I built a speaker enclosure out of MDF attaching the sides with PVA
glue and brads using butt joints and spraying the surface with
automotive primer-surfacer to get a smooth surface. The result was
very good, but there was a SLIGHT hint of the butt joint seam at the
overlap where one piece of MDF butts with the surface of the other
piece. I think there is a slight difference between the porosity of
the end vs. the surface or something between the two pieces. I let
the two pieces dry for about a week before sanding the edge flat.

I have been experimenting with different methods to hide the seam for
future projects. I have tried:

A washcoat of PVA glue covering the edge and the overlap area (first
effort not a spectacular success)
Using drywall joint compound to fill the inperfections (was not
impressed with the result)
A coating of superglue spread over the area (this seems to hold
promise)

Has any one tried an approach to stabilize the edge fibers of the cut
edge? It would appear that might hold the most promise from the
superglue result so far.

Any other thoughts?

eganders wrote:

| Has any one tried an approach to stabilize the edge fibers of the
| cut edge? It would appear that might hold the most promise from the
| superglue result so far.

I've had good results routing both edges straight, flat and square and
joining with epoxy only. I cleaned up very carefully with a sanding
block - and there was no trace of joints after painting.

Might work for you, too. FWIW, I don't like butt joints in MDF and
normally do a M&T-type joint.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/

On Aug 21, 10:52 am, "Morris Dovey" wrote:
eganders wrote:

| Has any one tried an approach to stabilize the edge fibers of the
| cut edge? It would appear that might hold the most promise from the
| superglue result so far.

I've had good results routing both edges straight, flat and square and
joining with epoxy only. I cleaned up very carefully with a sanding
block - and there was no trace of joints after painting.

Might work for you, too. FWIW, I don't like butt joints in MDF and
normally do a M&T-type joint.

A rabbet with a mini-mitre works well. (DO get that image of a bunny
with a pope's hat out of your mind NOW)
Porous-to-porous MDF joints can be very strong if one uses an adhesive
with sufficient capillary action to take advantage of MDF's weakness.
I have built bass boxes with 4x18" woofers which stood the test of
time and drunk roadies for many years.
A butt joint to the shiny side of MDF is only as strong as the first
layer of surface-tensioned dust....not good.

On Aug 21, 10:28 am, eganders wrote:
I built a speaker enclosure out of MDF attaching the sides with PVA
glue and brads using butt joints and spraying the surface with
automotive primer-surfacer to get a smooth surface. The result was
very good, but there was a SLIGHT hint of the butt joint seam at the
overlap where one piece of MDF butts with the surface of the other
piece. I think there is a slight difference between the porosity of
the end vs. the surface or something between the two pieces. I let
the two pieces dry for about a week before sanding the edge flat.

I have been experimenting with different methods to hide the seam for
future projects. I have tried:

A washcoat of PVA glue covering the edge and the overlap area (first
effort not a spectacular success)
Using drywall joint compound to fill the inperfections (was not
impressed with the result)
A coating of superglue spread over the area (this seems to hold
promise)

Has any one tried an approach to stabilize the edge fibers of the cut
edge? It would appear that might hold the most promise from the
superglue result so far.

Any other thoughts?

Automotive glazing putty (sometimes called 'green-stuff' even though
it's often red.) works very well. It is lacquer based and sands very
well.

"Robatoy" wrote:

Automotive glazing putty (sometimes called 'green-stuff' even though
it's often red.) works very well. It is lacquer based and sands very
well.

Also known as "spot putty", comes in a tube like toothpaste and is
usually red..

Lew

On Aug 21, 10:28 am, eganders wrote:
I built a speaker enclosure out of MDF attaching the sides with PVA
glue and brads using butt joints and spraying the surface with
automotive primer-surfacer to get a smooth surface. The result was
very good, but there was a SLIGHT hint of the butt joint seam at the
overlap where one piece of MDF butts with the surface of the other
piece. I think there is a slight difference between the porosity of
the end vs. the surface or something between the two pieces. I let
the two pieces dry for about a week before sanding the edge flat.

I have been experimenting with different methods to hide the seam for
future projects. I have tried:

A washcoat of PVA glue covering the edge and the overlap area (first
effort not a spectacular success)
Using drywall joint compound to fill the inperfections (was not
impressed with the result)
A coating of superglue spread over the area (this seems to hold
promise)

Has any one tried an approach to stabilize the edge fibers of the cut
edge? It would appear that might hold the most promise from the
superglue result so far.

Any other thoughts?

I have seen professional painters use a product known as painter's
putty on the edge surface of MDF. Probably available where the pro
painters shop. They apply it with the thumb.
Joe G

eganders wrote:
I built a speaker enclosure out of MDF attaching the sides with PVA
glue and brads using butt joints and spraying the surface with
automotive primer-surfacer to get a smooth surface. The result was
very good, but there was a SLIGHT hint of the butt joint seam at the
overlap where one piece of MDF butts with the surface of the other
piece. I think there is a slight difference between the porosity of
the end vs. the surface or something between the two pieces. I let
the two pieces dry for about a week before sanding the edge flat.

I have been experimenting with different methods to hide the seam for
future projects. I have tried:

A washcoat of PVA glue covering the edge and the overlap area (first
effort not a spectacular success)
Using drywall joint compound to fill the inperfections (was not
impressed with the result)
A coating of superglue spread over the area (this seems to hold
promise)

Has any one tried an approach to stabilize the edge fibers of the cut
edge? It would appear that might hold the most promise from the
superglue result so far.

Any other thoughts?

G'day,
I have used MDF quite a bit for varied projects and painted hundreds of
them.
Have never had to resort to any exotic fixes to hide butt joints.
Just apply a couple of coats of undercoat/sealer, sanding between coats,
followed by a few top coats. I use water based acrylic all most
exclusively, however the couple of times I have used an oil or thinners
based product the results haven't varied much. The thinners based
products may need an extra coat or two.

Hope this helps

regards
John

On Aug 21, 7:44 pm, John B ""johntoymaker\"@large puddle.com" wrote:
eganderswrote:
I built a speaker enclosure out of MDF attaching the sides with PVA
glue and brads using butt joints and spraying the surface with
automotive primer-surfacer to get a smooth surface. The result was
very good, but there was a SLIGHT hint of the butt joint seam at the
overlap where one piece of MDF butts with the surface of the other
piece. I think there is a slight difference between the porosity of
the end vs. the surface or something between the two pieces. I let
the two pieces dry for about a week before sanding the edge flat.

I have been experimenting with different methods to hide the seam for
future projects. I have tried:

A washcoat of PVA glue covering the edge and the overlap area (first
effort not a spectacular success)
Using drywall joint compound to fill the inperfections (was not
impressed with the result)
A coating of superglue spread over the area (this seems to hold
promise)

Has any one tried an approach to stabilize the edge fibers of the cut
edge? It would appear that might hold the most promise from the
superglue result so far.

Any other thoughts?

G'day,
I have used MDF quite a bit for varied projects and painted hundreds of
them.
Have never had to resort to any exotic fixes to hide butt joints.
Just apply a couple of coats of undercoat/sealer, sanding between coats,
followed by a few top coats. I use water based acrylic all most
exclusively, however the couple of times I have used an oil or thinners
based product the results haven't varied much. The thinners based
products may need an extra coat or two.

Hope this helps

regards
John- Hide quoted text -

- Show quoted text -

I have been over to Parts Express speaker building forum. They have
some people that are really into this subject. From their discussion,
this problem is more troublesome than I first thought. One of them
referred me to this forum:

http://www.diyaudio.com/forums/showt...hreadid=100520

Quite a bunch of experimenters and quite an interesting discussion!!
Read their discussion on using veneer to hide the joint.

By the way, I have tried to find 1/8 inch MDF of the type David Marks
uses with little success, but it would be nice to have 1/16 inch MDF
to cover the surface that has the butt joint in cases where you were
only going to paint the MDF.

Anybody know of an MDF type of material that could be a substitute for
veneer where you were only going to paint the surface? A very thin
sheet of MDF veneer (or other engineered veneer-like material) would
be easier to work with than real wood veneer that has flattening
issues. It would have to be very thin (yet thick enough to mask joint
movement of the MDF) in order not to have edge joint issues itself.

On Aug 21, 10:28 am, eganders wrote:
I built a speaker enclosure out of MDF attaching the sides with PVA
glue and brads using butt joints and spraying the surface with
automotive primer-surfacer to get a smooth surface. The result was
very good, but there was a SLIGHT hint of the butt joint seam at the
overlap where one piece of MDF butts with the surface of the other
piece. I think there is a slight difference between the porosity of
the end vs. the surface or something between the two pieces. I let
the two pieces dry for about a week before sanding the edge flat.

I have been experimenting with different methods to hide the seam for
future projects. I have tried:

A washcoat of PVA glue covering the edge and the overlap area (first
effort not a spectacular success)
Using drywall joint compound to fill the inperfections (was not
impressed with the result)
A coating of superglue spread over the area (this seems to hold
promise)

Has any one tried an approach to stabilize the edge fibers of the cut
edge? It would appear that might hold the most promise from the
superglue result so far.

Any other thoughts?

Cover the joints with stainless angle.