Question about using plaster.

[AlexThePalex]

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

[attachimg=1]

Knauf - Rotband: thickness 5 - 30 mm

[attachimg=2]

Knauf - MP75: thickness 10 mm and up

[attachimg=3]

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]

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

 

[AlexThePalex]

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]

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

 

[AlexThePalex]

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]

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.

[attachimg=1]

 

[six-point socket II]

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]

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

 

[AlexThePalex]

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

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?  [smile]

 

[Cheese]

Thanks for the video Oliver.  [smile]  I've never done a Q4 skim coat with a roller before. Man that sure simplifies the whole process.

 

[tjbnwi]

[member=44099]Cheese[/member],

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]

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]

[member=44099]Cheese[/member],
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.  [big grin]  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]

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.  [cool]

 

[tjbnwi]

[member=44099]Cheese[/member],
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.  [big grin]  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]

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]

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.  [cool]

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  [big grin]

 

[Cheese]

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]

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...-primer-surfacer-tuffhide-submittal-J1613.pdf

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

Tom

 

[AlexThePalex]

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.

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.

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.

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.