Stop creaking/cracking OSB thin set mortar?

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wigster

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Hi all,

I have a new build (direct L). I have an issue with cracking and creaking OSB boards. under my new carpet and floorboards on my first floor. I have removed the carpet and screwed doen (in one average size room over 1000 secrews) it helps for a while but not perfect but then it gets gradually worse. I have had my carpenter back to look and he removed some of the OSB sheets and added more bridgers between the 16" centres. My question is has anyone used a thin set mortar over the OSB. I put UFH in an upstairs barhroom (small) and the is no cracking.
 
Noise from OSB on floor decks is usually from their ends or sides moving - are the boards tongued & grooved (T & G) ?

It is always advised that boards are glued to each other and at their ends, and that their ends are alway, always, supported.

If you google, you should find a paper on this from the Wood Panel Industry Federation - WPIF - on how to lay OSB decks. PM me your email address and I'll send you an extract if you don't find it.......

I would not put thinset mortar or screed on OSB - it will crack. What you can do, and I just did, last week, is to put Hardibacker board over the deck, and you then tile that. Hardibacker is a cement based board that won't shrink, move or absorb water, and is specifically for tiling -either walls or floors, and comes in 6mm and 12mm thickness'.

I've used it in several places, and it's great.
 
I'll take one particular room. I screwed down the OSB with 5 X 60mm screws every 3 ". It did not help. We removed all the screws and the carpenter decided to take up some of the osb sheets. Whe the sheet removed when you walk on the joist there is a cracking sound which is random. He put in new bridgers and it has helped but there is still some cracking.

for example I will walk into a room and its perfect until I walk to a certain area then it will crack. As I walk out of the room through the same footsteps as I walked in the floor will crack for each footstep at the area of the first crack. If I turn around and walk back in the room is fine until I reach a particular area again.

My idea was to put a weight on the osb that is greater than the weight of a person. What about running 2x1 along each joist and mortar filling between each joist. Its a big job but walking through the house at night is like elephants walking through the house espically when you have a child trying to sleep.

I was debating to go concrete slab at the begining. Boy am I sorry now.
 
Are they std 44 x 220 joists, or I-joists ? Is the joist timber itself, faulty, I wonder?

It sounds to me like there is a fundamental joist issue. Is it possible to lift the sheets over the entire length of the affected area, at least over a pair of supporting walls?

I'm thinking it would be a good idea to put in an extra joist - or several - in the affected area.

I wouldn't bother with the extra weight in one spot idea. Eventually, it would seem, the problem will start over again - and maybe worse.

Sorry for your troubles, but it's not because you've got timber joists -it's either bad timber, bad joinery or something - all of which are curable.

FWIW, I have 70mm conc screed over ply over I-joist (13m long), and I have zero issues so far. If the joisting was going to move in my house, it'd certainly be at it by now, with all that on it....
 
Galwaytt,

If only it was in one spot. Its in every room of the house. 1100 sq feet. Most of the bedrooms are carpeted so its not too difficult to take up.
I do believe its the joists that are the problem. However, Putting in extra joists would be difficult as 1) pipe and wire crossing and 2) it would almost certainly crack the ceiling below. (This is what baffels me as there are no cracks on the ceiling below. The only room that I have had satisfaction is a walk in wardrobe. THis was more creaking and the screws sorted it. However there are two supporting block walls underneath. All other rooms span 4/5 meters minimum. The reason I mention re the weight is that if someone is standing in the particular area where there is a crack and I walk near it the crack will not appear!!! Would the joists (9 X 2) be able to support mortar?
 
...I still don't think mortar will do anything for you.

How about:

1. If you can access the side of the (offending) joists, to glue & screw on a second timber to the side of it, as a stiffening member ? You could do this between bridgings, if the bridging is already fixed. I'd machine down a plank slightly less than your original joist height (-6mm, say), and keep it off your ceiling boards below, so that you won't be pushing against your ceilings. Or a steel plate, if you're really dedicated.........:eek: kinda creating a half flitch-beam, as it were..........

2. Did you try laying another OSB board across the existing ones, at right angles ? Even if you did this for a section of floor for test, it'd give you and indication if it would work.......you could just screw temporarily to existing floor. (btw, what thickness OSB did you use?)

3. How would you feel about putting another board over the entire 1st floor? (or is it too late........skirtings/doors etc etc)
 
I have put a new layer of osb at right angles but to no avail. Most of the rooms ahve skiring/archritrave in already and I have removed this.

Do you think the joists are flexing left and right. I know the extra bridgers have made a difference but over time the cracking is getting worse again.

The reason I keep harping on re the mortar is that I have two bathrooms sidebyside. One I have UFH which I put down 6mm Ply ontop of the OSB. Then I put 18mm latex self levelling compount with tiles on top. No Cracks at all. However the second bathroom (nothing in there yet) has cracks all over it.

All osb was osb3 18mm.
 
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