Hydrotec since 1988
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Treatment of rising damp and saltpetre

What does rising damp correspond to?

rising damp (or “capillary rise”) refers to the moistening of the walls by water present in the ground. This upwelling depends directly on the porosity of the materials composing the walls: mortar, plaster, brick, concrete …

Untreated, rising damp can result in the appearance of saltpetre and the detachment of the plaster covering the bottom of the walls.

Where ?

  • In buildings dating from before 1930. The buildings constructed at that time did not receive a waterproof membrane at the foot of the wall.
  • In new homes when the bottom of the walls have not been properly sealed.
  • In the walls located on the ground floor and in the cellars.


  • Appearance of saltpeter (white crystals agglomerated or not)
  • Detachment of plinths
  • Crumbling of plasters
  • Paint degradation
  • Wallpaper peeling

Why do it ?

Make the walls permanently dry and healthy at the level of the ground floor of a house.
Guarantee: we guarantee the treatment of rising damp for 30 years.
Hydrotec has teams of methodical and well-equipped specialist technicians for this type of intervention.

Treatment of rising damp

In order to avoid any deterioration, walls affected by rising damp must be the subject of specific treatment. To do this, a water repellent is injected at the base of the wall. By migrating into all the capillaries of the materials, the injected product creates a horizontal barrier in the wall.

Once installed, this unalterable barrier will prevent capillary rise for the entire duration of the wall’s existence.
Hydrotec offers an odorless and non-toxic treatment. We mainly use CRD Gel and H10eco microemulsion; these two products based on silane-siloxane resins in aqueous phase do not contain any hydrocarbons.


Processing steps of injection treatment


Stripping of plasters contaminated by moisture and saltpetre

Stripping of the affected ceiling (often unrecoverable)


Drilling adapted to the wall thickness


Injection of the treatment product

Controlled pressure injection of a product creating a barrier that permanently prevents the capillary rise of water in the walls.


Application of Hydro+ anti-saltpeter coating

Found 4 to 12 months after treatment



FAQ – find out more


rising damp or capillary rise is a pathology of constructions linked to the porosity of materials, to capillarity and to the presence of moisture in the soils which touch the materials that make up the wall: joints, bricks, mortar are porous materials that conduct moisture present in soils (capillarity phenomenon). In the case of brick walls, moisture spreads throughout the mass of the wall. In the case of stone walls, moisture will propagate into the joints because most varieties of stone are not porous.
Soil drainage is usually not enough to solve the rising damp problem.


Use of a high frequency hygrometer
Before considering combating rising damp, it is important to make a precise diagnosis. The diagnosis is made using a high frequency hygrometer. This hygrometer has the advantage of testing the moisture of the wall in depth without having to drill or reveal pairs of small holes as is the case with resistive testers (so-called “spike” testers which are still used by many companies in the moisture treatment sector).
At Hydrotec, the hygrometry (the calculation of the moisture rate) of masonry in old and modern houses is determined with a high frequency tester, a material recognized and used by many experts, engineers and architects. This device does not leave holes in the walls.

An electronic hygrometer test is not always enough
Sometimes masking panels (or back walls) applied to damp interior walls make it impossible to assess the moisture level of the wall. It is then a question of dismantling an area of ​​the partition to access the wall, or of testing the wet wall from the other side, hoping that it is accessible.

The marking of ground levels
To diagnose the moisture of a wall and before considering the installation of the waterproof barrier, it is essential to ensure the height of the soil levels that exist on both sides of the
If the ground level of the garden is higher than the interior ground of the house, the technical delegate will have to adapt the technique of anti-moisture treatment of the exterior walls by proposing a casing (waterproof cementing inside a wall against the ground) or a protection of the wall from the outside (trench and waterproofing of the wall in contact with the earth).
These particular cases deserve a chapter on their own. They are explained on our site in the section “Drying out humid cellars”.

A wet wall is a cold wall
As water is a good thermal conductor, in winter a wet wall is cooler than a dry wall. In the wet and cold season, it will therefore come as no surprise that a damp wall acts as a thermal bridge that can reveal condensation phenomena and allow mold to develop on the area of ​​the wall affected by rising damp. We advise of course to ventilate, possibly install a mechanical ventilation system but without specific treatment of capillary rise, the wall will continue to suffer damage, to let appear efflorescence of salts, yellowish spots of moisture, halos. unsightly …
NB: when a wall is very dry, it is less subject to condensation phenomena and mold growth. The use of fungicides can therefore be avoided.


Sometimes accompanied by the development of mold and bad odors, rising damp is even more often accompanied by efflorescence of mineral salts, better known as saltpetre or saltpetre salts.
Saltpeter is composed of potassium nitrate. As moisture evaporates from the wall, nitrate salts crystallize on the surface of the walls as white crystals. As they clump together, these crystals form cotton wool lumps. Saltpeter salts accentuate

the hygroscopicity of a wall(these are called hygroscopic salts, that is, salts which are able to take up moisture from the air, thus preventing the wall from drying properly).

These saltpeter salts can clump together on the surface of walls and take on the appearance of cotton wool or a whitish beard. Mineral salts do not give off a specific odor. They are soluble in water. Once the presence of salts has been observed, we consider with the customer the possibility and the need to strip the wall plasters contaminated by nitrates (the plastering damaged by saltpetre and moisture is generally doomed to be replaced in the short or medium term. , subject to the precautions described below).

Watch out for similarities!

Many of us fear that dry rot will develop in our home. Certain efflorescence of salts could give one to think – fortunately wrongly! – that saltpetre is a species of fungus that is dangerous for your home and your health. It happens that an agglomerate of saltpetre can closely or remotely resemble a fungal development. To make sure this is not the case, you can take a sample of saltpetre in your hands (saltpetre is harmless) and find that it falls into powder; also note that the saltpetre does not emit any bad odor or smell of fungus; finally, you can put it in a little hot water to see it dissolve. It is then certain that it is not a question of a development of molds and even less of dry rot.


Following water damage

When a house suffers from a flood or a pipe leak, the screed under the tiles is soaked with water. The damp, even soggy, screed is itself in contact with the wet plaster at the bottom of the walls (in fact the plaster behind the plinth generally sinks into the screed and goes so far as to touch the concrete slab. . During construction or major renovation, the plastering is generally carried out before the screeds.) The water present in the screed then finds the ideal material (plaster) to effect a capillary rise. After accidental damage, it is generally advisable to wait for the screed to dry naturally, even if this can take several months.
If the baseboards come loose from the walls, then it is advisable to strip the plaster affected by the moisture to allow faster evaporation of the residual moisture contained in the screed.

Drying can be speeded up by installing moisture absorbers, but these are of very limited effectiveness and are expensive to use (refills with absorbent salts are expensive). The best solution is to install (rent or buy) an electric dehumidifier during the drying time.

Preparing the walls before treatment

Ideally, before drying them out, the walls should be stripped of plaster damaged by salts and moisture. For reasons of profitability and ease, still many companies recommend an injection through the plaster when it does
We do not hide from the customer that the treatment will be of better quality if the wall is stripped before injection. We work better when we see what we are doing: we will therefore inject a wall better if we can clearly see where the joints, the bricks are … Once stripped, the wall can also dry and be re-coated more quickly.

Injection treatment

The treatment consists of the injection of a water-repellent product (an approved product, in this case the CRD Gel or the H10eco liquid product).
During the injection, the injection product will migrate into the porous material of the wall and completely permeate a slice of masonry at the base of the walls.
Injecting a waterproofing product into a wall is a bit like inserting a waterproof membrane – but in liquid form – at the base of the masonry to create a tight and perfectly waterproof barrier that will prevent the capillary rise of water.

Injection products
Injection products are water repellents composed of silane and siloxane oligomers. The resin concentration is suitable for treatment by injection. Some products on the market are still formulated in a hydrocarbon solvent phase (toxic products). It is very surprising when we know the toxicity of solvents and we know that products in the aqueous phase (diluted in water) have been proven for several decades!
The products used by Hydrotec are formulated in aqueous phase. They do not emit any odor; they are no toxic: H10éco has obtained the Green label and the HCRD Gel, a product harmless to health, has meanwhile obtained a Class A + approval (the best efficiency among the products tested!) from the Belgian parastatal organization, the Scientific Center and Construction Technology (CSTC).

Following the injection treatment, the anti-saltpeter protection of the walls
Following the injection treatment, the moisture of the walls will begin its work of migration and evaporation. Drying a wall takes an average of 4 to 12 months. The drying time of a wall will depend on:

  • the thickness of the walls;
  • the amount of water contained in them;
  • the amount of salts present therein;
  • of the season (cold or hot, wet or dry season)
  • the presence or absence of heating;
  • the presence and quality of the plasters (cement or plaster? pickled or not?);

During drying, the saltpeter salts present throughout the thickness of the walls will also migrate to the surface. Some will come out and fall at the foot of the wall, but a quantity of salt will remain trapped and accumulate in the surface layer of the wall. Even though the treatment of rising damp has been carried out correctly, during the application of liquid plaster, the salts that remain trapped will migrate into the water used to mix the plaster. They are likely to pose a problem for the new coating applied to the wall. As the salts have the annoying tendency to dissolve in the water, they will spread in the new plaster coating and cause undesirable effects to the good progress of the operations: because of its hygroscopicity favored by the salts, the salted plaster can give believe that the treatment is not working well; Blisters will appear in the new paint, swelling in the wallpapers.

Many individuals and building professionals often underestimate this important aspect of treatment. We cannot stress enough the need to provide saltpetre protection before applying the plaster coat. Most of our after-sales service calls relate to sites where, for various reasons, the saltpeter protection step was omitted, an important aspect of treating rising damp if there is one!

What does the anti-saltpetre protection consist of?
The anti-saltpetre protection is a primer (coating or membrane) that is applied to the perfectly stripped and cleaned wall.
To clean up a wall permanently, the anti-salt screen can be created in two ways:

  • either we apply, following the instructions in the technical sheet, the “Hydro+” coating, a cement coating added with resins which is very resistant to salts;
  • or a “Hy-N3 membrane” is attached to the wall, which is provided with a nylon mesh and cells to which the plaster will attach.

We prefer to use the Hydro+ coating because:

  • It straightens the wall and allows you to add a layer of plaster which will not be too thick, a common case on old walls (we recommend a maximum of 2cm of plaster on Hydro+).
  • Unlike membranes, it is microporous.
  • The coating is resistant and it strengthens the wall;
  • Thanks to its tack coat and its cement / quartz base, Hydro+ plaster is hard and very cohesive, that is to say it adheres perfectly to the wall;

The HY-N3 membrane can be useful because it allows you to move faster, but it has several drawbacks:

  • The wall sounds hollow to the touch, a void remaining behind the membrane;
  • The membrane is difficult to attach to the old heterogeneous walls (which are rarely flat);
  • A crack often appears at the junction between the HY-N3 membrane zone and the Hy-N3 membrane-free zone;
  • Plaster is difficult to do on a plastic membrane, ceiling workers don’t like to use it.
  • It is not microporous.

Plating and painting work after treatment
One week after applying the Hydro+ anti-saltpeter coating, the plaster topcoat can be applied without the risk of the reappearance of saltpetre crystals, spots or blisters in the The plaster is usually allowed to dry for a good month before considering coloring the walls. We recommend applying a good quality primer and microporous paint.

Obligation of result and guarantee

The end result of a rising damp treatment depends on all stakeholders: moisture treatment company, architect, client, other companies that may intervene following treatment (painter, plaster).
The drying of walls is an operation whose success is guaranteed in the very long term if all stakeholders comply with the recommended technical instructions:

  • whether it is in this document;
  • in product sheets;
  • in the “estimate for the treatment of rising damp” drawn up by the Hydrotec technical sales representative.

We draw attention to the need to comply with the instructions for anti-saltpeter coatings.

With our thirty years of experience, we find that when the instructions are followed, the walls stay dry for many, many years. Correct treatment will be effective for the life of the wall. This is why we offer a 30-year guarantee on the treatment of rising damp. The generations that will survive you may be grateful to you for safeguarding your heritage from the damaging effects of moisture.