Hello
I'm a bit puzzled. My question arises after building a staircase in plywood, which is going to be tiled, where it's said to be wise to add a layer of gypsum in between, even though plywood is relatively stable, but not as stable as gypsum, from what I understand.
Anyway, gypsum is a stable material, but when you install it on a living material - what actually happens to the gypsum board when the other material moves?
If you screw or glue gypsum to a wooden surface, why is it guaranteed to be good with a gypsum board? If the wooden board is compressed or stretched, shouldn't that affect the gypsum board too? For example, causing it to crack?
I have understood that it works this way, after all these years as a hobby home builder, but I don't understand what happens under the gypsum board when the wood layer moves.
For instance, I've read that floor gypsum should be glued, and I imagine that the gypsum should move as much as possible with the wood material?
Thanks for the clarification!
I'm a bit puzzled. My question arises after building a staircase in plywood, which is going to be tiled, where it's said to be wise to add a layer of gypsum in between, even though plywood is relatively stable, but not as stable as gypsum, from what I understand.
Anyway, gypsum is a stable material, but when you install it on a living material - what actually happens to the gypsum board when the other material moves?
If you screw or glue gypsum to a wooden surface, why is it guaranteed to be good with a gypsum board? If the wooden board is compressed or stretched, shouldn't that affect the gypsum board too? For example, causing it to crack?
I have understood that it works this way, after all these years as a hobby home builder, but I don't understand what happens under the gypsum board when the wood layer moves.
For instance, I've read that floor gypsum should be glued, and I imagine that the gypsum should move as much as possible with the wood material?
Thanks for the clarification!
Perhaps it is that the plaster restricts the wood's movements?
And thus keeps the grout joints of the tiles intact without cracking.
And thus keeps the grout joints of the tiles intact without cracking.
I spoke with a chemist at work and didn't get a direct answer to the question, but I got a perspective.
Plywood is "deader" than wood because it is multiple layers of sheets, where all have fibers in different directions. So if it "wants" to be pulled in one direction, the crossing fibers will hold it back. That's how plywood works if I have read the official plywood documents correctly.
Gypsum also has fibers, which are even smaller and even more numerous and possibly in even more directions. Maybe the gypsum holds the material together a bit, maybe it can also absorb some of the movements in its own material.
But I still haven't reached a conclusion with any thought yet.
Plywood is "deader" than wood because it is multiple layers of sheets, where all have fibers in different directions. So if it "wants" to be pulled in one direction, the crossing fibers will hold it back. That's how plywood works if I have read the official plywood documents correctly.
Gypsum also has fibers, which are even smaller and even more numerous and possibly in even more directions. Maybe the gypsum holds the material together a bit, maybe it can also absorb some of the movements in its own material.
But I still haven't reached a conclusion with any thought yet.
As mentioned, the drywall (correctly screwed into the substrate) prevents the wood from moving. What remains is the risk in the drywall joints. And there, it also moves a little. If you assume that the board is screwed 20mm from the joint, then you have the movement in 20 + 20mm of wood that can move the drywall. If the board is completely free from surface layers, it will move a bit, e.g. if you only putty over the board joints and paint. The putty has no strength whatsoever and cracks.
If you place a reinforcement strip over the joint, preferably paper, it holds (try tearing an A4 paper apart, the strip is thicker. It is therefore a very small stretch of wood that can move near the joints, thus the material stresses are moderate.
If you then tile over it, the tiles and adhesive will manage to withstand the stresses. I have wondered what would happen if a tile grout was placed directly over a board joint, it's possible that the tile grout could withstand the moderate stress, as it has some elasticity.
If you place a reinforcement strip over the joint, preferably paper, it holds (try tearing an A4 paper apart, the strip is thicker. It is therefore a very small stretch of wood that can move near the joints, thus the material stresses are moderate.
If you then tile over it, the tiles and adhesive will manage to withstand the stresses. I have wondered what would happen if a tile grout was placed directly over a board joint, it's possible that the tile grout could withstand the moderate stress, as it has some elasticity.
Interesting product!verktygsgurun said:
2:36 in he says that you can speed up the tiling before the concrete has fully shrunk "thanks to the great flexibility" of S 48.
The same thing with gypsum bonding (or screwing) on wood. The gypsum would never be able to resist the force in a timber movement, shrinkage in concrete, or movement in a house, it would crack.
The thing that makes it work is that the dead material with just the right flexibility floats on top of the living one.
Initially, both plaster and wood are dead materials, biologically speaking. But when you say living, it means that wood moves, especially radially along the growth rings. That is, in the joints. While plaster is immovable and can bridge the gaps in the wood's joints. An example of this is ceiling moldings, which can last for hundreds of years. But if it rains in, the ceiling cracks. Therefore, it is important to keep the construction dry. I don't know how it goes if you scrub on the tiles. If it's an internal staircase, it should work!? Best regards, PerOF