Shouldn't be a problem. Just glue and screw it to your plywood base and all is good.

Trainman6446 has given you the correct answer. It is as simple as that. I have used homasote for over 30 years and once you have it on the plywood it is good as new.

Which is why you need solid (like 3/4" Plywood) support underneath it.    Glue and screw it to Plywood and it will flatten out without issue.

Ken L.

I really like homasote. I purchased "Homabed" years back. Homabed is a quarter inch thick roadbed material which is great. I laid mine on 5/8 plywood and haven't had a single problem with it at all. I started handlaying my layout and really like the way it holds spikes. Just used wood glue to fix it to the plywood. The picture shows the profile. It also holds ballast extremely well.

Thank you gentlemen!

It's been alternating rain and just plain hot and sticky since I started this new section.  The warped Homosote may just flatten under the weight BUT I am thinking of cutting it into 1-1/2" wide strips aka Homo-bed to get some fast profile. Switches will just be cut out as a group I guess. If it doesn't smooth out sell then it may be a challenge in the table saw so will go down as a sheet - glued and screwed as suggested.  I don't have a router but it cuts fairly easily with a box knife ... hmmm (sort of talking myself into this direction).

I went to Home Depot and got some 1" two foot square pink foam just in case. It doesn't seem to have enough density to hold spikes but I'll do a little test section to see. What should I use to hold ties to the foam? Never tried this before.

It'll keep me busy until the weekend at any rate. Not much time after listening to "Post Disaster Assessment" training all day.

Neil

"I went to Home Depot and got some 1" two foot square pink foam just in case. It doesn't seem to have enough density to hold spikes but I'll do a little test section to see. What should I use to hold ties to the foam? Never tried this before."

   I wouldn't use foam under the ties if you want to hand spike, unless it's very dense foam it would tend to crush under the spiking weight and would offer little spike withdrawal strength. Homasote is about ideal for hand spiking or a good soft pine or similar wood for a second choice. You want something that the spikes can be pushed into without bending but that grips the spikes once they are driven..The alternative is hand lay on foam using PC board ties and no spikes I guess.......DaveB  

Thanks DaveB. I found my Homosote a little wet but flattened out fairly well so I'm cutting it to shape. My experience with hand spiking into this works well and lasts a long time. It's now drying on my patio so we'll see how well it dries out. I'll be posting my progress under the new town of Haleiwa. 

Neil

"It's now drying on my patio so we'll see how well it dries out.
 

    I think it will be fine, Homasote is a lot tougher than it looks. Spraying it for gluing ballast doesn't seem to hurt it ....DaveB

All the Homasote I bought from Home Depot was somewhat warped.  I painted it with a latex to semi-seal it from moisture and used 1-inch drywall screws to fasten it down to the plywood subbase.  That pulls any warp out of it.

Now if yours got wet or soaked, you might want to check to see if it expanded.  You do want uniform thickness as much as possible.  If it is bloated or expanded from getting wet, it would probably be wise to buy fresh homasote from the hardware store and then seal it and keep it dry.  Any warping can be pulled out when you fasten it down with the drywall screws to the plywood.  You can used some spackle to fill the divots left by the drywall screws.  The paint you use to seal it and help it resist moisture can also give it a bit of a color base for scenery too.

Use screws and glue to hold the Homasote to the plywood.  Then just back out the screws after the glue dries.  No screws to hit with spikes, nails or drills.

3/4" plywood will warp if you lean it against a wall for a long time.  Foam curls too,

Its amazing all the myriad of "horror" stories about why Homasote won't work and how bad it is, yet it has remained a staple for the last 50 years.