Gypsum plaster cracks while drying

[paulssona]

Hello everyone,
Completely new to the forum and have been searching around for issues with plaster. I find Swedish channels (even producers like Finja etc.) are terrible at providing information on handling plaster. According to producers, it's the best thing since sliced bread.

I have just had to fill in proper holes left by a lazy carpenter. I followed the recommendations to keep the thickness within 50mm and did thorough prep work with primer, etc.

The problem is that the larger joints are now on day 2 of drying time (2-3 hours regardless of thickness, my r-v, Finja concrete) and they have started to crack. Maybe the weight of the plaster affects the frame and presses on it? But it is supported behind and there is plenty of other attachment surfaces from old reeds (the house is from 1937).

1. How the heck do I save this (see picture)? I will need to do another round to smooth out smaller uneven areas (the plaster was surprisingly easy to work with).
2. What are your thoughts on plaster as a filling material and what are your insights that the producers didn't want to convey?

Link to the plaster I’m using: https://www.hornbach.se/p/gipsputs-baumit-25kg/7196557/

Have a great day!
Andreas

 

[Trafikverket1]

Why it cracks, I can't answer, but are you sure it's really gypsum plaster you're using? It looks more like some kind of mortar. My experience with gypsum plaster is very positive, I've never encountered cracks like the ones in the pictures you posted. I've repaired large holes with gypsum plaster on old plastered walls without them sinking or cracking.

 

[paulssona]

Why it cracks, I can't answer, but are you really using gypsum plaster? Looks more like some kind of mortar. My experience with gypsum plaster is very positive, I have never encountered cracks like the ones in the pictures you posted. I have repaired large holes with gypsum plaster on old plastered walls without them sinking or cracking.

Thanks for your answer. This is the material I am using: https://www.hornbach.se/p/gipsputs-baumit-25kg/7196557/

 

[Trafikverket1]

I had tried sanding and then leveling off with https://www.hornbach.se/p/gipsspackel-casco-wallfiller-3kg/10140300/

Used Casco with good results. Not as long working time, so don't mix too much.

 

[paulssona]

I would have tried sanding and then evening out with [link]

I've used Casco with good results. Not as long working time so don't mix too much.

Thanks! Will have to wait until the stuff decides to dry, then I'll sand down and even out, and then glue the cracks with the wallfiller you sent.

 

[Trafikverket1]

Have tested something similar to what you linked (might have been the same now that I think about it) and it wasn't at all what I thought gypsum plaster should be. It was very grainy and the surface was not smooth at all like other gypsum plasters I've used, felt more like sandpaper. It also sounds strange that it hasn't dried, gypsum plaster usually dries very quickly.

 

[hapazard]

A tip is to fill in microlit when you smooth out. Apply the filler, press in microlit with the spatula, and cover with another thin layer.

 

[MrJay]

So these are rotbands you bought and you write yourself "within 50mm" even though the manufacturer specifies max 15mm:
https://www.baumit-selbermachen.de/mauer-verputzen/gipshaftputz-rot-30-kg_pid_3_8540.html

 

[Ludde Jakobsson]

Was on the same line as previously wrote. Too thick a layer at the same time. Let it dry and add another round.

 

[hapazard]

So this is rotband you bought and you yourself write “within 50mm” even though the manufacturer specifies max 15mm:
[link]

Mm, additionally: minimum thickness 10mm. So it's not surprising that it's cracking here...

 

[paulssona]

So this is Rotband you've purchased, and you mentioned "within 50mm" despite the manufacturer specifying a maximum of 15mm: [link]

I just noticed that Hornbach's German site listed the layer thickness, but the Swedish one didn't. I was following general gypsum plaster recommendations. Thanks for the information!

A

 

[paulssona]

A tip is to embed microlit when you are evening out. Apply the filler, press in the microlit with the spatula, and then apply a thin layer on top.

Thanks for the tip! I'll keep that in mind once it's dried...

 

[paulssona]

Have tested something similar to what you linked (it may have been the same when I think about it) and it was not at all what I thought gypsum plaster should be. It was very gritty, and the surface was not at all smooth like other gypsum plasters I've used, felt more like sandpaper. It also sounds strange that it hasn't dried; gypsum plaster usually dries very quickly.

Yes, you are absolutely right because it felt much grittier than it was described. But as someone further down wrote, it is a different form of gypsum plaster with significantly narrower tolerances. Well, everyday you learn.

 

[paulssona]

Thank you for all the answers!

What would you recommend for gypsum plaster that is actually gypsum plaster? I have some work left to do and might as well use the real stuff then.

 

[MickeTyr]

Thanks for all the answers!

What would you recommend for gypsum plaster that is actually gypsum plaster? I have some work left and might as well use the real stuff then.

Gypsum plaster is grainy and tricky. I would recommend gypsum mortar or Arden for similar jobs... unless you specifically want that grainy texture, that is.