Why Homasote

Rob,

I read so much about Homasote. I know what the material is. And when I see you using it I take notice because your track record of good advice is impeccable. What I don't understand is the advantage of Homasote over cork or Flexbed if one is not spiking track? Is there a reason why you selected it other than low cost? Your answer is of particular interest to me because I will be at the same construction phase very soon and will have to make a final decision.

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I also have a large surface (yard) covered with Homasote. Sound deadening is one reason. Glued Homasote is the right idea. Adding  nails, apart the sink holes it causes, transfers the sound to the wood and it ends up acting like a sound board. 

From what I read, cork will dry out and become brittle. Probably makes little difference once glued down and painted over.  Also spinking thru cork can  hit the wood, transferring the sound again. Any spikes thru cork and into the Homasote stays quiet.

Re: Why Homasote

Homasote is one roadbed material I'm using on the current layout, cork is the other.  One reason I'm using it for the yard under construction is that I already had the stuff on hand, and got it cheap from another modeler who was liquidating materials before a move.  It works just fine for broad, flat areas like yards, and is cheaper than an equivalent area of cork.  It's not as easy to get Homasote as perfectly flat as cork, so I will be using some spackling material to level out the yard before laying track.

I have no experience with Flexbed/Vinylbed, so can't speak to any pros or cons there.

Homasote/noise

     I don't know why people are so worried about noise on model railroad roadbed.  Real trains are noisy -- very noisy!  I would think, for realism, one would want rolling noise, track noise, click-clacks, etc. -- maybe even mic and amplify it. --Dave N.

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Personnaly not 'worried' about noise but do care about it.

Just add the engine noise to  the roadbead noise resonnating from the plywood to the click clack all ready present. Add to this the wirr of Tortoise motors.  I  like to hear my sound decoders without having to "pump up the volume"  because other noises null out sound.  I also use " environmental "  sounds at low volume.levels (Fantasonics and the likes of)  played thru small speakers in locations. 

Great Idea

Rob-

Great idea for fastening the Homasote to the plywood. I highly recommend Rob's method to anyone using this material. I used small nails to fasten the main line and sidings and drywall screws to fasten the larger sheets in the yards. In several places the Homasote warped up and I had to cut it out and replace it or re-screw it. Not much fun in an area where most of the scenery is complete.

Tom Patterson

Update on Adhesive Coverage

After working on the yard this week and trying to stretch out the adhesive as much as possible, I find the most I can expect for coverage from the 32 oz. can of contact cement is about 64 square feet of Homasote (i.e. two full sheets worth, with application on both surfaces for a total of 128 square feet of cement).  This is a bit less than the manufacturer estimate on the label, but those are often optimistic.  I managed to run myself out before reaching the east end lead, so it's back to Home Depot for more.

Homasote and adhesive

I have used Homasote since 1965 and have never used that much contact cement on a single sheet. I found it's enough to put a 1-1/2 to  2 inch wide strip around the outside edge. Then make a box pattern or checkered pattern by applying a two inch wide strip every foot across and then down the sheet on what ever size sheet you use. Do same matching pattern to the surface the Homasote is going to be applied to.

Then wait 20 minutes for the Contact glue to dry on both surfaces. When you use contact cement applying it to only one of the two surfaces you don't get anywhere near enough adhesion to hold the materials together.

Allowing the solvents to evaporate from both pieces before connecting then makes the two glued surface attract each other and bond on contact to give a firm permanent bond. 

If you are using that much contact cement on a single 4 x 8 foot sheet and not coating the base plywood at the same time your wasting your time as well as the glue. Then again if you want the Homasote to be able to be easily puled off the base plywood then do your way. '

With not allowing the Contact Cements solvents to soak into the adjoining plywood and drawing the contact cement into the surface you're basically making very thick masking tape and getting maybe only 20% the actual bond you can when applying to both surfaces.

Proper Adhesive Use

"If you are using that much contact cement on a single 4 x 8 foot sheet and not coating the base plywood at the same time your wasting your time as well as the glue. Then again if you want the Homasote to be able to be easily puled off the base plywood then do your way."

That observation's a non-sequitur.  As I said (and illustrated in the first photo, which shows the cement just having been applied), I'm covering BOTH surfaces - plywood and Homasote, and completely following the manufacturer recommendations for the product.  In so doing, I'm getting somewhat less coverage than the manufacturer estimates, while not applying the adhesive excessively.

Manufacturer Coverage Rates

I can tell you with 100% certainty that paint, adhesive, and mastic product estimated coverage rate is generated by calculation, not by testing.

Volume solids / Dry Film Thickness = coverage rate

There is no allowance for variation in DFT as a result of practical application nor is there an allowance for application efficiency. It is impossible for any applicator to produce a 100% uniform and exact DFT over the entire work piece. Additionally, the brush and remnants inside the can consume volume that is not deposited on the work.

Manufacturers have a vested interest in publishing the maximum coverage rate theoretically possible. It is the standard across the coatings industry to use the solids/DFT math method of calculating coverage rate.

Often said "Your mileage may vary." In this case.... "Your mileage will always be less than published." If your mileage is better than you are not using the product as the formulator originally intended.

Re: Manufacturer Coverage Rates

Thanks, Alan.  That explanation helps.  I was curious if the Homasote was absorbing some additional cement as I brushed, thus reducing the coverage, although as I worked this subjectively didn't seem to be the case.  In posting my experience, I was hoping to provide a realistic expectation for product use for anybody wanting to try the contact cement method.

Just a dumb question

Rob, just a dumb question. You are staggering your joints with the plywood joints underneath, correct?

I only ask as one of the pictures you show might indicate otherwise.

Am I Missing Something?

This may be a dumb question, but why "contact" cement rather than something like plain old wood glue?

I'm on my third layout and I use cork roadbed for the main and cork sheets for the yard area. I simply glue it down with Elmer's wood glue and have never had any problems with it - as long as I didn't have to pull it up once it was dry to realign the tracks.

Am I missing something?

-George

Wood glue needs air.

This may be a dumb question, but why "contact" cement rather than something like plain old wood glue?

Wood glue will work fine for something like cork roadbed, but wood glue or the white glue both need air to dry.  If you try coating a 4x8 foot sheet of plywood and a 4x8 foot sheet of homosote with wood glue and then joining them, the glue in the center may not ever set up.

PVA Glues

Wood glues contain a lot of water. In excessive cases it could lead to the warping Rob refers to in his OP. The contact cement will be devoid of most of its solvent after the initial tack set-up time. When the surfaces are joined there are very few volatile components left that could be absorbed by the ply or Homasote. The contact cement also offers the advantage of instant holding power. I have used contact cement on countertops. It has some serious holding power when used properly.

Re: Scarpia

"You are staggering your joints with the plywood joints underneath, correct?

I only ask as one of the pictures you show might indicate otherwise."

I have actually not staggered all of the joints.  For the benchwork around the outside walls of the room, I'm treating the installation as sectional/ "domino" in nature so the layout can be disassembled quickly if needed.  As such, the joints are not staggered as doing so would inhibit rapid disassembly.  I followed the same approach on my previous layout and am glad I did.  When we sold the old house the contract gave 30 days for us to be completely out.  Due to the sectional benchwork construction nearly the whole layout was dismantled in only three days, and I was able to salvage nearly everything for re-use.

Of course, the disadvantage to the design shown is the creation of zones of weakness at the section joints, but this can be largely mitigated by solid construction and fasteners (e.g. bolted section joints), and by using the aforementioned drywall mesh tape across the Homasote seams.  In areas of irregular shaped benchwork where I don't expect to salvage much beyond the track, I do stagger joints for strength.

Re: Am I Missing Something?

"This may be a dumb question, but why "contact" cement rather than something like plain old wood glue?"

You've gotten much of the answer already from the above posts.  Based on my previous experience with Homasote and wood glue I'll note the following. 

The big issue with me is dealing with materials that don't necessarily stay flat.  Plywood is susceptible to warping if a lot of PVA-type glue is used, and while that shouldn't be much of a problem if the underlying benchwork and roadbed are doing their jobs, it can still cause trouble.  In addition, Homasote sheet isn't usually perfectly flat, and the areas where I need to secure it aren't always easy to hold in position while slow-setting glue dries.  Contact cement creates an instantaneous and solid bond so clamping, weighting or mechanical fasteners (screws or nails) are not required. 

Drawing on success using contact cement on Homasote, I also started using it on rolled cork sheet to counter the "memory" of being rolled up.  Gluing this type of cork wasn't fun at all with wood glue, but very easy with contact cement.

To avoid Roll up or to counter it

I have started using Liquid Nails for adhering Homasote and Cork sheeting. It is the "Interior Projects & Foamboard Adhesive" easy water clean-up. The stuff really surprised me in that when it dries it sucks the two products together down tight with no highs or lows.

One thing I found out years ago is Homasote sucks up contact cement as you apply it. It seams to take or use three times as much contact cement that masonite uses when I apply it to kitchen cabinets. I have used barrels of contact cement over the years in my business and on the 32 ounce can is says recommended coverage 54 sq feet one surface per 32 ounce of DAP Weldwood Contact Cement so it doesn't go that far if you apply it according to manufacture suggested application. I use the original solvent base and don't know if the product you use saying Non Flammable has a larger surface area coverage. That may be your problem as you say you get 128 sq feet of coverage from one 32 ounce can and that is more than double the recommended coverage of a can so your doing good if the glue sticks and goes that far.

More Coverage

"I use the original solvent base and don't know if the product you use saying Non Flammable has a larger surface area coverage. That may be your problem as you say you get 128 sq feet of coverage from one 32 ounce can and that is more than double the recommended coverage of a can so your doing good if the glue sticks and goes that far."

The non-flammable is listing 190 square feet of coverage for 32 ounces, so I'm getting a little more than 2/3 that.  This isn't really too far off from what I'd expect based on using this cement on other materials like FoamCore board and cork, but it is less.  I could try to change application methods, but so far what I've been doing has been highly successful everywhere else on the layout.  My motivation for choosing the non-flammable was that the furnace room is off of one corner of the train room, and I want to minimize the chances of nasty surprises.

Again, if anyone is thinking of trying this, be realistic about what you can expect out of a can.  If you're going to do a really big area, the gallon size is more economical.

I have actually not staggered all of the joints

Gotcha. I wasn't aware that was a concern of yours (note that I'm 100% on board with that idea!).

Old Dogs and New tricks

Rob

I've never tried the Non-flammable Version as My heating system is Electric Forced Air in My work shop, I had this type of heating put in my home and work shop because of all the painting I do in the spray booth and just have never considered the Water borne version so maybe I'll try some on a home project. I use a number of Weldwood glues and use the dry power water mix for laminating and edge joint gluing. That water solvent Powered glue is the best wood glue I've ever used so I don't know why the water based Contact cement shouldn't be up there with the rest of DAP and the Weldwood products.

190 sq. ft. of coverage is definitely a plus but as I've never tried it and for commercial applications I'll need to check it out. I hate to have one of my counter tops start lifting when a hot pot is placed on it. The low order is also a big Plus.

Now one question ??, does the non-flammable Contact Cement cause the Homasote to swell at all that you have noticed.

Thanks.

Swelling?

"Now one question ??, does the non-flammable Contact Cement cause the Homasote to swell at all that you have noticed."

Not that I have noticed.

Thanks!

Rob and everybody...

Thanks for the info on contact cement vs wood glue. It's good to know stuff!

-George