Finish for a Maple Countertop with Undermount Sink

Here's a wide-ranging discussion about finishing kitchen countertops made with wood. October 19, 2013

Question (WOODWEB Member) :
We are doing a large maple island top which will contain an under-mounted bar sink and looking for suitable finish. My coating supplier (Chemcraft) has recommended we use an Acrylic Polyurethane (as opposed to our post-cat CV lacquer). Others have recommended epoxy floor finish. Are there any concerns with food-safe finishes after they have been fully cured (rolling out bread on countertop, - obviously no cutting on finish).

Forum Responses
(Finishing Forum)
From contributor R:
I like Chemcraft's suggestion on using Acrylic Polyurethane. Make sure to coat the bottom of the countertop with as many coats as you apply on the top surface. Same goes for the end grain.

From contributor M:
Just about any finish is going to be non-toxic and food safe after it has fully cured for a couple of weeks. If they were to continue leaching dangerous chemicals, no manufacture would put them on the market due to liability concerns. In addition, as long as they aren't hacking away at the top with knives (cutting board) there is really no way for the finish to get into the food.

From the original questioner:
That is what I thought about finish food safety. Future re-coating isn't a concern, but I would like to learn more about using polyurethane vs. CV 2k lacquer (which we use regularly). Bona Traffic is an interesting suggestion. I hadn't thought of using it on a bar top.

From contributor I:
That end grain around the sink opening is going to be the big deal. Don't exceed any thickness specs by the supplier, but coat the heck out of it. The wood is going to move, the finish is going to crack, the finish will fail, and water then gets in the end grain. Don't give them more than a 30 day warranty on that top as it's going to look a little rough in no time. I only allowed a sink in one top I put in, and insisted on a flanged sink. I coated the end grain with clear silicone. That was 20 plus years ago, no call back.

From contributor J:
Here are two alternatives:

1. Epifanes (brightwork for boats) varnish.

2. Rub on Oil - either Watco, Tried and True, General Finish Arm R Seal, Waterlox, Polymerized Tung (Sutherland Welles), and etc.

2K poly will look fake on maple with anything higher than a Satin finish.
Keep it dull.

From contributor U:
I agree that Epifanes makes a good clear gloss varnish that stands up to water pretty well. It contains some phenolic resin and some tung oil in the formula. I would suggest using CPES to seal the end grain. I have used Smith's for years and it works (maybe two coats around a sink). It will also help delay the darkening of the end grain that will eventually occur. It is a two-part material that is easy to work with. Even though I don't do much marine work anymore I still use it for wet areas and for outdoor applications.

From Contributor S:
I just completed a kitchen with walnut tops seemingly everywhere. The island had the only sink Ė an undermount. I used a polyester base coat with a top coating of verde chiaro, Asko/Chemcraft. It lays out very well, especially with a touch of slow reducer/retarder and has a great hand/feel off the gun. If you are going natural then there are no worries. A pigment stain will require a barrier coat prior to the polyester - cci's isolante for adhesion.

Now, using polyester requires rigorous heat schedule - thermal cure, 90 degrees for overnight or extended time at ambient temp to cure before you cut/sand. That system will work well. Even better might be base coating with epoxy, curing and then final coating with 2k pu is fine.

Excellent advice to balance coatings, especially with planks. Adding a bit more to the rim and immediate undermount area certainly cannot hurt. It's what I do. I did not see mentioned type of glue or moisture content, balancing grain or direction/rings, or plank width - these may also impact success.

I left my customer with a maintenance schedule that explicitly stated among other things that they must perform due diligence with making sure that they wipe dry the area below the rim after water use. Further, I spoke with the plumber to make sure that beaucoup de silicone was applied to the mount area. And then there is tongue oil. Gauge your client and determine whether they have the wherewithal to maintain. Do samples and test and test again.

From the original questioner:
So I will be using a Chemcraft product called Eurocryl as a self-seal (so I don't have to buy two products). I will keep the temps up as recommended. Maple top will be 2"x4'x9', comprised of about 6" planks edge glued with Tightbond 3. I don't alternate the growth rings, but select most pleasant faces. No stain. Any concerns here?

I had selected 35% sheen but can go flatter. I was concerned that too flat might actually develop shiny spots as it wears, and too shiny looks fake. Perhaps 15% or 30% sheen would be better?

Contributor U - what is CPES? Would using this affect adhesion with PU seal/topcoat? Also, will PU not pop the grain - like CV lacquer? I do like the CV look on raw maple, as opposed to a water based single component finish.

From contributor I:
I'm no fan of Titebond III. I would go with nothing over 4" wide and I would only use quartersawn stock. Actually I would not bid the job to start with. As far as I'm concerned it's a call back disaster waiting to happen. I know how my family treats a kitchen sink area. Only plastic or stone should be used in a real family kitchen as far as I'm concerned.

From contributor F:
First I would like to congratulate Contributor S for his brilliant job and technique. Second I think Contributor I is dead on about this being a recipe for disaster. The boards should not be 4", I personally think 2" would be best but 4' x 9' around water sounds treacherous and then finished by an inexperienced person. Good luck but I would do as much research about every aspect of this prior to finding anything.

From contributor M:
I built a wood top with a flange mount sink and so far it has held up quite well. I fabricated the sink cut out at my shop prior to finishing. I also made sure the sink was set into a hefty bead of silicone. The customer wanted an under mount sink, but I refused to do it because I know that they actually use their kitchen. Then again some people don't. I would consider doing it in the right circumstances, and I think that a penetrating marine epoxy sealer would be a good starting point, but even wood on boats need maintenance and repair.

From Contributor S:

I do not know Eurocryl and I would not begin to use an unfamiliar product, especially in such a critical application without thorough testing. It isnít worth it. Get a sample, do a glue-up of the stock being used if possible, finish per recommendations, cure it, and test the heck out of it.

Titebond 3 works for me and some folks wouldn't use anything but epoxy. Using biscuits or tenons to assist with alignment? Back in the 80's and 90's many solid panel manufacturers went by the rule of thumb no wider than 3". These were production outfits. If you can choose relatively clean and straight boards from a trusted source still check moisture content - no reason not to use 6"-8". Iíve done it many times, though I do alternate the rings and become testy when I can't. By popping the grain do you mean accentuate? Part of the attraction of wood is making it look alive and not two dimensional as laminate.

From the original questioner:
A couple of years ago I did a similarly sized island with 8x4 maple, Tightbond3 but with a flanged sink. At the time I used post-cat CV and haven't had any call backs. It also had a top venting dishwasher that was causing counter edge to steam up. I might have to check in on the customer to see how it looks now. In both cases the sinks are secondary small bar sinks so probably not washing dishes, etc. I really like the idea of using epoxy on edges (was looking at West Systems Epoxy for another exterior door project - both for glue up and exterior finish). Wonder if there would be any concerns with top-coating WSE with acrylic poly?

From contributor U:
Although I have used West System many times I wouldn't use it instead of CPES (P=penetrating) for this application. It is not made for penetrating end grain or surfaces that well. It is a bullet-proof coating, but thick and not always becoming. There are some bar-lacquers that some here might be able to recommend, and some epoxies that may be more suitable. I've used West for hull, keel, and topside repairs and coated with 2-part LP. Itís just not my choice for a finished surface indoors.

From contributor B:
I've been part of a kitchen remodel where they had an under mounted sink on an island with a maple countertop (1.5inch wide boards glued up). I was doing all the finishing and was asked to seal it - I said no way. I also told them to use food safe oil to seal and re-apply on their own. I agree with others who've recommended going narrower on your glue-up. All the pre-manufactured stuff is narrow stock and if you cut them you'll notice their impregnated with food safe oil to about 1/8" deep. Supply it raw with a can of food safe oil and walk away. Also, when you lay up your slab mark where your sink is going and position some biscuits close to the sink edge.