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I will be laying 18mm OSB/3 boards on 2 x 4 joists for a garden shed. I was planning to screw and nail them down using a mix of 50mm decking screws and galvanised nails. However, quite a few sites/videos recommend gluing the boards down too using a grab adhesive. However the choice is overwhelming.

What key label/ingredient should I look for when purchasing? I am in the UK so main consideration is atmospheric damp( the frame will be on blocks with airflow beneath the frame ). Being a shed( for storage only ), would it be problematic to skip the glue altogether?

The boards are not tongue and groove. I have read I should leave a gap between the boards for expansion and contract. Is there a recommended gap?

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    Sorry had to delete my previous Comment as I just realised I misread what you're actually asking about! Again to preface, I think you'll get better input on this on DIY. So you're asking about bonding the OSB to the joists yes? If so the fasteners are doing the heavy lifting here, the adhesive is there mainly to minimise the chance of minor movement in due course (e.g. to prevent squeaks) meaning it really it doesn't matter what you use as long as it's halfway reliable. So just pick something common that has good user reviews and go for it. – Graphus Mar 14 at 8:32
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    Yeah, this belongs more in DIY.SE. But, honestly, you are doing construction, so use construction adhesive. The choice should be driven by application, not chemistry. You want one suitable for being exposed to elements or not, whether it will be combined with mechanical fasteners, cure and application temperature. Relative humidity, even in the UK, isn't really going to be a problem. But read the label. Some glues bond with water in the air to cure, so there is an ideal RH range for those. – jdv Mar 14 at 12:27
  • Did you ever get this resolved? If so, please give a check-mark to the answer or write up your own answer explaining what you did to get it fixed and give yourself a check mark. That will help others with this kind of problem know that this has a resolution and is a good place to look for their answer. – FreeMan Aug 13 at 11:24
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Adhesive is used for sub-floors in homes to help eliminate squeaking from flex/movement.

Since this is a garden shed i do not know that is necessary. Just use lots of deck screws. If you want to there are several that would be sufficient. Here is link to a page that tested several, You can choose.

I think using 2x4 as floor joists is not a good idea, I do not know what size your shed is or how much storage weight it will hold so i cannot advise on joist size.

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  • 2x4 may well be sufficient depending on how many footings are supporting them, or if they're sitting directly on a prepared gravel bed and are there mainly to get the OSB out of direct ground contact. Of course, if they will be supported only at the ends, they're likely not sufficient at all. – FreeMan Mar 16 at 17:13
  • I would be more concerned with only 18mm and osb , I would be sealing it with paint so walking on it when damp won’t cause it to swell and fall apart. I do use 5/8 for roof decking but would want to protect it with paint or a floor covering. – Ed Beal Mar 18 at 14:02

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