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vintage_car 01-01-2010 06:19 PM

new cast iron sink with formica counter
My wife got a new...HEAVY cast iron sink for the kitchen. We have a stainless steel one right now. The countertops are formica. I'm concerned with the weight of the new sink not being able ot be handled by the formica. Should this be a concern, or am I over engineering this?

inspectorD 01-02-2010 08:07 AM

Its done all the time, enjoy your sink.

majakdragon 01-02-2010 08:10 AM

The formica is a thin covering. What matters is the wood under it. With the old sink removed, you should see at least 3/4" of wood. Sink should not be a problem.

vintage_car 01-03-2010 10:39 AM

so as long as there is 3/4" wood I'm okay for the cast iron install.

Nestor_Kelebay 01-06-2010 10:29 PM


Originally Posted by vintage_car (Post 38353)
so as long as there is 3/4" wood I'm okay for the cast iron install.

It doesn't have to be 3/4 inch thick. Some prefab plastic laminate counter tops are only 5/8 inch thick, and that's strong enough to support your sink too. And, 5/8" of fir plywood is stronger than 5/8" particle board, but both are strong enough to support your sink.

You're focusing your attention on the wrong problem. You'd do well to turn your attention to all of the areas where the particle board the counter top is made of could be exposed to water.

It'd be smart to paint the exposed edge of the hole in the counter top and the underside of the counter top around the sink hole with oil based paint. That way, if the water seal around the sink ever leaks, the water leakage won't be absorbed into the particle board. Or, at least you'll be more likely to discover the leak and have time to fix it BEFORE there's any damage done to the top. Ditto for the holes for the kitchen sink faucet.

Painting the back side of the front bullnose is also a good idea, especially in front of the sink and any built in dish washer. That way, the steam that comes out of the dish washer when you open the door (and which forms condensation on the underside of the counter top) won't get wicked into the particle board. If that particle board gets wet from water dripping off the edge of the top or from condensation forming on it from steam, the particle board will swell and the plastic laminate won't, and the usual result is that the glue bond holding the plastic laminate to the particle board will break. Once that plastic laminate is loose, it cracks and breaks VERY easily because it is so very very thin. Even catching your belt buckle on the laminate that's used to make prefab counter tops is enough to tear a big chuck of laminate off your counter top if it isn't stuck down well.

Pro's won't do any of that painting, but I do it on every counter top in my building cuz it's obvious that the paint won't do any harm, and should help maximize he lifespan of the counter top by keeping the wood dry.

Worry about the particle board wood getting wet, not about the sink being too heavy.

granite-girl 01-07-2010 10:04 AM

So Nestor- Are you saying that a cast iron sink is more likely to let water seep under it to the laminate ? Or just while it's apart & he has an empty hole, take care of that then ?

Bud Cline 01-07-2010 12:02 PM

It all depends on how far the counter top is spanning between any supports front to back or left to right. A typical laminate counter top is made of the laminate and the substrate. Again typically the substrate can be particle board or plywood. Plywood would be preferable but not used very often due to the cost. Particle board is much cheaper to use. Unfortunately particle board is susceptible to moisture and can sag from the weight of the sink over time. Atmospheric moisture is enough to cause the problem. If the open area of the cabinet supporting the top is a typical and nominal 22" X 34", the weight of the iron sink combined with a lot of moisture could cause the substrate to sag. Sealing (painting) the edges of the opening won't change anything if the bottom of the particle board slabs are raw - and they are.:) Reducing the open span would be a plus.:)

Nestor_Kelebay 01-07-2010 01:49 PM


Originally Posted by granite-girl (Post 38566)
So Nestor- Are you saying that a cast iron sink is more likely to let water seep under it to the laminate ?

No, I'm not saying that any sink would be more likely to leak water than any other.


Or just while it's apart & he has an empty hole, take care of that then ?

After the sink (and faucet holes, if any) have been cut, but before the top is installed, it's best to protect against water by painting any areas that are likely to get wet with an oil based paint. (Ideally, painting with boiled linseed oil would be best because it penetrates into wood more than modern alkyd paints, but any protection is better than no protection. Boiled linseed oil is gonna take days to dry versus a few hours for alkyd paints.)

Protecting the back side of the front bullnose (in my opinion) is something that everyone SHOULD do. Water dripping off the top in one area repeatedly or condensation on the underside or back of the front bullnose from repeatedly opening a hot dishwasher is gonna cause the particle board in that area to absorb water and swell. Since the plastic laminate doesn't swell, then somethin's gotta give, and the result is usually the glued bond between the laminate and particle board breaking.

That post-formed laminate used to make counter tops is darn near paper thin, and as soon as it's no longer glued down solid to something solid then it becomes extremely susceptible to breaking. And, that's usually the beginning of the end for plastic laminate counter tops.

I've painted every laminate top I've installed in my own building cuz I know it won't do any harm, but I can see that it will maximize the lifespan of the top by keeping the wood dry and the laminate well supported so it doesn't break. I call that doing what makes sense rather than asking a pro how it's supposed to be done cuz no pro will ever take the time to do this cuz the customer will never notice. And, most customers will figure that the cost of doing this should be included in their quote and scream bloody blue murder if it's not done.

PS: If I had a prefab laminate top that was already installed by a pro, I'd either caulk the joint between the front bullnose and the cabinet if it's tight (with even a latex caulk or something that was easy to remove) or try to sneak some paint or other sealant in there with a Q-tip or something if there's room. You don't have to seal the whole back of the front bullnose, just the bottom portion where water drops would collect. I'd seal the whole area behind the front bullnose over/infrontof the dish washer, tho.

Countertop Guy 01-15-2010 07:47 AM

As long as the hole you are putting the sink in is 5/8 smaller all the way around so the sink has a lip to sit on you will be ok. put some 1/4 blocks down 2 on each side to you don't smash your fingers. Caulk around the sink pull the block out and mist the caulk with soapy water from a spray bottle wipe with finger. Some counter tops are only 1/2 thick and this is done everyday.

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