Process for providing a fiber cement product

Abstract

A process for providing a fiber cement product is provided the process comprising the steps of: —providing an uncured fiber cement product; —curing said uncured fiber cement product; —drying said cured fiber cement product to obtain a humidity of said cured fiber cement product being less than or equal to about 8% w; —abrasive blasting at least part of the surface of said dried fiber cement product.

Claims

1. A process for providing a fiber cement product which is free of any visible effects of efflorescence, comprising a combination of the following steps in the following order: providing an uncured fiber cement product consisting essentially of fiber and cement; air curing said uncured fiber cement product under ambient conditions; air drying said cured fiber cement product after completion of curing, in a separate step and in a ventilated furnace at a temperature between about 70° C. and 105° C., to obtain a humidity of said cured fiber cement product being less than or equal to about 8% w; and upon completion of said air drying, directly abrasive blasting at least part of the surface of said dried fiber cement product, wherein said uncured fiber cement product is obtained using a Hatschek process and the abrasive blasting excludes sandblasting.

2. A process according to claim 1, wherein said product is a fiber cement sheet.

3. A process according to claim 2, wherein the largest surface area of said sheet is abrasive blasted.

4. A process according to claim 1, wherein said product is abrasive blasted using metal grit, corundum, carborundum or combinations thereof.

5. The process according to claim 1, comprising the step of using the fiber cement product as covering of a building construction.

6. A process according to claim 1, wherein the abrasive blasting is shotblasting.

7. A process according to claim 6, wherein the abrasive shotblasting is carried out with metal particles.

8. A process according to claim 6, wherein the abrasive shotblasting is carried out with a turbine propelling a high velocity stream of particles against the cement surface.

9. A process for providing a fiber cement product which is free of any visible effects of efflorescence, comprising a combination of the following steps in the following order: providing a fiber cement slurry comprising about 80 to 90% by weight cement, 1.5 to 5% by weight cellulose fibers and 1.5 to 5% by weight synthetic fibers; transforming the slurry into a green fiber cement sheet by a Hatschek process, prior to air curing; air curing said green fiber cement sheet under ambient conditions; air drying said cured fiber cement sheet after completion of curing, in a separate step and in a ventilated furnace at a temperature between about 70° C. and 105° C., to obtain a humidity of said cured fiber cement sheet being less than or equal to about 8% w; and upon completion of said air drying, directly abrasive blasting at least part of the surface of said dried fiber cement sheet, wherein the abrasive blasting excludes sandblasting.

10. A process according to claim 9, wherein the sheet is air cured for about 3 weeks.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a sheet according to the present invention, before and after being subjected to a so-called condensation test, and a comparative sheet according to prior art, before and after being subjected to a so-called condensation test.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(2) In a first embodiment, a fiber cement sheet, plate or panel is described which is obtained by means of a Hatschek process.

(3) A fiber cement slurry is provided, which comprises next to water Cement (type Portland cement) in an amount of about 80 to 90% w; Cellulose fibers in an amount of about 1.5 to 5% w; Synthetic fibers (such as e.g. PVA, PE, PP and alike) in an amount of about 1.5 to 5% w; Further additives such as pigments, anti-foaming agents, flocculants, fillers, reactive fillers comprising silica sources and other additives.

(4) The % w are expressed as percentage of the component over the dry weight of the slurry, i.e. the weight of all components without water.

(5) This slurry is transformed in to a green fiber cement sheet by means of a Hatschek process.

(6) This green sheet is subjected to a pressing step, compressing it to a thickness of about 8 mm and having an density of about 1.75 kg/m.sup.3. The dimension of the green sheet is about 3.1 m by about 1.3 m.

(7) In an alternative, a green sheet with similar dimensions and density is made, having a thickness of about 12 mm.

(8) In general, green sheets with a density between about 1.5 and about 1.8 kg/m.sup.3 can be provided, with a thickness between about 7 mm and about 13 mm.

(9) The green sheets are air cured by allowing the cement to cure under ambient conditions for about 3 weeks.

(10) After air curing, the sheets have a water content (or humidity) of about 10% w. using a ventilated furnace, the sheets are dried to a humidity between 4 and 6% w at increased temperature (typically higher than 70° C. and lower than 105° C.).

(11) The cured and dried product is subjected to an abrasive blasting operation at one of the main surfaces. The abrasive blasting operation used a martensitic stainless steel crushed grit of type “Grittal GM” (obtainable form the company Vulkan in Ontario Calif.). The sheets were held inclined to the vertical to allow the abrasive material to be removed from the surface by gravity. The abrasive blasting used in the present example may be performed by sandblasting or abrasive shotblasting. In the case of sandblasting, sand-sized particles, such as but not limited to sand particles are used.

(12) Such abrasive blasted fiber cement sheets, without a post treatment, were subjected to a durability test by exposing the sheets outside to climatological elements in Europe, i.e. rain, wind, sunlight, frost, etc, during several months, including a winter. No visible defects due to efflorescence could be noticed.

(13) This very same product was subjected to a condensation test, simulating severe weather conditions of humidity. The sample sheet of 19 by 7 cm is mount on a holder (holding the sample at its edges) and held above a demin-water bath at 60° C. for 16 h, the abrasion blasted surface oriented towards the water and on a distance of 25 cm of this water surface. This equipment is positioned in a closed cabinet, such that the water vapor cannot escape to the ambient. After 16 h, the sheet is dried to ambient conditions.

(14) In FIG. 1, an abrasion blasted surface before and after this condensation test is shown. Sample C in FIG. 1 is abrasion blasted surface before the test and sample D is this very same sample after this condensation test.

(15) Some whitening of the surface appearance is visible. This minor change in color is likely due to efflorescence, however no hindering efflorescence effect is noticed.

(16) In FIG. 1, a reference, untreated surface before and after this condensation test is shown. Sample A in FIG. 1 is the reference surface before the test and sample B is this very same sample after this condensation test.

(17) A severely whitened surface in sample B is visible, the whitening being broken into islands. This whitening is due to efflorescence of the surface.

(18) It is to be understood that although preferred embodiments and/or materials have been discussed for providing embodiments according to the present invention, various modifications or changes may be made without departing from the scope and spirit of this invention.