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Can you seal MDF with poly? Stair skirt meets concrete

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Forum topic by jaybee76 posted 10-09-2019 02:15 PM 358 views 0 times favorited 14 replies Add to Favorites Watch
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jaybee76

21 posts in 37 days


10-09-2019 02:15 PM

I used primed mdf for my stair skirt.

I need to seal the bottom.cut where it hits the concrete.

This of.course will not be seen but will be in contact with concrete

2 options, because i dont want to buy another product for 12 inches of mdf so it can sit in my cabinet

1- use either an oil or waterbased poly on the bottom.and call it good.

2- after cutting the skirt to size, go back and cut an 1/8 off the bottom

For number 2, there is no.floor i would install in the basement that WOULDNT hide that small of a gap so i am seeing this as the best solution

Am.i wrong?


14 replies so far

View WoodenDreams's profile

WoodenDreams

749 posts in 424 days


#1 posted 10-09-2019 04:48 PM

I don’t use MDF on any of my projects, but my work benches are MDF so I can replace the workbench tops easily. If your not going to painting it, I’d probably scuff sand it, then apply the poly, so the poly has a higher chance of not flaking or peeling off, then sand and apply your poly. You should be ok if you don’t plane on getting the floor wet with water. I’d say go for it, but I’m not a Home Improvement Contractor. Different area have different building codes.

View LesB's profile

LesB

2206 posts in 3956 days


#2 posted 10-09-2019 05:38 PM

Have you thought about putting a strip of rubber across the bottom of the skirt. One source is the building supply stores have “runner” carpets of various types and on type is just plain black rubber about 1/8” thick. It sells by the lineal foot and is abut 18” wide. Just glue it on with some urethane glue or contact cement.

With that comment it occurs to me that you could use a couple of coats of water proof glue as a sealant for the MDF

-- Les B, Oregon

View wildwoodbybrianjohns's profile

wildwoodbybrianjohns

328 posts in 60 days


#3 posted 10-09-2019 05:43 PM

You can get this type of plastic thing in any colour or clear, typically used for bottom edge of cabinet kicks where water or humidity is a factor.

Sorry for the tiny photo, but you get the idea.

-- Wildwood by Brian Johns: It is wiser to find out, than to suppose (S. Clemens)

View MrRon's profile

MrRon

5721 posts in 3756 days


#4 posted 10-10-2019 05:11 PM

I would just caulk the gap with a silicone sealant. The object is to seal the edge of the MDF from moisture. Once MDF gets wet, it breaks down; enough moisture and it turns to mush.

View bondogaposis's profile

bondogaposis

5542 posts in 2864 days


#5 posted 10-10-2019 07:49 PM

Cut it 1/8” short and fill the gap with silicone.

-- Bondo Gaposis

View therealSteveN's profile

therealSteveN

3916 posts in 1087 days


#6 posted 10-10-2019 08:15 PM

I use a lot of MDF, and find it to be a nice product for jigs, and pieces where I need not support much, if any weight. That being said there is enough movement with a stair, that I would shy away from MDF even for a non bearing skirt board, but mostly because your case has a wet area in contact with the MDF, being the concrete.

There are more experienced stair builders here than I am, but I know a solid skirt is a requirement to make a nicely finished stairs. I’m going to use some maybe not fabulous wood, but something much more robust than MDF for the job. Because I do know, once all is in place it’s a PIA to swap out a skirt board.

Even a 2×12 is going to wear, last against concrete, and get the job done. How much are you going to save using MDF instead? If you upgraded to a nicer hardwood, then you could also gain appearance.

My belief is MDF came into being along with trim guys who can’t cut squat, make all trim from MDF, and paint it white, after using copious amounts of Bondo, Spackle, and whatever to fill the huge gaps they didn’t make tight off the saw. I guess I really am a dinosaur. At least a skirt board is a board.

Sorry if I have offended anyone, but trim isn’t mush paper heated to the point of it being solid, at least till it becomes mush paper again.

-- Think safe, be safe

View jaybee76's profile

jaybee76

21 posts in 37 days


#7 posted 10-10-2019 08:41 PM

The skirt wont touch the concrete if it is cut 1/8 high.

I used MDF becauseit was already primed, not really to save money i guess. Wasnt really a motive behind it besides it made sense versus paying for pine and then hoping knots didnt bleed through. And i wasnt going to pay for no knot pine for a skirt board to.paint it.

Its painted the same color as the wall and was planned so in the design so mdf made sense at the time
Unless im going to use hardwood, which isnt going to happen, pine or another soft wood i would use in its place will take little to more abuse than mdf. Which leaves the moisture subject.

If the mdf isnt touching concrete then i dont see an issue. But i am listening and thanks for your input

View wildwoodbybrianjohns's profile

wildwoodbybrianjohns

328 posts in 60 days


#8 posted 10-10-2019 08:48 PM

My belief is MDF came into being along with trim guys who can t cut squat, make all trim from MDF, and paint it white, after using copious amounts of Bondo, Spackle, and whatever to fill the huge gaps they didn t make tight off the saw. I guess I really am a dinosaur.

- therealSteveN

Too funny!

Back when I worked in the NYC high-end market, MDF and particle-board were verboten. Not only is it repackaged garbage, but many of those nouvea riche people knew it continually off-gasses noxious toxins, off-gassing which increases over time, and they werent putting that in their 4 million$ brownstones.

-- Wildwood by Brian Johns: It is wiser to find out, than to suppose (S. Clemens)

View therealSteveN's profile

therealSteveN

3916 posts in 1087 days


#9 posted 10-11-2019 07:05 AM

My belief is MDF came into being along with trim guys who can t cut squat, make all trim from MDF, and paint it white, after using copious amounts of Bondo, Spackle, and whatever to fill the huge gaps they didn t make tight off the saw. I guess I really am a dinosaur.

- therealSteveN

Too funny!

Back when I worked in the NYC high-end market, MDF and particle-board were verboten. Not only is it repackaged garbage, but many of those nouvea riche people knew it continually off-gasses noxious toxins, off-gassing which increases over time, and they werent putting that in their 4 million$ brownstones.

- wildwoodbybrianjohns

Brian, there should be a law in this age of protectionism about how much of it is allowed in a home. Thing is Silly Sally Housewife wants her Kitchie to be gleaming whiteness, not that dreary wood. I call her a SAVAGE.

Before I quit doing trim work, when I got one of them, I’d just say, Gee I don’t do that. I found it useless to try to explain. Pretty soon it was all of them, none of them wanted the value, and beauty of wood anymore.

-- Think safe, be safe

View Tony_S's profile

Tony_S

1016 posts in 3596 days


#10 posted 10-11-2019 09:40 AM



The skirt wont touch the concrete if it is cut 1/8 high.

I used MDF becauseit was already primed, not really to save money i guess. Wasnt really a motive behind it besides it made sense versus paying for pine and then hoping knots didnt bleed through. And i wasnt going to pay for no knot pine for a skirt board to.paint it.

Its painted the same color as the wall and was planned so in the design so mdf made sense at the time
Unless im going to use hardwood, which isnt going to happen, pine or another soft wood i would use in its place will take little to more abuse than mdf. Which leaves the moisture subject.

If the mdf isnt touching concrete then i dont see an issue. But i am listening and thanks for your input

- jaybee76

Quit defending yourself. There’s nothing wrong with your decision to use an MDF product on your stairs.
I’ll build you a $50,000.00 staircase…and regardless of style and design, I guarantee you there will be an MDF product involved, be it a paint grade or stain grade surface. And it isn’t because we’re a bunch of hacks that don’t know how to use a miter saw.
Why? Because in most(no, not all) manners of speaking, domestically produced, it’s a superior product to veneer core sheet goods. As for 100% solid lumber, very very few consumers would be willing to pay the cost difference. Especially since, excluding hardwood treads, there’s little to no benefit in the end product.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View LeeRoyMan's profile

LeeRoyMan

288 posts in 240 days


#11 posted 10-11-2019 01:35 PM


There s nothing wrong with your decision to use an MDF product on your stairs.
I ll build you a $50,000.00 staircase…and regardless of style and design, I guarantee you there will be an MDF product involved, be it a paint grade or stain grade surface. And it isn t because we re a bunch of hacks that don t know how to use a miter saw.
Why? Because in most(no, not all) manners of speaking, domestically produced, it s a superior product to veneer core sheet goods. As for 100% solid lumber, very very few consumers would be willing to pay the cost difference. Especially since, excluding hardwood treads, there s little to no benefit in the end product.

- Tony_S

Thank You!

View Rich's profile

Rich

5001 posts in 1102 days


#12 posted 10-11-2019 01:50 PM

There s nothing wrong with your decision to use an MDF product on your stairs.
I ll build you a $50,000.00 staircase…and regardless of style and design, I guarantee you there will be an MDF product involved, be it a paint grade or stain grade surface. And it isn t because we re a bunch of hacks that don t know how to use a miter saw.
Why? Because in most(no, not all) manners of speaking, domestically produced, it s a superior product to veneer core sheet goods. As for 100% solid lumber, very very few consumers would be willing to pay the cost difference. Especially since, excluding hardwood treads, there s little to no benefit in the end product.

- Tony_S

Thank You!

- LeeRoyMan

I always listen to the professionals like Tony and LeeRoy. They know what they’re talking about.

View jaybee76's profile

jaybee76

21 posts in 37 days


#13 posted 10-11-2019 02:00 PM

Im cutting it 1/8 short to keep it off the crete and priming the back and any unfinished edge
Thanks everyone

View Rich's profile

Rich

5001 posts in 1102 days


#14 posted 10-11-2019 02:02 PM


Thing is Silly Sally Housewife wants her Kitchie to be gleaming whiteness…

- therealSteveN

Silly Sally Housewife? Kitchie?

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