Getting stuck into adhesives

Sid Bourne, independent consultant.

Always make sure you get full coverage of adhesive onto the backing of your material and don’t be a cheap skate to save a few pounds, cautions Sid.

IT’s that time of the year when I upset manufacturers – in this case adhesive manufacturers. I have to say, I’m having a go at some less well-known adhesive manufacturers, as to be fair most of the obvious ‘big boys’ have excellent technical data information and make it quite clear how the adhesive and correct trowel should be used.

This column stems from the fact I’ve been to many sites for hollow spots and buckling floors, which have come away from the wood-floor adhesive. I don’t need to add, because most of you already know, that Bob the Builder (and the general cowboy installer) will use anything to apply adhesive to get the most coverage – even their hair-comb.

I recently went to two installations where the complaint was regarding hollow spots throughout. Both contractors paid me to carry out the inspections for them, to determine why this was happening. On discussion with the installers they’d done everything perfectly from testing the subfloor to applying surface moisture suppressants and compounds of good quality and well-respected subfloor preparation manufacturers.

On just observing both installations you could clearly see they were excellent installers. The layout and provision for expansion were perfect, the subfloors were flat and so on.

When going around the floors on both jobs, I discovered that 30% of the oak planks were 150mm wide and 18mm thick and of random length, with the one product having longer lengths of up to 2.5m.

At the first inspections, I asked the installer to show me the trowels they’d used, and it was confirmed that these were the trowels recommended by that particular manufacturer. I looked at them and said that in no way would these notches be anywhere near deep enough to grab the solid planks that would give an excellent bond and coverage of the back of the oak planks. I measured the depth at 4mm/5mm (more like 4mm when applied).

Now to explain why this trowel is nowhere suitable: if we look at industry standards for solid wood conformity, it states that bow (banana shape) for glue-down of flooring boards won’t exceed 0.5% of the length at the time of first delivery.

If you have 2m long planks this would equate to an allowance of 10mm, so logically it’s the installer’s responsibility to not use a board with this much bow (you don’t need to be a rocket scientist to determine whether a 4mm or even a 5mm trowel will do the job - it won’t, not even if you weight it down). So you need to ensure you have a trowel notch that gives you a chance and of course you should be choosy in what you decide to glue-down.

This now shows you the issues you can come across – even if you have a good flat subfloor to within 3mm in 2m. I guess you’ll see where I’m coming from with this: regardless of how good an installer you are, you’re governed by the quality of the solid wood flooring and the size of the notch you use.

I asked the installers to uplift part of the flooring, as it had gone past being able to rectify by injecting adhesive unfortunately. And hey ho, what do you know - on looking at the backs of the solid planks the adhesive coverage was less than 50%. Failure is inevitable once the humidity starts to change and the wood contracts or expands.

I have to say I really feel empathy for the installers on these jobs, as they were clearly looking to do the perfect job.

In the US, gluing down is popular, but they limit the width-to-length ratio, so you have a good chance of getting success and the notches they use are double what we’re supplied in the UK, with the exception of some of the better adhesive manufacturers who have been in the UK for years and clearly give options of what notch to use, dependent on the product width and length. Some even stating what the maximum length is that you can glue down.

I wrote my report but owing to the fact the failure was caused by insufficient coverage, the manufacturer rejected it. Given that the trowel supplied for the subfloor was level (yes, level), and the solid floor was perfectly flat, it’s up to the installer to choose the appropriate notch trowel.

In the first place they should state this in their technical datasheet, so the installer can then make the choice rather than the adhesive manufacturer simply saying: use this trowel. This inevitably leads to failure if your subfloor isn’t level and your wood planks aren’t perfectly flat.

Now the poor installers have to replace the floors and start again; as luck would have it both consumers were excellent in understanding, but needless to say they expect new floors. If this was to go to court, I believe the installers would win as they’ve followed the manufacturer’s instructions as presented to the letter.

I can hear some of you say: well, why when the installers started to install, did they not take up planks as they go, to check coverage? I’d agree this is something you should do, which is what I said to both parties. I had to report why the floor failed and they never strung me up - which I think was very kind of them (I’d hidden my towing rope in the boot just in case!).

The way I see it is that installing wood flooring, particularly plank, is similar in many ways to installing large format ceramic tiles. Just look at the size of the notch and the thickness of the tile - they have to get full coverage otherwise the tiles crack and are hollow.

With wood, we get hollow spots, but we should ensure the planks are fully emerged into a deep enough adhesive bed and weighted at all times, which is another thing most manufacturers don’t state, as it 100% helps to do that. It keeps everything weighted and in place.

I don’t want to mix up accidental hollow spots with what I call cowboy hollow spots or Bob the Builder hollow spots. There’s a major difference; you’re lucky if Bob applies a teaspoon of adhesive and if so, he plonks down the adhesive as if he was putting a teaspoon of sugar into your tea, thinking that will do and then wanting to bury me in concrete when I condemn his jobs.

I hope that in some way, this makes installers think when they’re to fully bond plank flooring down of longer length and check your product for bow and if it’s possible to still get coverage and don’t be scared to use a deeper notch.

Of course, money comes into this as obviously the coverage will be less but give me a choice of replacing a failed solid wood floor, which now includes subfloor preparation again and plus the new floor and installation labour. I’d rather pay a bit more for less coverage and get complete coverage on the back of the planks, which won’t fail. It’s your choice.

Just to finish off, a couple of years ago I was at a meeting where the flooring contractor was present to carry out the replacement of several floors of glue-down flooring (engineered), which I’d inspected and failed. This was owing to the fact the initial installation company had installed the engineered flooring over 250mm wide, using the sausage method but as per usual, they didn’t follow instructions and merely placed small mushroom size blobs randomly.

To make matters worse, the subfloors at the time of install were wet and they failed. Surprise, surprise, so the main contractor decided to get another contract company and I was asked to attend, so we could ensure nothing could go wrong this time.

The new contractor, on reading my spec, told the main contractor that the adhesive would cost a fortune: why don’t you just use the sausage adhesive, he said, and we can get away with less than half of what Mr Bourne states (he was a very polite man)!

The main contractor looked at me and questioned this. I said: ‘No problem - if you want the same problem again!’

He said: ‘No chance we’ll go with what you’ve specified.’

The flooring contractor said it was a mistake, and that engineered flooring won’t move anywhere.
I said nothing and left the meeting after we’d finished.

To my horror, just a few months later I was called by the main contractor to say the floor had gone again in several apartments, but this time they were occupied. I went along and we lifted the floor in one apartment, to find the contractor had done the exact same thing as the previous installation company.

The main contractor went mad, saying: ‘I told them to do it to your spec’. I don’t know the outcome, but the floors were again replaced by an excellent contractor, who fully bonded the floor with no problems materialising. That was two years ago.

So the moral of this story: ensure you get full coverage of adhesive onto the backing of your material and don’t be a cheap skate to save a few pounds. Do it right first time, it’s just too costly to mess about trying to save a few pennies.
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