trouble with homasote

I think your issue came from not securing the homasote down tight enough.   I used 1/2 plywood and 1/2 homasote glued down on top, weighted **** near everywhere on top over night.   Mine has been up over 3 years with no issues and flat as a pancake.   I think I used liquid nails.   I'm guessing you'll need a putty/mud of sorts with a little sanding to get it good and flat.   Shouldn't be too bad to work past.  Good luck.

@42trainman posted:

I think your issue came from not securing the homasote down tight enough.   I used 1/2 plywood and 1/2 homasote glued down on top, weighted **** near everywhere on top over night.   Mine has been up over 3 years with no issues and flat as a pancake.   I think I used liquid nails.   I'm guessing you'll need a putty/mud of sorts with a little sanding to get it good and flat.   Shouldn't be too bad to work past.  Good luck.

Yeah, it sounds like a failure to bond, but I'd be inclined to either rip it apart and reglue properly if feasible, or scrap the existing (and likely warped) homosote and replace with a new sheet. If the homosote has not adhered properly to the plywood, I'd be afraid just patching and filling would leave the layout unstable and uneven, leading to more problems down the road. IOW, I suspect such a large variance indicates there's big gaps between the layers, with warping of the homosote, and that's not a situation onto which I'd want to expend further efforts in landscaping and accessorizing, much less attaching track.

Seems odd, I have the homosote on mine just placed on top of the plywood, in some cases it cupped up but a few screws solved that.  I taped the joints and painted. I any area with small mount of flex it tended to all come out in the wash when I screwed the track to the homosote.

I used screws to fasten mine. Then I painted it. It never cupped, warped or delaminated.

Same as Renovo PRR. My club and my home layout are both 25 years old. Never a problem with the homosote.

Did you paint both sides?  What fasteners were used in the Homasote and how close together are they?  May help others avoid this issue.

Bill

I used sheet rock screws and smoothed over the top of the screws with joint compound.  paint over the top. been down more than 10 years in my basement with a dehumidifier

I used liquid nail and screwed the homosote down to the plywood.  After the glue dried, I removed the screws and patched the holes then painted the homosote.  20 years in a basement and still level.

@Renovo PRR posted:

I used screws to fasten mine. Then I painted it. It never cupped, warped or delaminated.

I did the same exact thing with both my first layout and current layout and had the same results. No problems.

On this newest layout I also used a product for underneath the homosote recommended to me by Thom Thorpe called Advantech. It is known for being very flat.

Thanks all for your replies. I am still perplexed why the homasote bellied. I used 1/2 in plywood that is supported in 4 x 4 sections. The 1/2 in homasote is glued is fully glued down using a full tube of liquid nail per 4 x 8 sheet and then testing for any raise areas and using a lot of sheet rock screws to pull it down flat. The whole outside structure is 2 x 12 x 16 with 2 x 4 cross members. Why it bellied in some spots and not in others I don't know. I would tear it apart and redo it but since the layout is 40 foot x 45 foot, I will have to work with what I have. Thanks all.

It is possible that the issue is not any lack of support, it seems like you have plenty. Plywood can expand/contract almost 1/4" per 8' length - and I imagine homasote could do something similar. If that quantity of homasote AND plywood material was brought into the house and installed without at least 24/48 hours to 'acclimate' or relax into the temp/humidity conditions of your basement - the expansion/contraction that can occur when (in your case expansion) 40~45 linear feet of material is installed might be what’s happening. (shrug) I wonder if the expansion of the homasote and/or contraction of the plywood is a factor here. A nice 'tight' installation could contribute to this. Does it look like the panels are pushing their edges against each other or forcing their edges to bulge?

I don't understand what happened, but I have to believe one factor may have been not allowing it to "cure" long enough in the environment it was to be used in.  I brought the Baltic Birch and Homasote into my finished basement and it was stored flat for a few weeks before the actual build.  I have always had a couple dehumidifiers running keeping the humidity below 40% at all times.  When the Homasote was laid, I put lots of screws along the edges, but probably a screw a foot over the middle sections.  I used no glue as I was thinking if I ever had to pull some up.

I had absolutely no buckling of any kind for the Homasote, it's as flat today as when it was laid.  I do note you have significant runs with no breaks, that could be a factor in the issues with buckling.

Here's a shot of after the screws were filled before sanding and painting the surface.

@woodsyT posted:

If that quantity of homosote AND plywood material was brought into the house and installed without at least 24/48 hours to 'acclimate' or relax into the temp/humidity conditions of your basement - the expansion/contraction that can occur when (in your case expansion) 40~45 linear feet of material is installed might be what’s happening.

I came here to say just that too. Acclimation tends to get overlooked quite a bit even in home construction. I would even suggest that 24 hours is too short a time for wood to acclimate. Several days should do it.

You said you used 1/2” oak plywood under the homasote, is that correct.  I question why you would do that, first of all it’s very expensive and it is finish grade plywood, like for cabinets, not meant to be used as an underlayment.  I wonder if the glue you used didn’t adhere so well to it.

You can prob fix your issue with some well placed screws I would think.  Kerf the homasote if necessary.  It’s fixable.

Sounds to me like the wood shrank from loss of humidity. Homasote doesn't shrink, so given its sound attachment to the wood, it has to buckle. I've had track hump up and air electrical gaps close from large drops in humidity in the layout room. Consider adding a humidifier, even temporarily, to see what happens. The Homasote may flatten out when the wood absorbs moisture.

Would it be possible for you to take a straight edge (perhaps a 4' level) and bridge it across your worst belly and take a photo showing the gap? Then do the same on the underneath in the same area and post the photos. I can't understand how the homasote has deformed that much yet the plywood and supporting members have stayed level.

As cape cod northern said " check for the flatness of the plywood." Go underneath the table with a straight edge  and check for flatness. If the plywood is buldging down, that could be your problem.

It's possible the Paint when drying caused it to warp. How is the Homasite attached to the plywood, screws or glued?

Last year we tore up our HO layout to the plywood and temporally (just to see home much noise it would make) laid homesite on the plywood and threw down some Fastrack (no screws or glue). every thing is flat.

@William 1 posted:

You said you used 1/2” oak plywood under the homasote, is that correct.  I question why you would do that, first of all it’s very expensive and it is finish grade plywood, like for cabinets, not meant to be used as an underlayment.  I wonder if the glue you used didn’t adhere so well to it.

You can prob fix your issue with some well placed screws I would think.  Kerf the homasote if necessary.  It’s fixable.

Well, I used 1/2" Baltic Birch multi-ply for my 12 x 24 platform build, it turned out to only cost a little more than $100 over the cost if I had used 1/2" good one side plywood.  The Baltic Birch was a pleasure to work with, and it doesn't warp at all!

I have heard about Homasote for over 60 years, and have never seen a sheet of it.  I have gone to lumber yards back in the day and now our normal selection of modern big box building supply stores and you will get blank stares when you ask about it.  I just did a search for finding it within 100 miles, several stores out there all mom and pop or regional, and not a one stocks it, but they will special order it.  I have used 2X4 foot suspended  ceiling tiles placed upside down and glued, many times you can get them free or at  major discount because there be a pile of broken or damaged ones.  They have a sound deadening quality also.

Like William 1 said, I would try and slice the homasote in the middle of the "belly" and then screw each side down with lots of screws to get it back to level. If the middle rubs together, unscrew and cut out a small (1/8") section along the slice and re-screw. Once set, patch over the slice and screws with flexible speckling compound. 

If all else fails, perhaps you could cut out the "bellied" section and replace with a new homasote patch.

@CALNNC posted:

I have heard about Homasote for over 60 years, and have never seen a sheet of it.

It all depends on what part of the country you live in.  It's available at the local Home Depot or Lowes here in SE-PA.  However, when I bought it in 2019, it was $12 a 4x8 sheet, now it's $48 for the same thing!

My guess is that the particular sheet you have was defective from the manufacturer, with a void occurring during the pressing process under the top skin.

Seriously doubt the Homasote is defective. Most likely cause was moisture in the plywood, failure to acclimate the wood to the environment before gluing and screwing the Homasote to it, and subsequent shrinkage of the plywood due to moisture loss, which forced the Homasote out of shape. Homasote is an amazing product that can be repeatedly water soaked with no effect on size. Not so wood.

it’s $36 a sheet now around here, Chicago area.  I’m in the market for 2 sheets for a standard gauge layout I am building.  I’m putting it on 7/16” OSB on 1x4 framing and don’t expect any issues.  I’m going to screw it only for easy tear down which is inevitable.

We used some white glue and then liberally used sheet rock screws. No problems.  It might be a good idea to do as some suggested above. Just try using a liberal amount of screws now and see if you can make it “settle down.”

As others have stated, I too have 1/2" birch plywood with Homasote glued and screwed with sheetrock screws on top. No issues at all. One thing I did notice is that I saved some pieces of Homasote from my previous layout and when mating them together with the new homasote on the new layout there was a slight difference in thickness. Also some of my sheets do have thickness variations throughout the the same sheet, although not enough to take notice. I purchased mine at Lowes here in upstate NY.

Homasote is made from recycled paper, like cellulose insulation, pressed together with a wax emulsion binder.  The wax is used to provide moisture resistance.  Ok, I googled it.

Was considering using homasote only, skipping the OSB layer, it is pretty stiff and would prob be ok with joists @ 16” oc, but it’s only 2 sheets so I’ll do the joists 24” oc with the OSB.

Well, that homasote repair might just be as involved as this similar one:

https://www.youtube.com/watch?v=fQRbICp4NWo

@R2unit posted:

As others have stated, I too have 1/2" birch plywood with Homasote glued and screwed with sheetrock screws on top. No issues at all. One thing I did notice is that I saved some pieces of Homasote from my previous layout and when mating them together with the new homasote on the new layout there was a slight difference in thickness. Also some of my sheets do have thickness variations throughout the the same sheet, although not enough to take notice. I purchased mine at Lowes here in upstate NY.

I did notice some slight variation in thickness, but no more that about 1/16".  I got all 12 sheets of mine from the same pallet at HD, only rejecting pieces that were damaged in handling.  They even cracked a new bundle for me since they only had a few mothy sheets that weren't bundled.  Overall, I'm very happy with the Homasote base, and a bonus is it holds the track screws very well.  As long as you don't screw into the plywood under it, no issue with noise transmission.

@gunrunnerjohn posted:

I did notice some slight variation in thickness, but no more that about 1/16".  I got all 12 sheets of mine from the same pallet at HD, only rejecting pieces that were damaged in handling.  They even cracked a new bundle for me since they only had a few mothy sheets that weren't bundled.  Overall, I'm very happy with the Homasote base, and a bonus is it holds the track screws very well.  As long as you don't screw into the plywood under it, no issue with noise transmission.

Same here, I too had them open a new bundle. I only needed 4 sheets, the ones that were loose were all banged up. yes it holds track screws very well and cuts down on the noise.

Hello everyone and thanks for all your replies. First. I did mix up the type of plywood I used. It was birch plywood. I used oak panel in the room, and I mixed up the wood types. I did allow the wood and the homasote to get use to the room temp before I glued and screwed all together. I think the area of homasote that bellied was caused by the radiant heat I installed under the floor plus the heat radiating from the radiant heat I put in the concrete floor in the shop below. I have yet to insulate between the floor joist and keep the heat in the shop. The problem area is contained to 2 4x8 plywood sheets. I got under the layout and used a toe jack to push up the plywood in the middle of a 4x4 section. it pushed up the plywood to the bottom of my beam level, but there were still dips on both sides of the push up. I ordered 4 basement beam jacks the I will place in the 4 4x4 areas that have bellied with large surface plates above and below the jack so that the lift up covers a large area. Since I cannot tear out the affected areas, I have to work with what I have. I'll let all know how this fix works out.

@Renovo PRR posted:

I used screws to fasten mine. Then I painted it. It never cupped, warped or delaminated.

Same here.  And mine is in a heated garage bay that has significant summer-winter temperature & humidity fluctuations.

@KarlDL posted:

Same here.  And mine is in a heated garage bay that has significant summer-winter temperature & humidity fluctuations.

Ditto.  I didn't glue at all, just used lots of screws.  Nothing has warped at all, it's been down since July 2019, so it's had some time if it were going to go anywhere.

I guess I was not clear enough on my problem. The homasote is not bulging up, it is pulling down from level. I have added 3 photos of my beam level which is showing it is currently at level. the other 2 photos show where the homasote has pulled down from level by 1/2 inch and 3/8 inch. I have only had this problem with two of the 4x8 sheets of birch plywood that is supported on a 4 foot x 4 foot basis. The beam level is sitting on the 2x12 that go across the 4 foot end of the plywood with a 2x4 running across the middle. Both problem 4x8 plywood sheets run end to end. I am going to try using 2 3 foot x 3 foot sheets of 3/4 plywood glued together pushed up under one of the 4 x 4 affected areas and see if that works. I did jack up a 4 inch x 4 inch post in the middle of the dropped area and did push it back up to level but the areas around it were still dropped. Once I get an area pushed up, it may be a wait and see if the whole area will rise. Since the whole frame of the platform is 2x12's, it has a lot of down weight to push against my pushing up.  

Not sure if I understand, but if your framework has open unsupported areas of 4' x 4'; thats a lot.  I could see that if you put a spot post in that you could still have droop around the post.  You may need more intermediate framing.  Rather than more plywood (and weight) I would put in more framing within the the open 4 x 4 area if possible.

Bill

I gotta' go with Bill here.  48" unsupported is a lot.  I have 24" unsupported and I thought I was pushing it.

Homasote has no structural capabilities by itself. It needs adequate support form the sub-structure (layout frame). If you don't have any joists under the Homasote, I would add some running across in the short direction.

Usually for layouts they recommend joists (1x4s usually) every 16". That might be overkill unless you are one of the people who believes you need to build it strong enough to walk on. I think 24" centers is okay if you aren't going to walk on it, as long as you are using the plywood you specified. But 48" spacing... wow, that is quite a gap.