Cracks in the plaster: causes and solutions

When you see cracks and crevices in the plaster it's good not to overlook them, but don't even think it's some structural problem.

Crack in the plaster wall

In reality anything could be, both a minor problem and a serious problem.

For these reasons it would always be good to contact a technician to do an inspection and feel reassured about the nature of the crack.

Houses are built with heterogeneous materials that often respond differently to stresses, both physical and environmental.

Variations in temperature, in particular, cause building materials to expand and contract unevenly with respect to one another, and at points of contact, it is quite easy for cracks and fissures to form.

These cracks can then expand due to other stresses such as car traffic, closing and opening of doors and windows, and even wind pressure on roofs and walls.

If we were to add up all the cracks in the plaster in an average-sized house caused by a variety of reasons, we would get a "void" of about 0.20 square meters.

In most cases these cracks do not indicate a structural problem but a simple settlement of the building and the materials with which it was built.

For this reason it is not always indicated to immediately close a crack in the plaster in a new building. Or rather: we can close it, but the possibility of its reopening is far from remote.

Who pays for settlement cracks?

The question that many people ask themselves is who is responsible, that is, who should pay for the repair of cracks that appear on the plaster.

There is no clear-cut jurisprudence, if the cracks are understood as structural defects come out of ordinary maintenance and therefore their repair is the responsibility of the building company of the property.

But that the cracks are structural defects is all to be demonstrated, in the sense that, as written above, cracks in the plaster of new houses are quite common and in the vast majority of cases are more an aesthetic problem than a structural problem.

It is very difficult to assume a construction in which there are no cracks, but we must understand if these are "inevitable" given the diversity of materials in use or damage caused by inexperience in the use of materials.

crack joint wall floor

In the case of cellular concrete, for example, it is well known that the application of plasters which have not been specifically designed for this material may result in the formation of micro-cracks which appear as "cobwebs" and which are very unsightly.

In this case we can therefore say that the cracks in the plaster are due to inexperience of those who have built the building and he is therefore responsible for their elimination.

In other cases, where, for example, reinforced concrete slabs and curtain walls are combined, cracks may also form at the points of contact, but it is very difficult to prove that there has been inexperience, since those are the materials properly used for those structures.

For every crack its filler

I wrote that cracks in plaster can be static or "in the making".

A crack that is definitively settled can be treated with a hard acrylic putty while a crack that is subject to possible expansion (such as those around doors and windows) should preferably be treated with a polyurethane putty.

Another evaluation should be made with regard to the size of the crack: if the crack is large, it can be finished with filler or anti-shrinkage cement strengthened by a tape net similar to the one used to conceal the joints of plasterboard walls.

Modern synthetic sealants are the most effective for filling and repairing plaster cracks because they are so easy to use and have a very wide range of applications.

These sealants are in most cases sold in cartridges to be installed on special silicone guns that allow for gradual emptying.

For small repairs there may also be sealants in tubes (like toothpaste, to be clear) that are squeezed directly into the crack.

Finally there are putties sold in cans, ideal for skim coating.

For small cracks even plaster can be good, but being a very smooth material it tends to show a little if the wall plaster is, however, slightly granular.

How to fill cracks in walls

The most important thing, for the perfect success of the job, is to properly prepare the surface; residues of plaster or flaking paint must be removed if the next job is to bring satisfactory results once and for all.

Preparing the wall surface

First of all, the crack should be widened with the blade of a steel spatula, the same that we will need later to spread the stucco.

You can also use a special triangular scraper or a chisel, the important thing is to widen the crack.

Widening the crack is essential for two reasons:

  1. Widening the crack provides a greater gripping surface for the grout, which then binds better to the substrate
  2. The purpose of widening the crack is to remove all the parts that do not adhere well to the support, even if, at first glance, they appear to be stable

In dated houses it may be necessary to go so far as to uncover the bricks to avoid leaving gaps in the fill.

Filling the crack

Once the crack has been widened it is necessary to clean the surface of the wall and crack from dust and any plaster fragments, to do this a brush dampened with water and/or a good vacuum cleaner is useful.

Now after mounting the putty cartridge on the silicone gun we inject the elastic putty into the crack. By cutting the tapered nozzle high enough we can allow ourselves to reach deeper into the crack.

Any grout that may leak out is smoothed out with the spatula.

After drying, usually about 30 minutes, we can proceed to the application of the anti-shrinkage mortar.

We grout the crack using the trowel taking care that the grout penetrates well inside the crack.

At this point, to complete the work, you can cut to size the special mesh tape for cracks and apply it on the crack, over the mortar still wet, and then give a further smooth with a little more mortar.

Remove any excess mortar by gently wiping with a dampened sponge before the mortar finally hardens to prevent an unpleasant relief once dry.

This is the procedure to follow for cracks in the plaster of a certain size, for smaller cracks may be sufficient the simple application of a special stucco for wall, or plaster, which can then also be sanded.

Now you can proceed with painting! Two coats of paint should permanently cover your (former) crack ensuring a perfect result both from the point of view of aesthetics and durability.