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Locating a leak in the waterproofing of a roof terrace is often impossible. But there is an effective solution to keep it for a few more years before replacing the entire roof: the coating of a rubber-based product.

Text and Photos H. Séguret

Practical advice

Fresh stains and tools are cleaned with a rag soaked in white spirit. The roller does not wash. Let it air dry before disposing.
If plaster remains, you can use it to seal a gutter, corrugated sheets, planters or the buried part of wooden poles. On metal, first apply a rustproof primer.

When a roof terrace is no longer perfectly sealed, the most effective and durable solution is to completely replace the waterproofing system. Faced with this investment, catering is an interesting alternative: it offers up to ten years of respite for a few hundred euros.
● The coating used here is based on rubber (Igolastic Sika) in a gelled form. The solution is easily applied to sheepskin roller or brush. After drying, it forms an adherent membrane, flexible and impervious to water.
● The principle consists in applying two thick layers on the whole terrace, after having treated the singular points: blisters, tears and different surveys (acroteria, stumps...).
● The product consumption is around 600 to 800 g / m2. Warning: this solution is not used on old asphalt pavements. In this case, plan another formulation whose implementation remains the same (Liquid Rubber Rubson, for example).

The building site

To perfect the adhesion of the coating, the support must be well dry. Check the weather: it is also best to avoid rain during drying. The ideal is to have four or five days for the application. Avoid too much heat and cold weather. Finally, know that it is not advisable to walk on the plaster (even after drying), because it remains sticky. For this reason, be sure to start on the opposite side of the access.

The application

The preparation of the support conditions the performance of the seal. It must be as clean as possible: dust, foams and deposits mix with the coating, make it sticky and hinder its adhesion. It is therefore necessary to brush several times, to sweep, to start again, then to vacuum. This big cleaning offers the advantage of updating tears and blisters.
● Carefully equalize the contours of the tear, removing debris and loose parts. Cover the damaged areas with a calico made of glass cloth or polyester. Cut out strips of 50 cm, then drown them in a double layer of plaster. Also treat angles and surveys, which are often the seat of the main infiltrations.
● Apply two coats of plaster on the entire surface of the deck. The second is spent the next day (avoid stepping on the first one too much). Let dry 48 hours.

The usefulness of felt

It is advisable to spread sand after drying the second layer, before replacing the gravel. But they stick all the same to the coating and may cross the seal if you walk on it. The geotextile felt (Bidim) avoids this problem and facilitates the installation of gravel. But it makes difficult a new application of product: glued by the coating, it does not remove any more. However, it will not cause any difficulty when you replace the waterproofing system. Indeed, it is possible to put the new tarpaulins on top.

Group the gravel

Group the gravel

Group the gravel at an angle: roll with the back of a rake to avoid damaging the seal, then form a pile with the shovel (without exceeding the height of the acroterion). Pass the scrubber.

Tear off, scratch, equalize

Tear off, scratch, equalize

The defects of the upper layer appear. Tear off what does not adhere. Scrape off mud and debris with spatula. Equalize the contours of the tear to make them clear.

Clean, brush, suck

Clean, brush, suck

Continue cleaning. Spread the scrubber, insisting strongly on the deposits. Brush also lichens and mosses that develop on the surveys. Finally, carefully vacuum to remove dust.

Repair a tear

Repair a tear

To repair a tear, cut a piece of calico so that it protrudes a few centimeters. Apply a coat of plaster. Drop the frame. Dab with the brush and apply a new coat of product.

Repair angles and readings

Repair angles and readings

For angles and surveys, apply plaster. Fold a 50 cm strip of cloth in the length. Drop it on the corner. Dab with a brush. Spread the second layer of product. Overlap the next strip on 3 cm.

Apply the coating

Apply the coating

Apply the coating to the medium-haired roller. Start with the opposite side to the access. Make penetrate the first layer by proceeding in small sections. Also treat the acroterions. Insist on angles and repairs.

Unroll the felt strips

Unroll the felt strips

After applying the two layers of plaster, allow to dry. Then cut out and unroll felt strips. They must rise 5 cm along the readings and overlap on the same width.

Put the gravel back in place

Put the gravel back in place

Replace the layer of gravel, first with the shovel and then with the back of the rake to equalize. Clear the storage area and treat it like the rest of the roof (brushing, repairing, plastering...).


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