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Second drywall layer on a ceiling

Jasper57 | Posted in Construction Techniques on November 26, 2009 12:43pm

An earlier post moved me to ask about this…

Our living room ceiling is in rough shape. it was roughly texture-coated with a JC/paint mix (along with all the walls) by the previous owner and has suffered some damage and patching over the years. I am not handy enough with joint compound to skim coat the whole 11’x22′ area.

So, I am thinking to lay up another layer of drywall against the existing layer. To minimize seams, I’d like to use 4’x12′ sheets trimmed to 11′, but the box stores only sell this in 1/2″ thickness (not sure if it even comes thinner than that?). Placing a square against the intersection of the ceiling and wall reveals that there’s about an inch of sag close along that intersection (it’s an old house). I am guessing the new 1/2″layer probably won’t bend to fit that sag. I don’t mind covering the intersection with crown moulding, but I’m wondering how to fill that gap between the old layer and the new? Joint compound? beveled wood strips? Should I glue and screw or just screw it?

I’d like to get to get some input and hints from folks who have done such jobs before I get halfway into this and get stumped somehow. (I’d say I don’t want to screw up, but, really,  that’s exactly what I have to do.)

Thanks very much for any suggestions and Happy Thanksgiving!

Jasper57

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Replies

  1. Hudson Valley Carpenter | Nov 26, 2009 12:58am | #1

    Placing a square against the intersection of the ceiling and wall reveals that there's about an inch of sag close along that intersection (it's an old house).

    An inch of sag over how far?  Between the flat area and the intersecting wall, how far? Six inches?  A foot?  Two feet?

    I'm asking because 1/2" drywall can be made to conform to a mild deformity, by spraying the specific area of the new board with plenty of water, then applying mild pressure over several hours. 

    In this case that could be accomplished by placing the board on a lift, spraying the end of the board, then cranking it up into place, adding another click on the crank every half hour or so until it's home.

    BTW, 3/8" and even 1/4" boards are available from drywall suppliers, though you may have to call several to find that thickness in 12' lengths.  Or place an order and wait for a while.  And you  may have to pay a premium price for such a small order.




    Edited 11/25/2009 5:04 pm by Hudson Valley Carpenter

    1. Jasper57 | Nov 26, 2009 01:30am | #3

      Thanks for the prompt reply, HVC. The 1" sag is over a distance of about 12" to 14". At 6" out the sag is about 1/2"-5/8". I say "about" because it varies and the texture makes a difference also. I was planning to rent a lift and I just naturally work slow. Should I put a bead of construction adhesive on the sheet to bed the texture or is that unnecessary? The texture is about 1/16"to 3/32" at most.

      Jasper

      1. PatchogPhil | Nov 26, 2009 02:00am | #4

        I am curious why you want to have a "new" un-level ceiling?Why not a new but also level ceiling? 

        Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?

        1. Jasper57 | Nov 26, 2009 02:36am | #7

          Well, it depends on what you're looking to get me into. :)

          If you're suggesting that I rip out the old ceiling and sister new joists onto the old sagging ones, I'd have to deal with 3" of rockwool and 6-8" of cellulose in my lap as well as all the demo in the main room in which we live. If you're suggesting that I put the second layer up against shims or tapers or firring strips, somehow "building down" to a level nailing surface, I have to say the sag is not so obvious as to make me believe it's worth the extra effort. Also, I can't spare a lot of headroom so I'd like to keep it down to losing 3/8" or 1/2".

          If there's another way you're suggesting, hit me. Level is good, though in this old crackerbox, it might look out of place.

          Thanks,

           

          Jasper

          Edited 11/25/2009 6:39 pm ET by Jasper57

          1. Jasper57 | Nov 26, 2009 03:04am | #10

            "With that much sag in so short a length, I'd guess that your plaster is letting go. Trying to drywall over it will be an adventure. Much easier & better in the long run to simply strip the old plaster, leave the lath, (or strip the lath and level the ceiling) and drywall over that."

            Hi Mike,

            I don't have plaster and lath in this 1950 house, (thank God for small favors). There is one place where the ceiling got wet from a busted shingle (fixed now) and 3 or 4 of the nails pulled through, but I think that will draw up if I jack it gently back against the joist. Otherwise, it's tight to the joist, just ugly

            Thanks,

            Jasper

             

          2. Jasper57 | Nov 26, 2009 03:23am | #11

            "do this.

            Run strapping perpendicular to the trusses at 16" OC with the fiorst one 8" out from the wall/ceiling joint. Use structural screws to fasten these thru the SR to the bottom chord of the trusses."

            Then do your new SR to that."

            By "strapping", you mean what? 1x3 firring strips? Something thinner with shims, or something specially cut to an average thickness at each cross point that brings it to "level"? Won't there be gaps along the trusses where the screws could blow through the new SR? Or am I building a grid?

            I'm not trying to be argumentative with anybody. I'd like to do this as right as I can without tearing down the ceiling.

            Jasper

          3. Piffin | Nov 26, 2009 03:55pm | #21

            Yes furring strips are used for strapping. This is common in NE, but not everywhere, but there are a lot of advantages to using them.Let me explain my thinking further-
            I assume you have a low joint at the ceiling/wall joint because you have trusses. It was common to have that joint break when ceiling is screwed/nailed tight to the truss and climatic change causes bottom chord middle to uplift. So ceiling rock is not fastened tight within 8" of the walls.The rock can span 8" free and clear to the joint just fine, so adding 2/4" at 8" away from the wall provides adequate fastening for supporting the rock which will span the taper to the "sag"The other reason it might be showing a sag is a poor job of taping by a DIY or semi-pro building up too much mud there. Be carefull not to do the same"Won't there be gaps along the trusses where the screws could blow through the new SR? Or am I building a grid?"I am not sure what you mean by this Q. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          4. MikeHennessy | Nov 26, 2009 04:23am | #14

            You have rock lath & plaster, or drywall? Sagging that much? Pretty unusual in my experience unless it's coming loose (i.e., nails pulling out or through). It's hard to believe the framing is that out of whack, so something is probably going on with the sheet goods. As another poster mentioned, 1X strapping may be your best bet to tighten up the old and give a new base for the new.Mike HennessyPittsburgh, PAEverything fits, until you put glue on it.

          5. Jasper57 | Nov 26, 2009 04:48am | #15

            From what I can see in the attic, what I have is 1/2"drywall nailed directly to the ceiling joists. There is no strapping between the SR and the joists, though there might be some blocking set in between the joists where the existing 4'x8' sheets meet. This probably explains a lot of the sagging. Like I said, crackerbox.

            Jasper

          6. Piffin | Nov 26, 2009 03:59pm | #22

            I am picturing the sag at the perimeter joint and I think you picture it out in the center of the ceiling. now you have me wondering where I got that impression and which of us is right. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          7. MikeHennessy | Nov 26, 2009 04:17pm | #24

            Now I'm confused too. Thanks! ;-)

            Well, either way, Jasper should probably plan on peeling the ceiling and doing it right. Or, at the least, strapping perpendicular to the joists on the room side of the existing DW to pull things back in to the joists, and rock over it.Mike HennessyPittsburgh, PAEverything fits, until you put glue on it.

          8. User avater
            Dam_inspector | Nov 26, 2009 04:49pm | #25

            That sag could be a split joist. I'd want to at least know what's going on.

          9. DonCanDo | Nov 26, 2009 04:50pm | #26

            Make that at least 3 of us.  He called it a "sag" so I assumed the low area was 12" out from the wall.  It's just not possible for the the ceiling to sag next to the wall.  That could only be too much plaster/compound or a real framing issue.

            I guess we'll just have to wait until the OP checks back in.

             

            Jasper,

            if the deflection is 1-3/4" in the middle of the room, that's a lot different than a 1" sag over 12".  Which is it?

            When you say "I am leaning toward snapping a grid of 8" squares hanging firring strips every 16" perpendicular to the joists (ripped to decreasing thicknesses).", I'm not sure what you mean by a "grid", but it sounds like overkill to rip each piece of strapping individually.  If the ceiling has sagged over the years from its own weight, it's likely to continue.  Especially with the added weight of a new layer of drywall.  There's no need to target perfection.

          10. Piffin | Nov 26, 2009 05:16pm | #27

            "It's just not possible for the the ceiling to sag next to the wall. "True, but this can be DIY interpretation of things 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          11. JohnCujie | Nov 26, 2009 06:40pm | #28

            Sounds like the whole ceiling is sagging, CJ's spanned too far perhaps.I would do as the previous poster said, remove insulation and fix framing. Can you get a pair of LVL's in as a strongback, maybe punch a hole in the side of the house to do so? I'm assuming CJ's run the 11' way and strongback the 22' direction and that it would have bearing on each end.Jack up the ceiling and tie to strongback. Adding more stuff below seems like it would compound the problem.John

          12. Jasper57 | Nov 26, 2009 06:43pm | #29

            Quite a bonfire for what I thought was a matter of a few handy drywall hints. I'm sorry if  my descriptions confused matters. At this point I don't know quite what to say. It's Winter. We live here. There is no place to put our furniture or our lives (or our Christmas tree) for the duration of what sounds to me to be a major demo/renovation project. These may all sound like lame excuses to you guys, but there it is.

            I don't doubt that ripping out the ceiling and rebuilding the whole thing is, unquestionably, the best way to make a nice level ceiling, but is it the ONLY way?

            Mike H. says strap it and wrap it in SR and, as I said, I'm leaning that way. I will check all the joists and measure the deflection at each one, but the sag looks pretty consistent along the length of the room. I don't think that anything is split or racked. It's just a postwar house that was built cheap, probably with green lumber.

            I have attached a picture of the ceiling. It won't tell you much, though you can see one place where it has been patched. It appears to be discolored, but that's just the way the light hits it. There's another place where the PO patched a separated seam with drywall tape, then he built a sort of inverted mountain range of textured joint compound along the seam. Stains and patches like these are what I wanted to cover.

            Again, thank you all for your advice. I'll chew on all this while I'm chewing on some turkey and pie today and I hope you do the same. Have a great Thanksgiving!

            Jasper

             

             

          13. User avater
            Dam_inspector | Nov 26, 2009 06:51pm | #30

            That saggy area just looks like a bad repair job. I would be inclined to cut it out and properly patch it, then skim the whole ceiling. I re-sized your pic for those with slow speed internet connections.

          14. DonCanDo | Nov 26, 2009 07:01pm | #31

            Now that I see a picture, I'm going to suggest a different approach because the texture doesn't appear all that heavy.  As long as there aren't any significant cracks (I don't see any) and the section where the nails/screws pulled through can be re-secured, I would be very tempted to just skim-coat the entire ceiling.

            It does takes a bit of practice and the most important piece of advice I can give you is to always apply too little at one time rather than risk applying too much.

            First, I would sand down any of the really high spots and then apply multiple thin coats until smooth alternating direction by 90° for each subsequent coat.  Knock off any high spots or ridges with your 12" taping knife (it's what I use for skim coating, others like wider or skinnier... it's a personal preference) and save all of your (hopefully minimal) sanding until after the last coat.

            Happy Thanksgiving to you too.

          15. Jasper57 | Nov 26, 2009 07:23pm | #32

            The truth is, I started out to skim coat the ceiling, but there were some loose pieces of texture coating where the previously mentioned leak had occured. When I peeled that away, it revealed some damaged SR (about a 4'x4" area) where the paper coating was ruined and a few nails had pulled through, so I started leaning toward sheetrocking the whole ceiling. I have never been much good at taping and mud, though lately I've done a few decent seams.

            I had also considered taping off, with plastic, the walls and floor and spraying the ceiling with a texture gun until it all had a consistent texture and the patches were well covered, but I had no certainty that that would really work.

            I guess I could cut out the worst areas and go for it with a skim coat. At least it doesn't add much weight.

            Let's eat,

            Jasper

             

             

          16. Piffin | Nov 26, 2009 08:00pm | #33

            There is no bonfire happening here, just a good discussion."best way to make a nice level ceiling, but is it the ONLY way?"That depends on WHY the ceiling is sagging. I still don't have a definite whether it SAGs in the middle or if it is low at the perimeter.if the joists sagging from being over spanned, then you will waste your time applying another layer of SR to this because it will add weight and make the sag worse.If it is sagging because the SR got wet and is coming loose, then maybe furring can pull it back up.If the sag is what I first thought then....But so far there are a lot of un-knowns in what first appeared to be a simple thing. So you have to find out what the real problem is and what is only a symptom of the problem, then you can find out the option(s) for fixing it.
             

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          17. Jasper57 | Nov 26, 2009 08:36pm | #34

            I din't mean anything harsh about the "bonfire". I really appreciate all the thought you guys are giving this.

            Tomorrow, I'll climb up in the attic, take some pics and measurements and give you all the full tour.

            Thanks again,

            Jasper

          18. Hudson Valley Carpenter | Nov 26, 2009 11:06pm | #35

            One other possible way to deal with a bad ceiling, hang fabric from wall to wall with a short drape around the perimeter. 

            I've done that several times as a temporary fix, fastening it in the center of the ceiling and at the ceiling-wall intersection. 

            In every case the people really liked the appearance and the feel of the room, so much that it stayed that way.  

          19. Jasper57 | Nov 27, 2009 05:53pm | #36

            As promised, here are some photos of all the bloody business in this ceiling job.

            Photo #1 shows how the ceiling and roof is built. I measured the ceiling chords. They are 5-1/2" by 1-3/4". The span is 11'6".  I doubt, as you all have said, that they will bear the weight of a second layer of SR, though I wonder whether adding a strap from the roof chord to the ceiling chord might strengthen it sufficiently?

            Photo #2 shows the area where the shingle leak did some damage and it shows that there's no strapping across the joists. It also shows how much rockwool and cellulose is up there.

            Photo #3 show the area that I tried to scrape, planning to then skim coat it. I hesitated to show this pic earlier lest you all get the idea that the whole ceiling is like this. Also, this needs a lot of explanation. The mottled areas appear to be wallpaper paste. The texture came off easily in some areas, but in the part that got wet, the SR paper layer shreaded and came away, exposing the gypsum. There was just a hand-sized area of mildew between the SR and the texture coat. You can also see where the PO added to the topography with a layer of mud, tape and crappy texture. This all looked so depressing that it made me think that a second layer of SR was the best course of action. I'm glad I asked about this before doing it. (Really, I am.)

            Thank again,

            Jasper

             

          20. User avater
            Dam_inspector | Nov 27, 2009 06:21pm | #37

            I still think it's a patch and skim job. The damaged area looks like about a half sheet of drywall. If you skim it, scrape it down, then just apply enough compound to start filling in low spots. After it is all dry, scrape down any ridges and bumps and coat it again. It may be good at this point, or may need another coat. Then screen (sand) it and apply PVA primer.

          21. DonCanDo | Nov 27, 2009 07:00pm | #39

            I'm with you, but I don't know if that half-sheet drywall area needs new drywall or not.  A picture can't answer that question.  I can usually tell by rapping it with my knuckels, but a more sure-fire wayu is to try and push something through it like a screwdriver.  It will be very hard to do with sound, undamaged (or even slightly damaged) drywall and conversely, fairly easy with drywall that had been soaked.

            I remember pointing out a water stain to a customer with my tape measure.  As I touched the ceiling with the end of my tape, it went right through.  I told them "well, I guess we need a little more than just stain killer".

          22. PatchogPhil | Nov 27, 2009 06:54pm | #38

            You do not see any gaps between the ceiling joist(s) and the drywall while you are looking from the attic side? i.e. drywall is NOT sagging away from framing?You could prove that the low spot is just a big blob of "patch" slopped onto the ceiling. Drill a small hole in the ceiling between joists. Poke a screw driver or piece of wire coat hanger thru it. Measure how much goes in the hole before it pokes the surface on other side.If it is a big patch, I would cut out just the offending area down to the framing, and put in a new piece of drywall. Have the butt joints fall between joists. Use shims to create a beveled butt joint. Tape and mud it. Sand smooth. PVA prime it and the whole ceiling. Repaint ceiling.
             

            Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?

          23. User avater
            Dinosaur | Nov 27, 2009 10:39pm | #40

            What a lovely little house you've got there! Y'oughta be ashamed of yerself calling it names!

            View Image

            Seriously, there's a lot of these '50s 'crackerboxes' around and while they may not make the pages of Architctural Digest, they have already survived longer than most of today's McMansions will ever do. You could do far worse. Smile!

             

            Okay, down to cases. Let's get a few terms straight first.

            You have a stick-framed roof, not trusses. The 'upper chords' are rafters, the 'lower chords' are ceiling joists.

            Based on the tables in current building codes, 2x6 ceiling joists (for attics not accessible by a stairway, which means no regular traffic up there) are sufficient to span up to 14.5 feet. So at 11 feet, you should be good, even with a second layer of gyprock. But wait one on that. See below....

            It is possible one or more of the ceiling joists have been damaged over the years--either water damage or some former owner storing a whole lot of books up in the attic in one spot--but this you can determine by digging away the loose-fill insulation with a smallish snow-shovel or that hoe you were using and eyeballing the sagging areas. If you find a damaged ceiling joist, you need to sister it. This is not that big a deal, actually, unless the damaged part is at the end where it sits on the bearing wall. And even then, it's a doable project.

            However, it seems more likely the gyprock has simply pulled off the joists and sagged where it got wet. You'll see this from above when you rake that insulation out of the way. The backing paper may still be right on the joist, but poke a bit into any discoloured areas with a knife or screwdriver and see if the rest of the gypsum board has delaminated and sagged.

            If that is indeed the case, the easiest fix would be to bust out the sagging area and replace it with a patch. Rent a panel lift or some extendable props or build a T-prop yourself out of 2x4. Screw up the new gyprock leaving a quarter-inch clearance around the patch, and tape it with self-adhesive fibreglass mesh tape. Get yourself some setting type compound (Durock 90, for instance) for the first coat, and some general purpose premixed joint compound for the subsequent coats.

            Your first coat should be applied with a 6" taping trowel, and should fill the gaps around the patch. Don't try to fair in the patch with the setting compound 'cause if you screw up and put too much on it's harder to sand than the drying-type premixed GP compound.

            The setting compound will dry in about an hour and a half, so you can do another coat the same day. Your second coat is applied with a 12" gyprock knife, using general purpose mud. Fair out the joint twelve inches each side of the seam. Don't put too much mud on, just enough to cover the mesh tape well and fair it out on each side to a feather edge.

            Third coat is applied the next day. First use your 6" trowel to knock down any dried ridges you left. Now use a 14" or 16" knife and the general purpose mud to fair the joint out to 28" or 32" wide. Your goal is to make the joint wide enough that the hump in the center of it, where the actual seam is, isn't noticeable. It is a rare butt joint that can be made to dissappear in less than 24" wide.

            You sand the third coat with a pole sander and 80-grit gyprock sanding screen. Don't use regular sandpaper. You can buy or rent pole-sander heads equipped with a vaccuum port so as to suck the dust into your shop vac as you sand; it makes less of a mess but does not capture all so don't expect miracles.

            You will probably have to do a very thin, almost transparent fourth coat over some areas once you've sanded, but it will be mostly spot patching. Examine the job with your eyes shut, running the palm of your hand over the repair. If you can feel it, you'll see it once it's painted even tho you can't see it now.

            Yes, I know it will make a mess, but believe me, it will be no worse than the mess involved in scabbing a whole new gyprock ceiling over what you've got. Remember, you will still have to tape the seams in that, and you'll have more seams to tape, too.

            Buy a roll of rosin paper and tape it down to the floor, covering everything right to the baseboards. Use old draperies or painter's drop cloths to cover furniture and books. Close all doorways to other parts of the house with heavy drapes or tape plastic sheeting over them. This will limit floating dust moving into the rest of the house.

            Gyprock work is by nature dusty. There is no way to avoid it, so just grin and get it over with. If things go well, you can be done in three days.

            Think how nice it will all look when you're done.

            Dinosaur

            How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

          24. Jasper57 | Nov 28, 2009 01:27am | #41

            Thanks for all the detail and reassurance in your reply, Dino. I'll check the attic again to see if the sagging is all drywall or if it's the joists. I thought I would see nail holes if the drywall had separated, but I guess all that could be concealed by the texture coat. If the drywall has pulled away from the whole ceiling, I assume that I just jack it back up against each joist and run screws into it, then skim coat over the screws? No other measures needed besides that?

            Thanks for your kind words about the house. We raised two good kids in it and that is what really matters.

            Jasper

             

            Edited 11/27/2009 5:28 pm ET by Jasper57

          25. User avater
            Dinosaur | Nov 28, 2009 02:10am | #42

            If the drywall has pulled away from the whole ceiling, I assume that I just jack it back up against each joist and run screws into it, then skim coat over the screws?

            Bad idea. You might get away with it, if the sag was minor and the damage to the gypsum board extremely localised--like, limited to a 1" diameter circle around each nail that had pulled through--but much more likely you would not, and it would simply fall again. Gypsum board depends almost entirely for its strength on the face and backing paper; once those are torn, the compressed gypsum around the damaged paper cracks easily and progressively.

            Ripping down gyprock is not as messy as you think; it makes less dust than sanding joint compound which you're gonna have to anyway. When you do gyprock demolition, you can yank big hunks right off and carry them directly outside. When it's all down, just claw-hammer out the remaining screws/nails and the little nubbins of 'rock surrounding them.

            To get a clean edge at the limits of where you want to demo, cut the face paper with a knife before you remove the damaged area.

            Dinosaur

            How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

          26. PatchogPhil | Nov 26, 2009 04:51am | #16

            Do you have unusually low ceilings that you cannot level it out by lowering new drywall 1 or 1 1/2 inches? Or are you 7' 2" tall? :-)If the existing framing is so warped as you've reported, then yes something is majorly wrong as another posted has suggested. You should get an exact evaluation to make sure there is no structural problems that will get worse.If it is saggy existing drywall, but the framing is OKAY then adding more drywall or more mud will make it fall even more.Pictures would help. 

            Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?

          27. Jasper57 | Nov 26, 2009 05:45am | #17

            The height at the wall is 7'9". I struck a level across the room ceiling with an 8'6" metal straight edge. The deflection at the center of the room is an interesting 1-3/4"! I'm sure it varies elsewhere in the room.

            So, if I add a 3/4" firring strip and 1/2" SR, I'm at 7'7-1/4" in the middle of the room. Kinda low, if you ask me.

            I am leaning toward snapping a grid of 8" squares hanging firring strips every 16" perpendicular to the joists (ripped to decreasing thicknesses). I'll rig a 10' level on a tripod and shim between the strip and the old celing to bring the "strapping" down to the level. At the center of the room, I'll screw right into the joists, elsewhere, I'll run the screws through the strips or through shims against the joists in between the strapping. That should minimize the height loss and give me something solid to screw into throughout the room. Sound fair?

            There goes December.

            Thanks to everyone for getting me this far with the project.

            Jasper

             

            Edited 11/25/2009 9:46 pm ET by Jasper57

            Edited 11/25/2009 10:14 pm ET by Jasper57

          28. User avater
            Jeff_Clarke | Nov 26, 2009 09:09am | #18

            1950s isn't an old house.   Not after you've worked with 1750s.   Take time to find out why that sag is there - it should not be ignored.

            Jeff

          29. Piffin | Nov 26, 2009 04:02pm | #23

            That description makes it sound like you need to tear it down and fix framing 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

      2. DonCanDo | Nov 26, 2009 02:09am | #5

        I agree with everything raymond wrote.  And if you use 3/8 drywall you should use drywall adhesive (or construction adhesive) to prevent sagging between the (presumably 16" oc) joists.  If you use 1/2", it's still a good idea, but not as necessary.

        Butt joints are hard to conceal, but IMHO, easier than dealing with a piece of drywall that spans the room.

        1" sag over 12" is huge.  You're going to have a hard time bending drywall to conform and even if you could (moistening it and using 3/8 makes it a lot easier), it's still going to look awful.  I wouldn't try to bend the drywall.  I would shim it to within about + or - 1/4".   Shim on the joists and drive a screw through the shim.

        Before you do this, double-check that the ceiling is relatively flat everywhere else.  If it isn't, plan on strapping the entire ceiling to get it level.

      3. MikeHennessy | Nov 26, 2009 02:17am | #6

        With that much sag in so short a length, I'd guess that your plaster is letting go. Trying to drywall over it will be an adventure. Much easier & better in the long run to simply strip the old plaster, leave the lath, (or strip the lath and level the ceiling) and drywall over that.

        It'll be messy, but it'll be right.

        Mike HennessyPittsburgh, PAEverything fits, until you put glue on it.

        Edited 11/25/2009 6:18 pm ET by MikeHennessy

      4. Hudson Valley Carpenter | Nov 26, 2009 03:37am | #12

        The 1" sag is over a distance of about 12" to 14". At 6" out the sag is about 1/2"-5/8". 

        OK, my suggestion should work fine if you choose to try it.  Just be sure that the area of the new drywall that needs to be re-formed is wet on both sides and all the way through. It may take several applications of water. 

        Not to worry,, the worst that can happen still only costs you some learning time and a foot or two off one end of one board.

         I was planning to rent a lift and I just naturally work slow. Should I put a bead of construction adhesive on the sheet to bed the texture or is that unnecessary?

        As long as you can hit the ceiling joists with screws adhesive is unnessary, also a minor PIA.

        You've had some other good suggested methods proposed here so take some time to consider which one will work best for you and give you the most desireable result.

      5. AitchKay | Nov 26, 2009 03:39am | #13

        You want your ceiling as visibly-flat as possible, but that's pretty easy to achieve. You could string lines, and get everything perfect, but you don't need to.Buy the straightest 10' 1x4 you can find, hold it up to the ceiling on edge to see how wavy the ceiling is, and where you're going to want to add some shims. Focus on keeping the edges as straight as possible -- waves out in the middle are harder to see.I disagree with the idea of using smaller sheets, and piecing it together. The rental of the lift (probably around $30-$35 for the day) will more than pay for the aggravation of taping butt joints -- go full length.Don't cut the board too tight! At least 1/4"-38" shy in length, then split the difference when you hang it, with half of the gap at each end. Try to figure out if and how the room is out-of-square, and cut accordingly. A good trick here would be to buy a sheet of 1/4" lauan ply --it's cheap -- and have it cut in half. Use one of those lightweight 4'x4' pieces as a test square. You can always cut it all up into leveling shims.Aitchkay

  2. raymond128 | Nov 26, 2009 01:04am | #2

    Jasper
    I would not worry so much about getting 12ft sheets
    They are tough to handle and can break pretty easy. Unless you have experience with hanging board I don't suggest it.

    Here are a couple of things to keep in mind.
    A: get 3/8" sheetrock (it's light and won't tax the ceiling too much with the extra weight)

    B: locate where the strapping is in the ceiling. Even if it means poking a few holes in the ceiling to find them. You have to be sure when you sink the screws in that you are catching something that is attached to the framing so the darn thing will stay up there.

    C: use long enough screws to penetrate the strapping for good holding power.

    D: rent a drywall lift from your local Home depot or rental store.
    It really will make your life a lot easier.

    another hint is if you feel up to the task. get the joint compound that is powdered, it dries better and quicker that the premixed stuff.

    Hope this helps and good luck.

    1. Piffin | Nov 26, 2009 03:40pm | #20

      3/8" would sag unless strapping is at 12" OCand you assume he has strapping 

       

      Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

  3. Piffin | Nov 26, 2009 02:47am | #8

    do this.

    Run strapping perpendicular to the trusses at 16" OC with the fiorst one 8" out from the wall/ceiling joint. Use structural screws to fasten these thru the SR to the bottom chord of the trusses.

    Then do your new SR to that.

     

     

    Welcome to the
    Taunton University of
    Knowledge FHB Campus at Breaktime.
     where ...
    Excellence is its own reward!

  4. User avater
    coonass | Nov 26, 2009 02:53am | #9

    Jasper,

    I would skim coat this by mixing mud just thin enough to roll on and then pull it off with a 12' trowel. Leave the little ridges on the edges.

    When dry roll on another coat and skim off with a 24" trowel. Two might work but you may need to do another coat. Sand lightly.

    Much cheaper much quicker.

    Use the search function here for "d mix".

    KK

  5. fm | Nov 26, 2009 10:16am | #19

    I'm gonna make a suggestion which you can quickly scoff at and then ignore, but eventually end up revisiting.

    If you have access to the attic above this 11' X 22' room, why not take a scoop up there and move the insulation over to another area of the attic.  Buy a good respirator. 

    Move all the stuff out of the room (it'll need to be out if you skin over with drywall) then demo the old stuff, add new lighting if you need it, ducting, insulation, whatever.  You can inspect the framing, correcting it as needed.

    Now you are starting from a good foundation.  You will spend about the same money on materials, and end up with a FAR superior job than scabbing on new drywall over a wavy surface. 

    Now, back to your regularly scheduled programming...............

     

    Frank

     

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