Levelling compound for particle board subfloor

G'day all,
I have pulled off old carpets in preparation to install Aussie chestnut solid flooring (130x19mm planks). The underflooring is good old hardwood particle board. It's in a good condition but a bit wavy, sticking up on one of the joists, and low spots in between. The room is just 3x3m and the levelness variety is up to 7mm. I'm thinking of sanding a couple of mil off the humps and then pour a leveling compound on top.

I've checked both Bunnings and Bowens, and the only levelling compound that explicitly declares suitability for particleboard (non-concrete) sub-flooring is this one https://www.bunnings.com.au/dunlop-1...x-kit_p6650368, and it's quite expensive (I expect to pour 2-3 buckets into that room).

Is there any other widely available product? (I'm in Melbourne North East)

Another question - can I still nail the flooring (using floor stapler) through the levelling compound into the particle board beneath? (or will it create the leveller?)

Thank you in advance.

Do you really need a leveler if you can get it level from "joist to joist to joist"? 19mm T&G boards should be enough on their own, just treat the particle board as "insulation".

All my 19mm Tassie Oak is laid directly onto joists

I would use an electric plane instead of trying to sand.

I had to try and level our old floors before laying 19mm blackbutt boards on the cheaper softwood particle board and the belt sander battled. In the end I used the electric hand plane and it rips it down quick, just bash all the nails down a few mm before you do it so you don't chip the blades.



but as renovator says by the time you rip down the high spots a few mm I dunno if i'd bother trying to level a 3 or 4mm dip. especially in a small room thats probably going to get filled with furniture. as abobe when we did ours we glued and stapled it down to the existing particle boards with just sausages of construction adhesive.

The manufacturer makes no notes on use under timber overlay flooring

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• For ceramic, carpet and vinyl floor coverings

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I would contact the leveller manufacturer as well as the overlay flooring manufacturer for their advise.

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Originally Posted by droog

The manufacturer makes no notes on use under timber overlay flooring

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They do: https://media.bunnings.com.au/api/pu...802?v=b662b5e3

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DUNLOP LEVEL-FLEX TIMBER FLOOR LEVELLER canbe installed indoors only over a number of substrates including timber and concrete.

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The particle board manufacturer probably rests in peace since this are original boards from the the `80s or something.

Good point about electric plainer. I'm lucky to have one.

My concern is that since the waving runs across the board length, some of by T&Gs will come convex, i.e a bit open.

Re construction adhesive - I hear many use that, but all the pros on youtube say you shouldn't use the one that dries hard (like liquid nails) but but a flexible one like Bostik Ultraset SF, to accomodate for boards' seasonal expansion/movement. Any comments on that?

Re small room - eventually we'll do the whole house, so I'm starting with a small room to practice in getting it right. But I hear you. I'll rip the high spots and reassess from there.

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Originally Posted by aeroden

They do: https://media.bunnings.com.au/api/pu...802?v=b662b5e3

The particle board manufacturer probably rests in peace since this are original boards from the the `80s or something.

Good point about electric plainer. I'm lucky to have one.

My concern is that since the waving runs across the board length, some of by T&Gs will come convex, i.e a bit open.

Re construction adhesive - I hear many use that, but all the pros on youtube say you shouldn't use the one that dries hard (like liquid nails) but but a flexible one like Bostik Ultraset SF, to accomodate for boards' seasonal expansion/movement. Any comments on that?

Re small room - eventually we'll do the whole house, so I'm starting with a small room to practice in getting it right. But I hear you. I'll rip the high spots and reassess from there.

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The quote makes note of using it OVER timber substrate.
Where are the notes for using it UNDER new timber flooring ???

It is noted for use under ceramic, carpet and vinyl on substrates that include timber and concrete!

I believe substrate means subfloor in this context. Hence the quote reads that leveller can be installed over timber subfloor. While particle board is not a timber strictly speaking, when primed there shouldn't be material difference, shouldn't it? From what I've seen so far, these products go into two main categories - those that are only suitable for fully rigid substrates like concrete, and those that are suitable for relatively flexible substrates like particle board. Do you think differently?

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Originally Posted by aeroden

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My concern is that since the waving runs across the board length, some of by T&Gs will come convex, i.e a bit open.
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If the partcle board has sagged, you can't be sure it won't get worse, e.g. from a damp subfloor etc. I'm not 100% sure what you mean by the above statement, so for the removal of any doubt, when laying your T&G boards, you should run them perpendicular to the joists, regardless of how the particle board has been installed.

Also, do you know the joists/subfloor is in good condition?

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Originally Posted by aeroden

I believe substrate means subfloor in this context. Hence the quote reads that leveller can be installed over timber subfloor. While particle board is not a timber strictly speaking, when primed there shouldn't be material difference, shouldn't it? From what I've seen so far, these products go into two main categories - those that are only suitable for fully rigid substrates like concrete, and those that are suitable for relatively flexible substrates like particle board. Do you think differently?

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Yes the product you listed is suitable for use over the floor you have however the manufacturer specified that it is suitable for then laying "ceramic, carpet and vinyl" over the top of it.
You are installing "Aussie chestnut solid flooring", solid timber flooring is not listed for use over the top of the floor leveller. I suggest ringing the manufacturer and asking if you can use solid timber flooring over the top of their product.
It is possible they do not recommend it as nailing or stapling solid timber flooring over the top may crack their product.

Eventually I found Cemimax DL59 as per this blog post. It explicitly says it's suitable to go on timber'ish substrate and accept timber on top. It's not commonly available but I've managed to find one in Dandenong South. The price is very affordable - $33 per 20kg bag, and the primer is $38 per 5kg. I got a tub of DP89 primer and 3 bags of DL59 leveller and it was almost x4(!) times cheaper than buying that Dunlop stuff at Bunnings.

Anyhow, I've shaved the high spots with planer (a breeze of the job - thank for the hint!) - you can clearly see them on the picture, sealed the edges and underflooring joints, and drove a fresh line of screws along each joint to finish the prep. Then rolled the primer over and after 3 hours poured the leveller where I knew my low spots are. I've done 3 batches of 10kg powder. Just troweled it around to feather'ish edge and then worked very, very thoroughly with spike roller (got a cheap one for $20 from Amazon - worked wonders). As well, $9 spiky aerator sandals from Bunnings worked like charm (I've blunted the spiked a bit with an angle grinder).

I'll see tomorrow how it turns out

Well, unsurprisingly, the patch work resulted in patchy results - for thin layers, surface tension kicks in heavily affecting the self-levelling flow. Eventually I resorted to grinding off high sports here and there to create isolated lower areas and poured another 10kg of leveller topically here and there while screeding it with a straight edge. The end result is not perfect, but pretty good. Bottom line - next time if I decide to pour the leveller I rather flood the whole thing double depth of the bigger high/low spot difference - to make sure it actually levels.

One thing that amazed me is how much more rigit and and solid the floor feels with just those several mil of concrete on it. It's not like it was too flexible before but it's a whole another level. On the other hand that's another extra 40kg of thermal mass that will absorb heat. I'm curious to check with thermal cam later on if I can spot where the concrete is under the floor :)

I hear many of saying it's an overkill... I think it's a matter of perception. Where I spent most of my live, houses are built from stone, so nothing ever squeaks or flexes, and if it does - it's a sign of severe failure. Hence for me the, a lightweight frame construction with elevated floors style of houses feels very uncertain, as I'm living in a card board box if I exaggerate it a bit. So for me, it's a win to have a more solid floor, but I totally understand how for someone who's used to it, having a degree of flex in the floor is perfectly fine and they would never consider pouring concrete on timber underflooring.

Next thing is to see how my nailer likes shooting through this leveller :U

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Originally Posted by aeroden

Next thing is to see how my nailer likes shooting through this leveller :U

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So not intending on following the manufacturers recommendations ?

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Suitable for timber flooring as direct stick

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Personally I would go with the adhesive as recommended.

Both glue and nail. Not massively nail though - mainly to hold the boards firmly where I want them to be while the glue is drying. Also I'm keen to experiment. Inspired by this guy: https://youtu.be/S-rOknMPrTg?t=1368

Haven't watched the video, but if the nails/brads cause cracking/fragments in the leveler, you could get a crunchy sound/feeling underfoot

Yeap, that's my concern too, but there is only way to find out :)
The leveller see to be quite flexible - i've jumped on the leveller underflooring with all my might, trying to flex them when I land, and the leveller hasn't cracked.

I'll update this thread with how it goes. Currently acclimating the wood.