The article is all about the grades of plywood, the exterior grade and the interior grade too. You will know how these are different in terms of manufacturing and several other factors too.
The Interior grade ply is best when you are using it for indoor use. You can use them either in homes or offices but they should remain indoors and away from the harsh outdoor environment. Hence most of the furniture are made with such plywood.
The Exterior grades are stronger and are therefore suited for the outdoor environment. The plywood is used for furniture like tables and chairs in the garden or other similar furniture. These furniture takes on the harsh natural weather condition and still remain intact in its outer areas,
Major Differences In The Make
The plywood is prepared from wood veneers that are sliced for the purpose. These plies or veneers are then placed together to paste with one another by using resins. The logs of trees are used for rotary cutting them to obtain these veneers that gives the plywood. These veneers are then piled one on other after painting the surfaces with the resin. The veneers or wood slices are then pressed together to get the sheets of plywood. There are machines that are used for the pressing part.
The ones that are used mostly for interior use are treated with Urea Formaldehyde paste or glue. These are also called UF and are very common glue that are used for such purpose. The exterior plywood grade veneers gets Phenol Formaldehyde or phenolic resin as the glue to stick the slices together.
Strength – More And Less
The Interior grade plywood has got the glue that is not so strong and hence these grades are not that strong as the Exterior grades. The Exterior grades are treated with comparatively better glue that keeps on sticking the veneers even in harsh and extreme weather.
Costs Are Different Too
In Indian market the Interior grade plywood is called commercial grade ply and are slightly low in cost that the Exterior grade plywood. These are also called Boiling Water Resistant plywood or BWR and costs some more for the extra qualities.
Water Or Moisture Resistant
Phenol is used to make plastics and when this is used to make the resin for applying on the External grade ply, it has the qualities of plastic. Hence it is water resistant. The use of this plastic resin helps the ply to remain resistant to water. The tests that these ply go through are being submerged in boiling water for 4 hours. Then the strength of the plywood is checked after taking it out. They remain resistant to water and hence are fit for being used out of doors. They are also used for designing kitchen cabinets.
The Interior grade plywood gets treated with UF resin and it is not good for resisting the water content in its environment. Hence this plywood is not water resistant. It is also not good when exposed to the external weather condition.
This is the reason the Interior grade ply is improved by using lamination on it. This simple ply then become resistant to water. There are different brands of lamination from companies like GreenLam, Sunmica or Formica and some other brands too. The laminations are prepared by using papers that are covered thoroughly with melamine resins and phenolic or special resin. The ply then gets property of being water resistant.
Marinaply And Its Qualities
The shopkeepers and general people refer the exterior grade plywood in Indian market as Marina ply. Marine grade veneer or plywood are far superior grade of ply and has got Indian Standard code IS710. This plywood is used in different applications in the sea or ocean. They are used to prepare wooden decorative or useful parts in Ships and even in boats.
You must keep in mind the Indian Standard code for the Exterior grade and the Interior grade plywood would be IS:303 and these are clearly marked on any sheet of plywood that has got an ISI mark on it.