Btukfyl

after the installation of a new water heater and a relatively extensive plumbing fix, I wanted to save a buck trying to patch the drywall myself. It's the very first time I buy a piece of drywall or anything related to this activity. I re-created a map of the pipes on the new drywall using trilateration, then cut the drywall to match the existing, large hole, and cut it in a way that I could fit it.

The existing hole with plumbing:

The patch with holes for plumbing (this will be cut in a half going through the holes):

Poor picture (sorry) of the cut patch:

Dry fit of the "bottom" part of the patch:

Dry fit of the whole patch:

My question is: how much support should I install behind the drywall before I screw it to the metal studs, and start the operation with mud and all of that. I am really clueless, any advice will be appreciated.

It's a matter of preference, but I would float scrap lumber backing at four locations:

1. Down both sides


2. Across the bottom between the two studs


3. Across the between the two studs just below the plumbing penetrations


4. Anywhere else that seems too flexy when you do a little press-testing

This backing doesn't really need to be attached to the studs (doing so can make it difficult to keep everything flush), but should be fastened well to the surrounding drywall. Construction adhesive would reduce the number of screws necessary there.

I don't ever attach drywall unless it has attached backing on each side. To float the backing and have it come out solid and flush and not cause drilling issues is both a thing that needs to be practiced and it needs the appropriate access.

For something like this I would go to next stud for sure. Also I would build a little access box jutted out from the wall maybe 8" or so. Here is the deal if you float this and bump into the area it could crack - I hate working on something prone to failure especially in an area that has usage. A proper access box of maybe 20" tall by 8" out would allow you to service these turnoffs properly if there were issues without opening the whole wall up again. Also if you have to turn these off you are probably putting pressure and a good chance of damaging wall area behind it. I honestly have only seen this a handful of times in houses.

My answer:

1. Remove drywall until you can go to studs - almost no extra work and much faster and long-term than floating.


2. Build an access box (2x2s) and attach across framing.


3. Drywall access box and hole.


4. Be glad you did it right.

One option is to glue and screw plywood to the back of one piece of the plaster board, creating a ledge for the other piece to be glued and screwed to. Predrill into the ply to reduce the forced needed to get the screws started and use very sharp screws.

Do likewise around the hole where possible.

This will result in all edges being surported.

If you got enough depth wood can be used instead of ply.

Your patch looks too big for this, but drywall clips do exist and I’ve had good success with them. Here is one brand:

Walboard Tool 54-014 6 Count Drywall Repair Clips
https://www.amazon.com/dp/B002NGH8SQ/ref=cm_sw_r_cp_tai_R8bNCb3EWQH15

These clip onto the perimeter, and then you screw them in. If you have a stud in the way, it can be a problem slipping them on.

It appears to be supported by two studs. Unless you want to make a bigger patch (& hole) that goes halfway on to the next studs on either side, just screw it into the two studs and start mudding and taping.

Edit to add:
Leave about 1/8" (3 mm) gap, knife mud into it, embed tape into mud on the surface (paper tape is actually stronger unless you are using "setting" mud rather than the usual drywall compound that dries) and mud over that until you are happy with the appearance, using progressively wider knives and knocking off any high points when dry, before applying the next coat.