Q: We bought our new house three years ago and now there are little bumps on our walls. Where did they come from?
A: Each of those bumps indicates the presence of a nail from the wallboard to the wood wall studs. When your house was new, the drywall contractor nailed the wallboard in place, covered the small depressions made by the hammer's head with joint compound and sanded the wall smooth for the painters. Over the last few years, the wood materials used in the construction of your house have lost moisture to the generally drier air of your living space. This loss of moisture leads to a shrinkage of the wall studs, joists, rafters, beams, etc. In fact, the amount of shrinkage may be as much as 6%.
Here is the trick: The tip of the wallboard nail is fixed in place (there is no hammer force to drive it deeper into the stud). Let's call this our reference point. The shaft of the nail will not change dimension, but the dimensions of the wood piece will as shrinkage occurs. The result? The distance from the tip of the nail to the face of stud is reduced and the nail head pushes outward on the painted surface.
1. Use construction materials which are not subject to shrinkage: Metals studs or prefabricated panels.
2. If you must use wood, purchase only wood with a very low moisture content. The lower the initial moisture content, the less shrinkage you will experience after the structure is completed. Expect to pay a premium for drier materials.
3. Have the drywaller apply a textured surface to the wall so the bumps that eventually show up are less noticeable. Textured ceilings are an example of this practice applied to overhead surfaces.
4. If your bumps are now visible, use a hammer, set the nails one final time, patch and repaint. The majority of shrinkage occurs after initial construction, so you should not see them again.
Scott McVicker, S.E.