Hi all,
My concrete base pour last weekend didn’t go well and I’m looking for a bit of feedback on whether to take another shot with a new base pan and Y axis rail mounts or move forward with what I ended up with. Perhaps this will also help others avoid my mistake.
I used Quikrete crack resistant mix (No. 1006 ) with the exact 5pints/60Lb ratio given in the manual and mixed by machine. I don’t have much concrete experience and was afraid of having too much water in the mix so I didn’t add any more water. I did watch the mix ratio video and thought I had something pretty close. I mixed 100lb at a time, put it in the base, spread it around and repeated until I had 400lb in and it was looking pretty full. I spread the last addition around and started trying to consolidate the mix with a massage gun and plastic hammer. There was some consolidation, but it was nothing like the video of the base pour in the instructions. The base plate was very tough to get placed and I couldn’t get the mix smoothed out on top. Time ran out as the concrete set and while I got everything in place and the surface somewhat leveled, I’m very dissatisfied with the results. I removed one of the coolant drains to reveal what seems to be totally unconsolidated mix.
What I’d like to know is:
Is there risk to the performance and function of the machine?
Is it likely to crack if I end up moving the machine, I can’t imagine it’s all that strong.
I’m not far off biting the bullet and trying again, but hate the idea redoing the work if it’s no big deal. If I do need to redo, I hope Langmuir would sell me another base tray and Y axis rail mount. I can’t be the first to have screwed this up (I hope). If not I would have to break all the concrete out with a demolition hammer which sounds awful, but I’ve done worse.
In retrospect I really wish I had done a test mix and pour to dial this in.
The pic of the drain is what looks the most concerning. If that is representative of what a core cut out of the slab would look like, then I don’t think the concrete will perform as intended.
However, if the concrete is consolidated and free of voids inside then it’s possible this is mostly cosmetic. The trouble is, without some destructive testing its hard to know what the concrete looks like inside.
I suppose there isn’t allot of risk to trying it… If it doesn’t work, you will just be back in the same situation but with all the assembly/disassembly time wasted.
If it were me, it would bother me enough to start over. Find a friend or neighbor who is familiar with concrete that can help you.
You could use a diamond hole saw (cheap) to take a couple of core samples in less critical areas (like near the cable support at the back). If it were me I would repair those core samples with a small mix of epoxy granite (basically sand and gravel in epoxy).
Unfortunately, I think that the mistake that you made was vibrating it all at the end instead of as you went. A couple of random core samples would let you see how much air is in the mix. If you used 400lbs of concrete (vs 480 as specified) and got the right final depth then that would suggest that there is about 20% air by volume. I don’t know enough about concrete to really know the impact of that – it might be fine for most uses of the MR-1. I also had a little bit of concrete that didn’t fit (about 20lbs), so my concrete quantity was a little under the specification.
If you do the pour again I would suggest using a reciprocating saw as your vibrating tool. I read that trick here and it really did a good job on my machine. I pulled the blade and just used the piston as a hammer against the bottom of the concrete pan.
I ended up about 50 lbs low and had to flood with about a half gallon of extra epoxy. So far, things seem okay.
If you plan to flood epoxy, get all the exposed aggregate cleaned up and below the drain level.
Poke around the drain area you’ve exposed to check for loose sand or cement powder. If all is well cured, I’d imagine you’ve got enough mass to move forward.
The concrete isn’t for “strength” but for adding mass and dampening. I’d imagine filling the tub with loose sand would do almost the same thing (though it would likely sink in the middle because it’s not binding itself together.
Consider this. If the concrete were for strength, it would need to transmit a load to something else in either bending, tension, or compression (of which, concrete only works in compression). The base pan is flimsy and bendy so it’s certainly not transmitting there. The legs and base pan are capable of supporting the weight of the machine without any help from the concrete. There’s nowhere else for the force to go, so the concrete isn’t for force. It’s just about changing the mass properties of the machine.
If you move it though, you’ll want to be super careful as at this point, the concrete is holding itself together and if you’re too aggressive or load it poorly, it might fracture. (which is only a problem insofar as is is ugly or the mass becomes detached from each other or from the structural frame to damp less effectively)
The core sample was a great idea. I went ahead and drilled two 1" holes. One at the back near the cable mast and one about 2" away from the drain area I posted. Looking at the cores that came out and inspecting the walls of the hole gave me some hope as it looked more consolidated than I thought it would. The core is in pieces because the hole saw only cut about 1" deep. I think this gives me enough confidence to keep moving forward.
I did put a 3x3 grid of 3/8 rebar about 1" off the bottom face so hopefully that will help as well. I also got an extra 2gal epoxy kit to be sure I can cover all the high spots and fill the depressions.
Since you have 2 nice 1" holes in the slab now; perhaps consider utilizing them for additional drainage. Might have to experiment with different materials to line the holes with, but something in the PVC, PEX or Well PE variety should do the trick and the epoxy could be poured to seal the lip.
