You’ve just invested in a beautiful new Shed and coated it in your favourite Sadolin Superdec shade, you’re admiring your handiwork from the kitchen window… and then — horror! Little yellowish blobs of sap start appearing on the surface.

What. The. Heck?

Welcome to the world of knots and sap — the most misunderstood (and unfairly hated) parts of natural timber.

Let’s get into it.

Why does sap appear on timber?

All timber comes from trees (obviously), and trees are full of resin — especially softwoods like the Scandinavian redwood we use at Gillies & Mackay.

Now, this isn’t any old pine. We use the highest grade of Scandinavian Redwood, slow-grown in cold climates. That slow growth creates tight grain patterns, which means stronger, denser, more durable timber. Before it even gets to us, it’s been kiln-dried at the sawmills, which helps stabilise the wood and reduce movement — but doesn’t eliminate it entirely. Nothing ever can. It’s timber — it’s alive.

Even with the best care, knots will sometimes release sap during the first year — particularly as the timber adjusts to its new environment. This usually shows up as sticky or hardened resin around knot holes, especially in warmer months.

It might look alarming, but it’s completely natural, and it doesn’t mean there’s anything wrong with your shed or with the Sadolin finish.

Should I seal knots before painting?

It’s a fair question — and one we hear a lot.

We could pre-seal every knot at the workshop. But we don’t — and there’s a very good reason why.

Sealing knots too early can trap moisture, block the timber from breathing, and lead to bigger problems like blistering or flaking down the line. We’re in this for the long game. That means prioritising performance and longevity, not short-term cosmetics.

By letting the knots breathe naturally, the timber has time to stabilise in its new environment — and any work you do after that (like sealing or re-coating with Sadolin Superdec or Sadolin Quick Dry) is going to be far more effective and lasting.

Can I do anything about sap leaking from knots?

Yes — if you’re someone who wants to tackle it early, or if you’ve got a particularly enthusiastic knot doing its thing all over your finish.

Here’s what we recommend:

1. Let the sap dry fully (don’t go over it with paint while it’s sticky)
   
2. Gently scrape off any hardened resin with a Stanley blade or similar tool
   
3. Spot-prime the knot with Zinsser B.I.N — a brilliant dewaxed shellac-based primer
   
4. Once dry, re-coat the area with your Sadolin
   

We use Sadolin Superdec and Sadolin Quick Dry Opaque Woodstain exclusively — both give a durable, microporous finish that allows the timber to breathe while giving it a smart, weather-resistant coating.

Will sap leaks keep showing up?

Short answer: no — not forever.

Most resin bleed happens within the first year, especially during spring and summer. Once the timber has settled and released what it needs to, the knots will calm down and stay sealed. No more sap leaks!

From there, it’s just a matter of giving your building the odd check and refresh — and for that, we’ve got you covered. Everything you need to know about keeping your Gillies & Mackay building in top shape is in our AfterCare Guide.

Should sap leaks put me off buying a timber garden building?

Absolutely not.

We’ve been building Sheds, Garages, and Garden Rooms for over 30 years, and we guarantee our buildings for 30 years because we know the materials we use and how they behave. Natural timber will always do its thing, but with the right care and the right products (like Sadolin), it’s incredibly reliable, resilient and beautiful.

Yes, there might be a few surprise blobs in year one. But those quirks settle quickly — and what you’re left with is a high-end building that’s built to stand the test of time.

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Why do Gillies & Mackay use timber for their buildings?

Working with timber means working with nature, not against it. We choose the very best wood we can get our hands on — not to create perfection, but to create buildings with real character, strength, and longevity.

If you ever spot something on your cladding that looks odd or unexpected — like sap or stubborn knots — don’t panic. Chances are, it’s totally normal. But if you’re not sure, just give us a shout and we’ll happily talk you through it.

You’ve got this — knots and all.