Strengthening floor too stop washing machine vibration

[Optimystery]

I'm asking this here, as DIY forums are full of random guesswork.
I believe a structural engineer would understand this problem and be able to suggest a solution based on sound principles.

My previous Bosch washing machine gave up after about 12 years, so I've bought a new one.
This one seems to shake / wobble / vibrate a lot more.
It's not 'walking' or banging, but I imagine it can't be good for either the washing machine or the floor to shake from side to side this much, especially during spin cycle.
I have removed the transit bolts and plastic washers that it arrived with.

The washing machine is situated along an outside wall under a counter top, and this is a 1900s second-floor flat.
The floor and everything else in the room vibrates a ridiculous amount when it's on spin cycle.

I have it on 9mm plywood, levelled with compressed cardboard in the corners to get it level before sliding the washing machine in. Maybe this is a bad idea, but it's the only way I could think of to get a spirit level to show me the board is actually level.

I've also added the neoprene feet cups that I was using with the previous machine (which worked pretty well).
However either with or without the feet the machine noticeably wobbles from side to side when tumbling, and shakes violently when on spin.
These newer machines don't have a spin speed dial, only programmes, so I've set it to Easy Care (1200 rather than default 1400rpm, which is extreme).

I'm wondering if a granite slab (2.5cm thickness is probably the max I can get away with under the counter top) would help here?
Would something thinner like a large porcelain tile be liable to crack?
My reasoning is that even if vibration transfers through the slab to the joists, the slab would at least be dimensionally stable, and so the 4 feet would be transferring a balanced force downward, rather than individually.

Bosch recommend on their website to screw a thick piece of ply (min 30mm) into the floor, but I'm not sure that would fit under the counter, and seems like it would flex more. On the other hand, maybe having it attached directly to the joists might improve stability?
Other more extreme options might be to brace / sister the joists, but that's a bigger job without a guarantee of it working.

I've done a lot of googling and researching, and haven't found any definitive solution. Since I don't have the option of moving the washing machine, either fixing the floor or getting a stable platform seem like the only options.

Any advice from experts on here? How would you approach this?

 

[XR250]

I would start by adding a few stiff-knees under the joists down to some pre-cast "deck blocks" or the basement slab (if there is one) The compressed cardboard does not sound like a great idea but who knows.

 

[Optimystery]

This is a maisonette, so I have no access other than pulling up floorboards and either strengthening the space between joists up to the ceiling below, or possibly replacing part of the floorboards with a section of plywood.
I will try removing the cardboard and have to trial and error with adjusting the wm's feet to get it level.

From a physics point of view, would a slab of thick plywood screwed to the joists do much too improve stiffness, or would that just more efficiently transfer the vibration into the joists?

How about a paving slab? Seems like that ought to at least provide a flat surface with no flex in it.
I don't understand enough about how vibration and resonant frequencies get transferred, so am really guessing here.

 

[phamENG]

It sounds to me like you just don't have your washing machine level. Unless I'm mistaken, the operating vibration frequencies of typical washing machines are not really in the range of natural frequencies for wood framed floors. It seems extremely unlikely that a properly installed and operating washing machine would act this way as a result of vibrations exciting the floor.

Solving vibration issues in existing buildings (particularly wood framed residential structures with finishes applied directly to the structure) are some of the hardest puzzles we have to solve. And not all structural engineers are as skilled in it as others. I'd like to think I have a decent grasp on the concepts, but I don't consider my expert. Once you confirm that your machine is absolutely installed correctly and the issue is in the structure, you need a structural engineer with experience in solving structural vibration issues on site to assess the situation.

 

[XR250]

Adding some mass will likely help. Would have to be a trial and error process though.

 

[271828]

It is often not feasible to change the structure enough to reduce steady-state vibrations to a tolerable level. It wouldn't require a small change, like adding a layer of wood structural panel or adding a joist or two. Think on the order of changing the wood structural panel floor to a concrete slab floor.

Steady-state vibration problems are typically solved by fixing whatever is causing the vibration.

Something doesn't sound right about the washing machine. For example, it's not level, as phamENG mentioned, or there's actually something wrong with it. If you try your best at leveling it, and the vibration is still unacceptable, then ask the store for a replacement. These things are intended to work OK on a regular residential floor, after all.

 

[jerseyshore]

I agree with the above, lean the washing machine on two feet so that the other 2 feet reset, it should self level after that. Then make sure to properly balance the clothes as you're tossing them into the washer. Fix it at the washer as opposed to trying to re-frame your floor.

 

[JoshPlumSE]

I'm confused. Is this a vibration transmission problem. Where the floor is transmitting the vibrations to other parts of the house? It doesn't sound like it.

Instead, this sounds like a problem with the machine itself. If that's the frequency it's vibrating at, then there is nothing structural you can do. Unless you think the issue is resonance with the structure.

My guess is that there is a machine issues (bad springs, too much laundry, not enough laundry) that is causing this problem.

 

[jayrod12]

I know you said you removed all of the washers and bolts that lock the drum in during shipping, but are you certain you removed them all?

I only ask because I made the same mistake on my first front load. Thought I had got them all, but I had left one in place that doubled as a perfect hose clamp. Turns out without removing that one, it shook so violently that I couldn't hold it in place if I tried. Removed the offending bolt, purred like a kitten after that.

 

[XR250]

This is why I put a $200 Craigslist top loader in my new house

 

[Optimystery]

I'm going to try things methodically.

Ripped out the lino and thin particle board that was layed under, and removed the 9mm ply board with shims.
The section of floorboards looks a bit messy, like some new pieces were put in.
I've nailed everything down solid.
The advantage of this now is that I can just about get a spirit level on top of the machine under the counter top.
Front to back is harder to measure, but I've tried to do that based on sprit level on the floor, and adjusted the feet.
Left back is flat, right back slightly raised, then front 2 raised and checked that the top of wm is level at the front.
There's no rocking and it feels firmly planted.
Test (empty) spin cycle, still some vibration, but only noticeable to the touch.
Next I will try a normal wash again, and see how it performs.
If it seems stable but transmits a lot of vibration to the floor, I will try adding the neoprene coasters.

 

[Optimystery]

@jerseyshore not sure what you mean by resetting the feet. The feet consist of a rubberized foot with nut. You unscrew the foot to make it taller and then tighten up the nut to keep it in place.
The washer is supposed too balance itself in terms of load. I've read totally conflicting reports about what a sensible load should be: add a towel for balance (don't put heavy items together, or only put heavy items together), don't fill too little or too much. I think these machines are designed to handle a wide variety of loads.

@jayrod12 This one only has the 4 transit bolts & clamps, with caps to go over the holes

@JoshPlumSE The machine was visibly shaking at the top, probably 5mm, and dishes and pots on the table and dryer were rattling. Not so much an issue in the rest of the flat, but I'm sure it would be for the downstairs flat

@XR250 I probably would choose a top loader if I had a space for it!

 

[XR250]

A bit OT and I get why the OP and others need front loaders but I do not see the advantage for most. They cost more to buy, are less reliable, cost more to service, get the moldy gasket and can shake and make a bunch of noise. I suppose they use less water and possibly spin the clothes dryer. Not worth it to me.
I had a Speed Queen front loader in my old house and I much prefer my current top loader.

 

[hokie66]

My main objective in choosing a washing machine is to please the wife. She had a front loader, hated it because it took too long. She likes the new top loader.

 

[jerseyshore]

Some washing machines have auto-leveling feet. Or maybe it was my dryer, who can remember anymore.

My wife said she's too short and we need to get a front loader when pregnant. Happy wife, something something.

 

[hokie66]

Maybe you need to take on the job of doing the laundry while she is pregnant.