Hello,
I mixed gypsum plaster that was supposed to hold for 8 minutes, but it set into a gypsum block after 8 seconds. What did I do wrong?
I have a brick wall in the storage room that has gypsum plaster as a render. Now I've removed the skirting to lay a new floor and need to render the bottom edge. Bought 5 kg of gypsum plaster to be mixed with 0.5 l per kg, that is, 4.5 l for the entire bag. But I only used about 1/3 and whisked it into 1.5 l of water. Whisked it together, and everything looked fine, scraped down from the sides, and put the whisk in water. I was about to take the bucket and start, but saw that everything had set after just a few seconds. What did I do wrong? Tried again with the remaining 2/3 with the same result, sigh...
I mixed gypsum plaster that was supposed to hold for 8 minutes, but it set into a gypsum block after 8 seconds. What did I do wrong?
I have a brick wall in the storage room that has gypsum plaster as a render. Now I've removed the skirting to lay a new floor and need to render the bottom edge. Bought 5 kg of gypsum plaster to be mixed with 0.5 l per kg, that is, 4.5 l for the entire bag. But I only used about 1/3 and whisked it into 1.5 l of water. Whisked it together, and everything looked fine, scraped down from the sides, and put the whisk in water. I was about to take the bucket and start, but saw that everything had set after just a few seconds. What did I do wrong? Tried again with the remaining 2/3 with the same result, sigh...
Temperature? If the water is warm, it goes faster; if it's cold, it goes slower. The tricky part is that it's an exothermic reaction, so it generates heat itself. If you start with water that's too hot, it can go very fast.
Thank you for the interesting response. I live in Mojácar, Almería, Spain and it's now 35 degrees and the water is probably almost the same because we never turn on hot water when we shower here between May-October since it's at a comfortable shower temperature. Do you think that's the problem, should I use water that has been in the refrigerator instead?
There you have your problem. Look for cold water.B Birre said:
Wonderful tip, you are a living god when it comes to plaster. Yesterday, there was a mess with 5 kg of plaster that set immediately, my wife was mad because I took her liter measure, and I was upset over the failed project. But we reconciled over some good wine, food, and, well, as one usually reconciles after that. Today, a new attempt with water in the fridge and a new batch of plaster. Yesterday, I was lazy and stopped by the paint store and bought 5 kg for 9 euros (felt expensive, but...) This time, I went to the construction market and got a 20 kg bag for 2 euros. And a big difference in the product, I wonder if the other could have been old? First, I was supposed to wet the edge that was to be plastered, and then the nozzle came off, so I got soaked before I could stop the flow, just had to scoop out the water and try again. But a new attempt at mixing with cold water and it worked like a charm. Except that my cheap junk of a drill can't maintain a variable speed, so sometimes it went full speed, and I got completely sprayed with plaster. But a 50/50 mix according to instructions turned into a porridge, impossible to get onto the brick wall, but while I was standing there pondering this, I saw it setting quickly, so it was important to be fast, but it worked fine. I made a small batch again and got sprayed again, and then the Spanish neighbor's daughters came from the beach and stopped when they saw me standing there covered in plaster and with torn briefs, yes my work shorts went into the wash after yesterday's disaster, so I found a pair of briefs my wife wanted me to throw away anyway, and they giggled and asked what fun I was up to, I just hmhm mumbled, and then I heard them shout "mom, do you know what," then I didn't want to hear more. But it worked well with the plaster even though it was important to work quickly as the mix set super fast. Also typical, later when I went to the neighborhood trash bin to scrape out leftover plaster from the bucket, I heard a car brake and saw out of the corner of my eye the Guardia Civil stopping to look at the old man in torn briefs covered in plaster standing and hacking in a bucket, but they probably didn't want to know more about the misery than they already saw, so they moved on. It wouldn't surprise me if they took a photo to show colleagues about today’s...
Sounds like you bought pure plaster instead of plaster mix. That's a completely different thing.B Birre said:
Hi cpalm, Stefan, okay, maybe that explains why the building market's bag worked so well. Here, they use gypsum plaster a lot because it withstands heat and is somewhat elastic. But I still mixed the paint shop's mortar according to the instructions, and it set in a few seconds, so something must have been wrong with it. Now I've discovered with the bag's mortar that it's important to mix small portions all the time because it's 35 plus in the shade. I've worked with mortar, cement, plaster, adhesive, grout, and all that before, but never with gypsum plaster during my time in Sweden. I'll check with the Spanish construction guys I know here about what happened. And if it could be, as you say, that they sold a completely different product than what I was looking for at the paint shop. I speak Spanish, but something could have been communicated wrong, as usual, so I'll go in there and check with them. Thanks a lot for the tip, Stefan.
Yes, gypsum mortar behaves in many ways differently than lime and cement-based mortars if you are used to those. But it's hard to mistake the difference between pure gypsum and gypsum mortar (gypsum + sand). And the price, packaging size, and place of purchase also speak for it.