Will wood screws hold this up?

[Louis Brandt]

Hello,
I’m almost finished with the construction of my fireplace surround and mantel shelf project, and I need some advice with a last minute issue.
I’m using a double-thick layer of 3/4 inch plywood for the foundation boards. This includes the two vertical legs and the horizontal piece that connects them. The foundation itself is 48 inches tall by 58 inches wide and with its double layer of plywood, is 1 1/2 inches thick, with of course, a large opening for the firebox. The two legs are each 8 inches wide. I intend to secure this entire foundation to the brick wall of the fireplace by using lag screws and metal anchors, so I don’t anticipate any problems with the stability of the foundation as it relates to the brick wall.
My real problem comes with the next step. The project includes another horizontal piece that attaches to the foundation boards. This "architrave" (as I’ve seen it referred to in other designs) is made of 3/4 inch solid oak and is 11 1 /4 inches wide by 55 inches long. I’ve just weighed it, and it weighs 12 pounds. On top of this will sit the mantel shelf, but it’s the architrave that concerns me.
Without going into the reasons why, let me just say that I can’t secure the architrave to the foundation or to the brick with lag screws as I’m doing with the foundation boards. My intention is to simply use 4 long (maybe 2 inch) countersunk wood screws to attach it to the foundation boards, one screw near each of the four corners.
I should add that under the architrave, there will be a 36 inch tall by 4 1/2 inch wide solid oak pilaster attached to each leg. The architrave will appear to "sit" on the two pilasters.
But does anyone (and you’re all much more experienced than I am) think that I’d be making a serious mistake by trying to secure a 12 pound length of solid oak against this foundation by wood screws only?
Louis

[Cliff Rohrabacher]

12 pounds isn't that much weight.
The degree of humidity in the wood and the degree of humidity variation in the building will be an issue.
You can drive the screws in at opposing angles to increase holding strength
You can use more screws.

[Louis Brandt]

Cliff,
Well, we actually never use the fireplace, and the humidity in the room is pretty constant. But I'm not sure what you mean by driving the screws in at opposing angles.
Louis

[Jerry Olexa]

With a picture, we'd be able to give you better advice. No offense but it would be a easier to give you an accurate and better opinion. Just IMHO...

[Cliff Rohrabacher]

Cliff,
Well, we actually never use the fireplace, and the humidity in the room is pretty constant. But I'm not sure what you mean by driving the screws in at opposing angles.
Louis

When I am laminating two 2X4s to make a polke for my pole jacks I use nailes laid at an angle with respect to each other in pairs to make it brutally hard for the thing to pull apart.

Here is a perfect illustration: \ / That is what I mean. The screws create a literal wedge (or dovetail) which requires one to pull out lots of wood in order to pull out the screws.

That as opposed to driving them in like this: | | which being parallel places all the stress of any pull out force solely on the thread engagement area.

[Mike Alagna]

I do a lot of mantel and surround jobs and I don't think you will have any problems with what you are proposing. I agree that a picture would make it easier to better understand what you are laying out, but based on weight and materials etc., Screws will be fine, You can also glue the piece and between the glue and the screws it will not go anywhere.

[Louis Brandt]

Thanks to all of you for your help and advice. I always get great advice from this forum, and I appreciate it.
Louis