Outdoor Tile Countertop Substrate

by Steve
(New Hampshire)

QUESTION:

We have built an outdoor counter top substrate using 3/4" outdoor rated plywood. The Counter will have a roof over it. The tile will be 2"x2" porcelain (1/4" - 5/16" thick).

Do I need to put a cement backer board down or can I simply put a 1/8" thick later of thinset (with additive) and let it fully cure then install the tile using the normal notched trowel method of laying down thinset and tile?

Trying to avoid the cement backer board hassle... if I have to use a backer material how thick and what type? Note we are in a winter climate state (NH) but the counter will have a solid roof over it...

ANSWER:

Yeah, installing cement backer board can be a tedious process, but this is not a project you ever want to have to do over. Using the cement backer board is the right way to install an outdoor kitchen tile countertop.

Especially since you are using only 3/4" plywood substrate. You really should be using 1 1/8".

If you lived in a dry climate like Arizona, I'd say you could probably get away with just the plywood if you also sealed/painted the plywood.

But you live in NH and even with a roof the plywood will be subjected to plenty of moisture, which will take it's toll.

Outdoor plywood will still rot when exposed to moisture long enough. The only difference is that it's made with a water-proof glue, so you need to properly protect it with a long-lasting durable paint outdoors (before laying the cement backer).

If fact, cement backer board over outdoor plywood is the correct way to build an indoor tile countertop.

So, I recommend you do it. Use Hardie Backer 1/4".

Good Luck,
Ryan