I get emails all the time from people asking me, “ Do I have to seal my deck after pressure washing?”

It’s not a hard question to answer but the answer will be different depending on your specific deck.

I’m going to run through these real quick for you so you can find your answer and get on with it.

Let’s go..

Do I have to seal my deck after pressure washing?

It all depends on the condition of your deck and the reason why you’re pressure cleaning it. 

If your deck is in a great condition and you’re simply pressure washing it to remove dirt, dust or mold build up then there’s no need to seal your deck after pressure washing. 

You would be using a gentle soap solution and giving your deck a scrub then pressure washing to remove the cleaning agent and dirts.

As long as you don’t use too much pressure, washing won’t cause any damage to the surface of your deck.

You want to make sure you don’t exceed 12,000 psi

When you set your pressure washer above the 12,000 psi you’ll start to put swirl marks and etch grooves into the surface of your decking boards.

So, to pressure wash your deck without needing to seal it afterwards, make sure you keep the pressure below 12,000 psi, use a gentle cleaning solution like this… and your deck will be clean and looking new without going to the trouble of re-sealing.

If you clean your deck with a brightener with oxalic acid to remove mould and stubborn dirts then it might be time to seal your deck again. The idea with deck maintenance is to recoat it before the damage occurs.

So if your deck is in need of a heavy clean but it’s still in a good condition, it wouldn’t hurt to give it a thin maintenance coat

It’s all about being gentle and not too heavy handed with your cleaning products and the pressure you use.

If you can damage your deck by pressure washing it, this leads to the question…

Should I pressure wash my deck?

Yes, you should pressure wash you deck if you intents to strip it with a chemical stripper or if it has contaminants on the surface like dirt, grease or grime…

If you are using a chemical stripper to remove deck paint then you should definitely pressure wash your deck to help remove the old deck paint…

Or if you’re scrubbing with a brightener to remove mould, dirt and grime, you should also pressure wash your deck to remove all of those contaminants from your deck…

You just need to make sure that you use the right pressure so you don’t cause damage to your deck…

You can always adjust the pressure gauge on your deck so you don exceed 1200psi…

What do you do if your pressure washer doesn’t have a gauge?

If you’re using a cheaper pressure washer that doesn’t have a gauge to tell you what the pressure is, you can run into some problems. When I first started out, I was using a Karcher kp2 with a Tornado head and a multi pressure head.

I found that the multi pressure head, set to its hardest pressure, was perfect to scrub and clean dirt and mould of a deck.  The lower settings were useless.

The higher setting was safe to use and I never had any issues with etching or damaging the boards. What you will get after pressure washing is a light furr on the surface which would need to be sanded off by giving it a quick once over with an orbital sander.

The Tornado head was great at removing grey, or old coatings that were peeling.

Really, the only way to be sure is to test an area before you start. Some softer timbers like treated pine would still need the higher pressure setting but you would hold it a little further from the surface. 

Don’t be scared, just test it out.

If you have a petrol pressure washer, you’’l have 4 or 5 different heads to choose from.

Each head has a degree rating.

These are:

• Red – 0 degree – For stripping metal and concrete – Not for decking
• Yellow – 15 degree – narrow, hard stripping fan – Not for decking
• Green – 25 degree – Medium fan for cleaning and stripping – For decks
• White – 40 degree – Perfect for cleaning – Start with this one for decks
• Black – low pressure for detergents

With a deck that is uncoated and grey, it’s a different story…

 Once you pressure wash your deck, it’ll look like new timber again but it won’t stay that way for long.

In this case, you have two options…

If you like the grey look, then you could pressure wash to remove the grime then let it grey off again. It is best to seal it if you want it to last longer but you won’t get that grey look. I’ve personally seen hardwood decks go uncoated for 10 years without any maintenance or getting damaged. 

I’ve cleaned the grime off them and then let them go grey again. It doesn’t take long for them to grey off again. Usually only a few months.

If you have a soft cheap wood like treated pine then I’d recommend sealing it. Treated pine decks don’t last long when they’re exposed to the weather. They split and crack and will need to be replaced within a couple of years.

If you don’t want the grey look and you want your deck to be protected, then yes… you should seal your deck after pressure washing.

This is usually the case if you’ve had a new deck installed and you needed to let it weather off before you seal it.  When your deck is protected from the sun and rain then you’ll need to seal with 2 coats of oil or stain.

When your deck is exposed, I recommend sealing it with a third coat.

Clear coats and greying off for that natural grey look…

I haven’t come across a product that allows you to do this just yet. There’s a couple of products that claim to give you the grey look and protect your decking at the same time but the end product doesn’t look that good.

The current products available make your deck look like it’s been painted grey.

Your deck won’t look like it has greyed off naturally.

If you want the grey look, leave your deck unsealed and let it grey off naturally. 

Once a year you could run an 80 grit orbital sander just to remove any surface damage and keep it from splintering.

How long should you wait to stain a deck after power washing?

As a general rule, you should wait at least 24 hours to stain a deck after power washing. 

You want the deck to be completely dry before you put any sort or coating on top. If you don’t, you’ll trap the water underneath the stain and the finish will look blotchy and uneven. 

Sometimes you’ll also notice black patches underneath the coating.

You’ll find that the stain will also wear off a lot quicker as it won’t be able to penetrate into the decking boards properly.

Here’s the thing, if it’s a hot summer day and you’ve pressure washed your deck, you may only need to wait 4 hours before it’s completely dry.

Waiting 24 hours makes sure that your deck is completely dry, but really, once it’s dry, you’re ready to stain.

Just remember that you don’t want to oil or stain your deck in the heat of the day. The sun will cause the coating to dry on the surface before it’s had a chance to be absorbed into the boards and it will sit on the surface like a skin.

It won’t be long before your new coating will bubble and peel off.

You can oil in the morning before the sun gets too hot, or latter in the evening when the sun isn’t as harsh

I hope that helps.

That’s it from me.

Sincerely,

Jason The Deck Restoration Teacher

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