing any sub-floor is to gain a feel for the levels of the sub-floor. Doing this will enable us to work the next grinding stage to our advantage.
As well as unevenness or an out of level sub-floor, with most installations direct to concrete, there will be contaminants like paint, plaster, oils, laitance etc all over the surface of the concrete. All of which must be removed prior to doing anything.
The first step to address any level issues and contaminants was to grind the surface of the concrete. This process creates an extreme amount of concrete/contaminated dust. An adequate dust extraction unit must be used in conjunction with the grinding machine (as can be seen in these pictures).
In our initial assessment of the concrete levels, we found that the new concrete slab in the rear of the main lounge (which can be seen in the upper part of the concrete in the picture to the left – lighter coloured) was 12 mm higher than the rest of the concrete. This meant that as well as removing contaminants from the rest of the ground floor we had to remove this higher area of concrete. If we hadn’t have done this, to gain a flat sub-floor, the amount of material we’d have had to use to bring the rest of the sub-floor level, would’ve sent the entire project way over budget!
Once the grinding was complete, the entire area was swept, then swept, then swept again. You wouldn’t believe the amount of concrete dust is generated from this process. Once the majority of the dust was removed, the area was vacuumed twice and mopped repeatedly to remove as much loose material as possible.
We then patched any movement joints and large pitted area with Ardex A46 exterior repair mortar.
Application of Ardex R3E Moisture Tolerant Primer
Once all the Ardex A46 patching had been completed and dried, we applied Ardex R3E moisture tolerant primer.
There were three reasons for this. Firstly, when we install any wood floor, it’s wise to assume there is no Damp Proof Membrane beneath any concrete slab. Especially, when you don’t know for sure. Further into the installation I had specified a one coat liquid damp proof membrane called Ardex DPM1C. The use of such a dpm product requires any material installed beneath it to be moisture tolerant. This is extremely important! If not, the risk of failure of the entire installation is great.
Secondly, I wished to prime this concrete to assure a completely pin hole free surface with our next stage.
Thirdly, such a good quality primer will consolidate any stray loose particles in the concrete. Loose particles when preparing a sub-floor is BAD!
The Ardex R3E required sand blinding. This basically entailed chicken feeding silver sand across the wet R3E primer as we went. This is designed to greatly increase the bond of our next layer.
The Ardex R3E was applied using a squeegee to spead the primer and a short piled roller to gain a consistent film as well as really push the primer into any pitted/holes in the concrete sub-floor.
As I explained previously, there were several movements joints to address in this project. After a lot of contemplation and discussion with several companies and peers, we decided to use Vertex re-inforcement mesh to bridge these movements joints to essentially treble the strength of the self levelling compound that was to be installed next.
I must stress that all manufacturers require movement joints to be brought through to the surface of any fully bonded floor covering. However, I’m sure you can appreciate our predicament – as explained earlier – in this project.
Ardex K301 is a high quality water based self levelling compound that is suitable to be installed underneath a damp proof membrane.
There are two reasons why we used this slc.
Firstly, the next stage in the process is to install a full spec liquid DPM to protect the herringbone wood flooring from any rising moisture. When applying such a product it is required to be applied at a consistent film thickness of 250 microns. To gain this consistent thickness the surface it goes on top of has to be smooth. If the surface is rough, a consistent film cannot be guaranteed. I like to give the mental image of a craggy mountain ridge with snow draped across. Some places will be deep in snow and some very thin. This is not what we want to see with a one coat liquid damp proof membrane.
The second reason was to use the K301 to build up the entire area and get it looking somewhat like a flat sub-floor. We were not intending to go for perfection at this stage. It was primarily used to add material to very low spots across the entire floor and bring these low spots in line with the high spots (datum points).
In these pictures the K301 has sufficiently dried after the installation and been sanded to remove any laitance from the surface. We then vacuum and lightly mop the floor twice or till the floor is clean of any dust or loose particles prior to applying the liquid DPM. We needed to clean every surface in between layers to ensure a sound bond. Any failure at any stage of these layers will result in a complete failure of the herringbone flooring.
At this stage we took a look at the levels of the sub-floor ready for our final layer of self levelling (Ardex K15).
Many people believe self levelling compounds (slc) do all the work for you, as the name suggests. However, this is not the case at all. Slc’s will only self level a certain amount. The self levelling material still needs to be worked and smoothed to leave the correct thickness and a flat surface.
We use a lazer level on a tripod with a staff measure that gets positioned at different points in a room/s to give us a good idea of any high and low spots. We take a note of these areas so we know how we will be applying the next layer of slc. Going deeper and shallower in respective areas.
You must never assume a concrete slab has a DPM (damp proof membrane). If a property was built before the mid 1960’s (which is clearly vague in itself), many were not equipped with a DPM beneath the concrete slab. Even if it had a DPM, who knows what condition that DPM is in? For the cost of a quality liquid DPM, it really isn’t worth thinking about. A relative humidity reading should always be taken of the slab, however, rate of vapour emissions (which is essentially what an RH test is looking for) can vary and on occasion, throw out a curve ball. When we’re talking about a ten thousand pound herringbone floor, no chances should be taken.
We assumed the original concrete slab of this property did not have a DPM. With regards the new sections, they were installed two months prior to us starting this project. Normally, that would not be enough time to allow a new concrete slab to adequately dry. However, using the Ardex DPM 1C system, we were able to fast track the installation, keeping in line with our clients deadline. Ardex DPM 1C can be installed as an effective DPM (moisture suppressant) over slabs with a moisture reading of 98% Relative Humidity or slabs with no DPM beneath.
As mentioned earlier, it has to be applied assuring a consistent film of 250 microns. This is achieved by using an A2 notched trowel to spread the Ardex DPM 1C. The notches of the trowel keep the amount of material being applied consistent. As we go and while the DPM 1C is still wet, it is then rolled with a short pile roller leaving a consistent 250 micron film.
twenty four hours later, once dry we’ll then commence with the next step.
P82 primer is a water based two part synthetic dispersion primer and bonding agent. This means it will help our next and final layer of self levelling compound (Ardex K15) adhere to the DPM.
We need this exceptional primer as the DPM 1C previously installed is obviously non porous for all intense purposes. The DPM 1C is a one coat system, therefore cannot be sand blinded to aid bonding as the sand would puncture/bridge the DPM.
P82 primer is basically mixed together – part A and part B – and applied evenly to the DPM with a short piled roller.
Next day, once dry (well slightly tacky which was perfect), we applied the K15.
Ardex K15 is a premium self levelling compound (slc). That truly isn’t an over exaggeration. It flows exceptionally well and spikes (I’ll explain) amazingly for well over twenty minutes after mixing. Which helps remove the stress of rushing to get a large area of self levelling down before the adjoining section starts to go off.
K15 is a water based self levelling compound. On large and technically challenging areas such as this, it’s always best to have one person mixing and maintaining the mixing area and the other applying the slc. Each bucket is mixed, taken to the relevant area and poured. The pour is then spread evenly with a screeders trowel and to the thickness our previous level measuring assessment told us. Once poured and spread to the required thickness, the poured area is rolled using a spiked roller. Doing this both helps to even out the self levelling, remove trapped air, and fuse adjoining sections of slc if it is being applied by single buckets (not pumped).
This final layer of self levelling compound is absolutely critical in the sense of being level and flat. Any slight unevenness will both effect the overall appearance of the herringbone and effect the way the blocks go together.
We did have minor high and low spots that were dealt with by grinding the high spots and using additional adhesive in the low spots when installing the herringbone.
Once the K15 was dry, which in this instance took six days, we commenced with the next stage..
Preparation and Layout of the Herringbone
First thing to do is sand the dried K15 with 80 grit paper to remove any laitance and key the surface slightly for good adhesion of the adhesive. The sanding swirls can be seen in the next pictures. Once sanded, the area is vacuumed and wiped with a damp cloth (Almost no water at all). This is to remove any dust that will inhibit adhesion. The finger test is constantly done throughout the installation. The finger test meaning wiping the surface with a clean finger and looking for signs of dust. Very important!
Next step was to start the layout. When aligning and laying out a herringbone installation, we tend to rack out (without applying any adhesive) a row of the herringbone, roughly align the row to how we feel looks most symmetric to the room, straighten the row up using a lazer line along each block end. Initially, this is all done by eye and the help of the lazer line. We do NOT use walls to measure from at this point and rarely use walls as a finite guide. I see a lot of this advice across the internet about measuring from walls. Walls can be a great guide and help confirm lines, but they can also be misleading and not necessarily square to a room. Always be careful using walls as guides! Another way to set out is to use the ‘Trammel‘ method. However, I do tend to go for a more hands on approach using my senses and multiple reference points.
Once we had our rough crown line, we then positioned it central to the lounge and dining room doors. We then extended a run of four rows of the herringbone blocks (still without adhesive) through to the entrance hall and built a crown line up the entrance (Imagine a large ‘h’ shape). The aim of this was to gain an overall feel of how the herringbone was going to look in the entrance if positioned central to the doors and see how our initial crown line layout looked through the entrance. We were also looking for balance between the two main walls in the entrance. At this point it isn’t an exact science. It’s all about feel and senses. Doing a lot of walking around and looking at things from different angles. There’s a lot of discussion back and forth. A lot of carefully moving the rows around. A lot of confirmation measurements being taken (some from them deceptive walls!).
Once we felt the herringbone was in a good position, we could then start to strike chalk lines along our block edges, and further chalk lines further away to give use an aid later on for confirming we were still in the right position.
Herringbone can move all over the place very easily and quickly become banana shaped without you even knowing, until it’s too late! Constantly referring back to our lazer line, making sure each block edge lines up perfectly is a tedious but critical task. As we couldn’t nail the blocks in place as nailing would both break up our slc, puncture the DPM, and not give an adequate fixing, the installation relied solely on adhesive as the fixing method. Our first crown line was just short of ten metres long. Making sure such a crown line is straight is a tough task, believe me.
When we’re happy, it’s time to start gluing. On this installation we used Rewmar MS (Modified Silicone) polymer adhesive applied with a 6 mm V notched trowel. We then carefully bed the blocks into the adhesive being sure to stay consistent with all our reference points. The crown is then taped to help keep all the blocks in position and slight weight is applied. We used bundles of the herringbone (sorry no pictures) and left over night.
Next day it’s time to start really grinding out the installation. I do say that tongue in cheek. With the prospect of 2600 blocks of wood being installed over the next three days, it really can become a grind. However, seeing the floor coming to life as we go really is a magical sight and one of the most satisfying feelings.
Sand, vacuum, wipe floor, glue, wipe back of block, insert pre-checked block, sand vacuum, wipe floor, glue, wipe back of block, insert pre-checked block, sand, vacuum, wipe floor, glue, wipe back of block, insert pre-checked block…Repeat 2600 times!
Ok, ok, so the sanding, vacuuming, wiping, and gluing is done in larger sections but the blocks are inserted one by one..Feel any pity?? Thought not!
Sanding isn’t something we do. On this particular herringbone we commissioned the services of wood floor renovations, based in North Wales.
Firstly, the floor is sanded with a drum sander and edge sander using course paper to take the herringbone blocks down to level.
The saw dust from the initial sanding is then collected and mixed with a resin. This mixture is then used to fill any gaps in the herringbone floor.
Once dry, the floor then received several more sands with finer grit paper till the floor was close to its final surface finish. Like all the other stages, the surface is vacuumed in between sanding stages.
Three coats of extra matt lacquer were applied with incremental buffing.
The extra matt lacquer gave the herringbone a natural finish almost giving the appearance it hadn’t been touched but at the same time looking like it had been factory hand finished. A truly outstanding final finish that our client was extremely happy with.
I’ll now wrap this article up with a series of pictures taken of the completed project and hope it has given you an incite as to what’s involved when considering a herringbone floor.
© Copyright 2015 Wes, All rights Reserved. Written For: Fitmywoodfloor