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 homosote could do something similar. 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. (shrug) I wonder if the expansion of the homosote 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.