Plastering about to go down the drain?!?

[magnusk750]

If anyone happens to have time to respond quickly, there's perhaps a greater chance of saving it.

I've taken on something beyond my skill level... I'm not an experienced plasterer. I'm plastering a chimney stack, old, built with Mexitegel, a bit unevenly laid, all the old plaster is gone. I've applied a coat of plaster and mortar C, 2 mm. So far, so good, but tonight I thought I'd finish it by fine plastering with a 1 mm fine plastering mix. It went well to apply, but now, about two hours later, when I try to smooth it with a float, it's just a mess. The edges of the float catch, the surface doesn't release, and it becomes streaky, shaggy, and ugly. I've now paused and will let it dry for another 1-2 hours and try again.

Since the surface is a bit uneven, I assume I should have used a rounded karnis instead of a float, but I don't have one and likely won't get one until possibly tomorrow. Trying to sand the edges of the float rounder but not sure if it will help.

How can I save the situation?

The fine plastering mix seems to have been a misstep. The coarser mix felt easier to handle. I tried to smooth a small section just to see if it would work, and it did. Will I be able to apply a coarser plaster over the fine plastering? Is it worth cutting grooves into it while it's soft so that a layer on top can adhere?

Will it be possible to sand the fine plastering smooth once it has cured? Use 40-grit paper in a sander and go at it? The thing is, I'm leaving for a week tomorrow afternoon, so by the time I get back, it will have stood for quite a while.

 

[cpalm]

Is the polished surface completely smooth?
I'm far from a mason, but I've never had a problem with the trowel cutting through the mortar when plastering.
I usually use one of those plastic kanitz (but without rounded edges).
As you're suggesting, it might be a timing issue, although I usually plaster after a much shorter time than 2 hours.
If it turns out badly and you can't fix it, isn't it just a matter of taking a trowel or a putty knife and scraping it down before it's completely set, and starting over?

 

[magnusk750]

Well, it's as smooth as it got after I pulled it up on the wall with skånska. The idea was to smooth it out now, but it's just getting worse. I should add that this is the second time in my life I'm plastering, last time it went, well, it didn't turn out perfect, but not this bad.

 

[sixten88]

Let it be and plaster the whole surface with gypsum mortar when you come back. A bit more expensive but much easier to get a good finish if it is to be painted.

 

[cpalm]

Well, it is as smooth as it became after I applied it to the wall with a trowel. My intention was to smooth it down now, but it's only getting worse.

OK. Perhaps I expressed myself a bit awkwardly, meant that if a flat surface is not the goal, then the float is the wrong tool.
I still think it sounds like a timing issue. Either you haven't waited long enough or you've waited too long.

 

[magnusk750]

It's not a large area, just about two square meters, so it's entirely feasible to use gypsum plaster on it. I've never used gypsum plaster before, can it be sanded?

I just went out and tried again. It went a little better now on the driest part, although it felt like there was no big margin until it was so dry that it was too late to do anything. It wasn't possible to dampen the float, as that made it sticky immediately. It feels like it's going to be a long evening where I have to stand and wait while it dries and skim as needed. Watching plaster dry is as fun as...

 

[magnusk750]

OK. Maybe I expressed myself a bit strangely, I meant that if a flat surface is not the goal, then the notched trowel is the wrong tool.
I still think it sounds like a timing problem. Either you haven't waited long enough or you've waited too long.

The goal is as flat a surface as possible, no structured plaster or the like, but it's in a workshop and I haven't had any screed rails to level the plaster with. Tried to make it as even as possible by eye. A slightly rounded karnits would probably have been better, but there's not much to do about that on a Sunday evening. I've filed the edges of the notched trowel rounder, that helped.

 

[cpalm]

Could not dampen the trowel, as it became sticky immediately. Feels like it's going to be a long evening where I have to stand and wait while it dries and scrape as needed. Watching plaster dry, as fun as...

I think you should wait a little longer. The trowel shouldn't show the slightest hint of sticking to the plaster even if the trowel is soaking wet, then it's not dry enough. Once dry enough, you have plenty of time to scrape according to my experience.

 

[kest]

Have you tried applying only 1+2 mm and it's uneven so it's thick in some places?

It's not filler. The brick absorbs the water and I assume you didn't wet the brick?
So in some places, you barely have time to apply the mortar while in other places you can scrub?

Use plaster that you can sand down if you have to apply it so thin.😓

 

[magnusk750]

I have moistened the wall, or rather the base coat thoroughly before applying the finish coat, a couple of liters of water on two square meters, but it's true that the thickness is quite uneven, not as thin as 1-2 mm, but perhaps 3-4 mm up to 15 mm. It seems to be about timing. The thinnest areas can be scraped off, but not the thicker ones.

Now I'm planning to watch TV for an hour and then go out and check the drying situation.

But, while I have knowledgeable people here: I need to secure a new cleanout door in an existing opening. What's the best way to do that? The same plaster around the flange, and a couple of nails in the joints between the bricks? It's called "mexitegel," or what is it really called, limestone brick, very hard, difficult to drill for expansion plugs.

 

[cpalm]

it is true that the thickness is quite uneven, not as thin as 1-2 mm, but maybe 3-4 mm up to 15 mm.

Aha, there's probably your problem. I think it would have been much easier if you had scraped/cut off the stockputsen and let it take up the unevenness so that the finputs didn't vary so much in thickness.

Then I need to secure a new soot hatch in an existing opening. What's the best way to do that? The same plastering mortar around the connection, and a couple of nails in the joints between the bricks? It's mexitegel, or what is it actually called, kalksandsten, very hard, difficult to drill into for expansion plugs.

Would just mortar it in. Maybe depends a bit on what the connection looks like - how much grip it gets.

 

[magnusk750]

Dare one go to bed and get up at 6 o'clock tomorrow...?

 

[cpalm]

Then it is probably guaranteed to be too late, otherwise there is something wrong with the bruket.

 

[magnusk750]

At 2 AM it was still way too soft down by the floor, so I went to bed. Up five hours later, then I could take the last pieces. There are some holes in the plaster that I'll need to fill in when I get back, but overall it looks okay.

Thanks for the help, everyone who responded!