Not Needed

Homasote often gets blamed for expansion and contraction that can't be blamed directly on it.  Movement of subroadbed materials like plywood and dimensional lumber contributes far more than Homasote, and as such I've never seen a benefit to sealing it.  Then again I live in a drier climate.

If you decide to seal the stuff, waterproofing coatings intended for outdoor use, or other waterproof materials intended for woodworking could do some good.  Latex paint doesn't inhibit moisture transfer but some modelers claim it helps.

Definitely needed

In a damp climate like Michigan, you need to seal it. A couple coats of oil base exterior paint usually does the trick. If you are using flex track you and don't seal the Homasote, your straight track will end up with a wavy when the seasons change. If you are hand laying your track, you can rip it out and start over.

Ray

Allen, Mi

expansion and contraction that can't be blamed directly on it.

Yeah, I often wonder if they are using real homasote or if they are trying to use it without proper structural support? I've found small cutoff bits in my yard that got lost when doing projects and they still looked fine after years buried  in the dirt....DaveB

I have had several guys tell

I have had several guys tell me that I should seal my Homasote.    One guys uses black latex.  The latex for moisture and black for background.  Another guy uses Thompson's water seal.  In Model Railroader's February issue Tony Koester's "Trains of Thought" he was painting his Masonite hardboard with latex to seal it from moisture only to be told by a paint guy that latex "doesn't fully seal a surface.  It lets air and moisture in and out."  With the advice I have been getting, I was just getting ready to paint my Homasote with latex but if it won't help masonite it certainly won't help Homasote.

Ray, you say a couple of coats of oil base exterior paint.  You think that's better than Thompson's water seal?

Kimball

Paris, TN

told by a paint guy that latex "doesn't fully seal a surface

Yeah , from my boat building days I learned that only thin epoxy resin can seal wood well enough to make it moisture proof. and that stuff costs more than most layout bench work could justify. The way to tell if you are going to have a problem is to look at any wooden furniture or other wooden items in the layout space and see if they have moisture damage. If they do then build the layout somewhere else would be the best course of action or build it from steel and put up with corrosion or from foam and worry about mold. In the typical layout space a few gaps in the rails should take care of any problems from unpainted benchwork or roadbed. Using more plywood and thinner section solid wood helps as the thicker the wood the more it can expand and contract.....DaveB

I have been building layouts

Homasote and Water

Homasote (440 Soundbarrier) has a moisture expansion rate of 0.25% from 50%RH to 90%RH. That means an 8' long piece will expand to 8'-1/4" in length across the humidity range.

440 Soundbarrier

Latex paints and oil based house paints are not a moisture barrier. In fact, they are designed to effectively pass moisture. It is necessary to prevent blistering on hydrophilic surfaces - wood, drywall, plaster, etc. As DaveB stated, epoxy is the only consumer available paint product that will greatly slow down moisture transfer. Even epoxy is not 100% moisture barrier. If you can find a paint made with chlorinated rubber that is the hot ticket. Same base material automotive undercoating and pool paints are made from.

Homasote expansion vs plywood expansion

Alan,

Thanks for the info on 0.25% expansion for Homasote.  Can you tell us what is the expansion rate for plywood for the same humidy change?

Regards,

Dave

Wood Expansion

No I can't It is a much more complicated subject with too many variables.

Take a look: http://www.fs.fed.us/ccrc/topics/urban-forests/docs/physical%20properties%20and%20moisture%20relations%20of%20wood.pdf

Not needed

I have used homasote for the past 30 years on my layout. I live in Florida. My layouts have gone thru hurricanes, including Hurricane Andrews which I lost my home but my train shed survived. It has gone thru  humidity, hot and cold weather and none of my layouts have had constant temp control room. I would turn on the air condition when  I was ready to work/play on my layout. And I never had any issues with warping, expansion or contraction. I love using homasote on my layouts for many reasons, a few I like to mention is an excellent material to absorb the sound. Second, it is great with scenery, especiacially to plant trees, poles etc. The only bad thing about homasote that it is heavy, especially if you want to use it on modules, which I DO.

Homasote Sealing

The manufacturer of Homabed roadbed (made from Homasote) recommends it be sealed and includes latex paint in his recommendation. I have Homasote as a subroadbed and Homabed roadbed. I painted both with high quality latex paint (Behr that is both primer and finish coat). The Homasote subroadbed and the plywood on which it is mounted are painted both sides and all edges. My benchwork is painted on all surfaces and edges. Although the room has a controlled environment, I played it safe.

That being said, I have large pieces of raw Homasote in a garage that does not have a controlled environment. I monitored their expansion over time before I made a final decision to use it. I found no measurable dimensional change. I live in south central PA: we have all seasons and summer humidity.

Finally, for those concerned about the moisture resistance of latex paint, note that most exterior paint these days is latex.  

Dante 

Paint It !

The reason to paint it is not to prevent expansion.

You paint Homasote roadbed or decking to prevent dusting.  The stuff produces vast amounts of dust when cut and continues to do so on your layout.  This dust is picked up by the static charges on your locomotives and cars.  Eventually it will attach itself to all the oil covered surfaces like the gears in drive trucks.  Listen to the voice of experience here.

I have over 500' of homemade homasote roadbed on my layout.  During installation, the bed is sanded to smooth butt joints and transitions between varying thicknesses.  This leaves a very fuzzy surface that needs to be sealed.

Homabed recommends sealing with latex paint because of this dusting issue.

If you truly want to seal something against moisture, use waterproof shellac or polyurethane.

Homasote Sealing

Morris is quite correct about Homabed/Homasote dust: sealing solves that problem. However, sealing with a suitable product also can mitigate against expansion due to excessive moisture in the environment if that is a concern for your layout. Quoting from the Homabed instruction sheet: "... seal the roadbed with an acrylic or latex paint ......." and "This will prevent any moisture problems from the weather or room humidity and make your Homabed dust-free."

Now, sealing with shellac or polyurethane will work, but latex paint is much easier to use, and its color can provide a good background for future ballast. Cured acrylic or latex paint is definitely moisture-resistant (we're not talking about long-term immersion in free water on our layouts). Again, be assured by the fact that your home's exterior is more than likely to have been painted with exterior latex paint, which-unless of a low quality in material and/or application-usually resists the ravages of sun and wet weather for a few years, at least, before reapplication is required.

Bottom line: seal it!

Dante 

(No subject)

I started my layout over 20

I started my layout over 20 years ago, using Homabed and have not had a single problem with it. It was never sealed, with the exception of adding ballast, which cuts down the dust problem. It is in a dry basement, and I live in a rather dry climate. Moisture can be a problem, but the material, probably plywood in most cases could be the problem.

I've been using homasote for

I am hand laying code 70 rail

I am hand laying code 70 rail on my Logging Peninsula and some of my homasote is painted with latex and some is not painted at all. I have had rail warping on both, painted and non painted

Note: dry basement with no heat on all the time but does have heat ducts. Only heating basement when working on it, till it gets all insulated and dry walled.

Live in Western Ma.

PVA

I seal my trackbed, several materials, to prevent dust, I use a 50% PVA, water mix. I keep a jar of the mixture ready to use.

I live in New England

and my homosote is not sealed and doing fine after 5 years.

Splined Homasote roadbed

We built my friends large HO scale layout using splined homasote roadbed attached to L-girder benchwork with plywood brackets/risers. We "sealed" the splined homasote with good quality latex paint. The layout is installed in a climate controlled basement. What we found was that the track would move after going through one heating//cooling cycle. Or one cooling/heating cycle. If the benchwork/spline/track was installed during a warmer season (Summer), after the next full cool season (Winter) we'd find the track-work all catty-wompus. Same would happen if the benchwork/spline/track was installed during the winter and sat through the Summer - come next winter it would move quite a bit.

After going through one complete heating/cooling cycle however everything stabilized and we haven't had a problem since! That was about 8 years ago. So - don't know if its soley the homasote or if the benchwork is also contributory.

In my mind, sealing the homasote makes sense as it will protect the homasote from moisture same as the latex paint on the exterior of your house - in addition to cutting down on the dust.

While splined roadbed is great, cutting 4x8 sheets of homasote into strips is a wickedly dusty project! We cut it outside using a table saw and you can't believe the mountain of dust that creates!

Paul Mac

Unsealed--No problems

I live in Central Florida and have my layout in my garage (we don't have basements down here) that is build on Homasote (unsealed) glued and screwed to a plywood base over L-girder framework. The garage gets humid and hot in the summer and cool in the winter. The layout has been up and running for seven years now (wow, time flies) and I don't have a problem with running anything including large wheelbase steam or full-length passenger cars. The track is done with Code 100, yeah I know, it's not prototypical, but when I designed it I planned to use the cruder track because I wanted something more sturdy and reliable as I knew the layout was to be in the elements in the garage. The track was laid in the spring time (medium temperature swing of what the layout would experience throughout the year) with gaps between each section of flex track. The benchwork was allowed to cure for a six months before track was laid. Not on purpose, I just got busy at work. I don't know if any of this plays a roll into why my layout does not experience expansion issues, but this formula works for me. And no, my Homasote is not sealed. I do wonder if it will have problems in time when the scenery is slathered up with glue and water in.

I do wonder if it will have problems in time when the scenery

I doubt it will be a problem, homasote seems pretty bullet proof to me. I think the key was you careful choice of materials and your construction method. ....DaveB

never have

I have used homasote for over 30 years, I have never had an issue with warpage. All my homasote is mounted  on half inch plywood and supported every 16-18 inches. I have had issues with un-eveness of the homasote. A piece of cork glueed over low spots and rasped level takes care of that. And some of my basements have been "damp". In my mind,  trying to seal it is a waste of time. Brian

Sealing Homasote

Guys -  I certainly appreciate all the input.  I have used homasote since the '80s and enjoy the way it takes my track nails and the easy way it cuts.  I avoid the cutting "fuzz" by using Vermont American's Leather/Rubber cutting jigsaw blade #30022.  This blade is like a knife and just slices thru the homasote instead of sawing - producing all the "fuzz".  I get them from a vendor on Amazon.  Works like a champ.  Don't know if there is a table saw blade made for cutting leather or rubber but I'm sure it would do the same if you could find it.

I will use the latex to give me a base to start my scenery and cut down any dust.  Not that I notice much.  I keep it pretty well vacuumed up but that is without scenery.  I know once I get going on scenery that will be harder to do.

Again, thanks for all the input.

Smooth rolling for everyone!!

Kimball

Paris, TN