Laminated shuttering plywood

The utility model is related to the scope of civil engineering, in particular, to materials for making temporary formwork when erecting buildings and performing in-situ concreting, in particular, for fabricating of buildings’ bridging.

Nowadays the following types of board materials are mainly used for construction of formwork: fill-faced plywood; veneer glued with exterior and interior glue (damp-proof plywood), etc. The most types of formwork laminated plywood look like veneers bonded to each other, whereas quite frequently adjacent sheets are located with their respective fibers being normal to each other, the number of sheets will depend on the type of formwork and may be from 3 to 30 veneers, while thickness of each veneer is from 0.3 to 4 mm. veneers to be bonded are glued with various compositions of bonding.

A general drawback of the applied solutions is inconvenience of providing a necessary quantity of formwork sheets for each definite building. The problem lies in the fact that sheets are made of the definite unified size; but when laying formwork plywood (even when preparing formwork of a building not having inner columns or openings in a bridging, e.g. sanitary engineering holes), a difference will inevitable occur between dimensions of the required bridging and overall dimensions of plywood sheets laid. As a result, some of sheets have to be cut down to the size, and previously to measure necessary distances and mark them on a sheet to be cut down. The next step in making of a formwork is spreading of the carcass onto the laid sheets, for further concrete placement thereon. To observe construction established standards, spreading of the carcass should be performed with a sufficient accuracy of the distance between rods and their parallel alignment to each other. As a result, upon laying of the formwork sheets it is necessary, prior spreading of the carcass in each room, to apply reference points on the created formwork in form of marks, in order to provide for the correct carcass spreading. The mentioned operations (marking for cutting down of sheets and applying reference points for spreading of the carcass) are quite simple but rather time-consuming, though.

The engineering problem of the proposed utility model is creation of formwork laminated plywood which would allow to reduce the time taken for laying, thus curtailing the total time of construction, with simultaneous providing of a protection against affects of concrete in process of concrete placement, i.e. not losing their properties after the first use, and so being able to be used many times.

The abovementioned problem is solved by providing the formwork plywood made of two layers at least. The first layer is ordinary plywood consisting of multiple layers of glued veneers. Attached thereto is the second (external) layer which is a film covering, at least, one of the sheet sides. The plywood is lined with the special film consisting of the resin-impregnated subbase paper. Phenol formaldehyde, melamine and other widely-spread synthetic resins are used as these resins. The film density is from 60 to 1000 g/m²;

predominating values are 120, 220 and 400 g/m² which, on the one hand, will completely provide attainment of the result on availability of the formwork protection when it is subjected to concrete placement; on the other hand, they are inexpensive.

The problem shall also be solved due to the marking applied on the film in advance. As a rule, this marking is made as at least two groups of mutually parallel lines with a definite spacing between adjacent lines.

To perform the first layer, various types of veneers are used: birch, poplar, pinaceous wood and combinations thereof. Birch veneers is the predominant type, as it is most high-quality and maximally maintaining the original shape at multiple uses, while the number of veneers may be from 3 to 10. Adjacent sheets are located with their respective fibers being predominantly normal to each other.

The thickness of the first payer (plywood) is predominantly from 1 to 40 mm; however, formworks of larger thickness values can be used.

Laminated film can be bonded to one or both sides of the first layer, while two-side arrangement is predominant; such arrangement will allow to avoid overturning of plywood sheets when they are placed, and to lay them on any side.

Marking is predominantly applied on the film when the latter is fabricated, i.e. prior its attaching (bonding) of the laminated film on the first payer (plywood).

The marking is, at least, two groups of mutually parallel lines with a definite spacing between adjacent lines. The predominant type of marking is grid, i.e. the second group of parallel lines is perpendicular (normal) to the first group of parallel lines. The predominant value of spacing between adjacent lines in each group is 50 mm. Other values of spacing are also possible: from 5 to 100 mm, which are most frequently are divisible by five or ten.

Fulfilling of two types of marking on the film is also acceptable, which may differ or not differ from each other in their visual arrangement - e.g. the first type of marking may consist of solid lines, while the second line consists of dashed lines; or markings may differ from each other with colours or thicknesses of their lines. In this case, the predominant type of realization will be the one wherein lines of the second marking are shifted, in relation to the first marking lines, half a spacing between the first marking lines; however, other variants of the spacing of marking lines in relation to each other may be possible.

Also, formworks having three and more types of markings with various values of spacing may be used.

Edges of the plywood may be coated with water-acrylic paint for improving of water resistance.

A formwork sheet may have arbitrary dimensions in process of fabrication thereof; however, the most widely used are 1220*2440 mm, 1250*2500 mm, or 1500*3000 mm, as well as their derivates and other dimensions.

The utility model is realized as follows. When preparing a bridging, the entire area thereof is sequentially covered with sheets of film faced deck plywood. In the case when overall dimensions of the bridging do not allow laying an integer number of sheets, from the last but one laid sheet the distance is measured, by a known method, which remains from the side of the sheet closest to the bridging perimeter, to the bridging perimeter itself. A strip shall be saw-cut from the formwork laminated sheet the width whereof is equal to this distance, on the marking applied on it, and thereafter is will be arranged on the surface.

Similarly, when a complicated section is present in the bridging, for instance, when an opening for a column or a technical aperture should be cut, a notch shall be made at right angles according to the marking; this notch shall divide the sheet into two L-shaped sheets with further sawing off of the excess portion, also according to the marking; thereafter, the both these sheets are laid on their places.

Further on, when spreading the reinforcement bars there is no necessity in measuring and drawing equal distances between parallel rods on the coating, with observing parallelism between them, as pedestals under the carcass shall be installed directly over the applied marking with the spacing which is required for a definite problem.

The calculations made and experimental layings showed that the stage of laying on the area of a standard 49 sq. meter flat with use of this solution will give saving of time equal to 17 minutes in average, while the stage of carcass spreading saves 5 minutes more. The total saving in process of construction of a typical 16-storey house will save 20 working shifts, provided this solution is applied.

This solution can be similarly used in a case of accessory formwork, when bridgings are erected.