GB2033250A - Insulative Coatings by Spraying - Google Patents

Abstract

The production of insulating coatings by spraying is achieved by spraying a composition containing an inorganic binder, such as cement, and an insulating filler consisting at least in part of hollow particles separated from pulverized fuel ash. The insulating filler can also comprise exfoliated vermiculite and the composition can be sprayed in the form of an aqueous slurry. Other ingredients can also be used such as mica, cellulose ether, surface active agent, waterproofing agent, dust suppressant oil, air-entraining agent, wetting agent.

Description

SPECIFICATION Production of Insulating Coatings by Spraying This invention relates to the production of insulating coatings by spraying and in particular to a process for producing such a sprayed coating not containing fibrous materials.

The spraying of insulating coatings for such purposes as fire protection thermal-insulation, acoustic correction etc. is long established. Such coatings may be applied to structural parts of buildings such a walls, ceilings, girders etc. and also to pipes, and machine casings e.g. turbine casings.

There are two types of spray coatings commonly used, one being a fibrous spray coating for example that described in our UK Patent No. 1,148,685 which utilizes mineral wool and the other being a spray coating composed of cement binder and vermiculite as filler, not containing fibers.

The fibrous spray systems lend themselves to rapid production of thick coatings layer up to 20 cm thick can be applied in one application-and have excellent properties except in appearance, so frequently a decorative layer of a different composition is applied to their exposed surfaces.

The vermiculite/cement coatings are sprayed as a slurry in water, and are more decorative but not able to be applied in such thick layers, about 1 cm being the normal thickness applied in one application. a problem with this system is that the vermiculite tends to cause blockages, or "plugs" as they are frequently called, in the pipelines through which slurry is being pumped.

According to the present invention a process for coating a surface comprises spraying water, inorganic binder and an insulating filler onto said surface, said insulating filler consisting at least in part of hollow particles separated from pulverized fuel ash.

The invention also provides a composition for use in the process.

The inorganic binders which may be used in such systems are well-known and consist of water settable powders such as portland cement, cement fondu, gypsum, caicium silicate, sodium or potassium silicate.

The hollow particles separated from pulverized fuel ash are hollow glassy particles which form a proportion of such ash and are normally separated from it by flotation techniques, the hollow particles floating in water whilst the solid particles in the ash will sink. This hollow material is commonly referred to as pfa cenospheres, and is a light (density about 450 kg/m3), free flowing powder.

The spray is preferably in the form of a water-borne slurry containing all the components of the composition of the coating to be applied.

In the water borne slurry method a slurry of the coating ingredients is pumped by means of a slurry pump to a spray head where it is atomised by compressed air fed separately into the head.

The spray preferably also comprises exfoliated vermiculite as an additional insulating filler, vermiculite being less dense than pfa cenospheres and also having an angular shape which is thought to assist in giving good integrity to the coating, pfa cenospheres having a generally smooth spherical form.

Mica may also be included in the spray as a further filler to improve crack resistance in the coating.

A particularly preferred ingredient of the spray is a material which will retain water in the sprayed coating to enable the binder to hydrate on absorbent substrates which may otherwise rapidly suck the water out of the coating adjacent to its interface with the substrate and hence prevent a good bond being obtained. Very suitable materials for this purpose are cellulose ethers which also have the advantage of acting as viscosity controllers and thickening agents in a water-borne slurry system. An example of a suitable cellulose ether is hydroxy ethyl cellulose.

A further preferred ingredient of the spray is a surface-active agent to promote hydration oithe binder. The surface-active agent may be a powder or liquid. Examples of suitable surface-active agents are the sodium salts of alkylated naphthalene sulphonic acid(s); the condensation products of alkyl phenol and ethylene oxide; anhydrous condensation products of a long-chain fatty alcohol and ethylene oxide; and metal phosphates.

Water-proofing agents may be included in the spray to reduce water-absorption in the finished coatings and improved initial adhesion of the sprayed material to its substrate before the binder has set. As an example of such an agent metallic salts of a mixture of aliphatic carboxylic acids may be used.

Another preferred ingredient of the spray is an air-entraining agent which assists the pumpability of the slurry and also reduced the density of the coating as applied.

The preferred method of carrying out the invention is to intimately mix all the ingredients of the spray, except the water, thus making a dry powder mix which can be packed at a factory and readily transported. The proportion of the ingredients in the mix may vary widely but the preferred ranges are tabulated below, all proportions being given as a percentage by weight: Composition of Dry Mix Ingredient Percentage by Weight Pfa cenospheres 1 to 60 Vermiculite 0to70 Mica 0to20 Inorganic binder 20 to 45 Cellulose Ether up to 2 Surface-active agent up to 2 Waterproofing agent up to 1 Dust suppressant (oil) up to 3 Air entraining agent up to 1 Wetting agent up to 1 As dust suppressant a light oil can conveniently be used, of animal, vegetable or mineral type.

More preferably the amount of cenospheres is in the range of 1 to 20% by weight and the amount of vermiculite is in the range 35 to 65% by weight.

The dry mix is transported to the site where it is to be used. For use it is mixed with sufficient water to form a thick slurry, ether by hand or in a machine such as a cement mixer it is then fed to the hopper of a slurry pump and forced through a nozzle of a spray gun via a flexible fluid line. Compressed air is internally mixed in the slurry at the nozzle at the spray gun.

The pump is remotely controlled from the spray gun.

The surfaces which may be coated in this way are in particular walls, ceilings, pillars, girders and exposed pipework.

As applied the coating has a rough finish, which may be left or may be smoothed before the binder has set.

A typical slurry could be made up of a 1:1.5 dry blend of powders to water, on a w/w basis. In order to capitalise on the desirable characteristics of air-entraining agent it is essential that the slurry is vigorously mixed for several minutes before placing in the pump. Depending on the type of pump used, the powder to water ratio may be varied. The consistency of the slurry does affect the applied thickness which it is possible to achieve with one pass of the gun. In order to achieve initial thicknesses of 6 to 8 mm. or more it is essential that the water/weight ratio in the slurry should be in the region of 1:1.

The invention will now be illustrated by means of Examples.

Examples Spray coatings were applied to a test surface from water-borne slurries of the formulations detailed in the following table. In each case the figures in the Table are percentages by weight of solids in the slurry and slurries were made up by three minutes of high speed mixing with water, the ratio of solids to water being between 1:1 and 1:1.5 in each Example except Example 3, where the ratio was 1:1.9.

Table Example No. 1 2 3 4 5 Cenospheres 10.00 3.99 14.00 10.42 10.86 Vermiculite (exfoliated) 50.00 58.02 45.00 46.87 45.26 Clay - - - 10.42 O.P.C.* - - 29.98 31.23 Ferrocrete** 38.00 37.59 - - 43.44 CementFondu+++ 10.01 Water Softener*** - - - 0.53 0.22 Cellulose Ether 0.20 0.30 0.54 0.53 0.22 PVA powder+ 1.80 - 0.47 - Air Entraining Agent++ (powder) - - 0.10 - * O.P.C is ordinary portland cement ** "Ferrocrete" is rapid hardening portland cement available from Blue Circle Cement The The water softener was sodium hexa metaphosphate (wetting agent) + PVA is polyvinyl acetate ++ The Air Entraining Agent was a calcium salt of a lignosulphonate +++ "Cement Fondu" is a high alumina cement available from Lafarge Cement Company The compositions of Examples 1 and 2 both enabled coatings of thicknesses up to 20 mm. to be built up in one pass on flat surfaces.

The other compositions could be used for thinner coatings e.g. 6 mm. thickness, and gave rise to coatings of similar densities.

Claims (13)

Claims

1. A process for coating a surface which comprises spraying water, inorganic binder and an insulating filler onto said surface, said insulating filler consisting at least in part of hollow particles separated from pulverized fuel ash.

2. A process according to claim 1 in which the water, binder and insulating filler are sprayed in the form of an aqueous slurry.

3. A process according to claim 1 or 2 in which the binder is portland cement and/or cement fondu.

4. A process according to claim 1, 2 or 3 in which the spray contains exfoliated vermiculite.

5. A process according to claim 1, 2, 3 or 4 in which the spray contains mica.

6. A process according to any preceding claim in which the spray contains a cellulose ether.

7. A process according to any preceding claim in which the spray contains a surface-active agent and/or a waterproofing agent.

8. A process according to any preceding claim in which the spray contains an air-entraining agent.

9. A composition for use in the process claimed in claim 1 which comprises, Percentage by Weight Pfa cenospheres 1 to 60 Vermiculite O to 70 Mica O to 20 Inorganic binder 20 to 45 Cellulose ether up to 2 Surface active agent up to 2 Waterproofing agent up to 1 Dust suppressant oil up to 3 Air entraining agent up to 1 Wetting agent up to 1

10. A composition according to claim 9 in which the amount of Pfa cenospheres is in the range 1 to 20% by weight.

11. A composition according to claim 9 or 10 in which the amount of exfoliated vermiculite is in the range 35 to 65% by weight.

12. A process for coating a surface substantially as described herein and illustrated in any of the foregoing Examples.

13. A composition for use in the process claimed in claim 1 substantially as described in any one of the foregoing Examples.