1/4" & 3/8" exterior birch 4'x5' sheets

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Preparing to replace the floor in my bathroom I was looking for the best underlayment and came across something that might be good for 5x trailers. My past research into Baltic Birch found that it was somewhat expensive and what I found locally in 5'x5' sheets used interior glues.

Halex Corp has 4x4, 4x5, & 4x8 plywood in 5 ply 6 mm (~1/4") and 7 ply 9 mm (~3/8") thickness. Exterior glue and no core voids (though it may have patches on both faces).

I found a store online (not near me) with the 4x5, 6 mm sheets at ~$19 each.

Corporate website
http://www.halexcorp.com/halex_underlayment.shtml

Description:
Surface Knots
Knots in the surface of the plywood underlayment can cause discoloration or they can fall out and create a surface void that is clearly visible beneath resilient flooring. To prevent these problems, all surface knots should be plugged. Traditionally, these plugs can be made of plastic, rosin-type materials, or solid wood. Plastic and rosin-type materials, however, can yellow with age and spread the yellowing through the flooring. This is why Halex uses only solid wood plugs on the face of our panels – guaranteeing that the plugged areas will not be visible through the final flooring.

Type of Plywood
Traditional underlayment plywoods such as luaun, douglas fir, and poplar may be economical, but they can also cause discoloration or be prone to wood indentation because of their natural properties. Halex Underlayment, however, is Baltic Birch (also called Arctic Birch) plywood, a wood that is known for its light color, strength, hardness, and durability. It is available in 6mm and 9mm thicknesses, with 5 or 7 plies, respectively.

Number of Plies
Traditional Underlayment comes in 3 plies, and in thicknesses as thin as 5.0mm. In traditional 3 ply plywood, irregularities in only one ply such as knots, voids or bowing, can cause the entire panel to crack, break, or change shape. To prevent these issues, Halex plywood underlayment comes in a minimum thickness of 6mm and in 5 ply and 7 ply constructions, adding strength and durability, and virtually eliminating the risk of damage due to the irregularity in a single ply.

Grade of Glue
Exterior grade phenolic glue is considered to be the minimum grade of glue used in plywood underlayment for resilient flooring installations. Interior glue grades may appear satisfactory, but will delaminate in the presence of prolonged moisture or severe weather conditions. Halex plywood underlayment exterior grade glue, passes the APA boil test, and will not delaminate throughout the life of the floor.

Surface Texture
Many plywood underlayment manufacturers offer only a sanded face in their underlayment panels, believing that levelness and smoothness are only important factors on the surface. Halex, however, sands both the face and the back of our plywood underlayment panels, ensuring the smoothest, most level panel possible for the smoothest, most level resilient floor possible.

Core
Core voids, most often caused by open knots or delamination, can pose a major problem in plywood underlayment. Undetectable to the eye, they can cause the plywood underlayment to give under the pressure of high heeled shoes, furniture or appliances, and ruin a resilient floor. Halex plywood underlayment panels, however, are specified to have only solid plies throughout, from top to bottom.

Quality Assured

Ultrasonic Testing
Each panel of Halex plywood underlayment is ultrasonically tested to ensure that every panel is solid throughout and free from delamination.

Individual Inspection
After the ultrasound, each panel of Halex plywood underlayment undergoes a rigorous inspection for sawing and sanding irregularities, and visible knots and voids before it is wrapped in protective packaging for safe shipment.

Lifetime Warranty
Halex offers a Lifetime warranty, guaranteeing each panel of plywood underlayment will support resilient flooring without discoloration, delamination, or other manufacturing defects.