Grout Is Cracked and Falling Out
Grout fails where movement concentrates, and the repair depends on the joint: grout lines take grout, while changes of plane, corners, and cracks over one eighth inch wide take a sanded sealant grade, not more grout. New grout laid over failed grout fails the same way, so loose material comes out first.
The short answer
Rake out every loose and cracked section first, then re-grout stable lines with Custom Building Products Polyblend Plus Grout, and give corners and any crack over one eighth inch wide the sanded ceramic tile caulk grade instead. Polyblend Plus holds 4.4 stars from 234 reviews on Home Depot (November 2026). The grout versus caulk rule decides whether this repair lasts years or one season, and it is the sentence most guides skip.
Why does this happen?
Grout is a cement fill, strong in compression and poor in flex. In the middle of a tiled wall or floor it barely moves, and it lasts. At a corner, where a wall meets a tub, or where two planes meet, the building moves with temperature and load, and a rigid fill cracks along exactly that line. Water then enters the crack, softens what sits behind the tile, and each shower works more material loose. What looks like a grout quality problem is usually a movement problem underneath.
The width of the crack tells you the same thing. A hairline crack in a stable line can be cut out and re-grouted with confidence. A crack over one eighth inch wide, or any gap at a change of plane, is a joint that moves, and it needs a flexible sealant: a sanded ceramic tile caulk in the matching color, which stretches with the joint instead of splitting. Laying new grout over old failed grout fails because the new layer bonds to a crumbling base, so removal down to sound material is not optional preparation; it is the repair itself.
The fix, in order
Each step costs more than the one before it, so stop at the first one that solves the problem; the product is there only if the free steps run out.
Free step
Rake out all loose and cracked grout
Run a grout saw or utility knife along every failed line and remove material until you reach sound, hard grout or clean joint. Brush and vacuum the dust out. This free step is slow and unglamorous, and it is the difference between a repair bonded to the joint and a skim coat waiting to fall out.
Free step
Sort each joint: grout line or moving joint
Mark corners, tub and shower edges, and any crack over one eighth inch wide as sealant joints. Everything else is a grout line. This sorting, done with tape before you mix anything, applies the one rule that decides the life of the whole job, and it costs nothing but attention.
The product step
Re-grout stable lines with Polyblend Plus
Mix Custom Building Products Polyblend Plus Grout to a dense paste, press it firmly into the raked lines at an angle, and wipe the tile face clean as it firms. Work in small sections so the grout does not skin over before it is packed fully into each joint.
The product for this step
Custom Building Products Polyblend Plus Grout
Habit step
Seal moving joints with sanded caulk, then cure
For the marked moving joints, run a neat bead of sanded ceramic tile caulk in the matching color and tool it smooth. Then respect the cure time: keep showers off the repair for the full time the products state, because a perfect joint flooded too early will fail.
The evidence, in tiers
Tier 1 · The method
The grout versus caulk rule is the standard tile trade method: rigid grout for stable joints, flexible sealant at changes of plane and wide moving joints, and removal of failed material before any new fill, because new grout does not bond reliably to crumbling grout.
Tier 2 · This product
On Home Depot (November 2026): Polyblend Plus grout holds 4.4 stars from 234 reviews, the matching sanded ceramic tile caulk holds 4.3 stars from 894 reviews with 78 percent recommending it, and a grout color refresh product in the same aisle holds 4.6 stars from about 2,900 reviews on its dedicated listing.
We have not re-grouted a shower for this guide. The removal, sorting, and curing method follows tile trade practice and the product directions.
Tier 3 · What owners report
Owners report the rule working as stated: re-grouted flat lines holding for years, and corner repairs lasting only where the joint was switched to sealant. The recurring failure story is a cosmetic skim over loose grout, photographed beautifully on day one and back in pieces within a season.
The alternatives, conceded where they win
| Option | What it is | The honest verdict |
|---|---|---|
| Custom Building Products Polyblend Plus Grout | Polymer modified grout for stable joints | The pick for the grout lines themselves: dense, color matched, and made for the raked out joints this repair actually has. |
| Sanded ceramic tile caulk | Flexible sealant in grout colors | Wins outright at corners, tub edges, and cracks over one eighth inch wide, where grout is guaranteed to split again; it loses as a whole wall fill, where its softness and cost per joint are wrong for stable lines. |
| Grout color refresh coatings | Surface color and seal in one coat | Wins where grout is sound but stained, restoring color without removal; it loses on cracked or falling out grout, because a coating over failed material is decoration on a structural fault. |
The honest price comparison
The honest comparison is a tile professional re-grouting a shower, at call-out and day rates, or the far larger bill for water damage behind tile left to spread. Raking, grout, and a tube of sanded caulk reproduce the maintenance version of that visit for the cost of the materials alone.
Where it falls short
The weaknesses below come from the product's own review record. Hiding them would make this an advertisement, so they are here.
- It demands the removal step: readers who skim new grout over loose old grout, against the steps above, will watch the repair fail and blame the product.
- Color matching dried grout is imperfect, so a partial repair can look like a patch; test the color in one line and let it cure before committing to a whole wall.
- It is not a fix for movement in the structure itself or for water already behind the tile; those cases need the professional help the Read this first note describes.
The product, in short
Custom Building Products Polyblend Plus Grout
Questions people ask next
Why does grout always crack in the shower corners?
Corners are changes of plane, and the two planes move slightly against each other with heat and load. Rigid grout cannot flex, so it splits along the corner. Those joints should be flexible sealant in a grout color, not grout.
Can I just grout over the cracked sections?
No. New grout bonds to whatever it touches, and cracked grout is a crumbling base. The repair will look fine briefly and then fall out along the same lines. Rake failed sections back to sound material first, every time.
What width of crack needs caulk instead of grout?
Use one eighth inch as the working line. Hairline cracks in stable lines can be re-grouted after removal. Anything wider, and anything at a corner or edge, gets the sanded sealant grade, which can move with the joint.
How long before I can shower after re-grouting?
Follow the cure times printed on the grout and the caulk you use, and treat them as minimums in a damp bathroom. Flooding a joint before it has cured is the hidden cause behind many repairs that fail in their first month.
Home Depot product record for Custom Building Products Polyblend Plus Grout (November 2026) · Home Depot product record for sanded ceramic tile caulk (November 2026)
The Fix JournalCase 18Family & Friction