Describe your wainscoting. For thinner individual stuff I have put a dab of PL on each piece and shot some finish nails diagonally through the tongue and into the drywall. That combined with the baseboard and chair rail I've never had a problem with it. If you are talking sheet wainscoting I think the same procedure would work OK but I would get some fasteners into the framing wherever I could.

 

Your local lumber stores don't sell sheets of flat mdf?

 

Can we get a picture similar to what you're trying to achieve?

 

I found some flat mdf but its slick like a whiteboard so i cant paint it. I guess i could look a little harder.

 

We do MDF on drywall all the time. Sand the hell out of the edges and PL it to drywall&nail it. Sand it out surfaces before applying trim. Pics attached are all on drywall

 

Are you actually using MDF for your stiles and rails?

 

Awesome thanks.

 

Why can't you paint it because it's slick?

 

Sure. The one that has the window tie into the chair rail was actually plastic board (can't remember what it's called), now that I think of it. We've used poplar as well. Haven't done any stain grade yet.

What do you use?

 

I'd use any real wood. MDF is a very bad idea for applications like that. For one, you can't get joints nearly as strong as you can with wood. Second, MDF moves like crazy. It looks great after the install but come winter time next season its a different story, a couple of seasonal cycles and a masterpiece can look like a disaster as paint/caulk lines crack and joints separate, especially any type of scarf joint on long runs. IMO there is not a joinery method that will keep the stuff together on long runs consistently. Even if you put a back strap on your scarf and glued the daylight out of it...the scarf joint might stay together but will in turn cause the corner joints to be pulled in and separate/crack. Very bad situations, I've been in $6million dollar homes trying to find solutions to correct MDF issues in wainscot details like you showed.

I'd switch to real wood only on your stiles and rails, its a huge liability for you down the road if you don't.

Here is a great resource from a very trusted trim manufacturer. There is a lot of false information going around about MDF being stable. Its not.

Koetter Woodworking - MDF Movement

Don't take this as preaching at you. Just sharing what I've learned trying to save a guy some headaches. :thumbup:

 

Thanks, I'll look into it. No problems so far (fingers crossed!). Not my choice to use MDF. I can't stand it but if that's what I'm given to install I just ask for lots of PL to go with it.

 

Do you guys think painting the "endgrain" of the mdf would help with the expansion? What do you mean by PL

 

PL is construction adhesive. They have different grades for different applications but PL Premium is popular.

 

Lol.

 

Nino, where are you at?

I can buy sheets of MDF at the big box stores by me. I assumed that was national.

I use MDF as a backer only. I totally agree with Spencer on stiles and rails. Gotta be wood. If not for expansion, for the fact that wainscotting gets kicked, dinged, wacked, etc. MDF will chunk out if you hit it on the corner. Totally uncool.

 

Austin, tx. To be fair ive only looked at one store. Im just going to explain that to the customer and leave it up to her. Its just a matter of money to her.

 

When the drywall is uneven dew to bumps in the wall ive been uising biscuits to aline the rails etc,whats every one else doing,the biscuits do add alot of time

 

When the drywall is uneven dew to bumps in the wall ive been uising biscuits to aline the rails etc,whats every one else doing,the biscuits do add alot of time

Wow, you speak Tipitop fluently! :laughing:

 

Mdf for rails etc base and moulding in poplar

 

I read the article and it means younhave to take more care when using mdf, not that its useless

 

Its called having 2 young kids and being half aleep while typing

 

MDF shouldnt be shiny. That sounds more like Melamine. I would agree with not using MDF for the stiles and rails. MDF is very strong if it is hit 90° from the face but any angle other than that it will flake off. My opinion would be 1/4"-3/8" ACX backer glued and nailed onto the drywall (hit studs). Popular/white pine or similar grade wood for any of the trim. Stiles,rails,chair,base.

 

MDF shouldnt be shiny. That sounds more like Melamine. I would agree with not using MDF for the stiles and rails. MDF is very strong if it is hit 90° from the face but any angle other than that it will flake off. My opinion would be 1/4"-3/8" ACX backer glued and nailed onto the drywall (hit studs). Popular/white pine or similar grade wood for any of the trim. Stiles,rails,chair,base.

Hopefully that was auto correct spell check... **poplar** :thumbup: :laughing:

 

Hbh i dont remember exactly what it was but i just ended up using wood for rails and stiles and some sort of plastic material for chair molding. Idk what its called but the brand name of it is veranda. Its intended for exterior but its what she chose. Ill post some pics after its all touched up

 

Veranda is a pvc trim. Designed for exterior because of its anti-rot, bonus pest dont like the taste of it either. Im not sure if i missed it in your OP but if you are in business for yourself i would stay away from letting HO's buy materials for you to install. Bad for a couple of reasons. Look forward to seeing the finished product.
*edit* when trimming anything interior you want to stick with like materials if they are being fastened together. Different materials will react to weather changes differently. Someone on here talked about how brutal winters are on MDF even indoors. They were spot on!

 

MDF has a history of being unreliable. At least in my neck of the woods. Especially on any exterior walls. It looks amazing after installation and paint. But after a few winters it seperates. In a perfect enviroment where the humidity and temps are regulated there wont be an issue. But like i said here, its an issue. Trim looks nice by the way. I have a rental that i played with MDF a little to duplicate 100+ year old trim. Looks like a child trimmed it today only 3 years later. Ill take a pic and share.

 

Who the heck is dumb enough to put MDF outside? It's definitely an indoor material. They have Extira which is MDF like, more towards particle board. But it's for signs and things for exterior. MDF will melt like mud in a water environment.

 

Not on the exterior...on the inside of exterior walls

 

The first pic is the head no caulking. Sprayed in place. The second is the sill that was caulked due to it being so close the the shower. Did not look like this after the first year. In the summers we hit 90° with 75-85% humidity dropping to windchills of 30 below in the winter
***edit*** i forgot to mention these have bisquits due to the inability to toenail heads with MDF.

 

The first pic is the head no caulking. Sprayed in place. The second is the sill that was caulked due to it being so close the the shower. Did not look like this after the first year. In the summers we hit 90° with 75-85% humidity dropping to windchills of 30 below in the winter

The weather in Chicago is not really any different than Iowa. An uncaulked or unglued joint will open seasonally regardless of material. Using a quality caulk like Big Stretch or Tower Tech is important for keeping any paint grade seams from cracking regardless of trim material. "Painters Caulk" will always crack.

My entire house is trimmed in mdf and I have no open joints on either interior or exterior walls. My casing was preassembled with PVA glue and pocket screws. Base and crown are coped and outside corners are glued and pinned. With mdf I increase the amount that I add to the length measurements to insure a snap fit to account for the length shrinkage common to mdf and reduce the amount that I back cut the cope. When I snap fit the copes I run a heavyish bead of good caulk on the back of the cope and towel off the squeeze out. I know a couple of guys that don't cope mdf and use miters and glue for all inside corners for running trim. The glue is effective in that application but I'm not willing to sacrifice the speed I get coping so therefore I back caulk. Scarf joints are a butt joint with a dry biscuit for alignment assembled with yellow glue and a back spline hot melted on. The length are again cut long ensuring permanent pressure on both the scarf and the coped corner.

With mitered casing I switch from PVA yellow glue to PUR hot melt. MDF was designed with PVA in mind but I like the poly hotmelt for speed. Pulling apart an assembled joint tears up the material not the joint.

 

Gotta glue that stuff together and use biscuits. It moves a lot.

 

Note edit

 

This is my house trim. The 1x's are MDF. They open up in the winter when it dries out.

I used SW 950A, painters caulk. That was a mistake.

The side pieces on many of the windows opened up in the winter.

I have a humidity unit mounted to my furnace that automatically keeps the humidity as high as it can be in relation to outdoor temp in the winter without allowing condensation to form on the inside of the windows.

Baseboard and cap is mdf also buy for some reason it doesn't crack.

 

Makes me not miss all the humidity of the Midwest. Worst thing I've seen in my house is a 3" flat wainscot cap on an exterior corner of the house, every winter it opens up a hair.

 

Tell me more about the hot gluing any other guys doing thay on there miters,i find its to thick for joints.

 

Tell me more about the hot gluing any other guys doing thay on there miters,i find its to thick for joints.

Where?:laughing: