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How to repair hard plaster cracks?

Hi there,

In my hard plaster house, I have noticed cracks in the walls and uneven areas.

The cracks pictured haven’t broken opened the paint but are quite obvious. I have also included pictures where the plaster appears quite uneven and ugly. This house is very old (100+) and has barely had any maintainence.

What can I do to repair my walls that will make it smooth and crack free?

Thanks!

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Jewelleryrescue

Hi @CourteneyWilko

Actually, those walls quite good for a 100year old house.

The older plaster maybe horse hair plaster not gyprock as it wasnt around back then.

So we need to be carefull around it.

Now the raised cracks

Essentially you might like to buy a orbital sander 1/3 sheet or 1/2 sheet and 100 grit papers as it has a larger footprint to allow you to sand the wall back to even.

I you hand sand it is rubbing in one spot and may create a dimple (dip) in the wall. A sander will help average the rub down smoother more even,

Simply sand the raised bits back if you break through the skin if the plaster keep sanding but later, we will need to lay gyprock woven tape over the hole and patch it. See below fixing low patches or holes.

Low patches and break throughs

First we use a plasterers nylon mesh taped over (self adhesive) over the hole and patch area.

Then I like using Gyprock joint compound as it is stronger and using a 100mm wide steel spatula simply wipe the Joint compound across it into the mesh tape, the area is filled sitting a little higher than level. Dont try to get it perfect first try

Once dry next day, use your sander to sand the patch down and smooth and flush with the wall. If you find more little hollows just use more joint compound no tape required. until the wall is smooth and level.

Hope it helps.

EricL

Hello @CourteneyWilko

Thanks for sharing your questions about your plaster wall.

It's great that you've received excellent advice from @Jewelleryrescue. I have to agree with Jewelleryrescue, those walls look pretty good despite being 100 years old. Which leads me to think that at some point the walls could have been replastered. As to what method was used is difficult to tell unless you start scratching and sanding the surface. But before you do that, I suggest getting your walls tested for asbestos just to be on the safe side.

If the results are positive, I suggest engaging the services of an asbestos removal specialist. If the results are negative, you can then proceed with your repairs. I propose engaging the services of a licensed builder who is familiar with traditional methods of repair and plastering. This is also an excellent opportunity to upgrade your walls using modern materials if it is applicable.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you have any other questions we can help with, please let us know.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/48867#Comment_48867

Good Evening @CourteneyWilko

I have to agree, thos walls are in good condition for their age 🙂

The fine cracks and the uneven plaster remind me of walls I have where the previous owners/kids/teenagers someone has ended up against the wall and cracked it and then tried to repair badly over it.

With the house being so old I would sugest to have it tested as @EricL has mentioned just in case tho suspect it will be horse hair plaster as @Jewelleryrescue has also mentioned or more recent plaster,

If it comes back fine then I would be cautious (due to its age) I would create a fine small V cut that follwos the cracks (the point of the V being thecrack line itself.) I would use Selleys 180g Spakfilla Rapid Gap Filler - 180g and UNi-PRO Cork Sanding Block

IRWIN 1/3 92 x 230mm 120 Grit Un-Punched Sheets - 5 Pack or Paint Partner Assorted Sanding Sheets - 15 Pack will give you a range of grades. Start with the low number then medium and finally fine. You could skip the course stuff if you want 🙂 (I cut the sandpaper squares into three strips the width of the sanding block with a pair of scissors)

The high points on the wall I would use the course stuff to smooth nback, when you can pass your hand over without feeling it (close your eyes) then use the medium or fine to finish it off.

With the dips/gouges plus the V channel you have created then you use a UNi-PRO 75mm Real Good Paint Scraper and take maybe 10mm over the blade and drag it over the V cut and also dips, use enough force to push the plaster into the hole and also scrape excess off. The holes dont appear to be deep so it should be easy enough. Let dry, Id let dry twice as long as container says 🙂 Just to be safe. Then using a medium sandpaper sand as before, feel no ripples or almost no ripple switch to a fine grade of sandpaper. You will end up with a resonable amount of plaster dust so make sure you put down plastic sheeting. Try not to use your good vacumm cleaner as the plaster dust will kill it. Broom and dust pan I find is best.

Once you are happy then its time to paint 🙂 I would give it overnight to dry befor e painting btw. Ive seen deep gouges take a bit to dry depending on the season and where you are located.

Dave

Nailbag

Hi @CourteneyWilko

A @Jewelleryrescue highlighted the walls are in amazing condition for their age.

First thing to do is lightly sand the high-points to a level surface as the wall. Then fill the low points with a skim coating like this topping compound with a wide spatula. Allow it to dry fully, then lightly sand back with a 240grit sanding sponge. Rub your hands lightly over the surface and sand back anything thats not a smooth transition. It might take a second smooth coat to complete the process.

Once you're happy with the finish, use a lightly damp cloth to wipe the entire area then apply a prime coat prior to painting.

Nailbag

CourteneyWilko

https://www.workshop.bunnings.com.au/discussion/comment/48871#Comment_48871

Thank you all for the amazing advice!

We also have deeper cracks in the walls. On another forum I read that the deeper cracks are best filled by opening up a little more in order for the render to bond.
as pictured, I opened some of the deeper cracks (which exposed the cement underneath - this is a double brick house). Now I am concerned this was the wrong this to do…

There are also some deeper cracks around door frames and skirting. I am wondering if I should remove the skirting, cornices and door frames when repairing the walls? I am very confused on the order in which to fix these walls!

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/86522#Comment_86522

Morning @CourteneyWilko

🙂 Those cracks are a little different. You mention a renderd wall so that leads me to a question. Is the surface of the cracks plaster or a cement render?

If its a cement render then it changes the product you would use but will let one of the guys suggest what type as I have not done a lot of render repairs. Just had a squiz over the types of interior render and it may be worth having a look at the depths and widths that a product will cover. It looks doable 🙂

The process I think will be the same. If its plaster then depending on how deep/wide the cracks are you may need some mesh over the crack to help bond/secure the section.

As to the last question, if you are intending to remove the skirting and/or door frames then I would repair them at that point. I wouldnt remove them as they are covering the cracks as is and you will be creating a lot of work that may never be needed.

Dave

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/108639#Comment_108639

HI @CourteneyWilko,

Opening the cracks up was the way to go. If these are cracks through the brickwork then you might need to have someone that specialises in house/wall stabilisation check them out. You might find your foundations need to be stabilised to prevent further cracking.

Now that you've opened the cracks (and determined that there are no structural issues with the wall or house), you can pack mortar into them. You'll then, once dry, render over the crack right up until about 5mm from the surface of the wall. The rest of the depth can be filled with Hardwall Plaster.

I'm in two minds about removing the door and skirting trim to fix the cracks behind them. I don't really see any reason to do this, and you certainly don't want to damage that skirting in the process, as it would be costly and hard to replace.

Please let me know if you have any questions.

Mitchell

CourteneyWilko

https://www.workshop.bunnings.com.au/discussion/comment/108639#Comment_108639

Hi @Dave-1,

The bricks have a cement render which is then covered with a layer of hard plaster!

We were thinking of updating the door frames and keeping the skirting at this point! So would you advise to remove the door frames at this point?

Thanks again!

Court.

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/121611#Comment_121611

Afternoon @CourteneyWilko

It comes down to your preference. And also what type of door frames you will be replacing the old ones with. How many cracks go under any door frames? How big will the timber be on the new doorframe, How soon are you going to redo the doorframe? These all come to mind with the reno work that you are doing.

Thinking of and doing, If I started all the "thinking of" projects I have then my place would not get finished, maybe wait until your replacemnt of the door frame arrives and then do that little bit of teh crack underneath?

Dave

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