By CraftingStepByStepPublished Updated
Based on a video by Julie Weilbacher.
Grout is porous. Outdoors that means it absorbs water, holds stains, and slowly gives up its colour, and a mosaic that took a weekend to make starts looking tired in its first year. Sealing the grout is the step that prevents it, and it takes about twenty minutes.
This follows Julie Weilbacher's method, demonstrated on garden stakes and a stepping stone. The useful part is the distinction between the two types of sealer - penetrating versus membrane-forming - because the wrong one outdoors actively causes the problem it is meant to prevent.
Indoors, sealing is a matter of preference. Outdoors it is not.
6 steps · about 11 minutes.Check off each step as you go and your progress saves automatically.
Three things have to be true before any sealer comes out. The grout must have fully cured for at least three days. Any cracks must already be repaired - and then you wait another three days.
And do not seal unglazed or natural stone. It is porous enough that it drinks the sealer straight in, and you will not get it back off.
Tip
Three days is a minimum, not a target. Grout that still smells damp is not cured, whatever the calendar says.
There are two kinds of grout sealer and the choice matters. A penetrating sealer soaks into the porous grout and stays inside it. A membrane-forming sealer sits on top as a film.
The membrane is the one to avoid outdoors: it can trap moisture underneath instead of letting it evaporate, and trapped moisture grows mould. A sponge brush is the easiest applicator, though an old paintbrush is fine.
Tip
Read the bottle rather than the shelf label. Plenty of products described as grout sealer on the front are membrane formers on the back.
The careful approach is to run the brush along the grout lines alone, slowly and deliberately, keeping the sealer off the glass entirely.
It gives the tidiest result and there is nothing to clean up afterwards. It is also considerably slower, and on a busy design with a lot of small tesserae it is genuinely tedious.
Tip
Load the brush lightly. A heavy brush floods the joint and runs straight out over the tile you were trying to avoid.
The faster approach is to stop being precious about it: brush sealer over the whole surface, glass included, then go back and wipe it off every tile.
Pick one method or the other. Aiming for the grout lines, missing, and then wiping anyway is the worst of both - all the slowness of the first method and all the cleanup of the second.
Tip
On a piece with hundreds of small pieces, method two is almost always quicker overall even counting the wiping.
However you applied it, get the sealer off the tesserae before it has time to sit.
Left on the tile surface it dries to a haze, and hazed sealer is far more work to remove than wet sealer was to wipe. Work in sections so nothing is drying while you are still brushing somewhere else.
Tip
A dry cloth lifts wet sealer better than a damp one. Water just spreads it around.
Wait about 15 minutes and apply a second coat. Some brands want more than two, so check the label for the actual number.
Then leave the piece indoors to cure before it goes outside. And seal a mosaic before it ever goes out - seal one that has already spent a season in the garden and all you are doing is sealing in the dirt.
Tip
This is the step people skip when they are already happy with how it looks. Sealing is what decides whether it still looks like that in three winters.
Keep going
How to Make a Mosaic Coaster (Beginner Tile Craft)
How to Seal a Mosaic for Outdoor Use
E6000
E6000 Craft Adhesive, Clear (3.7 oz)
The industrial-strength craft glue that bonds glass, wood, ceramic, metal, fabric, and concrete. The one adhesive most craft projects reach for.
Gorilla
Gorilla Dual-Temp Full-Size Hot Glue Gun
Dual-temp so it handles delicate florals and heavy materials alike. A precise nozzle and built-in stand make it the everyday craft-table gun.
OLFA
OLFA 18" x 24" Self-Healing Cutting Mat
The pro-standard cutting surface. Gridlines for square cuts, self-healing so blades never leave grooves, and big enough for paper, fabric, and leather.
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5 questions covering what you just read. No signup, no score saved, and you can stop after this one.
Question 1 of 5
How long must grout cure before any sealer goes on?
Quick reference
5 questions, answers, and one-line explanations. Tap to expand.
1.How long must grout cure before any sealer goes on?
Answer: At least three days
Three days minimum, and another three if you had to repair a crack.
2.Which sealer type should be avoided outdoors?
Answer: Membrane-forming, it traps moisture
A film on top holds water in, and trapped moisture is what grows mould.
3.Which surface should not be sealed at all?
Answer: Unglazed tile and natural stone
Porous stone drinks the sealer straight in, so you never get an even finish.
4.What is the worst way to apply the sealer?
Answer: Aiming at the lines, missing, wiping anyway
That is the slowness of the careful method plus the cleanup of the fast one.
5.When should a garden mosaic be sealed?
Answer: Before it ever goes outside
Seal it after a season out and you are sealing dirt into the grout.
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