Member
· Västra Götaland
· 145 posts
Hello good people. I have an approximately 11 cm thick interior wall consisting of some form of lightweight concrete-like blocks (the building is from 1945), which I recently needed to extend by exactly 60 cm.
I then chose to continue building this wall with 9x19x59 cm lecablocks "lying on their height" (meaning 9 cm thick, 19 cm high, and 59 cm long), and the plan is to apply 1 cm plaster on each side so it ends up with the same 11 cm thickness as the existing wall.
This was about a month ago, so everything should have reached full strength by now, but when I feel the mortar in the joints, it seems much "weaker" than I'm used to. For example, I can scrape it away with the edge of a trowel without significant force. Is it supposed to be like this?
I built a brick wall (also indoors) a few months earlier, and the mortar in this is rock hard. But this was then brick instead of leca, and the joints are probably closer to 20 mm instead of 5 mm.
The only thing I can think of is that I mixed third to half bags of mortar at a time and that I might have made the mix a bit too loose, could this have ruined the mix? However, I can't remember doing it significantly differently for the brick wall.
I used Weber Gullex M 2.5 for both walls if that makes any difference.
I then chose to continue building this wall with 9x19x59 cm lecablocks "lying on their height" (meaning 9 cm thick, 19 cm high, and 59 cm long), and the plan is to apply 1 cm plaster on each side so it ends up with the same 11 cm thickness as the existing wall.
This was about a month ago, so everything should have reached full strength by now, but when I feel the mortar in the joints, it seems much "weaker" than I'm used to. For example, I can scrape it away with the edge of a trowel without significant force. Is it supposed to be like this?
I built a brick wall (also indoors) a few months earlier, and the mortar in this is rock hard. But this was then brick instead of leca, and the joints are probably closer to 20 mm instead of 5 mm.
The only thing I can think of is that I mixed third to half bags of mortar at a time and that I might have made the mix a bit too loose, could this have ruined the mix? However, I can't remember doing it significantly differently for the brick wall.
I used Weber Gullex M 2.5 for both walls if that makes any difference.
Member
· Västra Götaland
· 145 posts
It's just that I used a little too much water that I'm worried about. I seem to remember mixing it to a consistency like coarse putty (I could "plaster" it up as a join on an existing wall). But this might be a little loose if you compare it to "wet potting soil" that I've read some recommend?
I don't think there's a risk of freezing since it's indoors.
I don't think there's a risk of freezing since it's indoors.
Too much water, I don't think so. If it was possible to use it for masonry, then the mixture couldn't have been that bad. I rather think it has been too warm and dry in the air. The mortar has therefore dried too quickly. Perhaps you also used warm water for the mortar, which is not good.
Member
· Västra Götaland
· 145 posts
Good input there about hot water for the mortar. I seem to remember that I just "turned on the tap" and thus could have gotten various temperatures on the water, but both the dry mortar, the leca blocks, and the adjacent wall were at room temperature, so it shouldn't have affected things too much? However, it was the middle of winter (i.e., very dry air).
One thing I noticed that differed between leca and brick was that the leca absorbed water much less than the brick did; even the next day, the joints between the leca blocks were still dark (i.e., moist), and it took another day or two before the joints became light gray. For the brick wall, this only took a few hours. But this should be, on the contrary, a good thing for the leca wall compared to the brick wall?
One thing I noticed that differed between leca and brick was that the leca absorbed water much less than the brick did; even the next day, the joints between the leca blocks were still dark (i.e., moist), and it took another day or two before the joints became light gray. For the brick wall, this only took a few hours. But this should be, on the contrary, a good thing for the leca wall compared to the brick wall?
Member
· Västra Götaland
· 145 posts
Let's see. Here is the difference; the brick wall followed by the lecavägg.
[video=youtube;Um5uAlHP4HM]https://www.youtube.com/watch?v=Um5uAlHP4HM[/video]
[video=youtube;93wP2RnQ6eo]https://www.youtube.com/watch?v=93wP2RnQ6eo[/video]
Worth mentioning is that the joint in the lecavägg is much thinner than it looks. But I "spacklade" the joint evenly with mortar afterwards.
[video=youtube;Um5uAlHP4HM]https://www.youtube.com/watch?v=Um5uAlHP4HM[/video]
[video=youtube;93wP2RnQ6eo]https://www.youtube.com/watch?v=93wP2RnQ6eo[/video]
Worth mentioning is that the joint in the lecavägg is much thinner than it looks. But I "spacklade" the joint evenly with mortar afterwards.
Member
· Västra Götaland
· 145 posts
Thanks for all the input! I'm not worried about its durability for polishing, rather I'm concerned that the joint might break or crack if someone were to fall into the wall in the future or something similar. Although the existing wall has been standing there for 70 years without issues, my concern for the new wall is based on:
There's only one "row" of lecablock (they are not staggered like the blocks in the existing wall are).
The wall is only 9 cm thick (this is, in fact, the same as before).
The wall "ends" after this new wall; there is no adjoining wall or anything else that provides stability (previously, there was a corner to a wall here that I have now torn down).
The wall is very "rigid" compared to, for example, a plastered stud wall; in short, there isn't much that can flex under potential stress, so it will likely crack and break instead.
Is there any basis for this concern?
There's only one "row" of lecablock (they are not staggered like the blocks in the existing wall are).
The wall is only 9 cm thick (this is, in fact, the same as before).
The wall "ends" after this new wall; there is no adjoining wall or anything else that provides stability (previously, there was a corner to a wall here that I have now torn down).
The wall is very "rigid" compared to, for example, a plastered stud wall; in short, there isn't much that can flex under potential stress, so it will likely crack and break instead.
Is there any basis for this concern?
I don't know how you did it, but in such an extension, you usually insert one or two rebar (6mm) in every other or third course. The bars are then drilled into the joints or stones of the old wall. If you have done this, it will most likely hold.
Member
· Västra Götaland
· 145 posts
I did it this way with rebar when I previously built the aforementioned brick wall (which then joined an adjoining brick wall).
But this time, the lightweight concrete-like* blocks in the existing wall were so "soft" and held together so poorly that I didn't feel it was worth trying to anchor rebar in them. Instead, the idea became/is to plaster a mesh (regular welded plaster mesh 19x19x1.05 mm) on both sides of the new wall and also chip off the plaster and overlap the mesh about a decimeter or so into the existing wall. This should help make the wall hold together better?
*The blocks look roughly like Lecablocks, but instead of Leca balls, they contain 5-15 mm large "flakes" of brick.
But this time, the lightweight concrete-like* blocks in the existing wall were so "soft" and held together so poorly that I didn't feel it was worth trying to anchor rebar in them. Instead, the idea became/is to plaster a mesh (regular welded plaster mesh 19x19x1.05 mm) on both sides of the new wall and also chip off the plaster and overlap the mesh about a decimeter or so into the existing wall. This should help make the wall hold together better?
*The blocks look roughly like Lecablocks, but instead of Leca balls, they contain 5-15 mm large "flakes" of brick.
Member
· Västra Götaland
· 145 posts
I think I have figured out the problem.
First, a bit of background. I tried mixing a couple of different mortar blends; one according to the instructions, one with very little water, one with a lot of water (more than I have ever used before), and one with a lot and also warm water. Then I let these mixtures cure for two weeks, but afterward, I couldn't notice any significant difference in hardness/strength between them. So no help there.
But when I recently had to add another section to a wall, I did one thing differently; I made sure to rewater the joints plentifully a couple of times a day for 3-4 days afterward. A few weeks later, these joints were noticeably "stronger" than the previous lecablock wall (more like the brick wall).
The next thing I tested was rewatering the joints on the previous lecablock wall as well (even though it was three months since it was built); this if the mortar had dried too quickly, and the curing process had stopped. And after a week of abundant watering, these joints also became noticeably stronger.
Lastly, I can also add that with the brick wall, I soaked each brick for half an hour or so before building with it. This (plus the thicker joint) presumably contributed to these joints not drying out in the same way.
End of story.
First, a bit of background. I tried mixing a couple of different mortar blends; one according to the instructions, one with very little water, one with a lot of water (more than I have ever used before), and one with a lot and also warm water. Then I let these mixtures cure for two weeks, but afterward, I couldn't notice any significant difference in hardness/strength between them. So no help there.
But when I recently had to add another section to a wall, I did one thing differently; I made sure to rewater the joints plentifully a couple of times a day for 3-4 days afterward. A few weeks later, these joints were noticeably "stronger" than the previous lecablock wall (more like the brick wall).
The next thing I tested was rewatering the joints on the previous lecablock wall as well (even though it was three months since it was built); this if the mortar had dried too quickly, and the curing process had stopped. And after a week of abundant watering, these joints also became noticeably stronger.
Lastly, I can also add that with the brick wall, I soaked each brick for half an hour or so before building with it. This (plus the thicker joint) presumably contributed to these joints not drying out in the same way.
End of story.
Thanks for the info.
I laid my first wall ever by myself with yesterday. Lecablock. I'm pretty sure I mixed a too loose mixture of mortar b. It was a little thicker than porridge... But I thought, damn, I have to try anyway if I'm going to learn something.
So today I'll go down and water the joint a little!!
Thanks for the info and for also doing a proper investigation.
I laid my first wall ever by myself with yesterday. Lecablock. I'm pretty sure I mixed a too loose mixture of mortar b. It was a little thicker than porridge... But I thought, damn, I have to try anyway if I'm going to learn something.
So today I'll go down and water the joint a little!!
Thanks for the info and for also doing a proper investigation.