Valley leaks. use cement to fill in gap under tiles?


Here’s a diagram i drew up. a cross section of the valley.

i have a cement slate tile roof. from pictures I’ve seen, debris gets caught under the tiles.
so i was thinking… what if I put a little cement in the gaps under the tiles (where i marked the red arrows above). perhaps that would stop debris from accumulating under the tile, and maybe stop rainwater from getting under the tile and into the house?

Any drawbacks to this plan?


By your diagram there is not any headlap. Are these interlocking flat tiles or slate ? What is the vally material ? are there any singns of corrosion in it pinholes,line corrosion,pitting etc? can you tell how far the metal extends under the tile ? In most cases like this its the vally so we number the cut tiles pull them out nice and stack them in order. then put in new vally. the new vallys are in most cases for us 20 oz copper or lead coated copper with hemed edges out of minimum 18" stock. If there are two different pitches then you should consider using a W style vally. in short I think putting in mortor or caulk will be a waste of time. Check the headlap. the lenth of tile and exposure, this could also be critical.


yes. that’s what my tiles look like.
interlocking. with at least 3" overlap of each row of tiles.

valley is made of metal flashing material and extends 6" from each side of the valley i think.

there is a lot of dirt up there, so we’re gonna try to scrape it out first.

i just wanted to know if it’s ok to put a little concrete under those tiles, even if it doesn’t help much.


you can. on spanish tile it is common to mortor the vally openings. We like to use red slaters cement for that. we also red cement the hips.