Working with epoxy

This adhesive is perfect for special situations, but it also requires special shop safety techniques.

In many, if not most, cases, standard woodworking adhesives white glues, yellow glues and PURs will do the job and perform well. However, in a few situations, such as in a repair job when the joint is not perfect and tight fitting (especially joints with lots of end grain), when joining wood with a non-wood material or when dealing with repairing decayed wood pieces, we need an adhesive that will bridge a gap, is highly moisture resistant, is quite strong, is easy to apply, can be used on a weaker joint and/or can be used to make a fillet to increase the joint strength.

In these few cases, epoxy adhesives, even though they are fairly expensive compared to other adhesives, are the perfect choice. Yet, epoxy is a bit different from the rest of the adhesives, so let’s look at this adhesive more closely so we use it correctly and are satisfied with the results.

Safety

First and foremost, as with many modern adhesives, safety is an issue. For some people, skin sensitivity (in the form of a rash), builds up over time when exposed to the uncured adhesive. Therefore, use good ventilation and always wear disposable plastic gloves. Although epoxy does not stick to skin and can be removed when the adhesive hardens, never clean your skin with a solvent, as the solvent will likely aid in getting the adhesive deeper into your skin. Having said all this, allergic reactions are not common.

One real concern is sanding dust from dried adhesive. Use a good breathing mask.

In all cases, follow the adhesive manufacturer’s instructions for ventilation and other safety issues.

Chemistry

Epoxy adhesive is made from two separate chemicals. Part A, also called the resin, is a diglycidyl ether of bisphenol A. The second constituent, called Part B or the hardener (and is sometimes mis-called a catalyst), is a reactive amine (nitrogen with hydrogen atoms, similar to ammonia). When mixed together, these two form a fully-crosslinked thermoset plastic adhesive.

Mixing

Part A and B (or the resin and hardener) are mixed together just before the adhesive will be put on the joint. It is critical to mix the exact amounts of Parts A and B and then stir them for 15 to 30 seconds to assure complete and thorough mixing. If there is too much resin in the mix or even part of the mix, the result is a weak joint; if there is too much hardener, there will be moisture sensitivity of cured joint. Mixing is usually done by volume (2:1 or 1:1, resin to hardener). Weight can be used, but then is 43:100 or less. Obviously, follow label directions. The strength of epoxy is only about 60 to 80 percent in 24 hours even for the fast cures. It will take 72 hours to get close to 100 percent.

Generally speaking, small batches are better than large.

Application

Surfaces must be clean and free of oils, etc. Coat both surfaces of the joint. Then and this is where most people make a mistake do not use too much pressure. A good epoxy joint is a thick joint. Oftentimes, we will use screws, nails or fast-curing epoxy to hold the joint together until the main epoxy adhesive cures.

The rate of cure varies depending on formulation; most woodworkers will use epoxy with a 30-minute curing time, or even longer. The curing rate is also affected by temperature, going twice as fast for every 18 degrees F warmer. Finally, the rate is affected by the surface area. Since the epoxy generates its own heat that is needed for curing, if the adhesive is spread thin, then the heat escapes and the adhesive takes longer to cure than a thick spread where the heat is held in.

The mixed adhesive can be made thicker, almost like putty, if wood floor (or other approved fillers) is added. This thick adhesive will not "run" and so can be used to fillet a joint and greatly increase the joint’s strength. This thick adhesive is also useful when bridging a gap. Thickened adhesive would not be used for "normal" gluing applications.

After gluing

The strength of epoxy is only about 60 to 80 percent in 24 hours (strong enough to stay together), even for the fast cures. It will take 72 hours (or so) to get close to 100 percent. Avoid high stress on the joint for a few days.

To make sanding and finishing easier, scrape off any excess adhesive before it cures.

Surface films (called blush) form when the adhesive cures when it is cool and/or humid. These films should be washed off with soap and water on a rag before finishing.

Wear a dust mask when sanding.

Special note: Cured epoxy deteriorates rapidly when exposed to UV light. In applications where the joint will be exposed to light, use an opaque paint or varnish with UV inhibitor.

Never use polyester finishes on epoxy joints. Avoid finishes that have alkyd listed as an ingredient. Two-part polyurethanes are OK, but not one-part with alkyd resin.

Questions? Epoxy adhesive manufacturers can answer additional questions.

Preventing woodworkers’ hearing loss should go beyond OSHA requirements and begins with a plan

Hearing protection—Simple, low-cost protection devices such as ear muffs and ear plugs can help prevent permanent hearing loss for woodworkers, but it’s best to have a comprehensive hearing protection plan.

While many woodworking shops use guards and eye protection, if OSHA and workers’ comp figures are any indication, hearing safety is often neglected. In New York State, the Workers’ Compensation Board reported that for 2004, the most recent year that figures were available, occupational hearing loss was the second-highest cause of injury claims, second only to wrist injuries (presumably carpal-tunnel syndrome).

It is estimated that between 1.25 and 7.5 million workers will lose their hearing due to noisy working conditions. Of those, about a third will also develop tinnitus, a ringing in the ears that leads to side effects such as concentration problems, anxiety, sleep difficulties, depression and difficulty in social interactions.

According to NIOSH, construction workers and carpenters in particular are known to develop occupational hearing loss early in their careers, becoming substantially impaired by middle age. NIOSH is working with the construction industry, labor-management organizations and the Department of Defense to test new hearing loss prevention program elements. The program combines Task-Based Noise Exposure Assessment, new training materials and methods, surveillance and a new information management system.

Employees who have hearing loss contribute to the increased risk of other occupational injuries due to misunderstood directions or failure to hear warnings, such as back-up beepers or other alerts. The shame is that occupational hearing loss is preventable.

Employers must have a Hearing Conservation Plan in place to protect the hearing of their employees. OSHA 29 CFR 1910.95 states that an employer "shall administer a continuing, effective hearing conservation program whenever employee noise exposures equal or exceed an 8-hour time-weighted average sound level of 85 decibels." That’s roughly the noise produced by the operation of one belt sander.

Noise limits—A graphic look at how the louder the noise, the less time employees should be exposed.

It is a "best practice" to have a Hearing Conservation Plan to avoid workers’ compensation claims from injured workers and the resultant increase in insurance costs, and to increase work shop safety. Most importantly, it is a matter of good employee/employer relations to protect the hearing health of your employees.

The purpose of a hearing conservation plan is to identify people who are susceptible and protect them from hearing loss, and to detect small losses before they become big losses. Developing your plan

Hearing Conservation Plans consist of the following elements;

1. Noise exposure survey and monitoring. This determines the need for controls to be in place, i.e., what areas may be above the Permissible Exposure Level. It identifies those who may be at risk above the Action Level. It provides a protocol for informing employees about their exposure, and it requires monitoring of changes in noise exposure. This must be done whenever there is a change in equipment or production procedures.

2. Hearing protection. Some kind of hearing protection must be made available to those above the action level. It’s also required for those above the permissible exposure level and for those above the Action Level when a significant "threshold shift" occurs in their hearing. The hearing protection provided must adequately reduce noise, and it’s recommended there be a selection of adequate hearing protection devices available.

3. Audiometric testing. Baseline tests should be done within six months of employment if done in-house, or within 12 months if done outside. (NIOSH recommends within 30 days of employment.) Annual testing should be done for those above the Action Level. Testing determines if changes in hearing are work related. Testing must not be paid for by the employee.

Tools and noise—This chart from NIOSH shows sound levels for typical tools used in woodworking environments such as carpentry and woodworking shops.

4. Professional supervision. All monitoring and testing should be supervised by appropriate professionals, such as a physician, audiologist, or CAOHC-certified professional.

5. Training. As a shop owner, you need to engage employees in their own hearing loss prevention. Training should be done annually and should cover the effects of noise on hearing, the use and care of hearing protection devices, and the purpose of audiometric testing. This part of your plan should also address the format of training.

6. Record keeping. Noise exposure records must be kept for two years although other standards indicate that medical records should be kept for the employment period plus 30 years. Audiometric tests must be kept for the duration of employment.

An initial noise survey must determine whether a workplace meets the specified conditions.The cost of developing and implementing a plan depends on the size of the area to be tested and the number of employees exposed in those areas.

There can be other costs as well, since OSHA has the discretion to fine companies without a plan. Worker’s comp claims can drive up insurance rates. And the gift of being able to hear your customers and co-workers, your family and the world around us for years to come is priceless.

Taking shop safety into account: even if you try to follow all the rules, it may not be enough to avoid an accident.

In our business, we thought we had safety issues covered. Unfortunately, it’s usually not until something happens that you realize that you missed considering something. Luckily, in our case all incidents were recoverable ones and did not result in loss of life or limb, but it could have. And that’s scary.

Because we are now primarily a one-man woodworking shop, with my husband working daily in the shop and me doing the paperwork at home, safety is important to us after all, it’s our lives, health and livelihood that are at risk here. So we’ve taken care to observe all the obvious safety regulations, all the demands made by the fire department inspectors and any requirements by the EPA or OSHA. Sometimes these demands seem a bit excessive, but we abide by them, within the parameters of our small shop. And still, things happen that could have disastrous results.

The biggest concern everyone in woodworking seems to have is blades and how they can damage body parts. My husband, Bob, has worked in woodworking and metalworking for 30 years and rarely had any injury more significant than a sliver or burn, until one morning.

For the most part, Bob uses safety guards on all his machinery, but this particular morning he was cutting some very small parts. He took the guard off and did not use the push tool. For the first group of cuts, he was flying along with no problem. Then he was distracted for just a fraction of a second, and the blade came into contact with his fingers.

Now, Bob had thick gloves on and was very lucky the damage was not severe and he lost no body parts other than a bit of skin and his sense of invulnerability. And despite the injury, he managed to clean the saw off first before heading to the emergency room of the hospital. And it didn’t take him long to get back to work.

He has since used push tools, fences, fixtures, tape adhered to the saw anything to help move the wood along the blade safely. It was a hard, painful lesson to learn. That was probably one of the worst scares we’ve had in our 24 years of running our business.

Fire is probably the next biggest fear a woodworking shop faces. You can have fire extinguishers that are kept updated and even sprinkler systems in highly flammable spaces. You can store all your volatile chemicals, adhesives, paints in a metal nonflammable cabinet.

But sometimes it’s the little things you don’t expect that happen. Whether it’s wood dust and chips from the woodworking side of our business or metal chips from the metalworking side, chip and dust collection can be a hazard. Of course, although we do both metalworking and woodworking in our shop, we never mix the two.

But we did make one mistake. We used a heavy-duty plastic collection can to catch the wood dust and twice in a two-week period we had a couple of small can fires that we quickly extinguished. We smelled them, before there was even any visible smoke. We’re not yet sure about what caused the fires, since we used those cans for years. Was it the material we were cutting? The heat of the day? In the end it wasn’t important. We switched to metal cans and empty the cans frequently. We have not had a repeat.

There are some areas of shop life that don’t easily fall into the safety category one is stacking wood and the other is working alone. These are really two separate issues, but in Bob’s case they came together in a way that could have been disastrous.

While building some casework for a rush job, Bob needed a plywood panel that was buried within a vertical stack of wood. He started to carefully shift the pile and in the process caused the stack to fall on him, and he was alone.

He was surprised at how heavy the stack was and he was truly pinned under the wood. When the stack fell and he went with it, his glasses flew off. Luckily, except for being pinned under the stack, he had no other real injuries. But he was alone, the phone was nowhere near him and he didn’t have his cell phone with him. (The cell phone might not have helped anyway since it gets poor reception in the heart of the shop.)

Bob was able to extricate himself because of the steel-toed work boots he always wears. The panels were resting on the toes of his boots and Bob was able to pull his feet out of the boots, so that the boots held the weight of the stack, and Bob could wiggle out from under. He was pretty achy and the glasses were pretty messed up, but he emerged in one piece.

The experience taught him to stack things more carefully. He now stacks wood panels horizontally if possible, takes his time moving stacks and uses a tilt cart or lift truck to help move heavy loads to avoid a repeat of the incident.

The biggest lesson was about working alone, a hazard many one-man shops face. You need to have some way to quickly notify someone of an incident when you’re alone. Although Bob’s cell phone may not be the perfect choice, he keeps it clipped to his belt now at all times. When he’s dealing with moving large panels of wood, now I try to be there to help.

In the end, you can follow all the rules and still slip up. The key is to keep vigilant and keep alert and use some common sense.