By Abhijit Phadke
This article lists frequently asked questions related to waterproof plywood, and provides the answers to them.
What is waterproof plywood?
Most types of wood eventually gets damaged in case of a prolonged exposure to water. However a good quality waterproof plywood is built in such a way that it offers a better degree of resistance to water, compared to natural solid wood or commercial MR grade plywood. The reason for this is that a phenolic resin (which is a synthetic plastic resin) is used for glueing all the individual plies together. Use of a such a synthetic plastic resin helps in making the plywood waterproof.
What is the grade used to indicate waterproof ply?
Most countries have there own grading system. In India, 'BWR grade' plywood means waterproof plywood. BWR stands for 'Boiling Water Resistant'. There is also another similar sounding grade called BWP (Boiling water proof) which is usually used for marking block boards. In the case of waterproof plywood, the grade BWR is marked on the plywood sheets.
Is waterproof plywood same as Marine plywood?
No. Waterproof plywood (BWR grade) is different from Marine plywood. Marine plywood is specifically built so as to resist a prolonged exposure to water. Quality tests for marine plywood involve submerging a sample piece in boiling water for a period of 72 hours, and then checking its strength and other properties.
Marine plywood is costlier than waterproof ply and used for marine applications such as for constructing boats and ships. For making office or home furniture, marine ply is usually an overkill, and good quality waterproof plywood serves the purpose in most cases.
Is waterproof plywood exterior grade?
Yes. Plywood is also classified as interior grade and exterior grade plywood. Interior grade is meant for indoor use, while exterior is for outdoor use where the wood is likely to get exposed to natural weather elements (meaning a bit of rain and sunshine). In case of outdoor use, selecting Marine ply or Waterproof is a decision to be taken on a case to case basis, depending on the intended application. (For example for the purpose of roofing, marine plywood would be better).
In India, Commercial MR (Moisture resistant) plywood is meant for interior use, while BWR grade can be used outdoors. In other countries different grading systems are in place. e.g. In USA, the codes 'INT' and 'EXT' are used to indicate these grades.
Should waterproof plywood be used for home furniture?
The thumb rule is Marine plywood is better than waterproof BWR plywood, and BWR is better than commercial MR plywood. Given this basic equation, which type of plywood we as customers should choose, depends on our inclination and spending capacity.
My view is that for furniture that is likely to get exposed to a bit of water, for example kitchen cabinets or other kitchen furniture, using waterproof plywood (BWR) is a good choice. For other furniture which is likely to remain dry (e.g. drawing room, bedroom furniture, partitions, wall panels etc.) using commercial MR grade plywood is usually good enough.
Another thing to consider is that in most cases, all plywood used in home furniture and decor will be laminated, and the laminate surface covering helps in preventing water from reaching the plywood core, increasing the overall water resistance of the finished material.
What is the exact difference between Commercial MR grade and Waterproof BWR plywood?
The acronym MR stands for Moisture resistant. What this means is that a plywood of MR grade, can successfully withstand some amount of moisture and humidity. The important point to note is that 'Moisture resistant' is not the same as being 'Water resistant', and hence MR grade is not a water proof plywood.
The major points of comparison between MR and BWR plywood is listed in the table below.
|BWR grade plywood||MR grade plywood|
|Boiling water proof||Moisture resistant|
|Better strength and quality||Of slightly lesser quality|
|Phenol formaldehyde synthetic resin is used||Urea formaldehyde resin is used for bonding the plies|
|Exterior grade for outdoor use||Interior grade for indoor use|
What are the sizes and thickness in which waterproof plywood is available?
Waterproof plywood is available in all the standard sizes. The most common sizes are 8 feet by 4 feet sheets, and thickness of 18 or 19mm. Read the related article on standard plywood sizes and thickness for more information about this.
Can waterproof plywood be used for doors?
For the construction of doors, blockboard and flush doors are the preferred choice of material, instead of plywood. Flush doors have solid rectangular blocks of softwood covered on both the faces by a thin layer of ply of around 2.5 mm thickness. Flush doors are lighter in weight, cheaper and also has lesser tendency to sag and bend compared to plywood. People prefer to opt for a waterproof (BWP grade) flush door, instead of waterproof (BWR) grade plywood for their doors.