Plywood is not an approved substrate for laminate counters. Particle board is the standard. If you want to use MDF, use Medex.

Thanks @User. I felt like "upgrading" the particleboard might be wise long-term. Is that concern unwarranted? Which would you install?

Why are you having exposed areas anywhere ? A laminate counter is covered everywhere there are no exposed areas of substrate so explain better .

Why are you building anything laminate when you can buy post formed that will be much better done, with fewer issues?

I don't recall ever finding the area around drop-in kitchen sinks to be free from swelling from water penetration after a number of years. Though usually by that time, it's ready for replacement anyway.

@worthy are there any preventative steps that might help avoid that? I assume that is with particleboard, hence my questions as to whether a different substrate might be better suited for this? What if you laminated or varnished the exposed wood in the sink cutout area?

@Patricia Colwell Consulting isn't the whole underside exposed? I asked a contractor if they laminate the bottom of the substrate, particularly near wet appliances, but the answer was no. I've read dishwasher steam, etc. can cause swelling to the underside of the substrate right above it.

@User what am I missing? I see you buy the rolls of laminate and assume you need to have the counter ready to adhere it to. Am I going about this the wrong way?

Yes, you’re going about it in the most painful and risky way possible. You want post form laminate, that comes with the edges already done, from the production line. At a MUCH higher pressure and with better glues than you can do.

Most box stores can order slabs, or cut to your drawing size, and you just assembled and install on site. For additional local retailers, Check out VT Industries or Hartson Kennedy. They are the big dogs in the post formed world.

https://www.vtindustries.com/tops-surfaces/dimensions-laminate/

https://www.hartson-kennedy.com/laminate-countertops/

Also the area over the dishwasher tends to swell after some time - even with the little stick on plastic label.

If the stuff you're looking at is wide but in a roll, it's either a pvc film, vinyl or soft melamine. It's not suitable for a kitchen counter - you'd be lucky if it lasted a year or two.

The laminate for counters should come in stiff, but thin sheets. The sheets are 30", 36", 48", or 60" wide, and 96", 120" or 144" long. Not all colors from all makers come in all sizes.

If you are DIYing, you'll need at least an electric drill with appropriate bits, a hole kit for the drill, a hand held circular saw or a rotary saw for cut outs. Plus a router with laminate bits, maybe an edge trim kit and perhaps custom edge banding or be really good with tools.

Because you'll be cutting your own sheets of substrate too, you might need a panel saw kit to transform your circular saw into a panel saw. Or a table saw with extensions. Oh, add a lot of clamps. Usually, it's done with contact cement and you don't have a lot of adjustment time.

I'm not being mean or belittling- it's that I've seen this done and it's not a first timer kind of project. It takes tools, skills and experience. I've done a fair amount of DIY projects. I would not do this myself and I would not allow anyone else to do it who had never done it before.

Custom done laminate does look 10x better than the post form ready-made stuff which fits very few spaces properly and comes in limited colors. So do start with sheets (not rolls) and be sure you look at all the amazing options out there. Because there are really great designs that you won't find in stores--but most manufacturers will send free samples.

If you're going to try to DIY this, do at least get quotes from pros first and see if it makes more sense--like Bmore says, it'll take a lot of equipment and knowhow to do it right.

Sheets are rolled for transportation. You straddle the roll when you cut the ropes.

Post form is WAY more than the 4 colors on the shelf at the box store. It’s how 90% of all laminate counters are done. Because its better. Post form comes in all of the 1000+ colors that any laminate comes in. And with, or without, an integral backsplash. Depends on how you order it. As does the half dozen edge choices.

Anyone who thinks that custom square edge with a black line looks better than post form, doesnt know anything about post form. Or custom laminate. Ideal Edge not withstanding, custom laminate usually performs, and looks, much worse.

This is an old thread at this point, but perhaps someone else will find the commentary useful.

I know the problem that you're trying to solve, and post formed laminate countertops do no work in every application. Sometimes, the old school laminate build is the way to go. A lot of people do it, otherwise I doubt that Formica and Wilsonart would still be in business. And certainly they wouldn't continue to develop new sheet products.

Although it does seem counterintuitive, particle board is still the way to go for your base. Add wood strips along your finish edges and apply the band first, so you can create a good straight and clean edge to apply your horizontal material on top of. Trim the excess (overhang) from the horizontal material with a palm router, using a specific laminate trimming bit that has a guide wheel with bearing. Don't forget to lube the bearing a couple times throughout the process.

As for the underneath side of the particle board, that will be in an area where it could encounter water or steam, coat the underneath side of the particle board with Red Guard, Aqua Defense or a similar product. These product are designed to keep water out and should provide a sufficient barrier from moisture. I also like to apply clear silicone around the entire cut edge of the sink hole. Do this just prior to setting the sink in place. You can apply an ample amount of silicone to this cut edge of the particle board because no one will ever see it, and this is the most likely place for transient water to come in contact with your particle board.

Hope this helps someone.