the present invention aims to obviate these drawbacks and relates to a method for the protection of buildings against termites , which method is put into effect during the construction of the buildings themselves , and which is characterised in that said protection is permanent and complete , even though it makes use of new generation termicides , this combination of properties hitherto being considered to be impossible . in fact , it was known how to obtain complete and permanent protection prior to construction but only by pouring , etc ., substances which are now prohibited . it was also known to use less powerful substances , however , this depended on the use of preventative and / or curative renewal treatments ( therefore , the method was not &# 34 ; permanent &# 34 ;) and gave rise to the very considerable danger of allowing the presence of unprotected penetration paths ( therefore , the method was not &# 34 ; complete &# 34 ;). however , the invention proposes a method and means combining four essential properties , the simultaneous combination of which was previously considered to be impossible : 4 . &# 34 ; permanent &# 34 ; treatment ( no need to resort to preventative retreatments or curative treatments in the event of failure ). various plastic materials are also known for the controlled release of active ingredients . in particular , the document fr - a - 3 491 037 ( roussel - uclaf ) discloses packing and coating materials with insecticide properties and comprising a film of plastic material ( polyethylene , for example ) which is impregnated throughout by beans of a compound of the pyrethrin type . the document jp 59 - 62503 discloses a kraft paper sheet impregnated with termicide and coated on one of its two sides with a plastic film . the product is supposed to diffuse through the polyethylene . it is a strong composite product intended for &# 34 ; under floor &# 34 ; use , i . e . in precise areas . moreover , it involves old technology ( 1982 ), i . e . at a time when powerful termicides were authorised , even at high doses , parameters which are now strictly controlled . u . s . pat . no . 5 , 224 , 288 is also known , which is very significant in that it illustrates the state of the art immediately prior ( 1993 ) to the present invention . this american patent describes a fibrous mat impregnated with termicide . the fibres are mandatory , since only this arrangement ensures both a large surface area and adequate mechanical strength . moreover , this document states that , necessarily , the mesh size of the fibrous structure has to be smaller than the insect , otherwise the insect can penetrate the structure . therefore , immediately prior to the present invention , the person skilled in the art understood : that it was necessary to provide a large surface area to diffuse a sufficient amount of product ; that , despite this precaution , the insect could reach the fibrous mat and penetrate it , which shows that the chemical barrier was considered to be inadequate ; perhaps , because of the &# 34 ; immediate &# 34 ; loss of product &# 34 ; by capillary attraction &# 34 ; into the ground . therefore , the person skilled in the art was not directed towards a solution of the film or fibrous mat type but was diverted away therefrom . however , the invention relates to the application of an insecticidal plastic film for the protection of buildings against termites , using a method which comprises laying the film over the entire building surface exposed by the digging operations necessary for the erection of the building , including the foundation trenches , etc ., this point being important , as will be explained below . to judge the significance and originality of the invention it is necessary to view the situation in the context of the problem posed and its technical environment . for example , within the framework of the aforementioned patent fr &# 39 ; 037 , it involved protecting the substances with an insecticide film . however , on the one hand , the application of the film could be mechanised and it was carried out in accordance with certain procedures and in the factory : therefore , correct application of the film was ensured and its insecticide action guaranteed . if a tear or fault was noticed , the packing could simply be diverted and repaired . even it an undetected fault remained , it would result in only slight damage . however , in the civil engineering sector it was unreasonable to expert building workers to apply a thin film very carefully to the ground and around the foundations , to check with even greater care that no reinforcing rods , pebbles , debris , etc ., will perforate the film ( it should be remembered that termite colonies are in a state of perpetual expansion and that their instinct urges them to radiate about the termitarium -- they find the damp and &# 34 ; quiet &# 34 ; earth beneath a building to be particularly suitable -- and to spread , preferentially , along pipe systems , etc ., and that , therefore , a single unprotected passage is sufficient for an invasion of termites ), to dispose carefully and with caution of the filters and building materials , cement , etc ., so that these materials do not in turn perforate the film , namely to ask workmen to give up their practices associated with their technical sector and which are thus quite understandable . this was all the more unlikely since passages have to be provided , particularly in the foundations , for the advance of pipe systems , cables , etc ., of all types , which makes it necessary for the film to be perforated , cut , etc . finally , a film with controlled release of termicidal product could , by definition , only release small doses of product per unit of time , as confirmed by the aforementioned u . s . pat . no . &# 39 ; 288 ; therefore , at the very best one could expect a more or less repellent effect at the locations where the film has not been torn , perforated or badly positioned , or opened to pipe systems , etc ., an effect which would thus quite simply direct the insects towards the locations at which there is a tear , perforation , etc ., where they could penetrate the building without causing damage and , obviously , invade it . therfore , it was obvious to the person skilled in the art that a plastic film with controlled release could not provide any guarantee of success , taking into account the trade under consideration and its unavoidable constraints . the applicants , to their credit , have overcome the prejudices associated with the depositing of a film and have decided on a research programme , despite the investment involved and the almost certain risk of failure , that is according to the reasoning of professionals . it is also to credit of the applicants and their invention that they persevered after encountering the expected difficulties and , nevertheless , developed all the components of an original test programme and , finally , demonstrated that , contrary to all expectations , the termicidal film provides the desired solution . the accompanying drawings , illustrated by way of example , will enable the invention , its features and the advantages which it can provide to be understood more clearly : fig1 of the drawings is a vertical schematic section showing the theoretical application of the system for protection against termites according to the invention . fig2 is comparable to fig1 except that it represents the actual application with serious incidents ( tears , perforations , sheets laid with insufficient covering , etc .) which the person skilled in the art expected and which are in fact encountered . fig3 represents an enlargement of a zone a in fig2 and also the detailed means of the invention and its effects . fig1 shows that , in an excavation formed after the digging work intended for the construction of the foundations ( in chain lines ) for a building , there has been spread out a series of sheets 1 of a film of plastic material impregnated with an insecticide product . these sheets 1 overlap one another ( 2 ) and they cover all the building surface , even extending substantially at ground level ( 3 ). fig2 shows what happens in practice . some of the sheets are poorly positioned for covering purposes ( no or insufficient overlapping ), as shown at ( 9 ). pebbles or debris perforate the film . during the laying operation grids , reinforcing rods ( 6 ) and projections perforate the film . during the casting of the foundations , the film is deflected or stretched under the pressure of the cast material m and the danger of piercing occurs at those locations where there is a sharp edge , as showing at ( 4 ), under the film or at the numerous locations where there is a void under the film ( it is obvious that the film does not closely conform to well - prepared ground ; it can only be placed on ground irregularly littered with debris and , accidentally , with metal parts , etc . ), as shown at ( 8 ). in any case , the film has to be deliberately perforated to allow the passage of pipe systems or sheaths ( 7 ). each of these incidents creates a slit , opening or tour ( 5 ), many of which are unpredictable and cannot even be recognised , and only one of these slits , openings or tears is required to allow an invasion by termites . therefore , the problem posed is to attain the &# 34 ; zero fault &# 34 ;, in this case the &# 34 ; zero penetration point &# 34 ;. fig2 shows the gamble which this objective represents with the simple aim of laying a film . the invention lies in the manner in which it tackles the problem . there are two categories of tearing risks . a ) deliberate openings , such as those provided for the sheaths ( 7 ). these at least have the merit of being known . therefore , one could think of effecting local treatment of the tear by sealing , etc . but in this field there would not be a total guarantee ; b ) totally unpredictable accidental tears . no preventative measures are possible against the latter . it was also known that , by definition , the film could not release a substantial amount of product when the release is gradual , and that the film and its vicinity are subjected to washing effects by water and moisture and other product losses , as confirmed by the above - mentioned u . s . pat . no . &# 39 ; 288 . finally , termicides are degraded at the very alkaline ph values of the building materials . therefore , tears could not be prevented and the product released could be relied upon to form a sufficiently concentrated and extensive barrier to the neutralise the tear zones . nevertheless , the applicants decided to verify this latter point and found that , contrary to all expectations , the film treated against termites ( described below ) was able , despite the gradual release of small doses , to create 1 ) a repellent effect and 2 ) a contact and &# 34 ; shock &# 34 ; effect . the unexpected contact effect observed is essential . according to the tests carried out , an insect arriving in the immediate vicinity of the film is clearly disturbed after only 10 s exposure : difficulty in moving , disturbed orientation and similarly disturbed behaviour . this is wholly in contrast with the teaching of u . s . pat . no . &# 39 ; 228 . therefore , without being able to escape , the insect reaches the equally vary short period of time , at the end of which the lethal shock effect occurs . in the extremely general case in which the insect is thus faced with a sound film , it is either repelled or subjected to the contact effect then to the shock effect . in the first case , it may seek and find a less protected opening . however , in this case , the applicants have established that , contrary to expectations and knowledge , the insect is then subjected very rapidly ( in only a few seconds |) to the contact effect which leads to the shock effect . therefore , the applicants have established that even with not very careful installation practice , a termicidal film provides complete and permanent protection as a result of a double barrier illustrated in fig3 having a repellent affect ( protection of openings ) and a contact and chock effect ( destruction ). the plastic material film which forms the sheets 1 can be obtained by the extrusion of polymers , particularly polyolefins , such as polyethylene or polypropylene or polyvinyl chloride and analogous ( co ) polymers , the thickness of which is between 50 μm and 300 μm . the insecticide is incorporated in the plastic material during the production of the compound , the proportion being a function of the effectiveness or the active ingredient used . the production of the film is carried out starting from this compound by hot extrusion - blowing or by extrusion , it being possible for either one of these extrusion methods to be followed , optionally , by hot - pressing and analogous processes known to the person skilled in the art . the insecticides which can be used are variable and are those known to the person skilled in the art . in particular , it is possible to use : either insecticides of the chemical family of the pyrethrins of the type described in above - mentioned document roussel - uclaf ( permethrin or phenoxy - 3 benzyl (±) cis trans ( dichloro 2 , 2 vinyl )- 3 dimethyl - 2 , 2 cyclopropane carboxylate with the molecular formula c 21 h 20 cl 2 o 3 ; or insecticides of the chemical family of the carbamates , such as benfuracarbe ( dihydro - 2 , 3 dimethyl - 2 , 2 benzofuranyl - 7n -( n - ethoxycarbonyl )- 2 ethyl - n ispropylaminosulplienyl )- n - methylcarbonate ), with the molecular formula c 20 h 20 n 2 o 5 s ; the person skilled in the art will naturally be able to choose the most suitable and these examples are not restrictive . it would also be possible to use mixtures . as is evident , openings necessarily have to be made in the film formed by the sheets 1 , in particular for the passage of supply lines ( water , gas , electricity ) and outlet ducts . to obviate thie slightest risk and to be absolutely sure of restoring the continuous nature or the protective barrier formed by the plastic film , a preferred embodiment of the invention lies in treating these openings during the filling operation ( of the foundation , for example ) by incorporating into the substrate ( 11 ), which forms the covering filler , granules ( 10 ) of insecticidal plastic material , advantageously at a rate of ( about ) 1 volume of granules per 9 volumes of substrate . the openings have to be filled with this mixture over a thickness and a depth of at least about 10 cm the granules used have prererably ( depending on the nature of the ground , on the degree of washing with water , and on the estimation of the dose released , factors which the person skilled in the art could readily determine by routine tests from reading the following examples and tables ) dimensions of the order of about 2 to 3 mm in diameter over a length of about 2 - 5 mm . their chemical composition is similar to that of the film which forms the sheets 1 . they may also be waste from the production of the film or rejected pieces of film , etc ., and the like but this is not preferred ( problems in respect of homogeneity of the doses released ). as a precaution , one could proceed in the same way at the locations where the film is most exposed to probable tearing , as at ( 8 ). preference is given to granules and all geometries have roughness or sharp edges , such as cut rods . the great advantage of this variant is two - fold : it is easily carried out by the building workers , with no particular care needed ; and the preferred use of waste , etc ., from the film . the secondary advantages achieved by this method for protection against termites in relation to conventional systems for pouring insecticide compounds in the liquid phase are also obvious . the active insecticide materials are protected from external attach by the plastic material of the film in which they are incorporated , said film allowing slow diffusion . the quantities of insecticide products are very clearly lower than those used according to a conventional process . the following tables and examples allow a simple comparison to be made . the risk of pollution to the ground and phreatic strata is greatly reduced sines the insecticides held captive within the plastic material are released only at a very low rate . the danger of contamination of the environment in the event of an accident occurring during the conveyance of the insecticide film is absolutely zero , whereas there is a high danger associated with the conveyance of liquid insecticides to be poured . the protective barrier formed by the sheets 1 is especially visible during complementary digging work , so that it can be easily restored . this protective barrier can be easily removed in the event ot demolition . a ) study of the insecticide activity on reticulitermes santonensis of a polyethylene film treated with permethrin . several polyethylene films are used having a thickness of 200 μm and containing different amounts of permethrin . these films were obtained using the method described above . a control film of polyethylene is also used which does not contain any biocidal active material . the film to be tested is retained between 2 glass tubes which are open at the end , have an inner diameter of 50 mm and a height of 50 mm ( s = 19 . 63 cm2 ). a support of neutral material of 1 mm thickness is deposited on the surface of the film and supports a disc of filter paper which is moistened to saturation . the filter paper , which is thus not in contact with the treated film , serves after daily remoistening as nourishment and as water reserve for the insects required for the experiment . after the introduction into each of the devices of 25 reticulitermes santongnsis workers in a good state of health , a cover of polyurethane foam is placed on each of the devices . the mortality rate is verified after 6 hours , 12 hours , 24 hours and then each day for 7 days , starting from the date when the insects were introduced into the experimental devices . for each concentration of biocide in the plastic material there were carried out two repeats of the test which , itself , uses four experimental devices of 25 termites per concentration . ______________________________________dose of biocidein ( m / m ) in % of mortalitythe support 6 h 12 h 24 h 2 d 3 d 4 d 7 d______________________________________ 0 . 005 0 0 4 36 52 64 840 . 05 0 0 8 60 88 96 1000 . 25 20 36 84 1000 . 50 52 88 1001 . 00 100controls 0 0 0 0 0 2 8______________________________________ with a dose of 1 % of purmethrin incorporated into the polyethylene the material exhibits satisfactory anti - termite characteristics . b ) study of the insecticide activity on reticulitermes santonensis of a polyethylene film treated with benfuracarbe . the test methodology is the same as that indicated in the foregoing ; the films are obtained in accordance with the process described above . ______________________________________dose of biocidein % ( m / m ) in % of mortalitythe support 6 h 12 h 24 h 2 d 3 d 4 d 7 d______________________________________ 0 . 005 0 0 0 4 12 20 650 . 05 50 64 1000 . 25 1000 . 50 1001 . 00 100controls 0 0 0 0 0 2 8______________________________________ with a dose of 1 % of benfuracarbe incorporated into the polyethylene the material exhibits satisfactory anti - termite characteristics . b ) study of the influence of dilution by infiltrating water on the insecticide activity or the plastic material used by the method forming the subject - matter of the invention . samples of films treated as described above are held captive in the polyurethane foam . they are introduced vertically into the glass tube of a diameter of 50 mm and a height of 50 mm , at a rate of 4 samples per tube , treated with the same doses and with the same active principle . a device for dispensing liquid drop by drop is installed at the top of this experimental device . by means of the aforementioned device 8 liters of demineralised water are allowed to percolate through the foam supporting the films over a period of 48 hours and a rate of 40 drops per minute . this quantity of water represents , in relation to the experimental surface area , the approximate average of rain received in 5 years per square meter in various west european towns commonly recognised as being subject to termite invasion . following this dilution test , the films are removed from the devices and dried without being wiped . the insecticide activity is then verified according to the method described in paragraph a ) above . __________________________________________________________________________ dose of biocide innature of % ( m / m ) % of moralitybiocide in the support 6 h 12 h 24 h 2 d 3 d 4 d 7 d__________________________________________________________________________permethrin 0 . 05 0 0 0 8 8 11 32 0 . 25 0 0 13 37 69 100 0 . 50 30 56 72 90 100 1 . 00 100benfuracarbe 0 . 05 0 0 0 36 49 78 94 0 . 25 0 0 2 46 71 99 100 0 . 50 16 24 30 68 100 1 . 00 31 44 52 100treated 0 1 1 1 1 1 4controls__________________________________________________________________________ with a dose or 1 % of permethrin or benfuracarbe incorporated into the polyethylene the material exhibits satisfactory anti - termite characteristics after undergoing the dilution test . d ) study of the insecticide activity on reticulitermes santonensis of particles of polyethylene treated with different biocides , mixed with a substrate . particles of the following dimensions : diameter 2 . 5 mm , length 4 mm , obtained according to the above - described method , are incorporated into moistened fontainebleau sand ( 1 volume of water per 4 volumes of sand ) at a rate of 1 volume of granules per 9 volumes of sand . this properly homogenised mixture entirely fills a glass tube which is 50 mm in diameter and 350 mm in height . fitted to the base of this tube is another glass cylinder , 50 mm in diameter and 50 mm in height , which is filled with moist sand containing a block of wood as bait . care is taken to interpose between the two tubes a membrane of filter paper which will serve as a control passage . the device is covered by another glass tube ( 50 mm in diameter and 50 mm in height ) containing a disc of polyurethane foam conforming to the inner diameter of the tube , and 25 mm in thickness . this disc is traversed by two holes 3 mm in diameter and a piece of wood , which originates from the breeding of reticulitermes santonensis , is inserted into the centre of its upper surface . a population of reticulitermes santonensis workers in a good state of health is introduced through the upper opening of the experimental device which is finally covered with a lid out into the polyurethane foam . the depth of penetration into the treated substrate and the mortality rate are checked at the end of the 4 - week test period . 4 experimental devices were used for each biocide tested and at each of the concentrations of biocide in the plastic material . each of the tests was repeated twice . during each repetition 4 devices devoid of any biocide were used as controls . ______________________________________ dose of biocide depth of in % ( m / m ) in the penetration in the survival ratenature of biocide granules substrate in mm of termites______________________________________permethrin 0 . 25 150 18 . 00 % 1 . 00 10 8 . 00 % benfuracarbe 0 . 25 199 11 . 4 % 1 . 00 16 8 . 4 % treated controls 400 80 . 8 % ______________________________________ with a dose of 1 % of permethrin or benfuracarbe incorporated into the polyethylene particles , the material , which is mixed with sana in the proportions defined above , imparts satisfactory anti - termite characteristics to the substrate . these tests demonstrate the activity of the film laden with 1 %, as well as the granules ( 10 ) which may be used mixed with the filler ( 11 ), and also the satisfactory resistance to dilution . it was noted that the repellent etfect was effective practically whatever the dose applied . the person skilled in the art will readily know how to determine the doses required for the &# 34 ; contact &# 34 ; and &# 34 ; shock &# 34 ; effects described according to the invention by routine tests based on the above examples and simple soil samples , etc . the impregnation dose could be as low as about 0 . 5 %, the upper limit being dictated by economic and standardisation criteria , for example about 2 %, preferably 1 %. moreover , it should be understood that the foregoing description has only been made by way of example and that it in no way restricts the scope of the invention , and replacing the described details ot the embodiments with any others which are equivalent will not represent any departure therefrom . in particular , the film could be mounted a dozen centimeters along a wall , above the ground . it would also be possible to develop more or less vertical barriers arranged at a certain distance all around the location to be protected , over a suitable depth known by the person skilled in the dart . a film according to the invention is disposed vertically in a trench protecting at any distance desired the entire periphery of the zone in question , the locations particularly under threat being filled optionally with the addition of granules according to the invention . it would also be possible merely to dig a trench and fill it with the addition of granules according to the invention . new works can thus be better protected and / or &# 34 ; renewing &# 34 ; treatments can be carried out in combination with or in replacement of the old method .
a method protecting building structures against termites comprising over the entire erection surface exposed by digging erection of the structure a non - porous film of plastic material impregnated throughout the film with a low concentration of an insecticide whereby the insecticide slowly diffuses .