When the mortar or concrete has been mixed, you have about an hour according to the bag to use the mixed mortar.
We had a bricklayer helping us build a wall of natural stone, and he used the mortar two to three hours after he mixed it and claimed it was not a problem. He also said that you can mix in more water if it becomes too stiff to work with when the mortar has been standing for a while.
Since this sounds very strange to me and contradicts the manufacturers' recommendations, I thought I would ask what happens to the mortar/concrete if you continue to use it after the recommended time? And what happens if you mix more water into the mortar when it becomes too stiff to work with, i.e., starts to harden?
We had a bricklayer helping us build a wall of natural stone, and he used the mortar two to three hours after he mixed it and claimed it was not a problem. He also said that you can mix in more water if it becomes too stiff to work with when the mortar has been standing for a while.
Since this sounds very strange to me and contradicts the manufacturers' recommendations, I thought I would ask what happens to the mortar/concrete if you continue to use it after the recommended time? And what happens if you mix more water into the mortar when it becomes too stiff to work with, i.e., starts to harden?
How quickly it burns depends a lot on how hot it is where you are working.
OK, assuming a temperature of 20 degrees for example.Åsa Lund said:
But what I'm interested in trying to understand is what happens to the concrete/mortar in terms of properties if you exceed the recommended time by the manufacturer for how long you can use the pre-mixed concrete/mortar? For example, does the strength deteriorate linearly/exponentially after this hour recommended by the manufacturer? Does the adhesive ability change if you're building a wall and using a pre-mixed mortar that's been sitting for three hours after mixing, etc.
Then it has already solidified on its own and doesn't adhere to anything else.
No, that's not correct. It is "possible" to use mortar that has been sitting for a few hours, but I'm wondering about what happens physically with the mortar and how this affects the product properties over time.
You should never add more water, I believe it usually says so explicitly in the instructions.
I would say you have a couple of hours with mortar. But it depends a lot on the temperature. If it's 25C outside, it goes quickly, 1h? If it's 10C outside, you definitely have more time. I've occasionally mixed some "older" mortar into a newly mixed batch, but the main rule is that you shouldn't mix more than you will use within a few hours.
I would say you have a couple of hours with mortar. But it depends a lot on the temperature. If it's 25C outside, it goes quickly, 1h? If it's 10C outside, you definitely have more time. I've occasionally mixed some "older" mortar into a newly mixed batch, but the main rule is that you shouldn't mix more than you will use within a few hours.
Doesn't it also have a bit to do with whether the mill is in motion? I was thinking about how concrete mixers work with a rotating drum.
Interesting question! Maybe there's someone on the forum who can give a comprehensive overview of what happens with the concrete/mortar under different conditions, time, temperature, whether you keep it in motion, etc., and how these affect the properties of the mortar/concrete? @Locke ?snuttjulle said:
According to experts, you should definitely not add more water. Concrete does not harden by drying, but through a chemical process where the water reacts with the lime. The fact that the mortar becomes harder to work with after a couple of hours is not because the water has evaporated, but because the chemical process has started. If you have too much water, whether from the start or if you add it gradually, the concrete's strength decreases (read more about the vct number here).
That being said, it is not necessarily a problem in your particular case. If you mix a little splash of water into the last batch, it will be slightly worse, but a wall above ground is rarely exposed to significant forces, so it doesn't really matter if the mortar holds the highest strength class or not.
That being said, it is not necessarily a problem in your particular case. If you mix a little splash of water into the last batch, it will be slightly worse, but a wall above ground is rarely exposed to significant forces, so it doesn't really matter if the mortar holds the highest strength class or not.
Best answer
Having worked for over 40 years as a mason, I can say this.
Concrete - which is not mortar! should preferably not be watered down. If you do, it will become weaker, but it depends on how far along the curing process is. Generally, concrete consists of cement, sand, and stone. If it's from a concrete station, there's more to consider in the concrete, like water-reducing agents, fast-setting, retarders, hot water, etc. Concrete is only used for casting, not for masonry or plastering!
Mortar - can be roughly divided into: 1. Masonry mortar 2. Plaster mortar 3. Putty mortar. 4, Others.
Usually consists of various mixtures of lime, cement, but there are pure lime mortars and pure cement-based ones. And then sand in different fractions. There are also specialty mortars with some other additions.
The strength of the mortar is shown with A - strongest, then B, and then C which is the weakest. There are even weaker mortars, but that's nothing the DIY-er needs to think about. It's important that the strength does not exceed what you are using it for.
For example, I repaired an over 200-year-old plaster with a recipe of mortar equivalent to approximately G!
Why? Because the plaster leaches out with rain and time and becomes weaker. If you use a too strong mortar, it will tear apart the old backing = more damage.
How strength and adhesion change over the usage time. It's hard to explain as it varies between the different mortar classes, so there is no general answer. However, no masonry or plaster mortar should dry (cure) too quickly since crystals that hold the mortar together with other materials form during the drying time. Plaster is something that should preferably be misted with water the day after, (depending on the drying) to increase the time for crystal formation and also wear resistance.
The temperature determines how long you can use the mortar without deterioration, that's correct.
But if we say it's 20 degrees, you can water up masonry mortar once in the wheelbarrow, if you can stir it up with the trowel. But if you have to chop with the trowel = hard mortar, then it's less ideal. Otherwise, up to 3 hours of open time (depending on temp) is normal for most masonry mortars. There are exceptions, but then it's more specialized mortar.
Plaster mortar - similar to masonry mortar, maximum 1 watering but a little shorter open time.
Putty mortar - like Ardex A46 and similar. Follow what it says on the packaging for best results.
Then it is possible to plaster with masonry mortar and build with plaster mortar, but it doesn't turn out quite as well as with the right type of mortar.
Concrete - which is not mortar! should preferably not be watered down. If you do, it will become weaker, but it depends on how far along the curing process is. Generally, concrete consists of cement, sand, and stone. If it's from a concrete station, there's more to consider in the concrete, like water-reducing agents, fast-setting, retarders, hot water, etc. Concrete is only used for casting, not for masonry or plastering!
Mortar - can be roughly divided into: 1. Masonry mortar 2. Plaster mortar 3. Putty mortar. 4, Others.
Usually consists of various mixtures of lime, cement, but there are pure lime mortars and pure cement-based ones. And then sand in different fractions. There are also specialty mortars with some other additions.
The strength of the mortar is shown with A - strongest, then B, and then C which is the weakest. There are even weaker mortars, but that's nothing the DIY-er needs to think about. It's important that the strength does not exceed what you are using it for.
For example, I repaired an over 200-year-old plaster with a recipe of mortar equivalent to approximately G!
Why? Because the plaster leaches out with rain and time and becomes weaker. If you use a too strong mortar, it will tear apart the old backing = more damage.
How strength and adhesion change over the usage time. It's hard to explain as it varies between the different mortar classes, so there is no general answer. However, no masonry or plaster mortar should dry (cure) too quickly since crystals that hold the mortar together with other materials form during the drying time. Plaster is something that should preferably be misted with water the day after, (depending on the drying) to increase the time for crystal formation and also wear resistance.
The temperature determines how long you can use the mortar without deterioration, that's correct.
But if we say it's 20 degrees, you can water up masonry mortar once in the wheelbarrow, if you can stir it up with the trowel. But if you have to chop with the trowel = hard mortar, then it's less ideal. Otherwise, up to 3 hours of open time (depending on temp) is normal for most masonry mortars. There are exceptions, but then it's more specialized mortar.
Plaster mortar - similar to masonry mortar, maximum 1 watering but a little shorter open time.
Putty mortar - like Ardex A46 and similar. Follow what it says on the packaging for best results.
Then it is possible to plaster with masonry mortar and build with plaster mortar, but it doesn't turn out quite as well as with the right type of mortar.