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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:

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

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Poor picture (sorry) of the cut patch:

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

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Dry fit of the whole patch:

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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.

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  • 19
    Wow that's a pretty decent job for a first timer. I wish the drywallers would put in the same effort around my mechanical installs.
    – Joe Fala
    Mar 28, 2019 at 2:31
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    OK well it took me a day and a half - most contractors do not have that time
    – Alessio Sangalli
    Mar 28, 2019 at 4:40
  • This guy (“Vancouver Carpenter”) has some of the best drywall videos: youtube.com/channel/UCbZdXox6mKHdcT2QdVT-goQ
    – rrauenza
    Mar 28, 2019 at 14:36
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    an electrical outlet so close to so many water pipes/valves kinda scares me... but I don't actually know if that's against electrical code
    – unknownprotocol
    Mar 28, 2019 at 17:34
  • Water, gas, and electricity all in one place...what could go wrong?
    – evildemonic
    Mar 29, 2019 at 21:13

6 Answers 6

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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

1/2" or thicker plywood and 1-by or 2-by lumber work well. This backing doesn't really need to be attached to the studs in all cases (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.

Protip: If you don't have access to a dedicated screw gun (which is not the same as a drill, despite common usage of the term), these drywall screw setter bits are golden because they keep the screw from sinking too far into the drywall:

enter image description here

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  • I would say this. If you feel this is a long term fix then when framing a basement why wouldn't people space the verticals 36-48" apart? Given your answer you could just use plywood backing in the gaps. I only use this technique on ceilings since they are unlikely to get bumped into. Any experienced drywaller would use this for small holes that need backing where the hole isn't big enough to add framing. No experienced drywaller would go out and do this technique on an opening this big. In 30 years of using drywallers never even seen it suggested.
    – DMoore
    Mar 28, 2019 at 19:56
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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. If you can't do this then add an extra stud - it does not need to go higher than hole. You can add two support blocks.
  2. Build an access box (2x2s) and attach across framing.
  3. Drywall access box and hole.
  4. Be glad you did it right.
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  • Thank you for the insight. 1) Going to the next stud for me unfortunately is unthinkable because I would need to move the furnace to the left that has been there since 1972. On the right, I believe the next stud is after the corner - that is a task beyond my abilities. This is, unless I completely misunderstood what you mean there. 2) do you have an example of an access box? The 2x4's would protrude from the wall? All the pipes are fastener with proper straps very solidly and never touch the drywall.
    – Alessio Sangalli
    Mar 27, 2019 at 22:41
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    I hate to argue, but cutting out all that extra drywall is much more work than zipping a couple screws into some rough-cut scrap lumber. I can't figure out what your concerns are even for a carpentry novice. About the only thing you can do wrong is to run the screws in too far, but you can always add more screws.
    – isherwood
    Mar 28, 2019 at 1:22
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    I've made hundreds of such patches in my own homes over the years. I've never seen one crack. (You realize that more than half of all joints span voids, right?) Flush with what? Just screw it tight to the existing drywall. (I'll try not to take offense at your implication that this is a hack, short-term solution. The fact is that it's often done to achieve flatter butt joints using a recess technique. :) )
    – isherwood
    Mar 28, 2019 at 19:20
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    Not to be a jackass, but you might find this interesting.
    – isherwood
    Mar 28, 2019 at 19:31
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    @Dmoore: 1) It's in a furnace room. It probably doesn't need to be perfect. 2) If both sides of the drywall are supported, it's not going to crack, especially if adhesive is used too. 3) Some houses have studs 24 inches on centre, and the drywall is fine.
    – user5670895
    Mar 29, 2019 at 1:25
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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.

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  • Yeah I do not have much depth with the plumbing already taking most of the space, so thinner plywood is probably the way to go.
    – Alessio Sangalli
    Mar 28, 2019 at 1:20
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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 actually makes a stronger joint, 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.

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  • OK but won't I risk that the patch, along the sides will be weak? Also what is the recommended clearance between the patch and the existing wall; I guess too much is not good but also there should be a minimum width or the mud won't penetrate and remain too superficial?
    – Alessio Sangalli
    Mar 27, 2019 at 21:40
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    @AlessioSangalli This is a wall with plumbing penetrations, its not like its the middle of a wall in your formal dining room. You do run a risk of a linear crack appearing especially along the vertical edges. To help prevent this you need to use drywall tape along the edges, and for this application I would recommend drywall mesh vs regular drywall tape.
    – Glen Yates
    Mar 27, 2019 at 21:52
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    I can surely accept a lower level of quality in this utility closet (that is anyway next to my kitchen and living room). However I have no idea what I am doing that is why I will lookup what drywall mesh and tape are.
    – Alessio Sangalli
    Mar 27, 2019 at 22:31
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    Properly taped and mudded, there won't be an issue, because the tape & mud glue it all together, and it's ... non-structural anyway. Sure, you might find the edges of the patch while punching the wall, but in that case you are probably ripping it out to repair the plumbing, or just angry and punching holes in the wall, and in either case it does not matter at that point.
    – Ecnerwal
    Mar 28, 2019 at 1:35
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    @AlessioSangalli, You should use drywall tape or mesh regardless of whether you put backing behind the drywall (unless you don't mind a small linear crack). But I am rethinking my recommendation of mesh tape, as with sufficient flex, I have actually seen the mesh rip, so regular paper tape may be the way to go, especially if the joint is not backed.
    – Glen Yates
    Mar 28, 2019 at 16:36
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If you're joining drywall, I've found a good rule of thumb is if it's not within 3" or so of a stud, you need something to attach to the drywall behind the drywall. That's what Isherwood is referencing in his answer. The idea is that, if something hits a section of drywall, you want something to reinforce it, or you'll be back patching a jagged hole.

Scrap lumber is great... if you have scrap lumber laying around. If you're not doing stuff like this on a frequent basis, you might not have any. If you don't, a good and cheap solution is to buy a pack of wood shims (typically found in the door and window section of your hardware store). Be sure to cut the narrow end off the shims if you go that route. You will need drywall screws for this as well.

The catch with screws is to not "over-drill" them. You want them to sink just below the surface of the drywall, but not drive straight through the drywall itself. Worse for you is you'll be doing this on a live setup. Hopefully you have a driver that drives slower the less you squeeze. Just take it slow and you'll do fine.

As for location, I would do 2 in the top right (where the cuts jog further out), and one vertically to the left of the pipes along your cutout.

Additional tip: draw lines on the wall where your studs and supports are. It will help you a great deal in hitting the supports.

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  • Yeah as I suspected, this part took a lot of time and I still need some time. I did not have scrap wood (at least not the right size) so I bought some 6ft 3x1's for a price that is very similar to a 8ft 2x4 :( but it was too thick at just over 3/4" - that is too much considering the plumbing. So I had to waste a lot of time to rip those with my circular saw to just under 1/2". I just used a hand screw driver :) so I was able to get a lot of control. I do not need to install hundreds of screws, just a bunch so no big deal. I did pre-drill drywall and wood.
    – Alessio Sangalli
    Mar 29, 2019 at 5:28
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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

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.

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  • I thought I made a comment on this, but I do not see it. Great, I did not know such item existed. For now I made wood supports, very labor intensive (for my skill/experience level). But I will certainly consider those next time for a smaller patch
    – Alessio Sangalli
    Mar 29, 2019 at 5:31

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