Table of contents:

Apply and mend exterior plaster: how it works
Apply and mend exterior plaster: how it works
Video: Apply and mend exterior plaster: how it works
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The exterior plaster is the protective cover for the house because it protects the masonry from weather, UV radiation and frost damage. In our step-by-step instructions, we explain how experienced do-it-yourselfers apply and repair exterior plaster.

Table of contents Table of contents Apply and repair exterior plaster: Here's how

  • Types of cleaning
  • Procedure: Apply exterior plaster
  • Touch up exterior plaster

Table of contents Table of contents Apply and repair exterior plaster: Here's how

  • Types of cleaning
  • Procedure: Apply exterior plaster
  • Touch up exterior plaster

The exterior plaster not only ensures an attractive appearance of the facade, it also works as weather protection. In addition, it is vapor permeable so that the moisture in the house can escape to the outside. The exterior plaster, which is usually applied in two layers, is composed of a base plaster (flush-mounted) and a top plaster (fine plaster). The base plaster has a thickness of 10 to 15 millimeters and has the function of leveling out unevenness such as grooves or holes. The top plaster is three to ten millimeters thick and gives the facade the final structure. How many layers and which types of plaster should be used depend on the surface or the respective bricks. Rely on the expertise of professionals in the specialist trade and get detailed advice in advance.

Attention: Applying and repairing an exterior plaster is only something for ambitious do-it-yourselfers who are skilled in handling mortar, trowel and float. If you don't trust yourself to do the work, you'd better hire an expert. Here you will find experts in your area:

Types of cleaning

Basically, two different plastering mortars can be used for exterior plastering: plasters with mineral binders and synthetic resin-bound (pasty) plasters. While mineral plaster is always used for the in-wall plaster, you can choose between mineral and pasty plaster for the top plaster:

Type of cleaning

binder

characteristics

Mineral plaster

limestone, sand, Marble and quartz

Lime and / or

cement

Open to diffusion, non-flammable

Silicone resin plaster

Silicone resin

Weatherproof, open to diffusion, water repellent

Dispersion plaster

(Synthetic resin plaster)

Organic

petroleum-based

Resilient, water repellent

Silicate plaster

Mixture of

Potash water glass

and dispersions

Weatherproof, open to diffusion, water repellent

Procedure: Apply exterior plaster

You need the following materials:

  • Repair mortar
  • primer
  • Plaster base
  • clean
  • Plaster rail or plaster profile
  • Trowel
  • brush
  • Painter's puff
  • Mortar bucket
  • drilling machine
  • Board or scraper
  • Float or sponge board

Important instructions

Make sure that you only carry out the cleaning work at temperatures between 5 and 30 degrees Celsius. Otherwise the plaster can dry out. In addition, you should protect the plaster from direct sunlight, rain or frost with a tarp.

Before you start, you should test the subsurface for its load-bearing capacity. If new plaster is to be applied to old plaster, you can check the load-bearing capacity of the old plaster with a cross cut: To do this, scratch the surface into a grid. If plaster breaks off in the gaps, the subsurface is not sustainable. Then use a spatula to remove the loose elements and clear larger hollow areas. Fill up the unevenness with fresh mortar. Finally, remove the flush-mounted plaster. Afterwards it means: rub to smooth the surface (you can then switch to the fourth step)!

1. Prepare the surface

Please note: The substrate of the facade must always be load-bearing, absorbent and dust-free. Use a brush to clean the free wall. If you discover unevenness, holes or gaps in the masonry, you should remove them with a repair mortar.

If you are dealing with a very strongly absorbent surface, such as aerated concrete or sand-lime brick, you should apply an additional primer with a paint brush. With other bricks, it is sufficient to wet the facade beforehand so that the plaster does not dry out too quickly. In the case of a weakly absorbent substrate, it is best to spray a shot of cement mortar or apply a cement adhesive bridge (special mortar).

2. Mix in-wall

So that nothing goes wrong when mixing the concealed, you should take a look at the manufacturer's information. Mix the plaster in a large mortar bucket with a drill (whisk attachment) until you no longer find any lumps in the mixture.

Good to know: If the plaster does not stick to the outer wall after the work, you have either added too much or too little water. For this reason, we advise you to strictly adopt the manufacturer's prescribed mixing ratio.

Putz anrühren
Putz anrühren

The plaster is best mixed in a large bucket with a whisk.

Photo: iStock / Gogiya

3. Apply flush

In the first step, spread the plaster on the facade using a plastering trowel. Then smooth the plaster between two plastering rails with a board or a flare. This method of working should be “wet on wet”: This means that you treat a wall surface consistently and only mix as much plaster as you really need.

Advanced do-it-yourselfers can try the spraying technique: Throw the plaster diagonally from bottom to top onto the facade by turning your wrist gently but quickly.

Our tip: take the dressing time into account! The first drying period can take up to 1.5 hours - depending on the type of plaster. Then rub the plaster cleanly with a rubbing board or sponge board. The plaster layer must then dry - one day's drying time per millimeter of layer thickness. Attention: If you do not keep to the dry phase, you can expect the exterior plaster to crack or become brittle.

4. Apply finishing plaster

When the drying is finished, it is the turn of the top coat: the top coat is only a few millimeters thick. The technology in the order is the same. Mineral finishing plasters are used as finishing plasters, which you have to mix with water yourself, or pasty finishing plasters that are ready to use. A large number of structures and colors are available in specialist shops: Whether grooved plaster, felt plaster, scratch plaster, decorative plaster, window plaster or rough plaster - the choice is a matter of taste.

Touch up exterior plaster

Spalled plaster on the facade can be quickly made attractive again in just a few simple steps: we will show you how to do it. First, scrape the loose plaster off the masonry with a spatula. Repeat this process until no more plaster comes off. As soon as the wall is solid, you can touch up the exposed area with plaster that is open to diffusion. However, if your wall is fragile, you need to tap out the porous areas.

The new plaster must be open to diffusion. This is the only way that moisture can escape. Diffusion-openable plasters pick up moisture and allow it to evaporate. At the same time, these plasters are also hydrophobic, i.e. water-repellent. Before you spread the new plaster on the affected area, it must be properly primed with a brush. The primer has a drying time of 15 to 20 minutes.

In the meantime, you can already mix the plaster according to the manufacturer's instructions. As soon as the primer is completely dry, you can spread the new plaster with a smoothing trowel. The new plaster has to dry again for an hour. Then smooth the surface with a dampened felt board. Finished!

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