Skim coat a ceiling?

[phil]

sometimes I just type for too long
I checked out the details for the durabond - I got this:

"Sheetrock® Durabond® 45 Setting-Type Drywall Compound is a multi-use product. It is an excellent compound for embedding tape, bead, and trims on gypsum panels. It's special formulation provides a high strength bond with low shrinkage that finishes with a hard, plaster-like surface when dry and is virtually unaffected by humidity. It is also ideal for laminating gypsum panels to above-grade concrete surfaces. CGC Sheetrock® Brand Durabond® 45 Setting-Type Drywall Compound can also be used to fill, smooth and finish interior concrete ceilings and above-grade concrete."

this sounds a bit more appropriate than just using drywall mud if James wants to steer away from traditional drywall mud. I assume that when you mix it there is some cure time so maybe it is a bit of work mixing but would perhaps adhere better. I dont doubt that he could also use a finishing mud, it might be easier to work with in the final stages.

when I finished over plaster I put "kilz" primer. I think it says on the can it is ok for sealing in the calcimine paint. I used the normal drywall tape on top of the primered surface and wet the tape itself with 50 / 50 glue and water, then as I start bedding the tape that mix I use has some mud with glue and I bed it down tighter than normal ( more knife pressure) to avoid bulges in the tape. ( that you need to hide later) I wasn't sure if paint between helps the bond or hinders it if he uses plaster and not mud. If I did not use the glue I wouldn't squeeze the tape down as tight because I have seen where the tape can come loose if it doesn't have enough taping mud between the tape and the surface it is bonded to. In other words if it is used with only the taping mud and not glue as it normally is, then you need to use more taping mud or you will have adhesion issues.

I have a different problem , I hired drywallers that did not take enough time to put enough blocking where the sheets join , and as a result I have some drywall cracks where the sheets meet. It's a can of worms I keep looking at and wondering how to fix. all the areas where I applied the drywall are ok, but it is something to watch for. they were simply too lazy to put enough blocking where it was needed, slipping a 2x4 in there where sheets join would have taken an extra 5 minutes. My attic never had any plaster, it had beaverboard and 70's panelling. and it was all droopy. the only solution was to remove it. so in my attic using plaster wasn't considered since it never existed to begin with.

in my living room I had plaster on the ceillng and then old drywall on the walls from the floor to eye level. originally it had some sort of panelling or wainscott and i could tell it just had a scratch coat of plaster from eye level to the floor. when they took out the wainscott they replaced it with drywall so yea I just tore it all out since there wasn't that much plaster work left in there to save anyway.
One day I might want to replace the wainscot or panels but I can always just put that over the drywall. in my case I needed to finish it and I do have ideas about creating panels at a later date but I didn't want to delay completion of the room.


In James's case he is refinishing a room in a house with plaster walls and he might not want every wall dead flat. If he were to use drywall perhaps it would look too flat and thus out of place.

to fix it properly I might need to open patches and attach it better but I hate to stir it all up now. on one of the first places where the issue appeared I tried to fix it I put mesh tape but the crack transferred , I guess the sheets might shake when a door gets slammed from wind and that makes the crack come through , because the sheets move. I stopped using the mesh since it wasn't successful but I cant; exactly blame the mesh tape , because the root cause of that issue might really be more about how the drywall itself is attached.
My attic is all finished and I will just put up with the cracks for now but they bug me. eventually I may just have to clear the space to fix it and paint it again. the work is compounded because I also have rounded corners ( made of built up mud and tape) in the attic so they need to be feathered into any work I do and it is surprising how perfect it needs to be or it shows. After that happened I stopped hiring people and did it myself in a much slower but more careful way. It made me hate peeling tape and I started using the glue when I tape which commercial drywallers don't usually do. that's how I got onto using it on top of plaster to stop the cracks.

once a long time ago my dad hired drywallers, he was building a new house. the drywaller said he wanted to experiment by dipping the tape in glue and he did that house that way. that was back int he 70's.. I remembered the idea and tried it as my dad had used it several times with success. so when I use the tape I put it through a dish of 50/ 50 water and glue. its quite watery and then use two fingers to squeegee off the excess, then use it wet with the glue like that. of course as I go bedding it, that glue also mixes with the mud. I add more mud as I go so it doesn't get too much glue in it. the important thing to remember is that mud with glue cant' be sanded so when I use it I press it right down tight and wipe any dribbles up. then when I do my finishing coats I do not add the glue. the normal way is just to use the taping mud and that can be sanded so the drywallers put more on and that acts as a bridge with the subsequent layers. - to help build it up over the tape.

i did some taping this way where I used the glue , then I didn't put enough filler to hide the tape. I tried to hire a commercial painter and he was confused because he could still see the tape. he suggested I buy this bent trowel that was designed to build up the mud. I tried it and it did work but anyway the fix was simply that I needed more mud to properly hide the tape otherwise you could see sort of a shadow of it .
I needed to build more mud up to hide the tape even though the tape itself was quite well stuck.

Ive tried adding plaster of paris to mud in he way shown on the video I linked to in my previous post . I found it created a substance I could sand and work with and I could build it more than only mud itself so maybe what I was doing was sort of creating a substance similar to the durabond. at the time I was using a rounded form that I made up with a surface that matched the conrtour I wanted. I used it sort of like a sliding form or a trowel to apply the mix into the corners, and then after I go to the finishing stages, I put sandpaper on it and used it to sand with to keep the radius equal.

I had to recreate the rounded plaster near my bay window as I tore it all out and replaced the plaster there with insulation and soundproof drywall to deaden street noise. I didn't want to loose those rounded corners that were done originally with plaster. it did work but it was a lot of fooling around to get the rounded contours just right.

Maybe using the glue as a "sizing" would improve the bond between plaster coats. but I cant' say without trying that and others have done more of the traditional plaster work. Perhaps plaster bonds better to dry plaster without the use of sizing? I dont really know.

Anyway lets not change topic from the work James is doing. I just had to reflect upon my own experiences as a comparison. I didn't want to change the topic.

Phil

[mjt]

Durabond is drywall mud. It is just a "setting" type, not a premixed "drying" type. That is, it hardens via a chemical reaction (it "cures" much like plaster), rather than by water evaporation.

Keep in mind that "45" gives you 45 minutes of workability before it cures. You either need to mix small batches, be pretty fast at getting a smooth surface, or only use it for your base coats. "90" has a 90 minute work time...

[phil]

it sounds like the thing to use , like if the plaster has chunks missing that need to be filled or if you put up drywall and had some deep gaps between sheets to fill. Drywall compound in itself isn't very strong if you put it thick and it depends solely on evaporation so there is a lot of shrinkage. if you build it thick , like 1/16 or 1/8 over the surface you might see where you knock the wall with the vacuum cleaner or something, and a chunk falls out rather than only paint damage. If you paint between layers maybe that helps. plaster is a bit tougher this way. the paint acts as a protective shell so maybe after a few coats it is less likely to chip out.

for removing waves or dips and valleys over wide areas maybe it would be a bit more difficult to work with and of course how good you are at applying it would have a lot of effect on how long it takes to use up the mix. maybe he could use a straightedge to try to detect the areas that need a lot of filler and use that to build the basecoat to within about 1/16th or so, then switch to the regular types of mud for final work? how easy to sand it is a factor but really there shouldn't be a ton of sanding. It should be more about filling the hollows until it's flat, than a process of sanding the bumps off, because that's more work and more dust.

I know the pros who work with plaster or mud everyday can run circles around any homeowner because there is such a knack to it.. but I think anyone can there with perseverance. It just takes the inexperienced ones more coats and more time.

real drywallers or "tapers" also have some equipment to apply the tape and that can make things run faster with the right guy using them. most of that equipment is too expensive for the homeowner to make good use of and there is probably quite a learning curve to using them effectively which would make renting such equipment impractical unless you have a whole house to do.

maybe size of the job and factors like how some just hate doing drywall help to make a good decision. there are limits to where DYI does become less practical because the pro's can do it with much less effort and so much faster. Myself I just hate hiring out, so i dont unless I really need to. in my initial attempts at hiring I realized I wasn't stern enough. we got into an argument about how many walls they were supposed to do. now I'm a bit older I would be more likely to tell them that they have to complete the job as stated or take me to court and withhold the payment or part of it. Back then I was too nervous to be that stern, so I just paid them and sent them off and completed it when they were gone. I didn't feel the labor they did or what they asked for it was unreasonable but they tried to shorten the job by saying some walls were not in the contract and the contract wasn't well worded to specify exactly.

I later realized you could actually specify a certain flatness or there are standards they refer to.. usually stage 3 stage 4 and so on, probably there are ways to specify the flatness in contractual terms. what "finished" means is quite ambiguous. maybe there could be a tolerance like must be accurate to "within 1/8th over any 3 foot area". or similar. problem is even thousandths you can see and it is more about how the waves appear and how visually noticeable they are that is most important. If you can't specify it in a contract then you have trouble defending it in court. my take is it is the best to give out small jobs and pay in steps in order to make sure you are satisfied and avoid any bickering if at all possible. contractors that hire them again and again have more power than the average homeowner who is a considered a one shot customer.

live and learn..

[Vman]

My 2 cents on making drywall mud or plaster skim coats stick to painted surfaces or base coats: bonding agent. The easiest is the kind you paint on the surface, I use Plaster Weld. Its basically glue. The big boxes don't carry it, so you might have to check a building supply yard. If you have a small patch you can dilute wood glue 1:1 and paint it on your surface with a brush. Wait until its pretty much near dry, then apply your drywall mud or plaster. If you are making repairs to plaster/lath, paint it over the lath and along the plaster edges. I almost always use it for both skim coat and repairs down to the lath as extra stickiness insurance.

The other kind of bonding agent is an admix - it is mixed into the drywall mud or plaster itself. Guess what it is also a type of glue. You don't really need it for drywall mud but for skimcoats over painted surfaces, especially single coats, its a good idea. I just add some wood glue to my water before mixing up drywall mud. I don't use it in my lime plaster (but some manufacturers of lime plasters offer plasters with bonding agent mixed in, e.g. Takcoat by Limeworks in PA).

I've used both hot muds and premixed all purpose muds for skim coating. If I'm doing just a single skim (1/8" or so), I prefer to use USG EZ Sand (hot mud). Don't use Durabond, it gets rock hard and is not as forgiving in the sanding stage. If I am doing 2 or 3 coat repairs (down to the lath or where the basecoat is compromised), I prefer to use EZ Sand for the 1st, thicker coat and All Purpose (premix-air dry) for the 2nd coat. No particular reason why, except maybe to make my life harder.

I use drywall mud for my ceiling/wall repairs. In my basement where its fieldstone and brick, I only use lime mortars and plasters. But that's a different thread.

[Gothichome]

Vman, welcome to the district. I see you have been back reading. Judging from your post you must be an old home owner having a rubble stone foundation and some experience with the inner workings of proper plastering.
You must tell us more of your old home, what you started out with and you’re efforts in restoring your old home.
Ron