We are looking at making a frame around some windows using oak window boards.  To keep all the gaps even we are planning to use an expanding foam glue (like ista-stik, happy to hear recommendations of a better product).    

 

Has anyone had any experience using an expanding foam glue for oak wood to block? Is it as effective as advertised?

 

Due to some unevenness and  very limited time we don't have the option of using screws or anything else

Yes it works well.

Make sure you are 100 percent happy with the fit and levelness and packing before and foam is added.

Good idea to dampen the blockwork

Have bricks/blocks/suitable weights to keep the windowboard in position whilst it sets