What type of screws/hardware is used to attach shelves to mdf shiplap?

I think toggle bolts will do the trick for you. Check at the hardware store for how much weight each size will hold.

Here’s what I found. https://www.woodworkingnetwork.com/best-practices-guide/solid-wood-machining/why-cant-i-screw-mdf

I think the article gives an analysis of the problem and the solution. Feel free to show it to the expert at the store. If they seem to be confused, find another expert or another store.

The size of the recess in the support flange will determine the size of the screw you will need, I suspect a #10. The length should be about a half inch longer than the thickness of the MDF.

Drilling the proper hole as described in the article is very important. You can experiment on a leftover scrap of MDF

Adding some epoxy (as suggested) is a good idea but I suspect you could use Gorilla Glue. Let it sit 24 hours before adding the shelf, because it takes longer to cure, but it does swell to ensure a tight fit.

If if you are lucky enough that a screw hits a stud, just use the same size screw but feel free to go a little longer.

Hope me this helps.

The easiest and best way would be to get a stud finder put the supports where the studs are. They would normally be about 16" apart. Drill pilot holes as John suggested.

You would have to screw into studs. Mdf doesn't screw well and there are special screws made for mdf. Won't hold the weight either. It's just heat compressed recycled paper with resins. I don't know about building codes in Canada or where you live. Codes in the U.S. states, cities, communities require drywall as a fire barrier. Why would you not put up drywall?!

MDF Doesn't take water too well either. Why would you use it in the bathroom?

Hi ! I would think it you want to use the plumbing pipe , you need to attach the flanges into a stud !!! Use wood screws . That how I put them up for my wall pantry in my kitchen . Good luck !

I see! Only solution I have is if you can temporarily remove the some of the shiplap where the the shelves are going to go and toe nail 2X4's between studs for support of the hardware.

Can You hang pipe from the ceiling and use an ell for pipes coming out for your shelves? Depends on ceiling height. Otherwise without a stud to hold the weight of your shelves might be a problem.

It’s me again. I just started a project that involves MDF. I knew it didn’t hold screws well, but now realize it hardly holds screws at all!!! I totally understand that supports and the studs DO NOT line up. Therefore I would stick with my earlier recommendation of putting the supports on a backer board that does catch one or more studs.

in the event you can’t hit two (or any) studs then I would go with someone else’s suggesting and use butterfly toggles.

Hope this helps.