plaster base repair


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Old 01-13-23, 03:08 PM
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plaster base repair

Hello. I'm remodeling my bathroom and have to replace some drywall that was cut out. It appears to be plaster base board with veneer plaster. I have no experience working with this stuff. Where a new and old piece of plaster base meet will i need to remove the finish on the old piece in order to tape and blend together? I figure i can sand it down but will that sanded surface need to be treated before applying plaster? It's not a lot that needs to be replaced. Maybe 30 sq ft total.
 
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Old 01-15-23, 08:45 PM
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A couple pictures of what you have including a picture of the cross section of the wall material in question would help.
This is what I think you have. “Blue Board” is veneer plaster base. It is much like conventional drywall only has a different kind of paper finish so that plaster bonds to it. it is blue to distinguish it from other gypsum boards.
Your coating could be a one coat system or a two coat system. In a two coat system the first coat is a (usually) sanded plaster with a (usually) smooth plaster finish.

Maybe what you have is gypsum lath with gypsum plaster, a superior plaster system. The gypsum lath is 3/8” thick and the plaster brown coat is about 3/8” - 1/2” and the finish is 1/16” - 1/8”.

To repair the first system I described I suggest you do it with the same system if you can get the blue board. If you can’t get the blue board conventional drywall will work. What I am about to tell you will probably not be easy. it might be so difficult that you cannot do it. Scrape the plaster only from your veneer plaster base board. Use a sharp paint scraper. Try to get Dow to the paper of the board. If you gouge the paper a little do not worry. What you want to do is scrape enough of the plaster, i think about 6” wide that you can tape the joint of the new and existing veneer plaster base board with joint tape. I have not used FibaFuse for this kind of application but hai think this is what I would try. Then plaster the new board including the joint over to the existing wall you want to match. If you have a two coat system youcan do it that way or you can use a one coat material and just put it on in two passes. KEEP THE OLD WORK CLEAN. You do not want to lap your plaster onto the existing finished wall. Just keep it clean as you plaster. if you lap some plaster onto the existing clean it with the edge of your trowel.
Now, having said all this I think a more amateur friendly way of doing this is to use conventional drywall finishing methods. Treat the joint as an ordinary drywall joint or better yet as a ******* joint where the tapered edge of new drywall meets the non tapered butt end or cut side of a piece of wall board because with the additional thickness of the veneer plaster you will have that kind of offset. There are many posts in this forum about patching drywall. REad those then tell us what you indeed have and ask questions where this is unclear.
If you have gypsum lath and plaster about 3/4” total thickness this advice does not apply. Check in on this forum for other posts about patching gypsum plaster and then let us know what questions you still have.
 
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Old 01-14-23, 05:43 AM
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I have never seen plaster baseboard or trim at the floor. Are you sure that is what you have?

I am confused. Are you asking about repairing the wall or the baseboard?

Use sheetrock on the wall as plaster board is no longer readily available. It helps to sand the existing surrounding plaster if using sheetrock mud but more required if using plaster.

On the baseboard is the "finish" you are asking about paint? If so then yes, you will need to sand it down so you can have plaster to plaster contact when you do the repair. I would not attempt using sheetrock mud on baseboard because it can't handle water contact which is common at floor level.
 
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Old 01-14-23, 07:09 AM
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Thanks for quick response Pilot Dane. Sorry, I'm using the wrong terms. All of this is on the wall. The sections I removed are blueboard drywall with plaster skimmed over (not regular drywall with joint compound at seams). It's similar to this - https://www.homedepot.com/p/Gold-Bon...0840/205912175.

What I'm struggling with is how I connect the existing wall with new blueboard drywall. Does this make more sense? It sounds like I will want to sand down the existing skim plaster finish, tape the seam and then apply plaster to blend together?
 
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Old 01-14-23, 10:09 AM
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"...how I connect the existing wall with new blueboard drywall."
Are you coming straight off the end of an existing wall or is your new wall perpendicular?

The edges of your drywall must end on a joist. If two pieces of drywall butt together you make the joint between them right down the center of the joist so each sheet has 3/4" of wood behind it for support and a place to screw. You can also attach another stud to the side of an existing stud to support the edge of the sheetrock.
 
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Old 01-14-23, 12:16 PM
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Yes straight off the end of the existing wall. Once attached to the stud I'll have one side that is finished with plaster and the other bare blue board. What is the best way to hide that seam?
 
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Old 01-14-23, 12:52 PM
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You might need to float the whole wall to hide the transition.
 
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Old 01-15-23, 06:57 AM
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Marksr, sorry dumb question. Is that applying a fresh layer of veneer plaster over the entire wall? It's a small wall so not much of stretch but would I need to prepare the existing/finished wall at all?
 
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Old 01-15-23, 07:20 AM
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While I do drywall work I'm not well versed it plaster, but generally you'd float it all however far it needs to go to look seamless. Hopefully one of our members tightcoat will see this thread - he's a plaster expert.
 
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Old 01-16-23, 12:29 PM
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Thanks tightcoat! Do these pics help determine which ttype of wall it is?





 
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Old 01-16-23, 02:12 PM
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No plaster and no full float so it's a basic sheetrock job.

Don't forget to insulate and install a vapor barrier before closing up the wall with sheetrock.
 
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Old 01-16-23, 02:19 PM
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So it's not blueboard/plaster? There is a very thin hard layer on top which I thoughlt was plaster.
 
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Old 01-17-23, 02:59 AM
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I'd either cut off evenly or completely remove that piece of drywall and hang new drywall. The odds are it's 1/2" drywall but you'd want to verify that. There shouldn't be any issues mudding/taping to the existing painted drywall.
 
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Old 01-17-23, 04:02 PM
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Give yourself nice straight, square joints to work to. I would cut off that stairstep to make one nice joint.
Maybe you have veneer plaster, maybe not. if it is very hard you might have veneer plaster or maybe it was skimmed. Paint does not harden joint compound but it makes it tougher, maybe you are confusing hardness for toughness. I would scrape some of the finish off down to the paper at the joint then tape it like conventional sheetrock. If the existing finish is super smooth we can tell you how to get a finish that smooth on the new work. The most important thing is to keep everything flat or keep the illusion of flatness.
 
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Old 01-18-23, 06:46 AM
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Thanks all. I suspect veneer plaster because it's a consistent hard/brittle surface. Also, I understand that type of wall is more common for professional installation around here. I'm considering taking down the rest of the drywall on that wall. it's only another 3 or 4 feet to the corner and it's an inside corner behind a toilet. Would the same process apply on that corner? Scrape the adjacent wall down to the paper and join with tape?
 
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Old 01-18-23, 09:41 AM
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For an inside corner you'll probably use tape. Usually repairs like that are done without scraping the other wall which would be it's own can of worms. I would just go over it if using sheetrock mud but you might want to rough sand it if doing plaster to give it more grip on the existing, painted surface.
 
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Old 01-18-23, 03:11 PM
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I looked mor closely at the pictures. You have a light sand finish texture. This can be done with drywall material but I think you have veneer plaster. If you take off the plaster to the angle can you get your screw gun behind/beside the toilet? This kind of texture can be replicated with drywall mud. I’ve done a lot of it. Tape the angle without scraping.
To get a similar texture use a formula like this. Use about 30 mesh sand or mason and screened through a window screen. You want what goes through the screen.

I use a mixture like this. One box of all purpose joint compound. Start with a gallon of sand. If you need more you can add more. Add a gallon of cheap flat latex paint. The reason for the paint is that the sand has diluted the glue in the joint compound and the paint adds some stickiness and coats the sand granules in the mix.
Spread this on pretty tightly. let it dry a little then float it with a soft green or red sponge float. Wet the float before you start and you might have to wet it occasionally. Get one of each floats. You will have to decide which one you like the best. Floating with a sponge float raises some of the sand which is the texture you have. There might be a pattern to the float marks or they may be circular random. I can’t tell for sure but you will know.

And this kind of finish in drywall mud is harder than ordinary smooth drywall.

Now maybe in your market you can get the same material as is on the wall. If so the procedure is about the same. Tape joints, spot nails, spread on a coat of the plaster finish the difference is you must get it floated before it sets. Get it spread on quickly then try to float it. You only get one chance with plaster Work fast. Spread it on and maybe have a helper float it right behind you. Try to mix enough to do the whole wall but also balance that with getting it all on before it sets.
 
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Old 01-19-23, 04:42 AM
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One box of all purpose joint compound
Box mud isn't available everywhere but it's the same mud as you get in a 5 gallon bucket. IF I remember correctly a box is slightly smaller than a bucket.
 
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Old 01-20-23, 06:04 AM
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Yes, a box is about 2/3 of a 5 gallon bucket. The weight is on the box. I suppose the weight is on a bucket, too to compare the Dollars and cents as well.
There is a knack to dumping the box into the bucket. Open the box, flip the box top out of the way, untwist the bag inside the box and pull the excess around the outside of the box then tip it over on top of the bucket and usuaally it dumps right into the bucket and comes out of the bag clean and completely.

Not part of this discussion, Just thought you might want to know. Where mud is in boxes people know this. Might need to get it in buckets once in a while to have a clean bucket to mix the box mud in, and a lid to put on the bucket to store it in.
 
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Old 01-29-23, 07:18 AM
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Thanks all for the replies. I've been distracted with other aspects of the remodel and starting to look at the walls again now. Veneer plaster and blue board is readily available at my local home improvement stores so i picked some up to to do some testing/practice. I'm starting to think this is something I should bring a professional in for.
 
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Old 01-29-23, 01:11 PM
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Veneer plaster is not as simple as drywall. For one thing it is not sandable. It is hard. Timing is critical. You have to have it finished when it sets, There is no bringing it back once it starts to set, If veneer plaster materials are available it indicates that it is used in your market. Here even the major suppliers carry only a limited inventory of all the different materials that are distributed. Big box stores not at all. No one uses it so no one stocks it. A cycle. When we want to use it we have to substitute or improvise. Since you can get the material you should be able to find someone who can do your work.
 
 

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