How to Store, Cut, and Sand Thermo-Aspen: A Shop Guide

Store the bundles closed, flat, and indoors

Interior boards belong in a heated indoor space, lying flat off the ground on enough supports, with the bundles still closed. The handbook’s storage list for ThermoWood® products works as a checklist ITWA handbook, p. 34:

• Use a dry, ventilated space, and for anything going indoors, a heated one.
• Keep the boards away from dirt and UV light. UV and damp can cause surface micro-cracks that affect a later finish ITWA handbook, p. 33.
• Lay them horizontal on an even base, off the ground, on enough battens. The handbook credits an even surface and enough base battens with keeping boards from warping.
• Leave the bundles closed until use. Interior cladding goes straight from the package to the wall.

Thermory USA says to store its paneling in the room where it will be installed, ideally for a few weeks, at the installation temperature. The ideal storage range is 59 to 72°F. Keep the packages on a flat surface above the floor, for example on joists. On support spacing, the guide says: “Make sure that joists would be at least 11.8 inch steps to avoid bending” Thermory USA guide, p. 2. Read it together with the handbook’s rule of an even base with enough supports ITWA handbook, p. 34.

One flooring habit does not carry over

The USDA Wood Handbook tells flooring installers to break open bundles and expose all sides of the flooring to the air inside the building USDA Wood Handbook, p. 13-19. The ThermoWood® Handbook says the opposite for its products: bundles stay closed until use ITWA handbook, p. 34. Thermory USA agrees for its paneling: packages stay unopened until the shrink film comes off just before installation Thermory USA guide, p. 2.

If the storage room has a radiant heater or other heat source, Thermory USA caps the temperature at 77°F and says to keep humidity from getting too high Thermory USA guide, p. 2. Do not fire the sauna heater to hurry the boards along.

Give the boards days to weeks in the room before cutting

Before the first cut, check that the boards’ moisture content matches the room. At room temperature that conditioning can take several days, depending on the cross-section. Outdoors it can take weeks or even months, particularly in winter. The handbook says to build that time into the work schedule ITWA handbook, p. 31. Thermory USA’s best practice for its paneling is a few weeks in the installation room Thermory USA guide, p. 2.

The reason holds for any wood. The USDA Wood Handbook’s rule is to install wood at the moisture content it will see in service, which limits movement after installation USDA Wood Handbook, p. 13-3. ThermoWood® products leave the kiln at 4 to 7% moisture content, and the modification processlowers how much moisture the wood takes up afterward. In VTT tests on spruce modified at 428°F, equilibrium moisture content was about half that of untreated spruce ITWA handbook, pp. 7, 26.

Lower movement still means some movement. Thermory USA says its paneling “does not tolerate changes in humidity during construction,” and that wet work done after installation makes the paneling absorb moisture and swell Thermory USA guide, p. 2. Finish tile, grout, concrete, and other wet work first, then bring the bundles in.

Order early enough to cover the wait. Current boards are listed under thermo-aspen at Sauna Marketplace.

Cut with fine teeth and plan cross-grain work

Saw it as you would untreated wood, with one change. Use a fine-tooth blade, because large teeth can chip the edges of ThermoWood® products. ThermoWood® releases no resin, so blades need less maintenance ITWA handbook, p. 31. Thermory’s catalog describes aspen as resin-free as well Thermory catalog, p. 4.

Routing and notching take more planning. The handbook compares milling ThermoWood® to working hard, brittle hardwoods. Plan those cuts in advance to avoid tear-out and nicks, particularly against the grain ITWA handbook, p. 32. Mark the notches for vents, lights, and bench supports before you start.

Pre-drill screw holes near board ends. Thermal modification cut splitting strength by 30 to 40% in tests on spruce, pine, and birch. In screw tests, lower-density wood gave better results with smaller pre-drilled holes ITWA handbook, pp. 23, 24. The fastener guide covers the stainless grades.

If you glue

In the handbook’s gluing guidance, PVAc glues should carry as little water as possible and may need longer press and drying times, because the wood absorbs water slowly. Polyurethane needs water to cure, so dampen the surfaces if needed. Follow the adhesive maker’s instructions ITWA handbook, p. 32.

Sand only where a surface needs it

By the handbook’s account, planed boards rarely need sanding. It says sanding ThermoWood® products works like sanding standard timber and is typically unnecessary, because the surface is usually very good after planing ITWA handbook, p. 32.

Before some finishes

Not every finish adheres well to ThermoWood® products. The handbook says some treatments, particularly some water-based ones, adhere poorly because of the wood’s acidity and low water absorption. It adds that a surface sanded with P100 paper may hold a finish better than a planed one, and advises asking the finish maker which treatment to use ITWA handbook, p. 33. Read the finish maker’s instructions before you sand.

Thermory’s catalog calls for a breathable wood protector on all wooden surfaces, and sauna wax or another suitable coating on walls and floor grids Thermory catalog, p. 39. For ThermoWood® products, the handbook recommends mineral oil for sauna walls, ceilings, and benches, and rules out linseed oil, which enables fungal growth ITWA handbook, p. 33. The bench oiling guide walks through the steps.

Stains on a bench, later

For stains or stubborn dirt on a bench, Thermory’s catalog says to sand the entire length of the bench with fine-grained sandpaper. Then treat the sanded areas with a wood preservative Thermory catalog, p. 39. The questions page has more care answers.

Carry long boards with care and seal the cut ends

ThermoWood® takes a little more care to handle than unmodified wood, because its strength properties make it more prone to mechanical damage. The storage chapter names two weak spots: long boards, because of their reduced bending strength, and tongue-and-groove edges, particularly on long pieces ITWA handbook, pp. 31, 34.

Impact bending strength fell by about 25% in spruce modified at 428°F for three hours. In the handbook’s pine chart the change in Brinell hardness is very small; its wider Table 8 puts Thermo-D pine about 14% and Thermo-D spruce about 9% below untreated wood ITWA handbook, pp. 24, 25. The handbook has no aspen hardness figure.

Carry long boards supported along their length so they do not flex, and keep tongues and grooves from striking anything. Thermory USA also asks installers not to scratch the surface or drag boards over one another Thermory USA guide, p. 4. Edge shapes differ by profile; see the profiles page.

Seal the cut ends

The handbook says cut ends of any timber, ThermoWood® included, should be sealed with an end-grain sealer made for the purpose. Sealing significantly cuts water uptake through the ends and reduces cracking near the ends as they dry ITWA handbook, p. 33. In a sauna, pick a sealer suitable for sauna conditions, the same test Thermory’s catalog sets for every finish Thermory catalog, p. 39.

Run this list before the first cut

Thermory USA items come from its installation guide Thermory USA guide, pp. 1, 2, 4. Handbook and catalog items carry their own page.

• Every package was checked on arrival for transport damage. Thermory USA says never to install a defective product, and installed product is deemed acceptable.
• Any concern about quality or scent was raised before sawing, installing, or treating the wood.
• Wet work is finished and the room holds Thermory USA’s 59 to 72°F storage range.
• The boards have had their time: several days or more at room temperature ITWA handbook, p. 31, and a few weeks for Thermory USA paneling.
• Several packages are open at once so boards can be matched across the walls. Thermory USA notes slight shade differences between production batches.
• The order covers Thermory USA’s 5 to 10% material loss for wall paneling, which varies with board length.
• A fine-tooth blade is fitted, extraction is running, and the respirator is at hand ITWA handbook, p. 31.
• An end-grain sealer made for the purpose ITWA handbook, p. 33and suitable for sauna conditions Thermory catalog, p. 39 is ready.
• Battens and the air gap behind the paneling are in place. The framing guide has the numbers.

Size the order with the calculator below. The spec guide and the quantity post explain the coverage math, and the 3D sauna designer lays out the full room in SaunaDesignPro.