Urgent help with rendering; what am I doing wrong?

[Bozz50]

I am going to do a plastering on the concrete block wall in the basement. It's about 35m2 of wall. It's going REALLY badly for me. I've read all the plastering tips, both from Finja and Maxit. Even tips from dinbyggare.

Below, I’ll outline what I’m doing, what’s going well, and what’s not. Hope someone can help me with tips.

1) Wet down the part of the wall that is to be plastered, it goes well

2) Mix the mortar, I think it goes well, I get a good consistency anyway

3) Take some of the mortar and mix with water to prime the wall, goes well
...and now comes the bloody part:

4) Slap on mortar to attach the guide batten (about 60cm between battens), goes okay. Half on the floor though... :-[

5) Press the mortar where the guide battens are supposed to sit. Use the long spirit level to "push" the batten. Now the hard part starts, the batten does not stick to the mortar. Spjoink and the batten falls off. Well, press it back on and try to secure it with mortar from the top. Can't say it's secure, but at least it doesn't fall off

6) Start to "smack" the mortar from the bottom up. Still half on the floor. Here I’ve also tried different methods:
6.1) Just throw on plaster up to a certain height
6.2) Apply plaster and press it with the trowel
General for point 6 is that it takes waaay too long. Before I have got the plaster 30cm up the wall, an eternity has passed. >

7) Level off the mortar along the guide battens. Guess what happens to the guide battens. Exactly; spoink, now it’s getting tough. Panic spreads. Put the battens back on provisionally.

8) Now it needs to be supplemented with more plastering again. I'm still only up to calf height, fumbling around. Slap more mortar on. Level along the battens. Nah, ARRRRGH

9) Okay, try to press the mortar with the trowel to speed up the process. However, the mortar adheres significantly worse than the mortar that is thrown on. I notice this especially when I level with the straightedge, it comes off! Despite making a sawing motion.

10) By now the priming mortar has dried and I have to use the lime brush to splash the wall

11) I have been at it for way too long and the mortar in the tub (one bag mixed at a time; Finja KC masonry and plaster mortar C) adheres even worse if possible. Now patience is gone and I have plastered 80x60 cm in 2.5 hours. :'(

As everyone understands, I must be doing something fundamentally wrong. "The average handy person can plaster...". I feel anything but handy right now. How can it be going so terribly badly?

I beg and hope someone can encourage me to try again. Right now I just want to give up.

Help!!!

 

[poiu]

Can't you nail the moldings?
That's how they did it in school construction practice.

 

[Bozz50]

Can't you nail the moldings in place?
That's what they did in school building practice anyway.

Okay, thanks for the tip. I've been considering it. But you need to have steel nails and nail them into the joints on the concrete block wall then. Then they have to be driven in completely; otherwise, it'll be difficult with the scraping... :-?

Then what? How do I know the mortar is okay? Why can't I get the mortar on properly?

 

[Magnus_Nordmark]

[quote author=poiu link=1132348259/0#1 date=1132349636]Can't you nail the moldings?
That's what they did in school's building practice.

Okay, thanks for the tip. I've been thinking about that. But you need to use steel nails and nail in the joints of the concrete block wall then. And they have to be driven in completely, otherwise, it will be tough with the leveling... :-?

Then what? How do I know the mortar is okay? Why can't I apply the mortar properly?[/quote]

I've helped plaster some walls on house foundations... A lot of mortar ends up on the floor because it splatters when you throw the mortar... It will go better once you've practiced the "snap technique" a bit... It's also important that you get a good speed on the mortar when you throw it on the wall so it bites into the irregularities.

Now, I've only plastered on leca, which is a bit easier in terms of adhesion, so I'm not familiar with whether you should use some sort of mesh reinforcement since it's concrete block.

Good luck!

 

[Bozz50]

I've been involved in plastering some walls on house foundations... A lot of mortar ends up on the floor because it splashes when you throw the mortar on... It will go better when you've practiced the "snap technique" a bit... It's also important to get some proper speed on the mortar when you throw it on the wall so it grips the uneven surfaces...

Now, I've only plastered leca, which is a bit easier from an adhesion perspective, so I'm not familiar with whether you should have some kind of net reinforcement because it's concrete blocks.

Good luck!

I understand that it's training that's required. I'm very stubborn but might get a bit too angry. Since it can never turn out well if I make some general mistake (wrong technique, tools, approach, etc.), there will be more questions:

1) What trowel is suitable for snapping the mortar, size, type...? There's a triangular model with "curved" corners if you know what I mean, could that be something?
2) Should you press the mortar on after each hit, or should you just let all the mortar accumulate until it's time to scrape off with the levelling boards?

I've tried both variants on point 2. If you press it on, it becomes harder to scrape off. If you don't press it on, you don't get mortar everywhere, plus the blob you snap on is as big as a wet snowball on a garage door, sticking out from the wall. Also, it's hard to aim (that will probably come with practice). It often ends up with 5 blobs in the same spot >

As for adhesion, I don't really think that's a problem since the concrete block is quite rough after I used a scarifier on it.

I need all the help I can get, so come on, more, more, more! I have 30 bags in the garage that need to go up on the wall!

 

[krillek]

Can't you attach the moldings with nail plugs? Then you can drive them in level with the molding so it's easy to remove. When you're done, you just unscrew the nail plugs and remove the moldings.

 

[poiu]

Personal experiences from plastering a brick wall/former chimney where adjoining walls served as guides.

Wet the bricks thoroughly, otherwise the mortar dries out (I put down the plastering brush and used the water hose), but don't try to apply the mortar on a wet surface. The surface needs to dry first, otherwise it's almost impossible to get the mortar to stick.
Applying the mortar evenly = practice. In the beginning, you apply everything in the same spot.
Pressing the mortar in makes it stick poorly. Pressing on mortar perhaps works best on leca and for patching on plaster mesh.
Don't take too much mortar on the trowel, better too little than too much.
The mortar should not be thrown on, it should be "flicked" on. And if I remember correctly, it shouldn't hit at 90 degrees but a bit upwards.
The consistency of the mortar is important; moderate is best (how *** do you describe the consistency of mortar).

When I started that project, I was enthusiastic, but halfway through I was on the verge of tears, and that was for 2.5 m2. Though when I finally started getting the hang of it, I was naturally a bit happier.

 

[hempularen]

Got help from a relative who was a mason 20 years ago, to plaster a part of our chimney stack this summer.

I was very surprised by the consistency he wanted for the mortar; he wanted it so loose that it almost ran off the trowel. It worked great. I think a maximum of 10% ended up on the floor. The first layer was even looser.

He flicked it on at an upward angle just as mentioned here earlier.

 

[Bricky]

The tracks need to be wetted first, otherwise, they bend when they get damp. Ideally, they should be wetted, dried, and wetted again a few times. Then they will be great, and you can take them to the next job. You should apply the mortar until it's time to stock off. If you have applied it so it's covered, it's fine to use a trowel or a float. The most important thing is that it is really applied with the right snap and force; otherwise, it won't last very long. Plastering, I think, is one of the few things that might not be so good for DIY enthusiasts to tackle. It takes some practice before you get the hang of the steps. But you're starting to get that practice now. There shouldn't be much falling on the floor if you do it right, and the little that does can be reused when you finish the last touches, like filling up where the tracks have been. Good luck!

 

[gaia]

when you apply a thin coat, this thin mortar should become hard/firm (but not dry) before you move on to the next step... otherwise everything slides down and might come loose more easily? I have mostly worked with lime mortar without the thin layering and with only lime in the mortar, I had more time to smooth and fine-tune the surface. No max time of 30 min or so (ready-mixed lime mortar can be covered until the next day ) and it was less stressful and better suited for beginners . I've just pressed the render on and smoothed it out when it was firm enough and still moldable with a quite damp sponge float. I have no experience with KC mortar but I'm just guessing, so bear with my advice... Maybe you are waiting too short a time with your KC render between the different steps? Try to extend the waiting times a bit :-/. You can apply as long as the render hasn't dried completely... give it some time to be somewhat cured/firm on the wall... :-/ And as poiu mentions... the wall surface shouldn't be GLOSSY with running water droplets but just wet-dark-damp-matt... yeah, how do you describe this just-right state? Start on a wall that will be the least visible. After about 1-2 meters of wall, you're a pro, and the result is much better to look at and admire . And take it easy, it'll work out gaia

 

[cpalm]

The consistency of the mortar is important, just right is best (how *** do you describe mortar consistency).

I usually go by the sound. If it has the right consistency, you get a proper thud! when you tamp it, you can almost hear how well it adheres. If the consistency is wrong or too quick, it barely makes any noise. When mixing, you can scoop some mortar and tap it in the bucket to get a pretty good idea of how it will behave on the wall.

And as gaia writes, wait properly before you scrape off the mortar, and even longer before you smooth it. 15-30 minutes between might be just right.

You probably have to put up with half of it ending up on the floor before you get the knack and aim. It doesn't really matter since the mortar only costs 60:- per bag...

/C

 

[Bozz50]

I usually go by the sound. If it's the right consistency, you get a proper thud!
...
And as gaia writes, wait properly before you remove the mix, and even longer before you smooth it out. 15-30 minutes in between can be just right.
...
Unfortunately, you might have to put up with half of it ending up on the floor until you get the hang of it and your aim. It's not too bad since the mix only costs 60:- per bag...

/C

I can probably guess that maybe I've used a bit dry mix. I don't really have the thud, more of a "spffrrt."

Great with concrete hands-on tips, with time indications and everything! The 15-30 minute time is tough to maintain if you can't apply the mix quickly enough...

Well, actually, you might see it as a course in plastering where the course fee consists of 50-kronor bags of mix. I'm prepared to keep at it like a determined stubborn person. Luckily, my wife isn't as stressed as I am about getting the laundry room up and running.

when you are doing the thin grounding, this thin mix should be hard/firm (but not dry) before you move to the next step... otherwise everything slides down and may loosen more easily?

I take the garden hose with a fine spray nozzle and wet down the wall, and then when I've mixed the mix, I take a spade of it and make porridge for the thin grounding, then brush it on with the lime brush, by then the wall has absorbed the water already.

After the thin grounding, those damn guide strips go up. After that, the thin grounding has probably set just right, I think.

The strips need to be soaked first, otherwise, they bend when they get moist. Ideally, they should be soaked, dried, and soaked again a few times. Then they're great and can be used for the next job. You should apply the mix until it's time to screed off. If you've applied so that it's covered, it's fine to use the trowel or the float board.

Aha, so it's easier to apply more mix once the wall is covered with a "slapped on" layer? Are my strips perhaps too thin? I'm aiming for a thickness of about 6-10 mm. The wall varies by +-5mm and tiles need to be set, so it must be straight, otherwise, it'll look bad. Next job for me will be the piece of wall next to it...

And take it easy, it'll work out
gaia

Thanks..., rest day today, tomorrow I'll try again..., hope I get the hang of it then.

//Boussard

 

[Bozz50]

Hello again!

If several people read the thread and have the same/similar problems/questions, I'll share my experiences/progress below (ending with 2 questions).

Today went infinitely better. All the problems can be traced to poorly mixed/dry mortar (and maybe a bit of low blood sugar... ).

Today, when I mixed the mortar, I added a bit more water. I also mixed for a longer time and could see that the mortar was completely different. I could also hear the thump when I hit the mortar in the tub.

I took a couple of decking screws on the guides. But since the mortar became sticky/fluffy (like chocolate mousse but heavier) and adhered so much better, that part worked much better.

Now I really only have two questions left (and 28 bags to practice on... ):

-This is a concrete block wall in the basement, it's not directly warm and dry in the air, should the plaster be re-watered? For how long?

-I don't quite know when I should go over and level it. Should it be hardened, or can you do it fairly immediately? It seems a bit risky to smooth too early as you can almost see the plaster move on the wall. Or is that right? If it's dried, I don't feel it takes anything. Should you wet the plaster before leveling?

 

[cpalm]

Fun to hear it's going better!

-This is a concrete block wall in the basement, it's not exactly warm and dry in the air, should one rewater the plaster? How long if so?

It should not be necessary.

-I'm not quite sure when I should go on and trowel the surface. Should it be hardened, or can it be done fairly quickly? It seems a bit risky to start too early since you can almost see the plaster moving on the wall. Or is that correct? If it has dried, I feel it doesn't take at all. Should you wet the plaster before troweling?

A basic rule is that no plaster goo should stick to the trowel, at least not too much, and there shouldn't be small air bubbles forming on the plaster surface - then it's still too moist. But if you wait too long, as mentioned, it won't "take"; the mix should still be elastic, and if it "moves" slightly, that's normal... I usually do a trial run when I think it looks good. 20-30 minutes after you've trimmed the plaster is usually suitable, but it totally depends on how thickly you apply it and how much water you have in the mix. If it doesn't feel right, just wait a little longer.

Wash off and rinse the trowel thoroughly and often in the water bucket using a sponge, but don't add more water than that. What happens during troweling is that you "pump" up the binder to the surface so that it becomes a bit harder. The key is to trowel just the right amount. Too much water and/or too intense troweling will pull too much binder to the surface, weakening the core of the plaster. Too little, and you won't achieve a nice surface. Trowel until you think the surface looks good (which usually means about 3-4 "passes" on each part of the surface) and no more.

P.s. I saw you hadn’t received an answer on what type of trowel you should use to apply the plaster. I use a large square trowel with an S-shaped handle.

/C

 

[saturnus]

Isn't it easier to apply the mortar with a skurbrette on the wall, rather than throwing it up with a trowel? The wall should be somewhat dry on the surface so it "grabs" the mortar.