Grid or TextGrid constant width cells

Question

I am having problems with white spaces in lists displayed in Grid. The problem is that white spaces have less height and width compared to cells that contain text. I also tried none, None, None[], null, Null, Null[],nothing, Nothing. " " seems to be the only solution that is not visible. Spacings->{2,2} seems to be relative not absolute. it only adds padding to what is already there. how can I define constant height and width for all cells? and is there a better way to describe white space other than string " "?

b={
{" "," ",38," "," "," "},
{" "," "," "," ",35," "},
{" ",19," "," "," "," "},
{" ",30," ",46," "," "},
{" "," "," "," "," "," "},
{" "," "," ",52," "," "}
};
Grid[b,Frame->All]

Answer 1

Replace " " with Invisible[38]:

Row[{Grid[b, Frame -> All], 
  Grid[b /. " " -> Invisible[38], Frame -> All]}, 
 Spacer[10]]

Row[{Grid[b, Frame -> All, Spacings -> {2, 2}], 
  Grid[b /. " " -> Invisible[38], Frame -> All, Spacings -> {2, 2}]}, 
 Spacer[10]]

Alternatively, use the option ItemSize:

Grid[b, Spacings -> {2, 2}, Frame -> All, ItemSize -> {All, 1}]

or the option ColumnsEqual:

Grid[b, Spacings -> {2, 2}, Frame -> All, ColumnsEqual -> True]