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Ash lifting, despite screws

We received the following details on a flooring project giving the owners a few headaches:

Hello, we found your website this morning and are very impressed with all the content! We have been searching for a few days for some info regards our recent purchase of ash flooring so wondering if you could help?

We bought 110 sq m of 18mm solid ash, lacquered, 135mm wide with lengths 600-1800mm to do the whole house that we are rebuilding. They have been acclimatising inside the house since april (although without heating), when we opening the packs the long top planks almost sprung out and were bowed by about 5cm at each end which has settled down over the summer.


In July we laid two rooms (3mx2.5m and 2.5m by 2.5m) with expansion gap of 10mm around all edges using tongue tite screws on every board, 3mm foam underlay onto the floorboards. Last month the last few planks started to lift at the end length edges and it had appeared to use up the gap at one small section, so we lifted and relayed again using screws but this time leaving a 3mm spacer every third board (as advised by our joiner friend) as well as an increased gap at the edges of 15mm. We also didn't screw down the first and last rows of boards.

Within a few days it has started to lift at a similar place to before but not as badly (about 3mm up). These sections appeared to have used up the spacer gap on each side of them but not the edge one. As it is happening at the ends does this mean that we should try to seal the cut ends to try to stop the moisture getting in? As I believe Ash moves more than oak is a 3mm spacer every 3 boards sufficient for it?

The biggest room to lay is the lounge which is 7.5m x 6m, would the same plan work for here? And lastly as the floorboards are level does it really matter if we lay the floor at 90 degrees (if we do this in the lounge it will mean that the width will be the longer dimension.)

I know from your site that you PVA glue the tongue and groove so it may be hard for you to comment on this technique, but any general pointers relating to ash would be most gratefully received.

Kind regards, Gregor and Miranda.

Know your nervous wood-species

Hi Gregor

Thank you for your question. You are right, we have no experience with those screws for the simple - perhaps too simple - reason we don't believe you can screw a floor down.
(One of our purchasers of the Installation Manual gave us feedback on the tongue-tite screws here)

It is indeed worrying the boards jumped out the pack the way they did. It could indicate a problem with the wood it self. When a floor keeps expanding after having acclimatised for that long it can also indicate a moist problem in your home.
Ash can expand and shrink much more than Oak - it's therefore one of the wood-species not recommended to use on UFH.

With Oak the rule of thumb is 3mm gaps per meter width of the room with a minimum of 10mm. For Beech - another "nervous" wood this is 7mm per meter width. 10mm in a room 2.5 meter wide is not enough for this species but reading that even creating a gap of 15mm AND using spacers between every third boards did not help does look like a moist problem in the home.

Not sure what to suggest really. For the larger room you should consider a divider in the middle (with Oak 6 meter wide is the maximum you can go with a solid floor - knowing Ash works more I would be reluctant to say it can easily be done without a divider in the middle - where you "turn direction" of the T&G so that the Tongue faces the other wall in one half than in the other half of the room).

Are you able to take moist readings? Both of the floor already down, floor still in packs and the air humidity?

Feedback and update


Thank you for your prompt response, it probably helped confirm what we were thinking.

Just to give you more information, we ended up relaying the 2 small rooms where it lifted - lifting by shearing the screws having expanded and touched a wall. Though as the first row were fixed it must have snapped some screws in order to move far enough to touch the wall. Possibly not enough screws used? Maybe, but I have used similar style screws before with no problem.

I am more inclined to believe that the quality of wood is more to blame. It was purchased as a cheaper grade but I think it was either not dried properly or was dried to such an extent that sitting (for weeks) in a house in the UK it absorbed so much moisture that many of the planks had bent up by 10-15mm at the end of a 1.8m length. Now the heating is on there seems to be no problem (earlier the house was weather tight but unheated) we shall await summer to see what happens then as humidity inside rises.

Using a 2mm spacer every third plank was recommended by colleagues who are joiners and is supposedly common practice when the floor is fixed with screws or nails. Obviously leaves small gaps but it is a safer installation, especially over a large width and if the planks are dark it is not very noticeable.

Hope this helps if others come to you with a similar situation.


Further thoughts

6a00d8341c660f53ef013488946bef970c-piAs mentioned before and here again, we're not in favour of using screws to install wooden floors - especially not with nervous wood-species like Ash and Beech. These wood-species require more expansion room and correct acclimatising preferably in the room where it is going to be installed.

Acclimatise always to normal circumstances no matter what wood species or floor type you have: leaving them in a room without glass in windows or unheated during colder periods does not work. Not even for wood-engineered flooring.

Installing a wooden floor isn't rocket science - all it needs is some common sense, patience, the right preparations at the right time and of course quality materials and the right tools.

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