Frequently asked questions

Formtex^® can be used twice with optimal reduction of the w/c ratio in the outer zone resulting in a dense and corrosion resistant concrete structure with greatly extended lifetime. Formtex^® can be used several times to limit the occurrence of blow-holes in the surface.

It is not necessary to wait longer than normal before removing the formwork, but doing so will improve the results. Formtex^® absorbs and retains water so whilst in place it provides for good curing.

The basic function of Formtex® is to drain surplus water and air from the concrete surface.

Result

• A dense and uniform surface with few if any blowholes
• A low w/c ratio gives a darker surface with some colour variation.

Note

• Hydrostatic pressure varies in accordance with height causing difference in colour. The bottom of the structure will be darker than the top.

Yes, Formtex^® will drain off water from any type of  concrete. The quantities drained off, relate to the w/c ratio in the concrete mix. The higher the w/c ratio in the concrete, the greater the drained quantity. Irrespective of the concrete’s w/c ratio, the w/c ratio in the finished concrete surface will be lower when casting against Formtex^®.

When specifying a w/c ratio there are many factors to consider, among these is workability. It is a fact that with a lower w/c ratio, you get a stronger, denser and more penetration resistant concrete. These are all properties the concrete needs in the critical concrete cover zone. In order for concrete to be properly placed and compacted, more water is required than is needed to hydrate the cement. The only way to ensure optimal w/c ratio in the concrete cover with properly compacted concrete is to drain water from the concrete during compaction.

Visible drained water comes from somewhere! Laboratory tests have demonstrated that the water is drained from the first 20-30 mm of the concrete cover. Through the concrete cover the w/c ratio increases to the concrete’s original w/c ratio. The increased strength of the surface can be measured with a Schmidt-hammer.

The drained water is clear and yellowish depending on the use of admixtures. As the fabric’s pores are smaller than the cement particles there are no cement particles in the drained water.

Hydrostatic pressure forces surplus water out through the Formtex^® filter. Formtex^® will, therefore, drain significant quantities of water both when casting vertical, sloping and at the bottom of horizontal structures.