Understairs cupboard needs a shelf that will be 90cm wide.
In the absence of any other suitable wood in the barn I’m thinking if using a scaffold board that’s been in there for 6 months.
I’d like to glue two lengths of board together to make a piece that’s about 40cm deep – all I’ve got ATM is gorilla glue, will this do the job OK?
(It’s not going to be under a lot of stress, just needs to keep the boards together)

Any other suggestions greatly appreciated.

Assuming the shelves are properly supported at each side (like the below image) then you wouldn’t even need glue – just screw them in place. Or am I missing something?

If that’s all you’ve got, that’s all you’ve got. GG i s great in my experience. If they absolutely have to stay together I’d screw a couple of brackets underneath at a later juncture though.

Yes. PVA would also be fine (GG could be branded PVA for all I know). Assuming you’ve got fairly nicely mating surfaces – I guess you’re going to want to trim the edges off anyway so you have nice square edges and no gap in the middle of your shelf.

But as above, probably better to eliminate the need for glue at all.

Gorilla glue – the foaming stuff – Not really. Simple PVA will give you a better bond.

One of the problems you will have gluing them together is flatness. Usually they’d need to be as flat as a piece of mdf is flat, or there will be a multitude of gaps that aren’t sticking one to the other.

If you are looking for the thickness to be a part of the overall look, and tbh a thick shelf does look better than a thin one(in some applications) then you can get away with just sticking/pinning a lip to the underside of the front.

Example here on a mantelpiece i made. The boards are 18mm thick, but by adding a thin strip to the underside of the front, it gives it a much thicker and more appropriate look*. It also means im not wasting timber, as this hardwood(Bubinga) is pretty pricey stuff.

*The reason of the moulding on this narrow strip it to make the actual leading edge look a bit thinner and to give it a bit of aesthetic appeal.

It also ,while not needed here, adds strength to a board which would prevent it sagging we it made as a shelf and had the weight of books etc placed on it.

I use the green bottled Evostik wood glue. It’s bloody strong.
There are a variety of Gorilla Glues, aren’t there? Whether it’s suitable or not will come down to which variant you have.

Assuming you want to glue two pieces together to make the shelf deeper, you just need to make sure that the edges are both straight & fit well together. It would be worth clamping, if you can.
If you are worried about them splitting apart again, you could always use something like this with some short wood screws to reinforce it?

Flat Fixing Brackets

Assuming the shelves are properly supported at each side (like the below image) then you wouldn’t even need glue – just screw them in place. Or am I missing something?

Actually you’re not!!!

The shelve will be supported just like that and will probably just have the coffee machine and maybe a [20kg] kitchen mixer on it – Glueing might be overkill!

https://woodbin.com/calcs/sagulator/

That’s cool….. “acceptable”!

As they are supported both ends, I would leave them unglued, but if there is much bounce/give in them you could screw a baton underneath the boards front to back to stop the coffee machine rocking back and forth.