Our DIY Fire Pit: Building & Sealing the Wood Benches

Build a DIY fire pit that looks like a million bucks on a budget.

The fire pit is officially all done!!! To say we are excited is an understatement.

And we are not just excited that we don’t have any more manual labor in the hot Texas sun this week. But also just look at that view…

While the view was pretty awesome before, the beautiful wood and concrete fire pit built in the landscape definitely makes it look amazing. And those beautiful wood benches are going to last a very long time thanks to our partnership with Waterlox and their century old Marine finish.

Ever since I used the Waterlox Original formula on the wood vanity top in our last home’s master bathroom (it was so sad to say goodbye to it), I have been excited to try all the other Waterlox products.

And what better way to give their outdoor sealer, the Marine formula sealer, a test than to use it on the fire pit benches.

Wood & Cinder Block Benches

Using cinder blocks to build outdoor benches is not a new concept. But instead of using the holes, we only exposed the flat side to give it a modern sleek look.

But I do not only love modern design, I also love warm rustic elements too. So we paired the cold, gray cinderblocks with a warm, rich wood tone.

The benches are a simple design. And they are quite easy to build, which is great since you have to build 5!

Originally we had planned to put back rests on all 5 benches (as you can see in the design sketch in the post about building the bases). But when we started dry fitting them, I realized the backs on the front two benches got in the way of the view.

What is the point of having a lakeside fire pit if you can’t relax and look at the lake while roasting mallows???

So in a last minute design change, we hurried and removed the backs from two of the benches. This gave us the lake views we were hoping for all along.

Sealing Outdoor Furniture

The Waterlox Marine finish is formulated to work on boats (hence the name). It protects the wood from UV rays which is perfect for outdoor furniture. No more faded wood.

Plus the Marine finish, combined with the Universal Tung Oil Sealer, penetrated into the wood to protect it from moisture. But it creates a strong elastic finish. This means it will not crack, like some other outdoor finishes.

I have experienced cracking after a couple years on most of the outdoor furniture I have sealed with spar-urethane. And to fix it required sanding and re-finishing.

My other favorite part of this outdoor sealer is that you only sand your finished piece to between 120-150 grit. Usually I go to 220 so this saves a step. Plus there is no sanding between coats!

Since sanding is my least favorite part of woodworking, this makes Waterlox my new favorite finish for more than just it’s durability and appearance.

Fire pits are an amazing way to enjoy time with family and friends. For more ideas, check out these other 21 Amazing DIY fire pit ideas that are easy to build.

How to Build & Seal the Fire Pit Benches

Tools & Materials

If you missed it, I shared how to get the fire pit site ready and build the cinder block bases in this post.

Building the Bench Tops

Measure the bases

Before building the benches, it is super important to measure your bases. Of course the bases are not going to be perfect to the measurements planned.

Measure them in multiple places front to back and side to side. Then adjust the base if needed to give you 1/8″-1/4″ tolerance.

Also, it’s a good idea to check for square. One of our bench bases (the very first one) was not perfectly square and it caused us a couple headaches. We had build the bench top a bit bigger and chisel out a couple places to fit around the base.

Cut the frame boards

Cut the 2×6 boards for the frame. The front & back boards will be the measurement of the base + 2x the width of the boards (2x boards are typically 1 1/2″).

For our fire pit I used Douglas fir 2x4s and 2x6s. Since these typically have rounded edges, I decided to plane one side of the 2×6 boards. This gave the outside of the benches flat corners and removed any roughness that can come with 2x construction lumber.

Because the boards were planed, the 2x the width measurement had to be adjusted to the measurement after planing instead of the standard 1 1/2″.

Cut the side 2×6 boards and (5) 2×4 boards so they are the width of the widest part of the base + the tolerance.

The 2×4 boards will be used inside the frame to hold the bench on top of the cinder blocks and the 2×6 boards will sit on the outside of the cinder block base.

Assemble the bench frames

The bench frames are assembled with pocket hole screws according to the diagram in the plans. Drill 3 pocket holes set for you material’s thickness in each end of the 2×6 boards (not the planed side). And drill 2 pocket holes in each end of the 2×4 boards.

Start by measuring out the placement of the 2×4 support boards inside the frame. On the non-planed side, measure and mark 1 2×4 in the center, and two towards the ends so they will sit right on top of the larger edge cinder blocks of the bases and be flush with the inside.

Attach the 2×6 side boards to the edges of one of the front/back boards. Use wood glue and 2 1/2″ pocket hole screws. Make sure the edges are flush.

Then attach the 2×4 supports to the measurements you marked. Make sure these boards are flush with the top of the front/back board. Secure with 2 1/2″ pocket hole screws.

Once the side and 3 of the support boards are attached, attach the other front/back 2×6 board to the other side. Make sure to keep the planed side facing out.

Now before you move on, dry fit the frame to the base. This will let you know if your measurements earlier were correct.

If the frame fits, go ahead and secure the other two 2×4 supports. These will need to be tapped into place with a hammer or mallet. They should sit right up agains the 2×6 side boards. Make sure the pocket holes are facing out.

Tap them into place on the cinder block base. They can be adjusted slightly to eliminate any rocking that your frame may have from being slightly uneven or having less-than-perfect cinderblocks.

Secure them into place with 2 1/2″ pocket holes.

Build the bench backs

For the 3 benches that have backs, you will need to cut (3) 17 1/2″ long 2×6 boards so the top is 1 1/2″ wide and the bottom is the full 5 1/2″ wide.

You could just draw a line and cut them all out with a circular saw, but since you need to 9 total back rests, creating a table saw jig is the fastest way to make these cuts and make sure they are identical.

I adjusted the easy tapered leg jig I made for these DIY nightstands. I go into detail in the post about how to make the jig so I won’t do it again here. But the great thing is you can reuse the same jig over-and-over after a couple quick adjustments to your new project.

Using the jig I was able to cut all the back rests on the table saw in just a few minutes. I also planed the outside (make sure to mirror these for each bench since the angle cannot work if it is on backwards) of 2 of these to get rid of the roundover edges.

Put 3 pocket holes in the bottom of each back rest and attach them to the top of the bench frame with 2 1/2″ pocket hole screws. The two outside ones will be flush with the outside and the middle one should be centered right on top of the middle 2×4 support.

To add the top of the back to the benches, measure the distance between the 2×6 back rests. Make sure to measure at the base where they are attached to the frame. Cut (2) 2x4s to match those measurements.

Drill pocket holes in each end of the 2x4s and attach them to the top of the back rests so they are flush with the top and back. And aim the pocket holes toward the front because they will be hidden with the slats when they are installed.

I’d also recommend sanding the benches now before adding the slats. We did not and it made it harder to get into some spots for a good sanding.

Adding the Seat Slats

Measure the final width of the bench and cut your seat slats to that measurement.

• For the benches with backs: you will need 6 slats per bench plus 2 half slats to sit between the back rests. Cut one slat and 1 slat and 1 half slat from the 8′ long boards and the rest from the 10′ long boards.
• For the benches with no backs: you will need 4 slats per bench. These should be cut from 10′ long boards.

For the benches with backs

Since the half slats in the back do not sit on top of the center 2×4 support, you will need to put 1 pocket hole set for 3/4″ thick material on the inside front corner (on the bottom). Then attach these between the back rests so they are flush with the back of the frame.

Secure the half slats to the frame with wood glue and 1 1/4″ finish nails plus the one 1 1/4″ pocket hole screw to support the inside front corner.

For the hinged slat on the back of the benches with backs, you will want to rip a 1″ piece off the one slat. Attach this piece to the bench frame with a slight gap between the half slats and it according to the diagram in the plans.

Make sure it is flush on both sides. Secure with wood glue and finish nails.

Then flip the bench on its back and attach the (3) back slats. Secure them with wood glue and finish nails.

The top back slat should be flush with the top of the back. Leave a 1/4″ gap between all the slats.

For the benches with no backs

Rip a 1 1/2″ piece from one of the slats. Attach this to the back of the frame so it is flush with the back and sides. Secure with wood glue and finish nails.

Building the hinged seats

For the remaining seat slats, they will be used for the hinged seats.

To keep the slats together and spaced with the 1/4″ gap, cut (4) 12″ long pieces of 2x4s for each bench with a back and (4) 17″ long 2x4s for each bench without a back.

Start with the slat that had the smaller pieces ripped off the side. Measure out on it where the 2×4 boards will go so they are not in the same places as the 2×4 supports in the seats. Each bench will get 4 of them.

Attach the 2×4 boards to the first slat board so it is flush to the back of the board and secure with wood glue and 2″ screws according to the diagram in the PDF plans. Then add the remaining slats making sure to keep them spaced 1/4″ apart.

The final slat will only overlap the 2×4 a couple inches. This will allow it room to hinge open without hitting the bench frame. These boards are not structural in holding the seat slats, they are fully supported by sitting on top of the frame.

For the benches with backs you will only have 3 slats per hinged seat (one that is ripped narrower). For the benches with no backs you will have 4 slats per seat (one that is ripped narrower).

Sealing the Outdoor Benches

Before you can start sealing, you need to give the benches a good sanding with up to 150 grit sandpaper. You don’t want to use a super fine grit because the finish will need to have something to grab onto. But don’t worry, the finished benches are super smooth.

After sanding make sure to remove all the excess dust. We use methods like vacuuming, blowing it off with air (both an air compressor and left blower work), and sweeping.

Then remove any leftover dust with a tack cloth or rag dampened in mineral spirits. Let the mineral spirits evaporate fully before continueing.

Apply the Base Coat

Before applying the Marine sealer, you need to apply a coat of the Universal Tung Oil Sealer (UTOS). This will soak into the wood to give a base coat to other Waterlox finishes.

The UTOS is applied with a rag. Just pour a small amount onto the wood and buff it in. You don’t want to leave any excess sealer to dry on the wood, so make sure within 10 minutes to buff off any excess (they will appear shiny).

I found it was easy to just apply the UTOS to a section, then move on to the next section. When I was done with the second I gave a quick buff over the first before moving on to the third area and so forth.

Because these benches are sitting on top of porous blocks, make sure to add sealer even to the underside of frame.

Let the UTOS dry overnight before adding the Marine finish.

Apply the Marine Finish

The Waterlox Marine finish looks like most other sealers. I has an amber tone to it and will add warmth to your wood.

You want to apply the finish with a paint brush. I found at 2 1/2″ angled brush was perfect for the benches because it easily fit into the opening on the top of the quart jar and covered a lot of space on the benches to make quick work of applying the sealer.

Try not to overwork the finish with the brush as you apply it. It will level itself and remove brush strokes if you don’t keep touching it while it drys.

Also, make sure to stir the finish frequently while using it. You will be able to tell when it settles and needs to be stirred.

To apply the Marine finish, dip the brush into the stirred finish and apply with long smooth strokes. Make sure to apply a nice solid coat, but not too thick that it drips and pools on the underside of the benches.

This first coat will soak into the wood quite a bit. That is good! Let it dry overnight before applying the second coat.

Clean off any dust on the wood as needed before applying the second coat. Again apply in long smooth brush strokes. Since the second coat does not soak into the wood like the first, it will appear glossier as you apply it and is more likely to drip so keep an eye on it.

Let dry overnight. If you want you can apply a third coat. I am impatient and couldn’t wait to put our new benches on the fire pit.

The finish uses air to fully cure so you need a lot of airflow when applying it. We applied the finish outside under a couple 10×10 pop-up tents.

About 3 hours after applying the second coat of sealer, we got an unforecasted rain storm. There was so much water and the tents did not keep it out.

I was worried the sealer hadn’t cured enough. The benches were still tacky to the touch. But we noticed the water was only beading up on top of the wood, not soaking in.

And after the rain storm, the water dried and there are no water spots left behind on our beautiful wood benches.

I’m already super excited about the performance and durability of this finish! And the finish will continue to cure and harden over the next couple weeks till it is ready to survive anything.

Maintenance of the Outdoor Finish

The sun and weather will eventually breakdown any finish. Outdoor furniture sealed with the Marine finish will need to be maintained.

If you notice water is soaking into the wood at all (you will see a slight darkening of the wood when wet), it is time to reapply. But you only need to clean the surface and then apply another coat of the same finish. No sanding or removing of the previous finish!

COST BREAKDOWN

A project like this looks like it is super expensive, and because of the scale it is definitely not cheap. But we used budget friendly materials to make our DIY fire pit and I am so happy with the result.

So as part of this project we are sharing the cost breakdown of everything we bought to help you in planning and budgeting your own project.

• Waterlox Universal Tung Oil Sealer – $16.25
• Waterlox Marine Sealer in Satin – $82.00
• 2×6 boards – $145.50
• 2×4 boards- $50.75
• 1×6 boards – $166.00
• 2 1/2″ outdoor pocket hole screws – $20.00
• 1 1/4″ outdoor pocket hole screws – used some on hand
• 1 1/4″ finish nails – used some on hand
• 2″ outdoor screws – $5.00
• 3″ long stainless steel hinges – $33.00
• 1″ #8 stainless steel wood screws – $6.00

For the bases we spent a total of $351 (you can see the breakdown in this post). Which brings our grand total to… $875.50!

Not bad for a spot that will get years of use.

We are already loving the seating area that we created at the lake. It’s the perfect place to sit and watch the ducks. We even plan on storing duck food in the storage area created by the benches.

I added a few planters with tropical plants to give our DIY fire pit a tropical vibe and it works perfectly with the warm tone of the wood.

Someday I plan to maybe add built-in planters between the cinderblock bases on the outside of the fire pit area. I love the added greenery, and could even plant herbs and flowers that repel mosquitos, but that is a project for another day…

Right now I think we earned a chance to just sit and enjoy our hard work!

Thank you to Waterlox for sponsoring this post. I only recommend products that I use and love and all opinions are 100% my own. Click here to read my full disclosure policy.