Wooden signs might look great, but they are more prone to weather damage than other materials. In the winter, rain water will soak into the wood and cause rot unless you protect it. The good news is, waterproofing a sign is relatively easy and there are a few ways to do it.
Wood oils are excellent but clear sealers are probably the best option. This guide will take you through the different ways to make outdoor signs waterproof and answer any key questions you may have.
How to Make an Outdoor Wood Sign Waterproof? (Step-by-Step)
1. Choose the Right Wood
Some types of wood are more naturally resistant to moisture than others, so picking the right wood for your sign is the best place to start. I have listed the 5 best wood options for outdoor signs in this guide here.
Wood that has a high oil content is better at resisting moisture. Things like cedar, pine, and redwood are particularly good for signs. You can also buy cheaper options and just seal them up from moisture and rain water.
2. Clean the Sign
Before applying any kind of wood oil or sealer to your sign, you need to clean it properly. Dirt and grime will stop the finish from adhering to the wood properly and any dust particles will leave a rough finish. Use a damp microfiber cloth to wipe the sign clean and let it dry before moving forward.
Sometimes I will use mineral spirits to really clean up the sign, but mineral spirits will remove paint and stain so only do so if it’s a wooden carved sign or before that process.
3. Apply Your Finish
Wood oil is an excellent way to waterproof your sign and give it a nice rustic look. If you’re using wood that has an attractive grain, the oil will amplify it and protect the sign from moisture at the same time.
When using wood oil, take a cloth and rub it in a circular motion into the wood, letting it soak in. Keep applying it until it stops soaking in and beads on the surface, then leave it for ten minutes before wiping away the excess.
If you are using something like teak oil or danish oil, give it around 24-48 hours to dry between coats before recoating. Usually, you’ll need around 3-4 coats for an untreated wood sign.
Oil is great for waterproofing wood, but it does need to be applied more often, especially if you live in a wet climate. Outdoor sealers give a longer lasting layer of protection because they seal the outside of the wood with a solid barrier, rather than soaking into the wood. Many clear coats also have UV inhibitors in them too, so they stop the wood from graying in the sun.
Water-based sealers are often the best choice because they are easier to work with and dry a lot faster than oil-based products. However, oil-based products do give a harder finish.
Once your sign is clean and dry, you can apply your sealer with a good quality brush. Sponge brushes are good if you want a smooth finish without any brush strokes. You can also get aerosol spray sealers which are great for easy application.
When the first coat is dry, give it a light sand to smooth any leftover marks (if you are using a brush) and create a slightly rough surface for the next layer of sealer. Repeat the process 4-6 times for a good layer of protection. When you apply the final coat, do not sand it.
How to Seal a Wood Sign with Vinyl Lettering?
If you use vinyl lettering on your wooden sign, it’s crucial that you seal it properly or it will peel in no time at all. You can use the same clear coats to seal signs with vinyl lettering, and the process is very similar. However, there are a few key things to keep in mind.
Firstly, make sure that your vinyl lettering is properly stuck down and it is not peeling at all. If it is already peeling, your clear coat will not do much to stop it. Once you have checked that it is secure, you can start applying sealer. Go carefully around the edges of the vinyl letters with a small, soft bristled brush, to make sure you get a good coverage without pulling the edges up.
When the first coat is dry, the lettering should be fairly well sealed so you can proceed as normal. Just be careful when sanding between coats.
How to Seal an Outdoor Painted Sign?
A good quality exterior wood paint will give you some level of moisture protection, but if you want to avoid regularly repainting the sign, sealing it is a good idea. A good clear coat will stop the sun from fading the color too.
Spar urethane is the best clear coat to go over the top of paint as it gives good waterproofing and UV protection. Apply lots of thin coats, sanding between each one to give you a good barrier.
How Many Coats of Sealer Should You Use on an Outdoor Sign?
If you check the guidelines on most sealers, they will recommend at least 3 coats, but there is nothing stopping you from doing more coats if you want to. Personally, I would recommend 4-6 coats for maximum durability and waterproofing. Applying too many coats may ruin the finish but you can do a lot before you notice any difference. So, it’s really up to you how many you can be bothered to apply, but the more the better.
What are the Best Outdoor Sealers for Signs?
There are a lot of outdoor sealers on the market and it can be tough to decide which one is best. So, here are 3 of the top ones for your outdoor signs.
Spar urethane is an excellent durable clear coat for your outdoor signs, and this Minwax Spar Urethane Aerosol is ideal if you want a quick and easy option. The simple spray can is much easier to apply than brushing or rubbing oil into the wood, and you don’t need to worry about brush strokes either.
You get a nice clear satin finish and great protection from moisture. There is some slight yellowing when used on lighter colors, but nothing to be too concerned about, especially with a rustic wooden sign.
However, don’t make the mistake of thinking that aerosol clear coats are foolproof because they’re not. If you apply too heavily in certain areas, you can still get drips and sagging, so apply with a constant motion and opt for more thin coats rather than spraying it on too thick.
The coats dry very quickly because they are much thinner than they would be if you were brushing straight on. So, you can probably recoat in an hour or so, maybe even less on a hot day. But the coats are thinner so you may need to do up to 8 quick coats for the best protection.
The only time when you wouldn’t necessarily want to use this product is if you are sealing a carved wooden sign or something with heavily textured letters. It’s vital that you get into the gaps and small pockets where moisture can sit, and a spray isn’t the best for this. Ideally, you should get into those areas with a brush first before coating the whole sign.
Rust-Oleum has a good reputation for quality products, and their Varathane Diamond Spar Urethane lives up to that. This is a water-based sealer that gives a clear, rigid finish. It’s very tough to scratch or dent the hard surface, which is more durable than other clear coats that give you a softer coating. You also don’t need to word about yellowing with this product either.
It’s not going to be as quick to apply as the aerosol spray, but it is touch dry in about half an hour and can be recoated in 2 hours. Bear in mind that you won’t need as many coats as you do with a spray, so the total time is probably about the same.
If you are placing your sign somewhere that gets a lot of rainfall, this will give you the protection you need. Some people complain that it turns a milky white color when it gets wet, but this is only temporary and will disappear when it dries out again.
Tung oil is a natural oil taken from the seeds of the tung tree, and it is used to treat and waterproof wood. This Hope’s Pure Tung Oil is excellent for an untreated wood sign or for bringing an old weathered sign back to life.
You’ll get a lovely finish that brings out the natural beauty of the wood, but you do need to be a bit more patient with this one. It takes around a week for the coats to cure properly before you can apply another, and you’ll need around 3 coats for good protection.
It is quite a thick oil, but try not to apply it too heavily. Wiping small amounts in thin coats over the wood and it will soak in faster. If you try to lay it on too thick, things will get messy and you won’t get the nice even finish you are after.
If you are creating a rustic wooden sign, this tung oil is the best finish to use for that traditional finish.
Can You Use Wood Oil on Painted Wood?
No, you cannot put wood oil over painted wood. The oil works by soaking into the grain of the wood, rather than creating a seal on the top like spar urethane, for example. When the wood has been painted, there is a solid barrier over the top of the wood, so the wood oil cannot soak in and it will just sit on the top. Clear coats are the best choice for painted wood.
Can You Use Wood Oil Over Vinyl?
No, wood oil will not soak through vinyl either. If you have a wooden sign with vinyl lettering, the oil will soak into the surrounding wood but it could also cause peeling. It’s much better to go for a clear coat that will seal and strengthen the lettering.
Can You Stain a Wooden Sign?
Yes, wood stain is a good option if you want to change the color of your wooden sign and give some protection. You can find a range of stain products on the market but the best ones are those with a built-in sealer as they give the most robust moisture protection.
Will a Wood Sealer Change the Color of my Sign?
A sealer will not change the color of wood as much as wood oil. However, most sealers will slightly darken the shade of the wood. In most cases, this difference is only very minor but if you are very particular about the color, it’s something to be aware of.
Can I Use Acrylic Paint on Outdoor Wood Sign?
Technically, you can use acrylic paint on an outdoor wood sign, but it is not designed for exterior use, so it will need to be sealed before you put the sign outside. However, there are so many excellent exterior paints available, and these will last a lot longer when used outside, so opt for these instead.
Outdoor wood signs get a lot of wear and tear, so you need to waterproof them if you want them to last a while. The best option, in most cases, is a clear coat like spar urethane because it gives you a very solid waterproof finish and doesn’t change the look of your sign very much at all. It’s also much easier to apply. But wood oil is still a great choice if you want a rustic sign that highlights the wood.
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.