# prime before skim coating this plaster ceiling?



## DarrenLevine (Aug 3, 2016)

This ceiling was covered in popcorn, which i scrapped off. It was a massive PITA.

As you can see there are patches of the skin of the plaster, i did my best to scrape all the loose parts off, but it is what it is, so there's two surfaces.

So you may notice the discoloration toward the far end, this house was vacant before me and they had a pipe burst, and likely soaked a lot of the ceiling

So the two concerns moving forward, you can see the spider network of cracks, none of which are open, just visual, but is this an indication that i may get open cracks in the future? should i poke an explore hole in the worst area to see the condition of the plaster inside?

Other concern, i planned on doing a skim coat with the rubber squeegie, but a painter friend suggested i prime it first. I had already done some spackling to some parts before deciding on the skim coat, and that Spackle seems to have adhered fine, but if priming is a safer bet, then i'd go for it. you can see at the top of the picture the white patch of mud.

I know the other solution is throw up new drywall, but would prefer to avoid that if possible. i've had enough taping for the time being.

cheers
D


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## mark sr (Jun 13, 2017)

I'd only prime first if the remaining plaster is chalky.


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## ClarenceBauer (Mar 4, 2005)

If it is conventional 3 coat plaster than you would not prime. You will need to use a good veneer plaster to skim coat with. Drywall material over a plaster system is not a good idea as it will react differently with moisture and over time will delaminate.


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## Guap0_ (Dec 2, 2017)

Priming first helps show the imperfections. I think that's why he told you to do that.


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## t.carpenter00 (Jan 23, 2018)

The best solution is to put up new rock. But that's a pain too. But, even with a wet scrape, acoustic leaves behind a chalky film that will make anything you go over it with eventually suffer bond failure. I recently read did half a house because of it. If your not going to sand the ceiling - and ALL of the residual acoustic base off, then I definitely would prime it first. I'd use a good grip primer like Stix or Gripper. The problem then is after your first skim, your going to be fixing a billion air bubbles and craters with mud. I'd rock it. It really is less of a pain than what you're about to undertake. 

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## ClarenceBauer (Mar 4, 2005)

I have done 100's of plaster repairs & skim coatings in the past 40 years and find no reason to use a primer if the correct gypsum is used. Some times a bonding agent would be required depending on the existing condition of the plaster. I have also found away to skim coat over the calcimine coatings with out using a primer or removing the calcimine.


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## t.carpenter00 (Jan 23, 2018)

I agree with Clarence. But I've never done plaster so, drywall for me!


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## t.carpenter00 (Jan 23, 2018)

ClarenceBauer said:


> I have done 100's of plaster repairs & skim coatings in the past 40 years and find no reason to use a primer if the correct gypsum is used. Some times a bonding agent would be required depending on the existing condition of the plaster. I have also found away to skim coat over the calcimine coatings with out using a primer or removing the calcimine.


Clarance,
The paint in my house is delaminating in small spots on the ceiling. When I scrape the peeling paint back to where it stops peeling, and re-finish it, it begins to peel around the edges of the re finished area. Usually this happens a few months later. What gives?

By the way, when I scrape the paint spots, they seem to be peeling down to the skim coat. 

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## ClarenceBauer (Mar 4, 2005)

That is because the moisture in the new material is pulled into the existing plaster and it gets behind the paint that is left and the moisture pushes the paint away from the exist plaster. This is one area that you can use a product like Peel Stop only around the edges of the remaining paint you should not have to cover the entire surface with Peel Stop. Also it sound like the wrong or no primer was used over the original plaster or the plaster was painted before it had time to cure. How old is this plaster surface is it a lime based finish?


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## t.carpenter00 (Jan 23, 2018)

ClarenceBauer said:


> That is because the moisture in the new material is pulled into the existing plaster and it gets behind the paint that is left and the moisture pushes the paint away from the exist plaster. This is one area that you can use a product like Peel Stop only around the edges of the remaining paint you should not have to cover the entire surface with Peel Stop. Also it sound like the wrong or no primer was used over the original plaster or the plaster was painted before it had time to cure. How old is this plaster surface is it a lime based finish?


Dunno. House was built in 69.it has 3/8 sheetrock under 3/8 plaster. The skim coat feels ultra smooth, like glass, if that helps.


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## ClarenceBauer (Mar 4, 2005)

You nave what is known as Rock Lath plaster system. The 3/8 inch gypsum board should be 16" wide X 48" long with a 3/8 " plaster consisting of a base coat with a lime based finish. Excessive moisture will cause paint delamination.


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## t.carpenter00 (Jan 23, 2018)

ClarenceBauer said:


> You nave what is known as Rock Lath plaster system. The 3/8 inch gypsum board should be 16" wide X 48" long with a 3/8 " plaster consisting of a base coat with a lime based finish. Excessive moisture will cause paint delamination.


Awesome so fix the peeling places with the product you mentioned and then paint it with... A latex, or would an acrylic be better? 

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## mark sr (Jun 13, 2017)

I wouldn't get hung up with the minor differences between latex and acrylic, many paints are both.

The age of the house suggests that the original paint in the bath and kitchen would be an oil base enamel which can be problematic if latex is applied directly over it [without an oil base primer first]


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## ClarenceBauer (Mar 4, 2005)

Mark's statement ( PROBLEMATIC ) is correct lets say in 1960 the lime based finish coat was painted before the Lime had re carbonate ( hardened ) this could cause the oil based primer to form a soap like substance that over time will cause the paint to separate from the plaster finish. Linseed oil being the worst. Look up this word SAPONIFICATION?


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## t.carpenter00 (Jan 23, 2018)

I don't think that is what's going on here. It seems like it's just flaked an a few small spots in high humidity areas. Thanks for your wisdom I'll go find that product you mentioned. We can't find anything non standard here. This side of Missouri is one small box! 

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## t.carpenter00 (Jan 23, 2018)

Sorry I took over your post. I tried to send that conversation privately. But I didn't do it right! 

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## DarrenLevine (Aug 3, 2016)

Thanks all for the input, gives me much to consider.

I attached a closer shot of the ceiling, if that helps to identify what exactly i'm dealing with.

For those that say skim coat is fine, what type of mud would you recommend? I have plenty of plus3 on hand, but will go with whatever the pros think won't delaminate.


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## t.carpenter00 (Jan 23, 2018)

I would defer to Clarence. I think that if you don't re skim it with plaster, you better just hang over it. I see a 
s-storm of possible issues with a mud skim. Since I'm not there looking at it.

But if you're convinced mud is the solution, go with +3. This is a hard application to learn the intricacies of hot mud. 

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## ClarenceBauer (Mar 4, 2005)

If that ceiling is a true Gypsum plaster system than the use of any type joint compound will fail at some point depending on Humidity / Moisture.
In all my 40 years of working with plaster i have repaired Many repairs that were done using joint compounds over conventional plaster. Some of the repairs that were done using joint compound may have cost around $1,000 / $2,000 dollars at the time of repair. When i was called to correct the problem the cost would average 10 times the cost of joint compound. Believe it or not i was never short on repairs jobs. The crews are still going strong as of this date.
For Gypsum plaster check on some of the following products USG Diamond Veneer - Gold Bond Kal-Kote - Varience - TexSton - American Clay - Master of Plaster.
Of the above i would rate
Master of Plaster #1
TexSton #2
USG Diamond #3
Gold Bond #4
American Clay #5
There are others on the market i have not used which ever one you select make sure it is LIME BASED.


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## DarrenLevine (Aug 3, 2016)

Thanks Clarence,

Is there way to tell if it's true gypsum plaster?

Some clues for you: as you can tell by the photo, there's a base, and then a thin skin (a lot of which came off with the popcorn) And if i look at the top of the ceiling inside the attic space, it looks like a smooth board with holes and material poking out of the holes like little tubes (see attached)

Also, since i'm terrible at jumping between projects, the roughly 4x8 area of the ceiling that i did lots of patching with plus3 is probably a year old now with no separation. don't know if this would be any indication for longevity.

Thanks again for the education

cheers
D


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## ClarenceBauer (Mar 4, 2005)

OK you have what is known as Rock Lath which is a conventional plaster system consisting of 3/8 inch gypsum lath , 3/8 inch sanded gypsum or it could be a gypso- Lite plaster both of which were used. The finish coat ( White ) is made up of Lime , Guaging Plaster & Moulding Plaster. So what you need is a Lime Based material that will have the same make up which would be in the previous post. If you don't have high humidity / Moisture or you don't intend to retain the property use the joint compound BUT IT IS NOT WHAT I WOULD RECOMMEND based on what i have seen over the last 40 years.


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## DarrenLevine (Aug 3, 2016)

Your experience speaks volumes, Clarence, 

thanks!


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## DarrenLevine (Aug 3, 2016)

One more question comes to mind:

Would any of the texture applications be a safe bet? I know, i just took off popcorn, but wouldn't hate some of the other type of textures especially if it proves simpler than skim coat.

as i understand it, textures are typically gypsum based? All i know is that the popcorn i scrapped off did not go without a fight.

cheers


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## ClarenceBauer (Mar 4, 2005)

Yes you can apply a texture coating. It can be free style , dash , Knock down or you can get a texture roller they have about 7 different textures. Check the Kraft Tool Co. catalog page # 126.
www.Krafttool.com


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## DarrenLevine (Aug 3, 2016)

Sorry to revive this. The project got kicked down the road (unexpected duck adoption)

It has been a pain to try and find one of the lime based plasters Clarence recommend near me in northern NJ. Maybe i just don't know where to look other than the usual big box and a few local supply shops.

The only one i found is dap plaster wall patch 

The SDS ingredients list plaster of paris, limestone, and quartz:
http://www.dap.com/media/33829/00071006001english.pdf

Does anyone have first hand experience with this product? 

cheers


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## ClarenceBauer (Mar 4, 2005)

Check out these places.
Specialty Plaster in New Jersey , CS Stucco & Plaster in New Jersey or USG supply in New Jersey
Any of the above should be able to help. No Big Box stores will have any good plaster supplies.


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## ClarenceBauer (Mar 4, 2005)

I should have told you to ask for David Smith @ Specialty Plaster if he does not have what you need he will know who does.


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## DarrenLevine (Aug 3, 2016)

Thanks again,

your leads and 5 calls later i finally found some USG diamond.

Some odd things probably due to my inexperience:

first round i noticed some cracking, small and a bunch in parallel rows. i figured it may be because i pointed a fan at the ceiling, but i also noticed some in the second round which i did no fan.

In the second round i also thought to add a little dish soap, i googled around to see if this was as standard a practice as it is with regular mud, but could not find any specific mention, so i decided to try it. Perhaps it was this that made the second round rather difficult to work with, it didn't go on smooth easily, and had sort of a different more clumpy consistency. i scrapped that batch and did a new one without soap.

I'm wondering if i'm getting the consistency right, should i be about the same as mud, or a bit thinner like mayonnaise?

Thanks again, 
hate the stumbles, but love the learning.


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## ClarenceBauer (Mar 4, 2005)

USG Diamond plaster OK the mixture should be like " Mud " ( peanut butter ) consistency. When troweling it on skim a tight coat on than double back say in 15 min. skim another coat on and trowel smooth using a clean trowel and water, use a paint brush in your left hand brush on water than trowel using right hand keeping the plaster ahead of the trowel wet. The plaster should slick down smooth. DO NOT use any forced air movement as it will cause map cracking it needs dampness to cure. If Left handed reverse the brush & trowel.
You can also use a spray bottle to mist ahead of your trowel this may be easer than the brush.


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## DarrenLevine (Aug 3, 2016)

Thanks again, i'll try that on the next section


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## DarrenLevine (Aug 3, 2016)

Small update:

Haven't gotten to the next coat(really just next section, not another coat), i wanted to do a round of sanding to see how it all was looking. 

Switching to a random orbit, while heavier, made things a lot easier than the hand sander. Looks smooth enough for my needs

I noticed a 1mm wide fracture/crack, which is perpendicular to the joists, and looks to be situated under the knee wall of the floor above. also of concern: near the center of the room, there seems to have some low spots, as there are spots which in skim coating would tend to reveal the brown coat instead of taking the skim.
This room did get water damage from above, don't know the extent except for the water stains on the brown coat

I took a pole and did some poke tests, the low spots don't seem to have any movement. the 1mm crack i can see some movement, maybe 1mm or 2. 

Would it be advisable to put some screws with those zinc buttons into some of the joists around these suspect areas, or am i overthinking?

cheers


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## ClarenceBauer (Mar 4, 2005)

The cracks could very well be from the deflection of the floor above.
As for using the plaster washers it would help if installed along the crack on both sides but depending on what type lath was used.
Also keep in mind that the plaster washers would require a plaster coat of 1/8 inches to cover washer.


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## DarrenLevine (Aug 3, 2016)

another small update.

started driving regular drywall screws along the joists, no washers, your advice on having to do a thicker coat led to that. 

Interesting observations: in the middle of the room where most of the water damage was near the low points, the screws go in hard, meaning the drill/driver has to work extra hard to countersink. Also doesn't seem to be pulling up at all/no apparently sagging. 
whereas near the knee wall end where the noticeable crack/deflection is, they countersink much easier, and they did pull up a bit, less than a cm.

i'm tempted to drill an exploratory hole, i have one of those scope snake cameras, but it's a cheap one, it can't focus past a few inches


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## DarrenLevine (Aug 3, 2016)

slowly nibbling away at this project. almost done patching the bad areas. One thing i can't seem to get around is the few low points in which the smooth layer is too low to accept a level coat of the plaster. will this smooth(brown?) layer accept primer and paint, or should i just do what i can to get some plaster over it?


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