News: What To Expect With Your Oak Structure
13/01/2022
5 Things To Expect From An Oak Structure
An unexpected visual change to an oak structure is worrying. But, while the sight of a crack may have you concerned, you needn’t fret.
In this article, we'll put you at ease and highlight the natural changes facing oak timber structures. See, shrinking, colour change, and cracks are part of the natural ageing of oak.
By foreseeing these changes, you can sit back and enjoy the process. So what is there to expect with your oak structure? Let’s take a look.
Shrinking is Part of the Procedure
Should shrinking oak be a concern? Absolutely not. In fact, it's guaranteed to happen, and it’s a good thing.
Most of our products use green oak. Recently felled and unseasoned, green oak has a high moisture content. So, its natural green oak frames will lose moisture over the first few years causing shrinkage.
A warm house will speed up moisture extraction. So, for oak beams and trusses located indoors, the shrinkage is noticeable sooner.
Before you turn off your heating, here's the thing, you needn’t worry about shrinking timbers.
Shrinking green oak is natural and doesn't weaken the structural integrity. In fact, shrinking has the opposite effect! Green oak becomes harder and thus stronger throughout the drying process.
But what about joints?! How does shrinking affect oak joints?
Oak shrinks more in width than length, so all joints stay strong. As a matter of fact, oak shrinks around joints to create a stronger connection than before the shrinkage. So whether it be mortise and tenon or dowel connections, they become tighter throughout the shrinking process.
Does shrinking oak cause gaps?
Staff at Oak Timber Structures have years of experience in the timber industry. So, when cutting oak beams, we understand the levels of shrinkage to expect and use the process to strengthen the structure.
With this attentive cutting, there's minimal restorative work required. That said, it’s possible for shrinking to leave tiny gaps. We're talking around 5mm after a few years of shrinking.
If the gap is between oak beams and plastered walls, then simple decorating caulk between wall and wood will do the job and fill the gap. You can buy caulk for a few British pounds from most hardware stores.
Often, our customers add a cutout or rebate into the plaster. The slight inset into the wall conceals the natural contours of the beam and any movement in the future.
Why Does Nobody Care About Oak Movement?
You may have come across the term oak movement. While the definition sounds obvious, it might not be what you think.
As you learned in the earlier section, oak is a breathable and permeable material and, whilst oak loses water, it shrinks. Oak can also absorb water and swell. This is the natural process of moisture movement in all timbers.
So should you care about your oak absorbing moisture?
Oak absorbs much less water than other woods, so swelling is minimal. Also, frames and beams inside your property are less exposed to humidity. The low and consistent levels of humidity help mitigate swelling even further.
So what about your outside oak timber structures like gazebos or pergolas?
Well, even when outside, oak is still a timber less susceptible to the effects of humidity. But there's no stopping outside oak frame buildings from exposure to typical British weather.
Hence one reason we source our oak from Europe. Grown in a similar climate to Britain, oak from Europe is accustomed to a comparable climate. So, when assembled in Britain, European Oak doesn't run into structural issues as moisture moves in and out of it.
Although not a necessity, a coat of Osmo Oil Base Coat is great at repelling water. Then, followed with a coat of Osmo Oil One Coat Only, you’ll reduce both wood swelling and shrinkage.
Cracks and Splits Aren’t A Concern
Noticing a crack appearing in your dream oak frame can have you worried. But fear not, don’t call in the builders. It's part and parcel of the oak ageing process.
There are multiple types of splits and cracks in oak. We call them shakes and fissures. Appearing along the grain, they're induced by the oak fibres shrinking during the drying process.
Indoor Planed All Round air dried trusses with custom joint braces and curved support braces in place of a king post.
Not only are splits and cracks in wood expected, but most importantly, they don't affect structural integrity. Moreover, the cracked look is a telltale sign of aged wood. This traditional edge is a feature most people want from their oak timber structure.
But what if you don't want splits and cracks in your oak?
In time you will eventually get the characterful splits and cracks, it’s inevitable with oak and part of the appeal. You can, however, act to delay them. Cracks are also more prevalent and dramatic when the wood dries at speed.
So, limiting temperature change before assembly is key. Before building, keep oak somewhere dry and protected.
If you decide, you don't like the aesthetics of a particular fissure crack. Then, for interior cracks, Osmo Woodfiller will paper over the cracks, so to speak. It’s quick and easy to apply with a plastic trowel and dries within 30 minutes.
The Tannin Revelation
You'll hear talk of tannins when researching what to expect from an oak structure. So, let's start with the basics.
What are tannins?
When moisture leaves oak, it brings with it a natural acid called tannins. Natural tannins create dark streaks as they leave the oak. So it's common to find these streaks on the oak itself or anything you decide to place the timber on, like brick or staddle stones.
An exposed oak frame subject to rain is most susceptible. The elements increase the moisture content and, in hand, increase the chance of natural tannin stains.
The good news is, over time, the risk of tannins reduces. Chances are, you'll only see them in the first few months after assembly.
Now for even more good news. They're water-soluble. So, if you spot a tannin stain early, you can wash them off with the tried-and-true water and cloth combination. If you leave the natural tannins to stain over time, even then it's not a monumental task to remove tannin stains and Oxalic Acid Crystals will clear up the marks.
Expect natural tannins, but the stains they create are nothing more than a quick fix using simple household products. Be sure not to use harsh abrasives or other chemicals such as washing up liquid or bleach. This will damage the oak and leave behind sometimes obvious markings.
Never Underestimate The Look Of Silvering Oak
Picture this, oak garden rooms are the pinnacle of luxury, and yours is up. The roof has its shingles and you're proud as punch.
But wait, the best is yet to come. Your dream home or garden extension is about to go through the silvering process.
Ultraviolet rays from the sun change the colour of oak. From as little as 12 months, you'll notice your oak develops a silver hue. This is the quintessential oak look and one most people eagerly await.
But not everyone wants the silvered traditional look. There are ways to delay the process and treat oak to suit your needs. We cover all this and more in our Maintaining Your Oak Structure article.
But regardless of whether you want the silvering to occur, the change is natural and is yet another thing to expect from an oak structure.
The Bottom Line
So what to expect from your oak timber structure?
First off, you can expect one of the strongest timbers for construction. To understand the strength of oak, here’s a fact. While steel is three times stronger than green oak, it's also ten times heavier. So, considering the strength to weight ratio, you could say green oak is stronger than steel.
Oak is a low maintenance timber. You can expect little remedial work. It’s safe to leave oak untreated with no issues.
Whether a dream oak framed house or an oak beam. Remember, oak is a natural material. Once felled, it adapts to its new environment so you'll have to expect changes.
But these changes add to the charm of oak. Cracks and split offer a rustic, aged look. Over time, oak also changes colour. In as little as 12 months, you’ll find oak has turned to its traditional best with a silver hue.
Oak may shrink and swell, albeit a matter of millimetres. But the key takeaway is these changes don't affect the structural integrity.
Now you know what to expect from your oak timber structures, you can relax and enjoy the natural ageing of your new luxurious home improvement.
If you want any further information on what to expect. Please contact our helpful team for any advice.