Hello,
I have a somewhat damaged basement slab with some cracks and a slight "bump" in the floor around a drain. However, it doesn't seem to be on the verge of collapsing in the short term, and all the cracks appear reliably old, without any level changes in the floor. I think it's mostly a result of traces from breaking up and replacing the drainage pipe in the floor.
Now I'm planning to place a tower with a washing machine and dryer near the floor drain. Since it slopes about 4-6 cm/m, and given the state of the floor, I decided to cast a slab about 65 x 65 cm under the machines. I wanted to keep it limited so it wouldn't turn into a full-scale floor renovation. It was also my first concrete casting, and I wanted to start with something simple. Therefore, I laid thin plastic on the floor and cast a reinforced slab with a thickness of about 3-5 cm on top of the plastic.
The slab turned out excellent. Since it's cast in place, it fits perfectly into the small irregularities in the floor underneath. The basement floor is oiled with Jotun concrete oil. The slab got a coat of oil on the bottom (not on the top yet, it should probably cure a bit more), and the floor underneath was oiled. Then I placed the newly oiled slab wet-on-wet on the floor, against a wall, I should perhaps also mention. Perfect fit. "Rock solid." Completely satisfied.
Completely satisfied until now, as I've started to wonder if there's a risk that the slab might start to shift along the drain slope when the washing machine spins. To lock it in place, a few drill holes and stainless steel bolts in a suitable fixing compound (laminating epoxy and Hilti chemical anchor mix are both available at home) should suffice.
I would appreciate it if someone with relevant experience could comment on this. How would you have done it, drilled and fixed, or taken a chance that the slab stays put?
Best regards,
Erik E
I have a somewhat damaged basement slab with some cracks and a slight "bump" in the floor around a drain. However, it doesn't seem to be on the verge of collapsing in the short term, and all the cracks appear reliably old, without any level changes in the floor. I think it's mostly a result of traces from breaking up and replacing the drainage pipe in the floor.
Now I'm planning to place a tower with a washing machine and dryer near the floor drain. Since it slopes about 4-6 cm/m, and given the state of the floor, I decided to cast a slab about 65 x 65 cm under the machines. I wanted to keep it limited so it wouldn't turn into a full-scale floor renovation. It was also my first concrete casting, and I wanted to start with something simple. Therefore, I laid thin plastic on the floor and cast a reinforced slab with a thickness of about 3-5 cm on top of the plastic.
The slab turned out excellent. Since it's cast in place, it fits perfectly into the small irregularities in the floor underneath. The basement floor is oiled with Jotun concrete oil. The slab got a coat of oil on the bottom (not on the top yet, it should probably cure a bit more), and the floor underneath was oiled. Then I placed the newly oiled slab wet-on-wet on the floor, against a wall, I should perhaps also mention. Perfect fit. "Rock solid." Completely satisfied.
Completely satisfied until now, as I've started to wonder if there's a risk that the slab might start to shift along the drain slope when the washing machine spins. To lock it in place, a few drill holes and stainless steel bolts in a suitable fixing compound (laminating epoxy and Hilti chemical anchor mix are both available at home) should suffice.
I would appreciate it if someone with relevant experience could comment on this. How would you have done it, drilled and fixed, or taken a chance that the slab stays put?
Best regards,
Erik E
Member
· Västerbottens län
· 18 059 posts
My solution would have been to chip away the surface of the existing floor for better grip, drill in some reinforcement, and pour at least 5 cm of concrete. Then I would apply Jotun oil, but it requires completely dry concrete, so you'd have to wait a month or so.
Your slab, which is 65x65, doesn't distribute the load much more than the washing machine's 60x60 does, so it might have needed to be larger. Is your slab reinforced?
If you have laid the slab wet on wet, it will stay in place, as the washing machine isn't bolted and just sits ON the base without moving. Modern machines (even our 20-year-old Miele) adjust the spin cycle to prevent excessive vibration.
Your concern is probably unfounded, I would focus more on other aspects of the construction.
Protte
Your slab, which is 65x65, doesn't distribute the load much more than the washing machine's 60x60 does, so it might have needed to be larger. Is your slab reinforced?
If you have laid the slab wet on wet, it will stay in place, as the washing machine isn't bolted and just sits ON the base without moving. Modern machines (even our 20-year-old Miele) adjust the spin cycle to prevent excessive vibration.
Your concern is probably unfounded, I would focus more on other aspects of the construction.
Protte
Last edited:
Hello and thank you for the response. Tearing into the surface with chiseling or grinding was not an option for me. It would have been a gateway to a complete renovation of the cracked part of the floor, which I have decided to avoid.
I am considering setting up the machines on the slab and seeing how it goes. My thoughts were due to the fact that the slab is cast on a slope. It is therefore wedge-shaped and lies downhill like clay soil on a landslide slope, roughly speaking. The washing machine is quite calm, also a Miele, and it usually doesn't wander off on level ground. However, I fear that the vibrations might cause the slab to move in the slope's direction.
We'll see how it goes. If I don’t write anything else here, it has gone well.
Best regards, Erik E
I am considering setting up the machines on the slab and seeing how it goes. My thoughts were due to the fact that the slab is cast on a slope. It is therefore wedge-shaped and lies downhill like clay soil on a landslide slope, roughly speaking. The washing machine is quite calm, also a Miele, and it usually doesn't wander off on level ground. However, I fear that the vibrations might cause the slab to move in the slope's direction.
We'll see how it goes. If I don’t write anything else here, it has gone well.
Best regards, Erik E
Member
· Västerbottens län
· 18 059 posts
The chiseling in this case was 1 mm, just to remove the jotun and casting skin.
It can be done with Biltema's chisel hammer.
Protte
It can be done with Biltema's chisel hammer.
Protte