14mm timber floors over existing old boards

little buddy · Apr 27, 2010 9:15 pm

Hi everyone,

I was wondering if anyone could help.

I have an old house with the old pine boards on joists.
I am looking at putting new overlay timber floors down - 14mm x 130 mm Blackbutt boards. Laying in same direction as the existing boards.

One installer is suggesting installing these by glueing these onto the existing boards and secret nailing them.

Others have said that I would need ply down first.

I like the idea of not having ply because the height of the floors will fit under the external doors (I've got 20mm gap), but I'm not sure if I should be cautious about this approach??

thanks everyone

namtrak · Apr 28, 2010 7:32 am

14mm boards are known as overlay.

It is quite common to lay these directly over existing timber. Secret nailing could be an issue with the 130mm boards, just make sure the installer is trowelling a decent glue (Bostick Ultraset) on. The secret nails(staples) should go through the existing boards and into the joists for proper fixing. This is why the boards are laid with the existing boards.

The other installer may want to lay ply because the existing floor isn't level? A rough sand could fix this to a degree.

little buddy · Apr 29, 2010 9:43 am

thanks namtrak.

Not sure about why the other installer is suggesting ply as they never actually saw the floor to be able to judge if its level. I've had a few ppl suggest the ply + boards options too.

Also, the non-ply guy will be sanding first.

guest · Apr 29, 2010 10:09 am

Installers are correctly suggesting plywood because you want to lay the timber in the same
direction.
You should never install two layers of timber in the same direction.

Lex · Apr 29, 2010 10:36 am

I was thinking along the same lines as borg ... but was going to ask/suggest if you can lay the new boards square to the old ones, directly to the old floor?? (But you probably don't want to ruin the look by placing the boards gthis way :th:

)

namtrak · Apr 29, 2010 10:40 am

As an installer, I regularly lay the new boards directly over the old. This is a very common industry practice. The actual fixing is through a combination of the trowelled glue and nailing through the old boards into the joists below. This is why you lay the boards in line with the existing boards, if you don't then you are just fixing into the old floorboards and you also end up with a myriad of nails coming through the underside of the floor - which is a drag if you need to do any work under there. Not to forget that it can also be a danger if your wiring is near the underside of the floorboards.

Having said that, I have installed boards perpendicular to the existing floor, but I generally try and convince clients to go with the boards if at all possible. In most cases the new boards are laid perpendicular out of aesthetic considerations.

Cheers

guest · Apr 29, 2010 11:55 am

if you lay in the same direction I would have thought the substructure would not be strong enough especially for 14mm ( non structural ) boards.

namtrak · Apr 29, 2010 3:12 pm

Not at all, in fact the sub-floor (joists) are designed to hold the boards. Picture a bare sub-floor with joists at 450 centres. Now imagine the first set of flooring across those as per normal, with the flooring nailed into the joists at 450 with a touch of glue - no worries. Now, continuing on my pictorial journey imagine if you will, floor boards laid perpendicular (so in the same direction as the joists) to the original floorboards. All the floorboards (of the new ones) that are laid between the joists are only held up by 19mm of flooring and any nails which go into them are only going to pierce the old floor boards and not the original joists. And that is why we should try and lay new boards in line with the old wherever possible.

guest · Apr 29, 2010 3:22 pm

Not sure if i agree. If one board fails or is below optimial strengh than the 14mm non structial board will fail to. If laid at right angles then you take the wieght across many boards. Also you have the issue of expansion and contraction as well. You will double the issues you have with expansion and contraction. Where laid at right angles this will make your floor also more stable.

Any other views out there??

Melrich · Apr 29, 2010 5:11 pm

borg

Not sure if i agree. If one board fails or is below optimial strengh than the 14mm non structial board will fail to. If laid at right angles then you take the wieght across many boards. Also you have the issue of expansion and contraction as well. You will double the issues you have with expansion and contraction. Where laid at right angles this will make your floor also more stable.

Any other views out there??

I would lay same way as existing boards. That way the joists are properly supporting the floor. If you lay parrallel to the joists then you only have existing floorboards supporting the floor excepting where a new board runs along the length of the joist.

guest · Apr 29, 2010 5:29 pm

Melrich

borg

Not sure if i agree. If one board fails or is below optimial strengh than the 14mm non structial board will fail to. If laid at right angles then you take the wieght across many boards. Also you have the issue of expansion and contraction as well. You will double the issues you have with expansion and contraction. Where laid at right angles this will make your floor also more stable.

Any other views out there??

I would lay same way as existing boards. That way the joists are properly supporting the floor. If you lay parrallel to the joists then you only have existing floorboards supporting the floor excepting where a new board runs along the length of the joist.

if you are laying 19mm you may convince me. However 14mm is non structural and you cant just rely on the floor joist.

namtrak · Apr 29, 2010 6:03 pm

This is going around in circles a bit, it is assumed the overlay is laid on existing 19mm boards, which are considered structural flooring when laid over joists.

little buddy · Apr 29, 2010 8:35 pm

wow...thanks everyone for replying. what a nice surprise to come home to.

Because of the layout of my house and aesthetics i guess I'm going to lay the new boards in the same direction as the old boards.

A warning I got if I didn't use ply and laid them running in the same direction was that over time i might have problems with the floor sqeaking. Anyone had or heard of this problem?

namtrak · Apr 30, 2010 7:09 am

Trowelled glue stops the squeaking

Melrich · Apr 30, 2010 9:52 am

borg

Melrich

borg

Not sure if i agree. If one board fails or is below optimial strengh than the 14mm non structial board will fail to. If laid at right angles then you take the wieght across many boards. Also you have the issue of expansion and contraction as well. You will double the issues you have with expansion and contraction. Where laid at right angles this will make your floor also more stable.

Any other views out there??

I would lay same way as existing boards. That way the joists are properly supporting the floor. If you lay parrallel to the joists then you only have existing floorboards supporting the floor excepting where a new board runs along the length of the joist.

if you are laying 19mm you may convince me. However 14mm is non structural and you cant just rely on the floor joist.

Have to assume the existing floorboards are 19mm otherwise they would have to be on a substrate themselves. Ideally you want the new boards in someway attached to the joists.

little buddy · May 01, 2010 9:27 am

i've just got some feedback from an installer that by installing the plywood, the floor is installed to Australian standards.

are there really Australian standards???

namtrak · May 01, 2010 9:34 am

http://www.standards.org.au/default.asp

whatnext · Oct 11, 2023 9:03 am

Hi all

Thought I’d use this old thread rather than make a new one.

I am looking to direct stick 14mm engineered blackbutt on top of an existing hardwood jarrah floor in a 30sqm lounge room. The existing timber is very solid and pretty flat already however we will have the polish sanded off and some minor high spots grinded down to ensure it’s properly flat.

While we’d prefer to run the flooring in the same direction we will go perpendicular as for height reasons we can’t add a plywood base
.
I have checked the manufacturers installation guides and this is the approach they recommend.

One thing I just can’t get a straight answer on is whether a moisture barrier or any other layer is needed between the old timber and new engineered board? Does anyone know? Or just glue it straight down with nothing in between? Ideally I don’t want to add an underlay as it will create some height issues.

The same engineered flooring is being installed (direct stick as well) in rest of the house but straight onto the concrete slab. A moisture barrier is being used here (no underlay).

Due to some issues with the slab heights from past renos (previous owners), the above approach actually results in the new floor being the same level throughout the house. I am also trying to ensure the feeling under foot is as close as possible between the room with the hardwood subfloor and rest of the house with concrete subfloor. My hope is direct sticking with nothing in between will help achieve this.

Any advice appreciated!

chippy · Oct 12, 2023 5:36 pm

Is the existing flooring stuck down or is it on joists/battens?
If it's stuck down then you would assume that a MB was already installed before it was put down. Certainly if it's been down for many years and you've had no issues with movement then it's pretty safe to assume it's all good.
You will be fine to direct stick to it after a good sand and clean.

building-expert · Oct 13, 2023 9:00 am

I would sand back old floor to provide surface for adhesion of 14mm board on top, then direct stick and secret nail to keep it down. You will end up with a laminated timber floor 33mm thick that will be stronger and stiffer. Make sure your new floor timber is acclimatised before laying.