Best screws to use in MDF subflooring?

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  #1  
Old 05-03-14, 10:48 PM
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Best screws to use in MDF subflooring?

I live in a 1993 Redman mobile home (much nicer all around than the carpenter-ant-damaged, mold/rodent/dryrot infested stickbuilt house that was on the property) and for some reason there's a heat vent in the middle of the kitchen floor. This is not a convenient spot at all, and when I remodel the kitchen I plan on blocking it off.

Problem is, the MDF subflooring is week around the vent, and I need to put something underneath the floor to harden it up (one side is chipped according to my husband). I have no problem getting the wood pieces underneath the opening, and know to screw through the underlayment into the wood, but wonder what would be the best screws to use? Coarse thread...what?
 
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Old 05-04-14, 03:30 AM
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Welcome to the forums! The flooring is not MDF, but most likely either particle board or OSB. If you are abandoning the vent, you will need to remove the boot in its entirety to keep moist air from destroying whatever you plan on covering it with. Are you planning on relocating it to keep a balance of air in that area?

Once it is removed, you can screw a couple of 2x4 s under the floor from above, then place wood in the hole the thickness of the subflooring. What do you plan to do with the ugly patch?
 
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Old 05-04-14, 03:32 AM
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Welcome to the forums!

I doubt it's MDF, most MHs use 5/8" particle board for the subfloor. It's best to cut out the damaged and replace it with plywood or OSB. I've worked on quite a few MHs and what I often do is cut out all the bad PB, replace it with plywood/OSB and then overlay it with 3/8"- 1/2" plywood to give a clean level surface for the new floor covering. Along the perimeter of the MH, HVAC vents and plumbing areas are the usual problem areas.

It's not all the difficult to cut a new HVAC vent in the duct work. IMO it's not a good idea to just eliminate one of them.
 
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Old 05-04-14, 05:28 AM
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The MDF is some special brand just for mobile homes; when I put bamboo flooring down to replace carpeting in one of the smaller bedrooms, it was stamped with the MDF blurb all over it...and a heat vent in the kitchen floor draws every dropped crumb. It has to go.
 
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Old 05-04-14, 05:33 AM
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It's MDF; see previous post. Now, you wanna talk 'bout the siding, yeah, that's @$#%'s particle board. That's why vinyl is going over the top of it.

Not going to relocate the vent; there's plenty of them in other areas close by and blocking off this one won't be an issue in terms of warmth. Middle of the kitchen floor is nice in winter but otherwise it's a crumb-catcher.

I know how to do the patch, but I want to to know the best screws for the job.
 
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Old 05-04-14, 05:58 AM
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I've never seen MDF used as subfloor ..... and I've seen a lot of MH subfloors over the yrs
I would think any deck screw would work fine.
Are you sure the siding isn't masonite? You'll need to either rip it off and replace with plywood/OSB or make sure the vinyl is nailed to the framing [the siding won't hold the nails well]

I have a house built around an old MH, what I did in the kitchen was install the HVAC vent under the cabinet with a grille in the kick plate.
 
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Old 05-04-14, 06:24 AM
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Trust me, it's MDF. Says 'special MDF just for mobile homes' and is bloody thick.

Siding isn't masonite; it's sawdust board, aka particle board. There are places where it was water damaged and it's very distinct and obviously particle board. Most of the existing siding is in good enough shape that the vinyl can be screwed to it, and where it had to be repaired, my husband used OSB. You can't necessarily just replace with OSB/ply, although that would be nice to do, nothing is perfectly square anymore because the poor house took a bit of a hit going over huge speed bumps getting it out of the park where we found and bought it. Putting up the 2 or 3 sheets of T1-11 siding that we did do was a day-long, screaming argument-generating process.

Thought of using your kick plate idea for the vent, but a kitchen has enough heat sources of its own (dishwasher, oven) it really isn't necessary.
 
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Old 05-04-14, 09:42 AM
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Wish I could swing by and take a look, I've never seen PB siding or MDF used as a sub floor. MHs can be challenging to work on as many things aren't standard as compared to a conventional home. When the structure gets racked - that adds a new set of challenges.
 
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Old 05-04-14, 10:15 AM
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Remember back, oh, say, the mid-90's when there was a rash of lawsuits about composite house siding falling apart? A friend had the same crap on her house and got some money to offset some of the cost of replacing the stuff. Good enough for stickbuilt must have made somebody think it was good enough for mfg. housing and they stuck it on mobile homes back then. Probably same deal with the MDF sub.

'many things aren't standard....' ROFLMHO - understatement of the week.
 
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Old 05-04-14, 10:24 AM
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The siding you are referring to was Masonite. It has become a curiosity thing, now. Is there any way you can post a picture of the subflooring and the siding. We don't like to give bad advice, so knowing what we are up against would certainly help us help you. http://www.doityourself.com/forum/el...-pictures.html
 
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Old 05-04-14, 10:34 AM
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Subflooring is MDF; covered with bamboo flooring or carpet or linoleum throughout the house, so you'll have to take my word for it.

Siding's not an issue; covered in plastic (vinyl). And it's particle board, not Masonite. Masonite (or what I call Masonite) is like pegboard without the holes; Home Despot calls it 'tempered hardboard'. Particle board is sawdust with a ton of glue and heavier than crap. What I have is definitely particle board (albeit carefully pressed into wood grain/T1-11 lookin' stuff).
 
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Old 05-04-14, 11:13 AM
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Actually....true Masonite is not the same as tempered hardboard. It's made in much the same way, but not quite. It's a little confusing since trade names seem to get used pretty generically.

Masonite - Wikipedia, the free encyclopedia (check the part about deterioration near the bottom)

Hardboard - Wikipedia, the free encyclopedia

The pictures tell the story the best. Real tempered hardboard (like old clipboards) couldn't be peeled apart at the edges. The 1/4" pegboard I have on the wall in my garage is actually masonite, whereas the 1/8" sliding doors on the garage cabinets (here when I moved in) are tempered hardboard. The first will snap and tear with a ragged split surface if bent too far or separate and bulge if dropped on a corner, the second will snap more cleanly and is very resistant to corner damage.

Different types of something made by a similar process.
 
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Old 05-04-14, 11:52 AM
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OK. We're not being of any help. Answer to question. 1 5/8" sheetrock screws or 2" ceramic coated torx head decking screws. Good luck.
 
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Old 05-04-14, 11:56 AM
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Oops...yeah, kinda skipped the real question. I second the deck screws. Sheetrock screws are kind of weak in the head area and can snap off.
 
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Old 05-05-14, 03:37 AM
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the mid-90's when there was a rash of lawsuits about composite house siding falling apart?
I painted 100's of masonite sided houses back in the 80's but don't recall ever seeing any PB siding. Pics would be nice if for nothing but to satisfy our curiosity

just for mobile homes' and is bloody thick.
While I've worked on a few MHs that had factory plywood subfloors, the majority have been 5/8" PB. It isn't uncommon for PB to swell when it gets wet. I wonder if you removed the floor vent and took a pic of the cut edge of the subfloor would it give more insight. I'm wondering if the MDF stamp signified a manufacture's name rather than the type of material ??
 
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