Looking for suggestions for filling gap

[Lester Sak]

Hi all,

I've been working on remodeling my kitchen for months now and finally into the home stretch. Stripped down to studs, insulation, replaced dropped ceiling with sheet rock, built all cabinets and decided to try Stone Coat Countertops epoxy for the counter top. The counter is 3 pieces of MDF that will be joined with dominoes and epoxied. The longest piece needed to fit between 3 walls. I should have tried scribing a pattern first but didn't and there is a tapered gap on one side that that gets to about 3/4" wide which I need to fill. It doesn't need to look pretty as the Stone Coat epoxy will cover it, but it needs to be flat/level with the rest of the counter top with no gaps so the epoxy doesn't leak through before it sets. I thought I could scribe on 1/4" plywood to use as a template to cut a filler piece which could be epoxied in place. I've tried making the plywood even with the edge of the MDF (following the gap) as well as flush to the wall and scribe following the wall but neither gives me a piece that would fit. I've also considered using foam backer rod and then covering with the same epoxy to be used to joint the 3 pieces (knife grade). Any suggestions as to what I'm doing wrong when trying to scribe or other ideas?

BTW, a floating floor will be installed when this is all done :)

Appreciate any suggestions!
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[Jeff Monson]

Are you putting in a back splash? I'd try incorporate a piece into the back splash to cover any gaps to the wall.

[Richard Coers]

MDF is cheap, redo it correctly. I would joke in the shop, "that's a gap you can throw a cat through". Now about MDF, that's about the last material I would use for a countertop. What kind of sealing do you plan around the sink and faucet openings? What about the edges at the walls and the underside? If those joints get any leakage at all, MDF will swell like a sponge. Maybe you have sourced some special water resistant MDF? Then there is seasonal movement. MDF moves more than plywood, it could easily cup in width with only epoxy on one side. I've found numbers as high as .3% in width and length. That would be quite a bit over 10' length too. Don't fit it too tight to the wall.

[Frank Pratt]

Listen to what Richard said, cause it's good advice. My worry would be that because a kitchen counter gets lots of rough use, any microscopic crack or pit in the epoxy surface is going to let moisture in over time & swell the MDF. Using Medex or other water resistant (it's not waterproof) MDF would help some in that regard, but not completely.

I think MDO would work well there. It's primary use is for outdoor signs & it stands up very well to moisture.

[Lester Sak]

Are you putting in a back splash? I'd try incorporate a piece into the back splash to cover any gaps to the wall.
Wife isn't sure whether she wants a 4" back splash or all the way up to the bottom of the upper cabinets, so I need to do something now in order to be ready for the epoxy coat.

[Lester Sak]

Richard & Frank,

Thanks for the feedback.

Richard, I agree MDF is cheap and makes sense to just get another sheet, cut it and be done with it. The problem is I need to finish this up before the range gets delivered, my shop is too small to work with a full sheet so it has to be done outside and weather isn't cooperating. I also need to find someone who has a van or pickup to help me get it. If possible, I'd like to fill the gap so when I'm ready to pour the epoxy I can do it.

The product I'm going to use is from Stone Coat Countertops (https://www.stonecoatcountertops.com/). If you're not familiar with it, you can see a short video here (https://youtu.be/QiJsM8KHFhw). They use regular MDF with 2 coats of paint. The epoxy is poured on, colors added and allowed to dry 24 hours when a 2nd clear coat of epoxy is poured. The only waterproofing is when installing an undermount sink for which they apply 2 coats of Redgard (https://www.custombuildingproducts.com/products/surface-preparation/waterproofing-membranes-underlayments/redgard.aspx)to the underside of the counter top. There will also be a bead of silicone between the counter top and wall.

That being said, any other suggestions would be appreciated, especially if I can figure out how to properly scribe a piece that can be made to fit.

[Paul F Franklin]

Cut a rectangular piece as long as that section of MDF and maybe 6" wide. Lay it on top of what you have, holding it tight against the wall, and scribe a line. Remove the piece, cut it off at the line, and attach the rectangular piece with dominoes and you're done.

[johnny means]

Scrap the Dominoes and scab the bottom of the top with more MDF. Use plenty of glue and screws to pull everything nice and flush. Dominoes aren't going to prevent telegraphing.

[Lester Sak]

Cut a rectangular piece as long as that section of MDF and maybe 6" wide. Lay it on top of what you have, holding it tight against the wall, and scribe a line. Remove the piece, cut it off at the line, and attach the rectangular piece with dominoes and you're done.

Paul,

I laid the filler piece under the counter top and flush to the wall so that I could use the counter top edge to scribe against. Because of the wall, I couldn't use a pencil to trace so instead I used a safety razor embedded in a small block of wood at a 90 degree angle with the rigid back removed (the same setup I use for trimming edge banding). I was able to run the razor flush against the edge and scratched a line in the filler piece which I cut on the band saw. Worked well enough and the gaps are small enough that they can be caulked.

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[Tom Bender]

Did you make the cabinets from MDF? If so, plan on some water spilling in the sink base. It will destroy an MDF floor in that cabinet. Waterproof it really well, and the sides too while you're in there.

[Lester Sak]

Did you make the cabinets from MDF? If so, plan on some water spilling in the sink base. It will destroy an MDF floor in that cabinet. Waterproof it really well, and the sides too while you're in there.

Hi Tom,

No, the cabinets were made from pre-finished 3/4" maple ply so I'm good. Thanks for pointing it out though!

[Art Mann]

My opinion is the same as that of Richard and Frank. There is a reason nobody uses MDF for a counter top. You need to have a plan in place for when the MDF gets wet from seepage somewhere and dissolves. I have replaced many MDF cabinet doors where the MDF substrate was actually made for the purpose but water still dissolved it.

[Mark Daily]

That epoxy looks really nice- I hope it’s as easy to work with as the video claims. It will certainly seal the top of the MDF, but as others have mentioned, how will you prevent the bottom from absorbing moisture possibly just from humidity?

[Lester Sak]

That epoxy looks really nice- I hope it’s as easy to work with as the video claims. It will certainly seal the top of the MDF, but as others have mentioned, how will you prevent the bottom from absorbing moisture possibly just from humidity?

Hi Mark,

I'm hoping it's as easy to work with as the video claims too, lol. I'd mentioned applying 2 coats of Redgard (https://www.custombuildingproducts.com/products/surface-preparation/waterproofing-membranes-underlayments/redgard.aspx), a roll-on elastomeric waterproofing membrane to the underside. Between the 2 coats of epoxy, the Redgard underneath and caulking around the perimeter I think I should be ok.

[Mark Daily]

Hi Mark,

I'm hoping it's as easy to work with as the video claims too, lol. I'd mentioned applying 2 coats of Redgard (https://www.custombuildingproducts.com/products/surface-preparation/waterproofing-membranes-underlayments/redgard.aspx), a roll-on elastomeric waterproofing membrane to the underside. Between the 2 coats of epoxy, the Redgard underneath and caulking around the perimeter I think I should be ok.

Oops- I missed the part about the Redgard. Looking forward to seeing pics!