There are actually three layers of plaster applied to lath to make the complete job. The first two are a mortar like stuff that sometimes contained animal hair and is the origin of the term horse hair plaster. The first coat is called the scratch coat and was applied with firm pressure to force the mortar through the gaps in the lath and create the fingers that help to hold it in place.
The second coat was know as the intermediate coat and was the same mixture as the scratch coat. This intermediate coat built up and leveled the surface. Collectively these first two coats are grouped as one and called the brown coat by most people. They are grouped because there is no way you will separate those two layers once that have cured. We are going to call the brown coats substrate in these articles. If the substrate has failed you will need to go all the way to the lath to affect the repair. We will deal with that topic in another article.
One of the plaster failures that sometimes occurs is where the hard coat, also know as the top coat, the white layer pops loose from the otherwise sound layer of the substrate, the mortar like coat. This is most common on exterior walls, bathrooms and kitchens though I have seen it in other places where one would not suspect moisture being present.
In a typical installation the hard coat or top coat is normally no more than 1/8″ thick and sometimes it is less. Repairing even a large section of it is no big deal if the substrate is firmly attached and sound. The size of the problem area will determine the methods required.
Products made for finishing drywall are all I ever use and they work great! Using real plaster is an art form I have never come close to mastering.
This is one of two situations where I prefer to use Durabond. The manufacturer states and based on my personal experience I agree that the Durabond product has a superior grab and hold when compared to other drywall compounds when it is applied over the plaster substrate. Since Durabond is not a sanding type product one needs absolutely sure to keep all filled areas well below the final wall finish level.
Multiple coats may be applied after each prior coat is set. Before the final coat or coats of a sanding type setting compound or even regular old premix is applied the Durabond need to be completely dry. Dry usually takes 24 hours from the last application and should not be confused with set which can occur in a little as 5 minutes.
The exact method you will pursue will be based on the overall size of your faulted area. Before we begin I strongly suggest that you pick at the edges of your fault to make sure the entire loose top coat has been removed. Once you are satisfied that nothing else is about to pop off in the near future you have to plan an attack for repairing the damaged area.
Most of these top coat pops that I have encountered that I considered worth repairing by skim coating were less than 8 square feet so I will explain the methodology for doing a 2×4 foot area and one two to three times that size. For either one the first step is exactly the same. Cover the entire substrate with the smoothest, thinnest coat of Durabond that you can apply. The substrate is always a semi-soft friable material and every time you pull a drywall knife full of compound across it you will dislodge some small crumbs or sand mix; those crumbs or sand will foul your compound and make the ultimate finish more difficult. The sooner you seal that surface and prevent that from happening the smoother the rest of the repair will go.
In either of the two following scenarios your ultimate goal is to never put any non sanding mix on the wall above the finished grade.
For a small 8 square foot or less area I suggest you skim the perimeter on two different sessions doing opposing sides first. Do the left and right and then the top and bottom after the first is set. Keep moving towards the center in both directions. Once you are close to finished grade, change over to a sanding type product and repeat the process. Some sanding is inevitable with this process. Your final goal is a wall that looks and feels smooth. Keep in mind that I said looks and feels. That is not the same thing as is.
For a much larger area I would apply a few thin stripes along the shorter dimension where it is easier to keep a thin even coat and fill the voids, always feathering to create the flattest possible surface. This is the exact same method used to skim coat an entire wall. Change over to a sanding product when you get to the point where you might need to sand to achieve the perfect smooth wall. As we said before in another article, it always easier to do another thin coat than it is to sand off a hastily applied glob.
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Plaster can add an interesting, textured look to any wall. However, in a damp environment like a bathroom, it’s not uncommon for plaster to begin to peel over time. The process for repairing peeling sections of plaster in a bathroom is the same as it is for any room in your home — but you must prepare the wall a little differently to ensure that you aren’t trapping mold beneath the new plaster.
The high humidity and wet conditions in a bathroom make its walls a prime breeding ground for mildew. When the plaster peels or cracks, mildew can actually grow beneath the top layer where it’s not necessarily visible. Before attempting any repairs, clean the damaged plaster to ensure that it is free of mold and bacteria. You can treat the areas with a mildew-killing tile cleaner or create a homemade solution of 1 part bleach to 6 parts water. Apply the cleaner to the peeling spot and allow it to sit for at least 10 minutes, so it has time to fully penetrate. Wipe down the wall with more of your cleaner and rinse thoroughly to ensure that there is no residue to interfere with the repair and painting process.
Scrape and Prime
Next, you must remove the peeling and damaged sections of plaster from your bathroom wall. Use a drywall knife or other scraping tool to gently scrape away any peeling or soft sections of plaster until all that is left is smooth, solid wall. When you’ve removed all the peeling areas, apply a plaster bonder to the wall. As the bonder dries, it hardens, providing a solid surface to plaster over.
To refinish the area of the wall that has peeled, you must apply a new layer of plaster so it blends with the rest of the wall. Finish plaster is usually used for repair work. It comes dry, so mix it with water according to the manufacturer’s instructions before application. When applying the plaster to the peeling section of the wall, it’s best to create several very thin layers so you can minimize the sanding necessary to help the repaired area blend with the surrounding wall. Use a drywall knife or trowel to apply the plaster for a smooth, even finish. Allow the plaster to cure for several hours or as directed in the manufacturer’s instructions.
Once the new plaster has cured, you can paint it to match the rest of the wall. Start by covering the section with a coat of latex primer to ensure that the paint adheres to the plaster properly. If you can purchase the same paint shade that you used on the wall originally, simply paint it to match the surrounding wall. However, if you don’t have leftover paint and are unable to find the exact shade that you used originally, you may need to repaint the entire wall to blend the repaired section in with the rest of the wall. If your peeling plaster occurred near a tiled section of the bathroom, you also need to apply a new bead of caulk along the tile edge. Choose a mildew-resistant caulk and make sure that it is paintable so you can finish it to match the rest of the wall.
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Regardless of whether your ceiling is peeling because of a leak, exposure to high humidity, or simply age, the repair process is the same. You must thoroughly remove the old paint, seal the surface, then reapply a new coat of paint. Before you get started, remove all of your furniture from the room and drape a dust sheet on the floor.
Preparing the Surface
Before you start painting, you must prepare the surface so the new paint has something to which to bind. Stand on a ladder and remove all of the paint. Use a 4-inch spackling knife to pry off paint that’s firmly adhered to the surface. Hold a roller pan underneath the knife to catch the falling paint. Lightly sand the surface with 80-grit sandpaper to remove the imperfections, then go over it with 120-grit sandpaper to make it smooth. Shine a flashlight over the surface of the ceiling. Imperfections can be difficult to see, even in daylight. The flashlight brings them to your attention so you can sand them down.
Applying an Undercoat
The undercoat prevents moisture damage from occurring, which significantly increases the longevity of your new paint. Mix together 3 parts matte paint and 1 part water in a bucket. Use a stir stick to mix it. This thins down the paint for use as an undercoat. Apply the thinned paint to the ceiling using a paint roller and nylon paintbrush, ensuring you completely cover the edges. Leave it to dry for at least six hours.
Applying the Paint
If you are planning on painting your walls afterward, apply the first coat of ceiling paint at least 2 cm down onto the wall. It’s much easier to cut in to the ceiling line when you paint a wall. Apply a layer of matte paint using a roller and nylon paintbrush. Matte paint is the best choice for painting over old ceilings and peeled paint because it defuses imperfections on the surface. Leave it to dry overnight, then apply a second coat.
Safety is paramount. Before you begin, make sure you take proper precautions. Thoroughly ventilate the area. Use a stepladder and if possible, get somebody to hold it for you when you are working. Wear a dust mask when you are sanding the ceiling to prevent inhaling the fine pieces of paint or old plaster. When you are applying the paint, wear safety goggles. The paint may drip, especially the undercoat, and getting it into your eyes could cause serious long-term damage.
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Based in Bristol, Ryan Malone has been working in the construction industry since 1977. He has earned various home related qualifications, including diplomas in plumbing and heating, painting and decorating, and advanced construction.
How do you fix peeling plaster?
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How to repair Peeling Paint on Plaster – YouTube
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Why are my plaster walls peeling?
1. Your painted surface is exposed to a lot of water. Water is the primary cause of flaking paint on bathroom walls and ceilings, as well as on exterior walls. When water penetrates through the coats of paint, it causes the layers to separate and detach from the surface.8 Apr 2019
How do you fix crumbling plaster walls?
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Repairing a crumbling plaster wall – YouTube
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How do you keep plaster from peeling when painting?
If you have some PVA glue put some in a bucket and dilute with water at a ratio of 50 parts water:1 of PVA. Brush onto the fresh plaster and allow to dry. Then put a coat of paint diluted 1:1 with water. That hopefully should cure your problem.12 Apr 2012
Can you plaster over peeling paint?
Yes, you can plaster over paint, however, there are factors which should be considered first. Paint that is in ‘good condition’ won’t have damages or cracks and won’t be peeling either. It is also best if the walls themselves are clean of dirt, and dust.
Why are my plaster walls bubbling?
Moisture in concrete, wood, drywall or plaster may cause a bubbling paint problem. Failure to sand shiny, slick surfaces or failure to prime them may be to blame. When doing new wall repairs, failure to remove all joint compound dust may cause blisters and bubbles to develop.
Do plaster walls need primer?
Painting plaster walls is just like painting any other drywall. The primer that you use is the key. You need to us the best primer for plaster walls to seal the wall because paints won’t take to it evenly without a good primer.
How do you remove emulsion paint from plaster walls?
Scraping. The easiest way to remove old paint, if it is already loosened, peeling or chipped, is with a putty knife, plastic scraper or an oscillating tool with rigid scraper blade. Simply work the flat edge of the tool across the surface of the wall to remove loosened pieces of paint.14 Dec 2018
How do you repair plaster walls before painting?
- Step 1: Prepare the Room. Before starting, cover the floor with plastic drop cloths and fasten the cloths in place using painter’s tape.
- Step 2: Smooth and Patch. Smooth and remove loose plaster pieces and any jagged edges on the surface around the crack with a putty knife.
- Step 3: Sand, Prime and Paint.
Is crumbling plaster dangerous?
Asbestos plaster is most dangerous when it is damaged. Damaged asbestos plaster is known as “friable asbestos”, which means the material can easily break and crumble, releasing asbestos fibers into the atmosphere.
Should I worry about cracks in plaster?
Vertical and horizontal cracks in drywall or plaster walls typically indicate drying and shrinkage, which is normal after construction. Jagged cracks, stair-step cracks and 45-degree angle cracks generally signify structural movement or settling issues that are occasionally serious but usually harmless.23 Aug 2018
How do you resurface plaster walls?
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How to Smooth Out Uneven Plaster With a Skim Coat – YouTube
After a century or so, plaster walls and ceilings can develop a variety of problems from neglect or abuse. Your plaster can tell you a ton about issues that may be developing around your house if you know how to listen to what it is saying.
In this post, I’ll show you how to diagnose the most common plaster problems and what they mean. Plaster is often like the canary in the coal mine. If there is a problem brewing, it will likely show up first in the plaster. So, knowing how to diagnose plaster problems will help you solve little problems before they become big ones.
This is probably the most common problem people notice with their old plaster walls. The good news is that cracks in your plaster don’t necessarily mean trouble. Sometimes they are a warning sign, but other times they’re just like wrinkles on our faces that appear with age. How do you know the difference?
- Hairline Cracks – These cracks are small enough that you can barely fit a fingernail in them. It doesn’t matter which way they are running either, vertical, horizontal, or diagonal, these are the most benign of all the cracks, and unless they are growing or you really can’t stand the sight of them, there is no reason to mess with them.
- Delaminating Cracks
Delaminating Cracks – These cracks are a sign of plaster pulling away from the lath behind it. These show up on both ceilings and walls, but can be the most dangerous on ceilings. When plaster begins to pull away from the lath, there is a chance it may fall away from the wall or ceiling and come crashing down. The cracks often run parallel to the lath (horizontally on walls and lengthwise on ceilings). You may see multiple cracks or bulges running parallel on the ceiling like in the picture, which is a sure sign of plaster pulling away from the lath. You can use the video tutorial to learn how to reattach the plaster and prevent further damage.
Photo Credit: //www.warreninspect.com
Settlement Cracks – If a part of the house is sagging, you may find converging cracks running across your plaster walls. Yes, you’ll want to patch and fill these cracks, but address the bigger issue of foundation problems first. A group of cracks converging in one direction are often signs of settling. If you see this kind of crack, call a professional, especially if they are new and growing.
This is the early signs of water damage to plaster. Brown water stains will begin to show up soon after a leak begins. The easy way to solve them is with a stain blocking primer, but that won’t do anything to resolve the water issue. You need to find the leak and seal it up before things get worse. Don’t delay.
Once the water damage becomes severe, then the plaster will begin bubbling and bulging. You may reach this stage without any noticeable water stains, but when this happens, a portion of the plaster will have to be removed and patched. Use the steps in my post How To: Patch Plaster to repair the damaged sections.
If not repaired soon, the damage will just continue and you run the risk of developing mold in the affected area. Water and plaster are not a good combination, so find the source of the leak first and do everything you can to stop the water.
Plaster is a pretty incredible material. I have seen a plaster wall come completely loose of the lath and bulge out about 4 inches from the wall without falling or even cracking! It’s not just cracks that mean plaster has come loose of its lath. Just like delaminating cracks, bulging plaster looks exactly the same, except this time there aren’t cracks in the surface.
If you see bulges in your wall or ceiling and the plaster can be pushed back up against the wall, then it’s time to reattach that section of plaster. Use the steps in my post How To: Repair Plaster Walls to get things stabilized again.
Remember, plaster is the canary in the coal mine and these are just some of the most common plaster problems. It will start showing you leaks and settling before anything else, so look for the signs and fix the issues before they demand your attention in a more expensive way.
If you have any plaster issues not mentioned here, leave a comment below and I’ll try to answer as many as I can about how to resolve the issue. Good luck and watch that plaster!
Founder & Senior Editor
I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.
Chipping plaster walls can make a room look very run down, but can be restored to their once pristine condition in a few easy steps, dramatically improving their appearance. Here is how to fix chipping plaster walls.
Step One – Prepare the Wall
The plaster wall must be prepared thoroughly in order for the repair to look seamless and to ensure its permanence. All traces of loose plaster should be removed with a soft brush and the wall should be completely dry to the touch.
Step Two – Prepare the Filler
By far, the easiest way to repair plaster walls is to purchase a ready-mixed plaster filler, which can be obtained from any reputable home improvement retailer. These fillers guarantee that they will not shrink, crack or lose adhesion to the repair. Follow the manufacturer guidelines before commencing on your repair.
Step Three – Apply the Filler
Use a filling knife or a trowel (depending on the scale of the wall to be repaired) to apply the filler into the repair, ensuring an even pressure is maintained and the action is a smooth upward motion. When the filler is flush with the surrounding wall, finish off the surface by wetting your float and gliding it over the surface of the filler. If more than one glide of the float is required, remember to clean and wet the float before repeating. This will ensure that the surface will be smooth and silky.
Step Four – Finishing the Filler
When the ready-mixed plaster feels firm to the touch but is not yet completely hard, repeat the wet float process again to finish your wall repair to a high standard. It is worth mentioning at this point that if you are struggling to achieve a perfectly smooth finish, you can purchase a finishing skim product. As the name suggests, it will skim the surface of your walls up to 3 mm in depth and will level any rough or uneven plaster. This product is usually applied with a paint brush and a special skimming tool is used to polish it to a fine finish.
Step Five – Let the Wall Dry
It is recommended to let your plaster wall repair dry for a period of approximately twenty four hours, to ensure it will not be damaged in the decorating stage. If you decided to use an extra skimming coat of filler, this will require a further twenty four hours of drying time also.
Step Six – Look after Your Tools
Plaster will dry hard on your filling knife and float if not cleaned thoroughly, so the use of warm water and detergent will ensure that your tools are ready to use the next time your plaster needs repairing.
Start to Finish
- plaster trowel
- sandpaper block
- ball pein hammer
- 10″ drywall knife
- cold chisel
- utility knife
- mesh drywall tape
- plaster mix
- joint compound
Like this? Here’s more:
use cold chisel and ball peen hammer to scrape
Smooth Damaged Areas With a Scraper
The first step is to prep the area by removing any loose or flaking plaster. Use a cold chisel and and ball pein hammer to chip away the damaged plaster and us a scraper to scrape away excess debris. Take care not to hit too hard with the hammer as it could damage the wood lath behind the plaster.
This process might make the hole larger, but will give you a clean area in which to apply the new plaster.
Mix New Plaster
Once the surface preparation is complete, mix up only the amount of plaster needed for the repair. Follow the instructions on the packaging to ensure the proper mixture. Mix it to the consistency of cake frosting.
Apply the Plaster Mix to the Damaged Area
Apply the mixture with the 10″ wallboard knife and spread a 1/4″-inch layer over the hole. Cross-scratch the first coat as it begins to set to allow the second coat to adhere well.
If needed, apply drywall/plaster tape to the wall to fill in larger, bumpy areas. First, apply a thin layer of plaster or joint compound and then apply the tape. Apply more plaster or joint compound mixture over the tape and use the drywall knife to smooth the surface until it’s even with the wall, pressing to remove pockets of air and plaster/drywall mud from beneath the tape.
Once the first layer has dried, apply a second layer. Apply another 3/8″- to 1/4″-inch layer and cross-scratch as you did the first time. Allow it to dry thoroughly before you continue.
Apply Joint Compound
After the second layer has dried, mix joint compound according to the manufacturer’s instructions and apply it very thinly using the 10″ wallboard knife. Blend the layer into the wall and allow it to dry.
One of the easiest mistakes to make when renovating a historic home is to tear down the old plaster walls and replace them with modern drywall and joint compound. This not only destroys the historic architecture and features that make a historic home great, but it also adds to the overall costs of the project exponentially. Despite the rumors you can repair old plaster yourself.
Lime plaster has been in use for thousands of years from Japan to Egypt and has been employed in many historic structures around the globe. Lime plaster is a far superior product than today’s modern wall coverings. With its crystalline structure, it repels moisture well while allowing for the contraction and expansion that often occurs in older homes during changing weather conditions. In fact, as the plaster’s structure calcifies (ages), it increases in durability and strength!
A Little History First
Traditional lime plaster was used for wall coverings until WWII. It was applied in a 3 coat process over thin wood furring strips called lath that were made of cedar, cypress or some other rot resistant non-staining wood and attached to the studs. The lath was soaked in water prior to installing the plaster to prevent it from sucking too much water out of the the plaster too quickly and spaced similar to the above picture with room between each piece for plaster to be pushed thru when applied. This spacing allowed the plaster to “key” in the lath and gave it extraordinary holding power when done properly.
The plaster was then applied in successive coats, typically 2, and a smooth finish coat was applied on top. Plaster took weeks to dry properly and fully cure before the walls could be painted. The whole process was slow and required a skilled plasterer which cost more money. After WWII, the building industry needed a faster way to cover walls and the relatively new product, drywall (getting its name from the fact that it didn’t go up wet like plaster), slowly crept into everyday use.
- Assessing –There are many reasons for lime plaster to fall into disrepair. Knowing the cause of the damage is crucial to applying the correct solution to the problem. From water damage to vibrations from nearby traffic to peeling paint, historical plaster damage can be caused by many problems. Is the plaster peeling from the lathe? Is the plaster soggy or crumbly? Are new coats of paint peeling from the walls? If you answered yes to any of these questions; don’t panic. While each condition is unique to each situation, lime plaster can be repaired easily, economically and effectively. A common occurrence in older plaster, cracks are commonly caused by expansion and contraction of an exterior wall. In the case of heavy cracking, it is possible to that the house it settling improperly. This should be inspected by a Building contractor or structural engineer immediately! Repairing small cracks is the focus of this article though.
- Dealing With Cracks –This repair can be done by drilling several small pilot holes in the materials at various intervals. By measuring the depth of the penetration, you can determine if the lathe is detached. Many times a few well-placed screws can draw the lathe and plaster back together. In extreme cases of detached lathe, more holes are drilled into the affected area and an elastomeric adhesive is injected between the separations. Clamping washers are then applied to the surface of the plaster to press the loose plaster back tightly against the lathe and allowed to dry. Once the plaster is secured, the holes and cracks can be filled flush with a mixture of lime and gypsum, allowed to dry and then painted. Check out my video on fixing cracked plaster to learn how to do it yourself!
- Peeling Paint –Another common dilemma when dealing with older homes is peeling paint, and it can be repaired with just a few simple techniques. More often than not, peeling paint occurs when many layers of paint have been applied to the plaster over the years. Calcimine is the common culprit of many peeling paint plaster problems. Calcimine is a water soluble paint material that was typically used in older paint products. The calcium in the paint reacts with the moisture content of the calcium in the lime plaster and creates a bond between the water molecules. This bond easily allows water to slip in and out of the paint’s surface, so even if you apply new paint, it peels over time. To remedy this problem, the old paint must be removed. A wallpaper steamer is the perfect tool for removing old paint from lime plaster. Gently use the steamer and a plaster knife to remove the paint without gouging the plaster. Once you’ve removed all of the old paint, wash the plaster with a rag and room temperature water. Don’t get the walls too wet; a light wipe down will suffice. Allow the plaster to dry 24 hours before repainting.
- Patching –Patching plaster in anything more than small amounts is something best left for the pros, but if you are a brave DIYer then you can try to tackle the task on your own. Old plaster is made from much different materials than current drywall joint compound. For decent sized holes the best thing to use for repairs is called Big Wally’s Patching Plaster. You simply mix with water and apply. Once your plaster is mixed apply it with a putty knife and press it firmly into the supporting lathe. Make sure the plaster isn’t sagging in the hole. If so, your mix is too watery and you should add more plaster until it is firm enough to hold under its own weight. Once the plaster has dried, give it a light sanding to smooth out the surface and wipe it down with a damp rag before painting.
While some damages can be easily repaired, it’s easy to quickly get in over your head when it comes to plaster repairs in a historic structure. Plaster work is an art form and many delicate cornices, crown molding and ceiling medallions were sculpted by hand by skilled craftsmen. So, before you rip that old plaster down to insulate and cover with drywall think twice. You might have a unknown work of art on the walls or ceiling of your home that deserves restoring.
Founder & Senior Editor
I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.