RTA cabinets? Take pic of entire cabinet. I am a little lost as if it caused center of cabinet to collapse how did drawer fronts get too high wouldn't they now be low in the center also?

Cabinets today are built like everything else and that is to look good with little thought given to structural design. This is a common failure along with drawer and doors pulling out of the cab cases. If I were to put two cabinets side by side and show someone the quality differences and then paint the poor one a pretty color they will always choose the poor quality one regardless of the quality.

Take the pic. Look to see if anything broke in the center of the cabinet or if the rear panel popped. If the stretchers cracked (mdf or particle board) there is not much you can do as it will always fall back into position. When counters are installed they usually lay plywood first to level and strengthen the tops.

Grab the bottom of the cabinet where it is low and see when you pull it back up what moves.

Do you have legs on the cabinet? If so, do you need more or could you put a toe kick space all the way around and a same size board through the center of this 48" cabinet to make it sturdier?

If the frame sagged, it's not robust enough for stone at all. Buy better quality. Even 2 cheap 24" particle board cabinets from the local hardware store wouldn't sag under granite. But what that looks like is just extremely poor quality design and execution.

Hard to tell from pic, but there does not appear to be a vertical support below the adjoining drawers. 48" is too great of a span if this is a frameless cabinet.

Graham

If a pro did the work, have the pro correct it. If this is a DIY project, however....

Add a 2"x2" or 2"x4" vertical support below the spot centered between each pair of drawers IF there is a horizontal board that will be behind the doors of the cabinet and under which you can add such a post.

Measure the vertical space inside between the floor of the base cabinet and the top (ceiling) of the cabinet AT THE SIDES, which should be supported and not sagging. You're wanting to determine the height the cabinet should be at the sagging point. You'll need stick your head inside the cabinet and look closely at the top of the cabinet to note if there is any framing at the sides that does not exist where the support is needed because you'll need to allow for that as you decide the length of the vertical support.

Empty and drawers in the sagging cabinet but replace the drawers into the cabinet and set a long level atop the countertop. You'll need to watch any movement of the sagging section as you tap in the support to ensure you're adding enough support but not adding too much support. Set the bottom of the support post you've cut on the floor of the cabinet just barely inside the cabinet (so it will be behind any doors to the cabinet). Because of the sagging, the support post will, at first not fit and will need to be tapped into a vertical position, lifting the sagging cabinet as this is done.

Thanks to everyone who commented. I uploaded more pictures for those who want to see more before offering a suggestion. I also uploaded a 2-D illustration of what I'm trying to describe.

There is some sagging at the front of the cabinet only, in the center where the two drawer boxes meet. We purchased a jack post BUT the cabinet has a toe kick (not yet installed) so it's a false bottom (to my DIY thinking) and can't support a jack post, so we returned it.

Someone mentioned that the quartz people will probably use a sheet of plywood between the cabinet and the quartz. When the cabinet is glued to the plywood, and the plywood is glued to the quartz, will that pull the sagging drawer front area upwards?

I don't think it sheds any light on the subject but I'm providing the link to the actual Base Cabinet 48".

I took Sophie Wheeler's advice and measured the interior, vertical height of the lower cabinet area at the sides (no sagging) and in the center. The difference amounts to 1/16", is that critical?

Granite doesn't bend. It cracks. That cabinet needs to go away and be replaced by 2 24" cabinets. At this point, getting that back level and plum is gonna be more work than order what should have been ordered in the first place. That cabinet is build incorrectly to be able to provide proper structural support. It should never be that wide without a center stile.

Nope, no center stile. The plan is to do a [waterfall countertop[(https://www.houzz.com/photos/waterfall-countertop-phbr0lbl-bl~l_40080), so the horizontal slab will be supported on one side (left side of the photo) by the vertical slab. Does that bit of physics do me any favors?

Sometimes we have to kiss and say good-bye, and this is one of those times. Just purchase new cabinets for your island to avoid future problems.

Whoever designed that cabinet, had no brains whatsoever. This cabinet will fall apart the minute you put stuff the drawers. This has to be a Chinese cabinet, they always make stuff like this. We replaced last year about 18 vanities which were purchased online, they all fell apart within 2-6 month period. Some failed because of stuff like that and some just started to delaminate.

As mentioned in my earlier response, it needs a vertical support under the center of the drawers, just add one.

Graham

As crappy as that is made, I wouldn't even add a center stile. The whole dang thing might collapse under the weight of stone even if you did the stile. Cheepchinesecrap is really awful when it's awful, and that thing is a liability to life and safety. If you put those cabinets in the rest of the kitchen, time to rethink that too. Get that garbage out of your house before it falls off the wall, or collapses under stone, and kills someone.

I'm glad to report that I went to the cabinet provider, 27estore, with all your advice (and a link to this thread) and they were very accommodating. They sent me two 24" cabinets to replace the sagging 48" absolutely free of charge, including freight. The only caveat they gave me was not to lay the old granite countertop atop the new cabinets, even temporarily. I connected the two cabinets with the aid of squeeze clamps, re-leveled, etc. and the new quartz countertop was installed almost one month ago without incident.

I want to thank everyone who contributed to this discussion, even the self-described "truth teller" who at times mistakes obnoxious commentary for honesty. I tell myself your heart is in the right place.

Pics of the new base cabinets before and after countertop installation.

chachi69, I'm looking at the 27estore cabinets and it appears they are from Europe. What do you now think of the quality of their product?

We purchased the High Gloss Cabinet Doors (polyester white, Group D) for our upper cabinets and HPL Panels (dark elm textured, Group A) for the lower cabinets.

Two thumbs up for the high gloss doors. They were covered in a protective film with the company/manufacturer seal and they definitely hail from Spain. I don't know enough about engineered cabinet doors to tell you exactly what the core is comprised of but I'll guess it's a high quality MDF, because they are very easy to drill into and have excellent screw-holding power. We did not need to use cabinet screw dowel inserts on these doors despite their heavier than expected weight.

The HPL panels, on the other hand, were not individually shrink wrapped at the factory and there was no indication as to their derivation but I'd guess China before Europe. Their core, by contrast, is a coarse particle board that is not easy to work with and has terrible screw-holding power; we needed to use Blum 8mm Screw Dowel Plastic Inserts for every screw on those doors. And trace amounts of glue are visible upon inspection at the edges where the laminate or veneer meets the banding. It's not noticeable unless you really look for it but it is indicative of the overall quality of the HPL panels. Also, two drawer fronts or cabinet doors would be bundled together before being wrapped in plastic, so two sides were in direct contact and rubbing against each other while in transit. This usually resulted in minor scratches or scuffs on the face, so there was typically only one pristine side to work with per piece. We love how they look but they were definitely challenging to work with.

Overall, however, we are very satisfied and I do recommend them — with the following caveats.

1. I would order the high gloss doors again in a heartbeat.
2. I would not order the HPL panels or anything in Group A again.
3. Order a sample (as we did) and make a few practice drills into it (as we did not). This will help you gauge the quality and ease of use in advance.

Hope this helps.