Author Topic: Question about using plaster. (Read 2560 times)

Alex · « **on:** December 06, 2019, 03:59 AM »

I have a question about using plaster and the recommended thickness of the layer you have to apply.

I have to plaster almost half of the walls in my house, because those walls are covered with ugly drywall with wallpaper over it, and I want to make it all straight white walls with plaster and then paint it.

But I am a bit baffled by the number of options of available plasters and their different applications. I find they have different thickness recommendations, for instance:

Knauf - Fix & Finish: thickness 1 - 3 mm

Knauf - Rotband: thickness 5 - 30 mm

Knauf - MP75: thickness 10 mm and up

Now, I was wondering why exactly they have a minimum thickness. I mostly need to do thin layers of 1 to 5 mm, but the Fix & Finish plaster most suited for that is almost double the cost of MP75. Over an entire house this will add up, so I was wondering what would happen if I used the MP75 instead.

six-point socket II · « **Reply #1 on:** December 06, 2019, 05:54 AM »

Hi!

Are you going to sand up to Q4 surface quality? If yes, "Fix & Finish" should be first choice. It should be what is available in Germany under the name of "Multi-Finish". And yes, 29,95 Euro / 25 kg is not cheap. It's a top layer type product.

Rotband should be "dirt cheap", it's a very basic "does it all" product, mostly used as under/ first layer. 30kg = 8,50 Euro Rotband will need a thicker layer as it is not even nearly as fine as other products. And if the layers are too thin, you "break" the structure/layer back open.

MP75 is even cheaper, yes. (30kg, 6,45 Euro) It's also a basic under/first layer type product. And as the name MP (Maschinenputz) indicates, is especially suitable to be used with machines.

All that said, if you're set on using Knauf, contact their support directly if you have detailed questions, they have a superb "professional user support".

Kind regards,
Oliver

Alex · « **Reply #2 on:** December 06, 2019, 06:22 AM »

Thanks for the reply Oliver. I am not a professional user so I don't know if Knauf would help me. I doubt a trained tradesman would ask such silly questions as me.

You say you can break the layer of Rotband open if it's to thin, during which process could that happen? Initial application, or when you flatten/skim it out later? Or could it crack months or years later?

Fix & Finish is luckily not as expensive as in Germany, €15 for 25 kg, Rotband €13 for 25, but MP75 is only €9 for 25 kg and they say it is also suitable for a fine finish.

I've used Fix & Finish before, it is great stuff and easy to use. Rotband is more difficult to use because it hardens pretty fast, and yesterday I did my first patch with MP75, and it worked pretty good.

I think I'm going for Q3 finish, but I am not sure if my skills will allow that. I have some experience with plastering walls, but not a lot. I'll see where it ends up and learn along the process. I have a lot of meters to practice on.

six-point socket II · « **Reply #3 on:** December 06, 2019, 07:19 AM »

Hey Alex,

You basically already answered the question relating to my concerns with Rotband. It dries pretty quick both on the wall and on tools, so when you flatten/skim it, the surface is very prone to breaking open/ (being scratched open while working) in a not totally dry but in-between state. It's not very, let's say user friendly in that regard. And the window to flatten/skim is pretty tight. It's really more for rough stuff, spot repairs, base layer type stuff.

I've never had Rotband break open after it dried. No risk of that. I was really only speaking about application and critical "in-between" state.

If the MP75 has the 8mm minimum thickness. Since I'm no pro either, I can't explain or foresee what would happen with thinner layers. My educated guess based on my experience with plaster is that it could bond/dry too fast and not tie positively.

I doubt Knauf would not reply, as they also cater heavily to the DIY market (at least in Germany) with a lot of products. And if you use their professional products ...

-> knauf-direkt (@) knauf.de

You could ask if there are known problems relating to thin layers not tying positively with the MP75.

Just don't call, the 0900 number they offer is ridiculously expensive.

Kind regards,
Oliver

Alex · « **Reply #4 on:** December 06, 2019, 07:59 AM »

Alrighty, send them an email, lets see what they'll have to say.

-------

Ok, got the answer from them, it is about strength against impacts. They put their plasters through strength tests where they push against it with a steady force, or do impact test with metal balls. If the plaster is thinner than they recommend you don't get the resistance values they want.

So in short, if you use a thinner layer the plaster will stick and look good, but might not be as impact resistant.

Good to know.

Cheese · « **Reply #5 on:** December 06, 2019, 11:00 AM »

Just curious what a Q3 & a Q4 finish is?

FWIW...here's a section from the bathroom of plaster over gypsum board. 10 mm gypsum, 6 mm plaster brown coat & 3 mm plaster top coat.

six-point socket II · « **Reply #6 on:** December 06, 2019, 11:38 AM »

Quote from: Alex on December 06, 2019, 07:59 AM

Alrighty, send them an email, lets see what they'll have to say.

-------

Ok, got the answer from them, it is about strength against impacts. They put their plasters through strength tests where they push against it with a steady force, or do impact test with metal balls. If the plaster is thinner than they recommend you don't get the resistance values they want.

So in short, if you use a thinner layer the plaster will stick and look good, but might not be as impact resistant.

Good to know.

Thanks for sharing!

That's great - so I guess you can go with the MP75 then. Great!

Kind regards,
Oliver

six-point socket II · « **Reply #7 on:** December 06, 2019, 11:45 AM »

Quote from: Cheese on December 06, 2019, 11:00 AM

Just curious what a Q3 & a Q4 finish is?

(...)

Hey Cheese,

it refers to the surface quality of plastered drywall.

Before I try to write it all down in my own words, here's a pretty comprehensive 3 minute video.

Kind regards,
Oliver

Alex · « **Reply #8 on:** December 06, 2019, 11:52 AM »

Quote from: Cheese on December 06, 2019, 11:00 AM

Just curious what a Q3 & a Q4 finish is?

I had to look that up to. Found this PDF which explains it in detail.

http://www.eurogypsum.org/wp-content/uploads/2015/04/EUROGYPSUMFINSHINGUK.pdf

Quote from: Cheese on December 06, 2019, 11:00 AM

FWIW...here's a section from the bathroom of plaster over gypsum board. 10 mm gypsum, 6 mm plaster brown coat & 3 mm plaster top coat.

Shouldn't you better leave that in your bathroom instead of plastering it all over the internet?

Cheese · « **Reply #9 on:** December 06, 2019, 01:34 PM »

Thanks for the video Oliver.

I've never done a Q4 skim coat with a roller before. Man that sure simplifies the whole process.

tjbnwi · « **Reply #10 on:** December 06, 2019, 06:23 PM »

@Cheese,

Here it would be referred to as level 1 through level 5. You may have heard of L5 finish, that is the highest level drywall finish. L1 is usually just fire taped.

I use the Tape Tech finishing knives. I also spray on an L5 finish.

Tom

DeformedTree · « **Reply #11 on:** December 06, 2019, 09:13 PM »

Bit of a tangent, but is Plaster the Norm in Europe, or has it largely been replaced by Drywall like in the US? Or is there a 3rd or 4th option that is the norm (400 years of patch...aka charm)?

Is there a reason for going the route you are on verses stripping wallpaper, or just tearing down the drywall and going new. Or do you just prefer plaster, or looking to learn new skill?

Cheese · « **Reply #12 on:** December 06, 2019, 10:02 PM »

Quote from: tjbnwi on December 06, 2019, 06:23 PM

@Cheese,
Here it would be referred to as level 1 through level 5. You may have heard of L5 finish, that is the highest level drywall finish. L1 is usually just fire taped.

I use the Tape Tech finishing knives. I also spray on an L5 finish

Thanks for that Tom...I've never heard of a L finish or a Q finish before...it's all new to me.

By the way I HATE drywalling and mudding.

I'm assuming the L5 would be the equivalent of a Q4? The Q4 is a full skim coat to make sure the walls have a uniform texture.

So what's up with the Tape Tech knives? What are the advantages? I've always used Marshalltown aluminum and also have some Marshalltown stainless knives.

Cheese · « **Reply #13 on:** December 06, 2019, 10:07 PM »

Quote from: DeformedTree on December 06, 2019, 09:13 PM

Is there a reason for going the route you are on verses stripping wallpaper, or just tearing down the drywall and going new. Or do you just prefer plaster, or looking to learn new skill?

Plaster walls are a great sound absorber...nice and quiet. They may also offer some insulative advantages. And then there's the always present $$$ factor for resale.

tjbnwi · « **Reply #14 on:** December 06, 2019, 10:20 PM »

Quote from: Cheese on December 06, 2019, 10:02 PM

Quote from: tjbnwi on December 06, 2019, 06:23 PM
@Cheese,
Here it would be referred to as level 1 through level 5. You may have heard of L5 finish, that is the highest level drywall finish. L1 is usually just fire taped.

I use the Tape Tech finishing knives. I also spray on an L5 finish

Thanks for that Tom...I've never heard of a L finish or a Q finish before...it's all new to me. By the way I HATE drywalling and mudding.

I'm assuming the L5 would be the equivalent of a Q4? The Q4 is a full skim coat to make sure the walls have a uniform texture.

So what's up with the Tape Tech knives? What are the advantages? I've always used Marshalltown aluminum and also have some Marshalltown stainless knives.

L5 is a full skim or a sprayed on coating. I can do either.

The Tape Techs lay the compound down glass smooth with very little to no lap marks. I have the full set.

Tom

Cheese · « **Reply #15 on:** December 06, 2019, 10:27 PM »

Quote from: tjbnwi on December 06, 2019, 10:20 PM

L5 is a full skim or a sprayed on coating. I can do either.

The Tape Techs lay the compound down glass smooth with very little to no lap marks. I have the full set.

The sprayed on coating is even more interesting. That's a step up from the roller application I assume. What kind of gun do you use for that?

DeformedTree · « **Reply #16 on:** December 06, 2019, 10:49 PM »

Quote from: Cheese on December 06, 2019, 10:07 PM

Quote from: DeformedTree on December 06, 2019, 09:13 PM
Is there a reason for going the route you are on verses stripping wallpaper, or just tearing down the drywall and going new. Or do you just prefer plaster, or looking to learn new skill?

Plaster walls are a great sound absorber...nice and quiet. They may also offer some insulative advantages. And then there's the always present $$$ factor for resale.

The sound properties are over sold, make anything thicker, heavier, more solid it does better on sound. Grew up in a house with a mix of plaster and drywall, no real benefit. Having had to rip out plaster in my house, I find plaster to be complete evil, worst dust ever. Add to that the frustration of when you need to modify something like cut in a switch or outlet, the wall just starts to shatter/flake off. I really don't like drywall either. If I lived in an old masonry house and was going over masonry, plaster would be no brainier. This is why I'm curious what drove him one way or the other given he has drywall. Also just curious what is normal over there. Maybe they make wallpaper that looks like plaster

Cheese · « **Reply #17 on:** December 06, 2019, 11:01 PM »

Well, it's interesting, I've removed 4" plaster covered walls with 1" rock wool insulation in our house and replaced them with 6" of drywall covered walls with R21 fiberglass insulation and the original walls "seemed" to be quieter. No dB measurements were taken...just a gut feel.

tjbnwi · « **Reply #18 on:** December 07, 2019, 12:50 AM »

Quote from: Cheese on December 06, 2019, 10:27 PM

Quote from: tjbnwi on December 06, 2019, 10:20 PM
L5 is a full skim or a sprayed on coating. I can do either.

The Tape Techs lay the compound down glass smooth with very little to no lap marks. I have the full set.

The sprayed on coating is even more interesting. That's a step up from the roller application I assume. What kind of gun do you use for that?

I have an Airlessco that with spray thinned compound. You do have to strike it once on the surface. Tuff Hide will achieve a level 5 if sprayed properly. Also needs a larger sprayer, goes on @ 20 mills.

https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/sheetrock-primer-surfacer-tuffhide-submittal-J1613.pdf

Roller and a finishing knife is pretty common on higher end smooth wall.

Tom

Alex · « **Reply #19 on:** December 07, 2019, 03:11 AM »

Quote from: DeformedTree on December 06, 2019, 09:13 PM

Bit of a tangent, but is Plaster the Norm in Europe, or has it largely been replaced by Drywall like in the US?

Plaster is the norm in Europe because brick houses are the norm in Europe.

Nevertheless, drywall is used for lots of things, mostly during renovation. But to make your walls entirely out of drywall like in the USA is not done so often here, only when you want to split an existing space into smaller rooms on the cheap. Even then people mostly choose for another option, namely lightweight celular concrete blocks because they are more durable. But both options mostly get plastered over.

Quote from: DeformedTree on December 06, 2019, 09:13 PM

Is there a reason for going the route you are on verses stripping wallpaper, or just tearing down the drywall and going new. Or do you just prefer plaster, or looking to learn new skill?

Yes, there is a very good reason. The walls are not made out of drywall, but brick, which were then insulated with rockwool plates of 5 cm thick and then covered with drywall. This was done by my father 30 years ago. He did a lot of work on the house over the years, but he was not very good at it. So everything looks very ugly now.

So I'm not going to tear that down. The drywall is good, it only looks ugly, which I'm going to improve to modern european standards. And I am indeed looking for the skill. I do a lot of renovation work for people, carpentry, woodworking, painting and other handyman work, and from time to time people ask me if I can plaster a wall for them. But it is a difficult skill to learn so I welcome to opportunity.

Quote from: DeformedTree on December 06, 2019, 10:49 PM

If I lived in an old masonry house and was going over masonry, plaster would be no brainier.

Here plaster is always a no brainer and the norm. The rest of my house is done with plaster and I am going to keep it like that. I absolutely detest the look and feel of painted drywall. As I am also a musician, the added soundproofing is very welcome.

Quote from: DeformedTree on December 06, 2019, 10:49 PM

Having had to rip out plaster in my house, I find plaster to be complete evil, worst dust ever.

Well, maybe use proper protection? I always wear a full face respirator during demo. Bit odd to judge plaster that sits on the wall for 80 years by the one moment you have to tear it down. Most people judge building materials on their "stay put" properties, not their "come loose" properties.

demographic · « **Reply #20 on:** December 07, 2019, 07:58 AM »

Quote from: DeformedTree on December 06, 2019, 09:13 PM

Bit of a tangent, but is Plaster the Norm in Europe, or has it largely been replaced by Drywall like in the US? Or is there a 3rd or 4th option that is the norm (400 years of patch...aka charm)?

I can't really comment for areas other than the north of England but for what its worth...
Here we usually use a plaster skim finish over plasterboard on household and smaller areas. As far as I'm concerned its a far better finish than taped and jointed walls.
Larger areas on commercial buildings tend to get plasterboard then taped and jointed, otherwise the plasterer has to go nuts to get a load of plaster on in one go.

Then in places subject to flooding risk (I live in Carlisle which has had considerable flooding over the last 20 years) it's quite common to just plaster over the brickwork in the downstairs of properties so if it floods it takes far less time to sort out.

Bear in mind that I'm not a plasterer so have gaps in my knowledge of the subject.
I sometimes screw plasterboard on walls I've made but generally avoid it if I can.

Cheese · « **Reply #21 on:** December 07, 2019, 09:22 AM »

Quote from: tjbnwi on December 06, 2019, 10:20 PM

The Tape Techs lay the compound down glass smooth with very little to no lap marks. I have the full set.

Thanks again Tom @tjbnwi , I found this video on Tape Tech...it all makes sense, I like the design. The Marshalltown knives always take off more compound than I'd like and the outer edges usually leave tracks.

https://youtu.be/_bB5AAbfVcw?t=3

Alex · « **Reply #22 on:** December 07, 2019, 09:31 AM »

Hmm, remarkable how I get little to no answer to my question and this thread now seems to be about something that has no bearing whatsoever to my original question.

Is there no one here with any real experience in plastering?

Bert Vanderveen · « **Reply #23 on:** December 07, 2019, 10:04 AM »

Quote from: Alex on December 07, 2019, 09:31 AM

Is there no one here with any real experience in plastering?

My experience is limited to small projects using Fix & Finish, which is the most forgiving plaster, because excess can be easily sanded off and deficit corrected by using it like a putty ('plamuur'). The fact that you need to apply quite thin coats helps you achieve a flat surface — which can be improved by defining sections with strips of leveled out plaster, which allows you to use a wide scraper. It does often take a couple of passes to get a really good result.

When and if 'real' plastering is necessary, I leave it to a pro.

Hope this helps. : )

tjbnwi · « **Reply #24 on:** December 07, 2019, 10:28 AM »

Quote from: Alex on December 07, 2019, 09:31 AM

Hmm, remarkable how I get little to no answer to my question and this thread now seems to be about something that has no bearing whatsoever to my original question.

Is there no one here with any real experience in plastering?

Plastering is no longer widely used in the U.S. My experiance with it is very limited. My uncle could plaster anything, he was a trowel tradesman, I'd ask him for advice, but he past away 20 years ago.

I did look at the Knauf website. I can't tell from reading it if the products you're asking about are for brown/base coats or are the actual topcoat. I do know here (as shown in Cheese's photo) plaster is a built up system. Lath or drywall/blue board, brown/scratch coat then a white/top coat.

You answered one of your questions about the minimium thickness.

Here, as I pointed out, to achieve the finsih level you're looking for it would be compounds and finishing knifes.

Reading the description of your wall substrates, I see no reason why the method would not work.

If plaster white coat is the way you really want to go, look into plastering darby's.

I strongly recommend you remove the wall paper or use a conditioning sealer. The mostuire in the topcoats can lossen the paper causing bubbles in the skim coat.

Tom

DeformedTree · « **Reply #25 on:** December 07, 2019, 12:38 PM »

Alex, sorry we couldn't help much on the actual act of plastering. In the US it's basically dead everyplace outside of episodes of "this old house". That's why I was curious what goes on over there. And since you all live in castles and many hundred year old brick farm houses, plaster makes sense. But that's also why I'd expect more people over there to know and this forum is clearly mainly Americans. If plaster is still common, I wonder if tools and methods for doing it have goes easier over time. Like a Festool Plasterex that spreads it on the wall perfectly for you.

Something that is a combination of a concrete power trowel, shaper origin, material spreader.

I agree with learning a skill when the opportunity is there. Good luck

Jiggy Joiner · « **Reply #26 on:** December 07, 2019, 01:42 PM »

Over here, the thickness of the finish coat depends on the type of plaster, and what the finish plaster is going onto.

For finishing over drywall (plasterboard) and probably most surfaces, I like to see a minimum of 3-4mm because it will cover the scrim joints, and give good coverage on the angle beads.

Finish on top of sand and cement render, or bonding coat may be a little thicker still by time it has filled any keying lines etc. Although I’ve often seen it very thin.

When skimming over old finish, we normally first coat with Gyp-bond or similar which is textured PVA. Then skim finish, if no angle beads are used, I’ve seen the finish as thin as 1mm, which often cracks.

All said and done, providing angle beads are covered, and scrim joint etc, and the overall is flat, the finish can be various thickness.
Generally though, it will be 2-4mm
I favour a good thickness to help eliminate cracking.

That really goes for other types of plaster too, for bonding plaster, on very uneven walls, the thickness before the finish goes on, could be between 3-25mm or more.
The bonding is applied to pull out dips and uneven surfaces. Quite often this type of plaster will be around 13mm before finish.

I’ve taken out brick walls where the bonding coat has been 70mm in places. In that instance personally, rather than load the wall up with thick bonding, I’d dot and dab the wall nice and plumb, then skim it.

Girl_w_Style · « **Reply #27 on:** December 19, 2019, 03:57 PM »

Not sure if u got all the info u need already but just a tid bit from a trade plaster & decorative finisher....

If your existing walls have wallpaper on them, that needs to be stripped off before any plaster work is done. Wallpaper is made in layers & when the top decorative layer delaminates from the base paper it will cause sagging...plaster has a high water content that will quickly cause this to happen.

As for the plastering- have u considered hiring out? The guys who plaster for a living can have it done in a day or less & it will be perfect...its not a hard skill to learn but mastering it is.

If your intent on doing it yourself & don’t have previous experience with a trowel I HIGHLY recommend you practice practice practice on a few sheets of primed drywall in the garage.

Alex · « **Reply #28 on:** December 19, 2019, 04:53 PM »

Hello Girl with style, welcome to the forum and thank you for your reply.

It was always my intent to do this job myself, as I want to learn how to do it. I know the basics, read the theory, watched the tutorial videos on the net, and still it is a very hard thing to do to get it right. But I'm getting there slowly but surely and I got a lot of wall space in my own house to practice on.

I want to learn it because I do a lot of jobs for people in and around the house and they often ask me if I can plaster a wall for them. I always had to say no, better hire a professional plasterer, but the last year I got the opportunity to practice a bit in my own tempo, and with my own unique appraoch I turned a big mess into a perfectly flat wall. But unfortunately not in the efficient way it is supposed to be done, not how a professional plasterer does it.

Started working in my hallway now and while I did mess up my first two walls, the next ones were quite promising. Gladly, if you mess up, you can start over again. Only the sanding with my Rotex 150 is extremely tedious and very messy, so I am trying to get to the point where I can avoid that.

I'll get there eventually, I was just hoping to maybe get some tips from people with real plastering experience.

Girl_w_Style · « **Reply #29 on:** December 19, 2019, 05:46 PM »

Ahhh gotcha!! My house is a constant lab experiment in progress too haha.

Good on u for tackling such a skill head on! The trowel handling & pressure is honestly the hardest part, as I’m sure you’ve noticed by now.

Glad to hear you’ve been making progress, its crazy how fast u start to develop your own style & rhythm when plastering...careful tho- it can be addicting! Lime plaster work is my meditation

Alex · « **Reply #30 on:** December 19, 2019, 06:01 PM »

Nah, the trowel handling is ok I guess, what I find hardest is flattening and smoothing it all with these two things (dunno their names in English):