How to lay outdoor waxed concrete on a slab (terrace, balcony...)

You want to install waxed concrete outside, for example, to create a terracebalcony or pool deck?

A few key points for laying waxed concrete on an outdoor slab

Here's everything a craftsman or advanced do-it-yourselfer needs to know about the subject.

Substrate preparation

Application to exterior concrete paving must be carried out on a substrate complying with DTU 13.3. This document provides for the use of expansion joints at the discretion of the mason and architect.

You will also need :

expansion joints between the paving and the house, and between the paving and the pool
a slope of 2 % to ensure drainage of rainwater

Waxed concrete is applied directly on the slab, which has been abundantly moistened the day before and possibly the morning of, or even as you apply it if it's very hot, using a small sprayer (to avoid standing water).

This allows the concrete to set slowly and adhere perfectly to the substrate.

Concrete application

In general, both coats of concrete are applied on the same day.

It's best to apply early in the morning, when temperatures remain cool. If it's too hot, it's best to wait until the following day to apply the top coat.

Sanding between the two coats with 40-grit sandpaper is recommended.

The use of concrete with a SikaLatex admixture and glass fibres is recommended, with a trellis laid out according to the rules of the trade.

As you smooth, spray with a curing compound. These precautions, together with the expansion joints, will enable you to slow dryingto prevent cracking.

After installation

Seals and gaskets

It is imperative to saw joints within 24 hours at most after casting.

We also recommend apply a sealant on the concrete at the garden's junction, on the edge of the concrete slab, to prevent capillary suction of water from the ground and watering or rain on the terrace or balcony, or from the swimming pool.

Once both coats are dry, lightly sand with 40/60 grit and apply 2 saturation coats with water- and oil-repellent protection.

Ideally, the surface should remain dry for 48 hours.

Finish

Regarding surface appearance, a Flemish reader finish gives the best rendering.

On millimetric waxed concrete, it's best to avoid flashes, which will be difficult to recover.

The waxed concrete applicator must perform a sanding and dusting of the slab surface after drying. Installation is on a slab with less than 4 % interior humidity.

In order to ensure a grain size that complies with skid-resistance standards for pool edges (PN 18), the finishing layer must be lightly scrubbed with a dry mason's sponge and sanded.