by TanyaMadsen »
Sat Sep 11, 2021 6:17 am
This question comes up in the forums all the time, so I think it's time to shed some light. When you're trying to block sound from coming through a door, you want something that is both dense and heavy. Here are my thoughts on hardboard.
When hardboard was introduced in the 1930s it was hailed as wood's greatest miracle invention; stronger than steel yet lighter than aluminum. Time has done little to tarnish this reputation though few even know what it is today. It can be purchased under various trade names like Masonite®, Para-Bord®, Thermatape® or Dricore® (but isn't Dricore just CoreForm™?) CoreForm™ is an acoustical sub-flooring material, not really sub flooring. It can be used under carpet or vinyl but isn't very useful for soundproofing a door unless it is the only material you have to work with.
Hardboard's biggest benefit is that it weighs almost nothing. It has an R-Value of .5 per inch which means that if you were to use 1/2" hardboard on your walls and ceiling you would effectively double the thermal insulation in your room. Unfortunately, acoustic properties are more about density than they are about weight so this is not helpful for soundproofing doors. Then again, it doesn't actively hurt either though I have certainly seen heavier materials used incorrectly with better results so don't let anyone tell you that weight is the only thing that matters. The reason I bring this up is because hardboard has a very high fiber content which would make it absorbent so it should be avoided if possible, but you have to work with what you have sometimes.
Hardboard can be cut to fit your door openings but it will break down into smaller pieces that are more difficult to work with. It seems to me that cutting even thin 1/8" hardboard over and over again would eventually damage the saw blade so thicker material would require fewer cuts. Cutting thin material repeatedly will warp the good name of anyone who works with it though so take note if you choose this route. You could also use something like acoust sheathing, which may come in 4'x8' sheets depending on the material.
The next option would be to buy sound panels which would work better than either of the two options I've stated so far, especially if they are vinyl or rubber-backed since they will grip your door frame and not slide around. Still, unless you have them in hand already for another reason it's difficult to know how heavy they might be until you get them home. If heavier is better then that could be a win but what if you can't support what you're putting up? You might well wind up with something that slides down over time unless you secure it properly without blocking too much sound through the door itself. Sound panels come in various thicknesses, R-Values and weights so you would need to research before making a purchase.
One last thing I will mention is that hardboard can be easily glued (with the right adhesive) and offers reasonable impact resistance (R-2 per inch). If you're gluing it directly onto your walls or ceiling, this could help with soundproofing your door while making up for some of its shortcomings. However you would probably want to test it first on a small area where it won't show (like under the bottom of the door?) and wait at least 24 hours before bringing any foot traffic over it just in case.
