It's called `building', not `precision engineering'. A conventional two-storey brick-built house is basically four brick-and-mortar walls holding up two wood rafts. Those walls were laid by hand by men who knew what they were doing, and used a spirit level frequently, but we're not talking laser levels and automated mortar-laying. My house does not have one straight line or right-angle corner in it. The rafts are made of joists running from one side wall to the other, with planks of wood nailed to them to make floors, and boards nailed to the underside of the upper raft to make ceilings. Those planks were cut straight on a machine, but laid by eye. Gaps in the front and back walls were left that were roughly the size of the window frames ordered by the builder. Add in some more-or-less square stairs, a couple of internal walls, and there's a lot of gaps, slack and empty spaces in a perfectly sound and strong house.
All that coping, skirting boards, filling plaster and other such decorating-and-finishing is to fill up or hide the gaps, make everything look neat and tidy, as well as stopping small things from falling below the floors, or, for that matter, coming up from the earth under the ground floor.
The structural load is carried by the side walls (which are solid in a terrace) and the joists, with a bit done by the front and back walls.
None of the finishing work is structurally significant.
Now that may seem obvious when it's said, but I'm not a builder or a decorator, and I was never quite clear on whether (say) tearing out skirting board would result in the collapse of the wall.
Okay. Laugh. I deserve it. It's not what I trained to do. Nor my father before me, nor either of my grandfathers.
But I'm doing some of it now. And I need to understand this stuff or I don't feel comfortable.
Why do we get cracks in plaster and between finished work? Was it badly done?
Nope. It's because you don't want precision-joints.
Some of that slop between the parts has a useful purpose.
The ground your house is built on expands when there's rain or a lot of moisture in the air, and contracts when the sun stays out for long enough to heat the ground up. That means your house moves slightly. In different directions every year.
The same temperature changes that affect the ground, also affect the materials in your house. Everything moves slightly all the time.
You move the furniture around, and that changes the load on the joists and hence the supporting walls.
Have some vigorous, errrm, married life and the load shifts around on the joists supporting the bed, and that pushes at the ceiling boards in the room below.
That's where all those hairline and other cracks in the plaster come from. If everything fitted precisely, there would be more cracks, not less, since everything would be connected to everything else.
So hairline cracks are a consequence of the features, not a bug.
That's why it's okay to plaster a hairline crack over, and / or slap a good think coat of paint on it.
By `plaster' of course, I mean Polyfilla or decorators' caulk.
Other gaps need silicone, which everyone says has some bend and flex in it, so shouldn't crack. (Instead, somewhere near the silicone will crack instead.)
Large gaps and holes need filling with foam, and then a final coat of filler for the paint.
And no, the filler or the tape will not `resist' further cracking. Any force large enough to shift a chunk of wall, ceiling or floor a fraction of a millimetre is going to laugh at a bit of adhesive tape.
And the bit where I use tape or some careful work to get a good sharp square edge on the corners and edges?
Have you seen my house?
No comments:
Post a Comment