Sewing Waterproof seams: Sealant or seal tape?

Sewing Waterproof seams: Sealant or seal tape?

Why do you need to seal stitch lines and seams?

Waterproofing seams and stitch lines ensures your handmade waterproof jacket is just that: waterproof.

Sewing two pieces together creates tiny little gaps where the pieces are connected by the stitching. If you’e adding pockets and fastenings to your garment every time your needle punctures the surface of your waterproof or water resistant fabric it leaves a little hole. Even when plugged with polyester thread, it’s an easy way for the water to creep in.

Basically anywhere you are joining or adding pieces risks impacting the integrity of the garment.

A glimpse of light through the seams sewn between two components of waterproof fabric.

I’ve made and owned water resistant gear in the past that doesn’t have sealed seams, and they work … well, ok. In light showers, for short walks, the water is repelled. But for longer journeys and wetter conditions you’ll want some certainty that you will stay snug and dry. In this case you’ll want to seal the seams as you sew your garment using iron-on tape, or brush-on sealant from the tube.

If you want to make a raincoat, poncho or jacket that keeps you snug and ensures you stay dry, you’ll want to seal the seams.

What is better: Seal tape or sealer from the tube?

There are two main methods for sealing seams on homemade raincoats and wet weather gear. Iron-on sealant tape, and liquid sealer. I snapped these both up on eBay for around £10 each.

Roll of iron-on seal tape and a tube of seam sealant liquid.

Testing iron-on seam sealer clothing tape

5m of light grey iron-on sealer tape, 20mm wide, set me back £10 on eBay. I don’t recall seeing colour options so I grabbed the grey roll. Later on I spotted a few different monochromatic shades. I probably would have purchased the darker grey or black for this garment if I’d taken the time to look around.

How seam sealant tape works

After each piece of fabric is stitched together the seam allowance is pressed flat and the tape is ironed to the inside. The tape has two sides, a textured top side and thin sealer underside. As the tape heats up the sealant melts and becomes tacky. In its melted state it adheres to the seam, and as it cools and hardens it cements the bond. This finishes the seams and neatly seals the gaps created by contraction.

Tips for using sealant tape

1. Watch your heat

Pay attention the heat of the iron to find a sweat spot that’s warm enough to melt the tape but not distort the fabric. I did a bunch of test pieces and noted the best iron setting. You’re only a hasty iron press away from melting your pieces, so it pays to take it slow.

2. Turning corners

You can apply the tape around a light curve. Or cut the tape and step around a tighter corner.

3. Conserve your tape

The sealant tape instructions said to leave a bit of hanging over the edge of the seam, and then trim. But I wasn’t too keen to bulk out the seam allowance and waste my precious tape. So I worked by pressing the tape straight from the roll, so I could trim it to length accurately. I tucked the roll in my pocket to keep it from rolling away. With one roll of tape I was able to seal the one entire jacket.

Testing a tube of seam sealant

The tube of sealant was cheaper than the tape, at £7.99 for 60ml, which I guess would go quite a long way. Again, like with the tape, I played around with a load of test pieces before using it for realsies.

How seam sealant liquid works

Sealant liquid is the consistency of glue, you squeeze it out and scrape it flat with a little scratchy brush. The liquid sealant took about 30 mins to dry enough so it wasn’t too tacky to keep working on the project.

Straight away the strong chemical odour and messy runny mixture put me off. Fiddling about removing the lid and putting on the spout did not fill me with joy. It’s tricky to manage the amount of sealant applied. The instructions say to apply the sealant and then brush it into the seam with the little scratchy brush. This worked ok when I got the knack, but I noticed that the liquid and the bushing action did cause the edges of the pieces to curl up.

Tips for using liquid sealant

1. Manage the mess

Lay down paper or newspaper to protect your workspace from escaping sealant.

2. Ventilate your space

Sealant has a strong, unpleasant, chemically odour. So if you can’t apply it outdoors, crack a window.

Results: Iron-on tape or liquid seam sealant?

For my task of sealing the seams on a sew-at-home raincoat, the iron-on tape was easier to work with and produced better results.

I love how easy it was to work the sealant tape into my construction flow. The neatly pressed seam allowances aiding future construction steps. The tape created minimal mess and doesn’t have a very intrusive odour.

The sealant liquid is better value for money, and would be suitable for covering larger surface areas. Working with liquid sealant on sewing projects requires setting up another space for application and leaving pieces for the suitable drying time.