An Introduction To Metal Wall Studs - Part 2
Ok let's get back to working with metal wall studs in my basement, adding some needed storage under the stairs.
In the last post, I had finished the basic frame work for the platform. The next step is to cover it.
Most of the time the go to material to cover home projects is plywood. Plywood is a good choice. Its relatively cheap and easy to get, its renewable and will degrade in a landfill over time, and will hold up for quite a while. It also takes paint and other treatments well. Because I am in a basement and this project may be exposed to water, particularly water with raw sewage should the drain ever overflow, or the basement flood I am going to use another material.
Cement backer board is a type of building material usually used in high moisture areas like bathrooms and kitchens. Its often used under tile. It is a cement composite with a fibrous reinforcement (typically fiberglass) molded into common construction thickness sheets (1/4, 1/2, 5/8"). It is extremely hard and waterproof, meaning it will not deteriorate from moisture over time like plywood or drywall will. Though it will crack if you apply incorrect pressure with your screws, as we will discuss later.
It comes in a 3x5 foot size with a finished side and a rough side. Price is comparable with plywood. One piece of cement board will run around $15 (about $1 a square foot), where a 4x4' piece of plywood will run you around $18 (about $1.10 a square foot). It bonds with drywall mud well, and paints after a coat of primer comparable with drywall.
Cutting it can be a pain though. Like drywall you use a box knife but its hard so it takes some effort. The edge will be a bit rough but you can clean it up with a palm sander and some 60 grit paper.
If you are going to do much cutting of either this, or of drywall I suggest you pick up a 4 foot piece of steel angle. Something like is in the first picture. Get it 1/8 thick, and if you can one with one side a bit longer. The one I have is 2 by 1 1/2". Get steel not aluminum. You will use the angle to break the cut section off.
One longer side means your box knife can be used with less blade sticking out, useful when you're putting pressure on the knife. Buy the type of box knife that you can break off a short section to get at a new tip. You are going to dull a section each time you make a cut, once on the front of the board and once on the back. I found it took me on average 15-20 passes with the knife on each side, to score the material enough that it would break clean. Get lots of blades.
Another tool to get is a "dead blow" hammer. All hammers bounce to a degree, even if it doesn't feel like it when you hit your thumb with one. A dead blow hammer doesn't because it has a small hollow chamber in its head filled partially with loose lead shot. When struck the momentum of the shot deadens the blow. These hammers are also usually covered in a flexible material, or have heads with a replaceable flexible face. For cuts where the off fall of material (the extra you aren't using) is long enough, a few blows with the palm of your hand will snap it. For shorter pieces a dead blow hammer used carefully does the job. You can see the result of one such in the third picture.
Here again the piece of angle comes in handy. Put it under the board, with the score just past the corner of the angle will help it snap. Strike the off fall with the dead blow hammer along the length every few inches. You aren't looking to make it snap with the first pass, just loosen it. Too many blows in one place, or too hard and the off fall will crack.
Two last things to pick up, a couple of "drywall sponges". These are flexible pads covered in a sanding medium, typically used to smooth out drywall mud before painting. Get the ones that have angled sides which allow you to get into tight places. A rough one, like a 80 grit, is good for knocking the cut burr or taking off the rough spots of the separation on the board.
And second, a pair of knee pads. You'll want to hold down the steel angle while you are cutting it and you'll want some cushion under that knee. You can either wear them or do what I do and just lay it on the steel angle.
Note: You can cut cement board with a jig saw, and I've used one to make small notches or trim a corner but for long cuts the cement board will dull the blade very fast. What does work, is a multitool like a Dremel, and a handful of cut off wheels. If you have to do a thin strip, try that. Be sure to wear safety glasses though. Its quite common for the cut off wheel to bind, and when doing so shatter. Sparks and fast flying debris are a hazard as well.
(in addition to the tools from Part 1)
1) Four foot length of steel angle (2x1 1/2, 1/8" or 3/16" thick).
2) Box knife with lots of blades.
3) Several drywall sponges, 80 grit.
4) Knee pads.
5) Dremel multitool and cut off wheels (optional).
6) Several carpenter clamps (you can use C Clamps too) as well as two wood blocks per clamp.
Start With The Sides:
Its easier the do the sides and then the top because when you go to fill in the gaps, its less visible and will hide any imperfections better. Its also stronger. Measure the height you will need. If you are on a slope like I was, then you may need to put a slight angle on one cut. It doesn't matter that much on which side you start though I try to put the pieces that are going to be overlapped on at the corners on first. In this case the long side in the indent will be overlapped by the shorter, which itself will be overlapped by the outside edge of the platform near the stairs.
Measure then cut the piece off of a fresh board, or if you have a scrap on use that. Try for a continuous strip if you can. While you can use a piece that is cracked, "butt joints" which is the term for where two fresh pieces join are harder. You want the board to be a little shorter than the height of the frame. You'll fill the crack later before paint. If you have spots that are too high, you can use a palm sander with some 60 grit to knock them down.
Put the cut piece of cement board up to the side and mark where you are going to drill the screw holes. For a taller piece, use two screws, placed near the under screws holding the metal frame together. For a shorter piece, use one, placed in between the screws. Lay the piece on a wooden board or scrap piece of plywood and drill a 1/16" pilot hole at each location. Once you have all of them drilled, put the cement board piece back onto the side. Secure it with some blocks of wood and carpenter clamps, being sure not to over tighten them. The board will crack if you do. Drill the pilot holes into the metal frame through the ones you just drill in the piece.
Remove the cement board. You want to now drill out each of the holes to the diameter of the screws you are going to use. You want the screw to slide easily thru the hole, this way the screw doesn't grab the cement board piece itself, but instead grabs the metal frame under it, and tightens the board to the frame. If the threads of the screw grab the cement board too, there is the potential for a gap under the board.
A word on screws. While you can use Phillips head drywall screws for this, there are specific screws for cement board which are preferable. They use a Star bit or Square bit. These bits engage with the screw better and don't slip off and damage the screw like a Phillips head can. The also have slight serrations under their head which help to countersink the screw. Help but not do the entire job. They also have slight bumps on the top of the screw head, which help you tell if they are fully seated and below the surface. Buy a box of them. Usually the manufacturer throws in an extra bit, but you'll want to get a pack of 2 for extras or if you lose one. You should also get a screwdriver that has a removable tip, and put a star bit in in too. This will help you tighten down the screw the final bit.
A word on working inside and making dust. Here is a big word of warning, which applies to any project you do inside your home, but especially if you are in your basement or near your furnace. IT GETS DUSTY QUICK! This dust can get inside of many things but the biggest danger is it gets into your furnace. This dust can damage your furnace by coating the transfer coils. Change your furnace filter weekly through a project, even more often if its bad. Hang plastic sheets and segregate the furnace area from the project area. Turn the furnace off while you work, and if you can, vent the rooms with a fan to the outside. Practice clean work areas. Sweep up, vacuum and try and avoid tracking the dust throughout the house.
The Downside of Cement Board: The biggest problem with using cement board is its strength. The fiber reinforcement and the cement itself dull drill bits pretty quickly. So you'll need extras of all your common bits. In addition you'll need a few countersinks. These are triangular shaped cutters that you will use to open a cavity at the top of the screw hole which allows the screw to seat flush with the finished surface. For this project I went through 3 of these bits. At about $15 each, yes its a big additional expense but given the other advantages of using cement board in a moist environment, acceptable. Shop around, you can often find sets of them cheaper.
You can use countersink bits that are bigger than the size of the screw head too, even smaller ones to cut the hole. Drill it, then put the screw in the hole upside down to test for fit. If it doesn't completely go into the hole, cut a little more. You'll make the final cut once the board is on the frame. Don't put too much pressure on the bit. It heats up quickly and the hotter it gets the quicker it will go dull. You'll also polish the hole if the bit is too hot, and not actually cut. If you see some brown discoloration, stop and switch out the bits. Be careful, the bit will be hot enough to burn you.
You can also pivot the drill a bit from side to side in a circular motion to help cut the hole, especially as the bit gets dull. Another trick is to save one bit for the final adjustment, and make the rougher cuts with the ones that are dull.
UPDATE: I found a work around that saves money on countersink bits. I had an old carbide tipped concrete hammer drill bit. It was worn down so it wouldn't cut concrete anymore. I found it worked ok on the cement fiber board. Pick one that's the size of your screw head. Once you've drilled the pilot hole, use this bit to drill a little way into the board. Pulse the trigger so it only drills a second or so. Once you get it deep enough for the screw, do a final pass with the countersink to taper the edges.
Once you have fitted the new piece of cement board and are ready to install it, there's another bit of prep work you'll need to do. This has to do with the way the metal frame is put together and the screws used. The round heads of the frame screws typically indent into drywall, which is softer than cement board. Since they don't, the pressure point they cause can crack the board. You can do a couple of things, install the exterior screws carefully and don't over tighten them, or make a depression on the back side of the cement board for each screw. What I find is the easiest is to apply some filler at the point where the exterior screws are being installed. The filler I use is auto body putty, often called by the most well known manufacturer, "Bondo".
Bondo is a two part filler used in auto body repair, but is also incredibly useful for a wide range of other application. It consists of a grey primary and a red activator. Its mixed in a 50 to 1 ratio of filler to hardener. The putty is sandable and can be worked with tools. It takes paint well once primed. You can see the can of filler in the picture below. A small tube of hardener comes with the quart container, but most people buy an additional tube.
Getting the 50/1 ratio is hard to do by eye, and most people add more hardener than is recommended. This doesn't change the fill capacity of the putty, but it does make the putty harden quicker. Too much and it will harden before you can apply it. Mixing too much hardener is called mixing it "hot" because it will actually warm up as the chemical reaction happens. If you ever work with fiberglass resin, you can actually get the filler so hot it smokes.
Its not recommended that you mix on cardboard or paper because it will absorb some of the resin in the filler, and use the plastic cap that comes with the quart can instead. Most people, as I do ignore that, and just mix on a small paper plate with a plastic knife or spoon. Don't use plastic foam plates, the resin in the filler will melt the foam and make a complete mess.
If you use the plastic lid, you have to wait and let the excess filler harden to get it out. The plastic lid is of a type that the filler doesn't stick to it, making it useful but then I just throw away the used paper plate and use a new one.
Ok now to install your first side piece of cement board.
First, put the piece of board on the floor aligned with the frame. Place a couple of screws handy, along with your screw gun and the screwdriver with star bit. Open up the can of filler and spoon out a hefty spoonful onto your paper plate. Put a small bead of hardener (about a half inch long) onto the top of the grey filler. Mix well until it is a consistent color. I use the handle of a spoon to mix it, since its easier to dab filler with that than the spoon itself.
Put a small donut of putty about 1-1 1/2" large around each screw hole, on the back side of the board. Try not to get the filler into the hole itself but if you do, don't stress. If you have some extra, dab a small bit at the long spaces between the screw points. Unless you really made a hot batch you'll have several minutes to work with it. Once you get it all on the board, lift the board into place and using the screw gun, screw the board to the frame. Don't go all the way in and over tighten if you can help it. Use the screw driver to tighten them in. You may find that the countersink hole is not deep enough and the screw head does not go flush. That's ok for now, you'll adjust the depth after the filler sets up.
On the center expanses between the screws you can put a carpenter's clamp with wooden blocks. Just don't hand tighten them too much. Some minor waviness of the board is ok. Once the cracks are filled and the board painted you won't notice any minor imperfections.
While that is drying, measure and cut your next side piece of cement board. It takes about 30 minutes for the filler to reach complete hardness and you can remove the clamp to work on the project further. I usually let the whole thing dry overnight for good measure though.
1) A box of cement board screws (#8 by 1" are good), screw driver and star bits.
2) Appropriate drill bits for size.
3) Several counter sinks.
4) One quart can of body filler, additional tube of hardener.
5) A package of small paper plates, a package of plastic knives or spoons.
Once you've let the side pieces dry over night, remove any remaining clamps. Remove any screws that don't sit flush, one at a time and adjust the depth by drilling the countersink a bit more. Reinstall the screws.
Fixing A Cracked Side Piece
It does happen that when you are cutting a piece that it will crack on you when you go to break it off. This happens if you use too much force with the hammer but it can also happen if you are using a thinner cement board. For this project I had some scrap 1/4" thick cement board and used it for my side pieces. It separates easier after being scored, but can break too. It can also crack when you are installing it. You can use it but you need to put some extra support under it with some more frame screws.
If you haven't put filler on it yet, you can take your time. If you have then you'll need to be quick about doing this fix. One reason not to mix your filler too hot. If it cracks before you do filler its easier to fix. After you have drying filler you're best bet is to just throw it away and cut another, or scrape the filler off and mix more when you are ready.
What you want to do is provide support for the crack, that doesn't put stress on it when you screw it to the frame. You do that by putting 8 frame screws on either side of the crack, then installing the exterior cement board screws between them (see picture). Cement board sands well, and the crack once supported will take paint and be next to impossible to notice.
When you are ready to install the piece, place filler putty in between the frame screws like you would for normal installation AND put a hefty amount under the crack itself. Don't screw exterior screws into the cement board when you install it, but cover the area with a wooden block long enough to cover all the new screws, and clamp it. Let it dry then drill the holes for the exterior screws. Be sure to mark on the frame where the frame screws are though.
I'm going to stop here, and we will get to installing the top piece and the shelves in two weeks. Here's a picture to tide you over.
Sun, 01/23/2022 - 18:38
Update to Cutting Holes in Cement Board
I found a work around that saves money on countersink bits. I had an old carbide tipped concrete hammer drill bit. It was worn down so it wouldn't cut concrete anymore. I found it worked ok on the cement fiber board. Pick one that's the size of your screw head. Once you've drilled the pilot hole, use this bit to drill a little way into the board. Pulse the trigger so it only drills a second or so. Once you get it deep enough for the screw, do a final pass with the countersink to taper the edges.